Conceptual ecology and invasion biology: reciprocal approaches to nature

CONCEPTUAL ECOLOGY AND INVASION BIOLOGY: RECIPROCAL APPROACHES TO NATURE INVADING NATURE SPRINGER SERIES IN INVASION ...

Author: Marc William Cadotte | Sean Maurice McMahon | Tadashi Fukami

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CONCEPTUAL ECOLOGY AND INVASION BIOLOGY: RECIPROCAL APPROACHES TO NATURE

INVADING NATURE SPRINGER SERIES IN INVASION ECOLOGY Volume 1 Series Editor: JAMES A. DRAKE University of Tennessee, Knoxville, TN, U.S.A.

Conceptual Ecology and Invasion Biology: Reciprocal Approaches to Nature Edited by

MARC WILLIAM CADOTTE University of Tennessee, Knoxville, U.S.A.

SEAN M. MCMAHON University of Tennessee, Knoxville, U.S.A. and

TADASHI FUKAMI University of Hawaii at Manoa, Honolulu, U.S.A.

A C.I.P. Catalogue record for this book is available from the Library of Congress.

ISBN-10 ISBN-13 ISBN-10 ISBN-13 ISBN-10 ISBN-13

1-4020-4158-6 (PB) 978-1-4020-4158-7 (PB) 1-4020-4157-8 (HB) 978-1-4020-4157-0 (HB) 1-4020-4925-0 ( e-book) 978-1-4020-4925-5 (e-book)

Published by Springer, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. www.springer.com

Printed on acid-free paper

Cover design by Jeff McMahon All Rights Reserved © 2006 Springer No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Printed in the Netherlands.

#ONTENTS #ONTRIBUTORS &OREWORD 0REFACE

IX XV XVII

)NTRODUCTION HISTORYANDTERMINOLOGY

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0REFACE (UMAN ACTIVITIES AFFECT NATURAL SYSTEMS IN EVERY CORNER OF THE GLOBE AND ONE OFTHEMOSTWIDESPREADANDPOTENTIALLYDISRUPTIVEOFTHESEISTHEINTRODUCTIONOF NON INDIGENOUS SPECIES INTO NEW ENVIRONMENTS 4HESE INTRODUCTIONS CAN HAVE PROFOUNDCONSEQUENCESFORRESIDENTPOPULATIONS COMMUNITYDYNAMICS ANDECO SYSTEMFUNCTION/VERANDABOVETHENEEDTOUNDERSTANDHOWANON INDIGENOUS SPECIESCANAFFECTANATIVECOMMUNITY INTRODUCTIONSOFFERECOLOGISTSTHEPOTENTIAL TO LEARN ABOUT HOW COMMUNITIES ARE PUT TOGETHER HOW SPECIES CONTRIBUTE TO ECOSYSTEMFUNCTION ORHOWPOPULATIONSEVOLVEINTHEFACEOFNOVELENVIRONMENTS AND NOVEL SPECIES *UST LIKE THE RAILROAD SPIKE THAT PIERCED 0HINEAS 'AGES SKULL TAUGHTPHYSICIANSMUCHABOUTTHEFUNCTIONOFTHECEREBRALCORTEX ENVIRONMENTAL PERTURBATIONSCANTEACHUSABOUTNATURALSYSTEMS)NVASIONSCANINFORMECOLOGI CALTHEORYBYSERVINGASNATURALEXPERIMENTS /N THE OTHER HAND MODERN DAY ECOLOGISTS USE SOPHISTICATED CONCEPTUAL TOOLS TO AID IN THE UNDERSTANDING OF THE FUNCTIONING OF NATURAL SYSTEMS 4HESE TOOLS WE FEEL HAVE BEEN LARGELY UNDER UTILIZED IN UNDERSTANDING SPECIES INVASIONS 7ESEEHERETHEPOTENTIALFORARECIPROCALAPPROACHTOGAINADEEPERUNDERSTAND INGOFHOWECOLOGICALSYSTEMSAREPUTTOGETHER 7EHAVEASSEMBLEDANEXCELLENTGROUPOFAUTHORSTHAT EACHINTHEIROWNWAY ATTEMPT TO USE THEIR TOOLS TO EXPLORE THIS RECIPROCAL RELATIONSHIP 4HE AUTHORS IN THISVOLUMEWEREINVITEDBECAUSEOFTHEIRRECENTPUBLICATIONS WHICHSHOWTHEIR USEOFNOVELAPPROACHESTOEITHERUNDERSTANDINGTHECAUSESANDCONSEQUENCESOF SPECIESINVASIONS ORELSEUSECONCEPTUALTOOLSTOUNDERSTANDHOWNATURALSYSTEMS FUNCTION 7E ASKED AUTHORS REGARDLESS OF THEIR INDIVIDUAL APPROACHES TO THINK ABOUT THIS RECIPROCAL RELATIONSHIP BETWEEN INVASIONS AND THEORY 4HE CHAPTERS HEREUSEEXAMPLESFROMNUMEROUSORGANISMS ECOLOGICALSYSTEMS ANDGEOGRAPHIC LOCATIONS ANDAREEVENLYSPLITBETWEENTHEORYANDNATURALEXAMPLES 4HISVOLUMECOULDNOTHAVEBEENPOSSIBLEWITHOUTTHEINVOLVEMENTOFOTHERS 7EAREGRATEFULlRSTANDFOREMOSTTOTHEAUTHORSFORPRODUCINGSUCHlNEWORKFOR US7EWISHTOTHANKTHECHAPTERREVIEWERS WHO ASPERUSUALINSCIENCE SELmESSLY REVIEWEDCHAPTERS ANDGREATLYIMPROVEDTHEQUALITYOFTHISBOOK7EOFFERASPE CIALTHANKSTOTHESERIESEDITORANDOURMENTOR *IM$RAKE WHOALLOWEDUSTOFOCUS OUR CREATIVE ENERGIES ON TO THIS PROJECT AND TO AGREE TO MAKE THIS THE PREMIERE XVII

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ASDOINVADEDECOLOGICALSYSTEMS ITISINTHEINTERESTOF THERESEARCHERTOWORKTO BOTHUNDERSTANDINVASIONSBUTALSOTOCORRECTORMITIGATETHEDAMAGINGIMPACTOF NON NATIVEPOPULATIONS .)3POSEAWIDEVARIETYOFTHREATSTOTHEIRNON NATIVEHABITATSTHROUGHIMMEDI ATEANDLONG TERMINmUENCESONSPECIESCOMPOSITIONANDECOSYSTEMFUNCTIONING 0ARKERETAL "ECAUSETHENEGATIVEIMPACTSOF.)3ARElRST DIRECTLY AND PRIMARILY ECOLOGICAL ECOLOGISTS AND EVOLUTIONARY BIOLOGISTS CONSTITUTE THE FOR WARDLINEINMEETINGTHECHALLENGESPOSEDBYTHEINTRODUCTIONANDSPREADOF.)3 4HE MANY PATHWAYS THROUGH WHICH AN INTRODUCED POPULATION CAN AFFECT NON NATIVEHABITATSANDCOMMUNITIES HOWEVER AREDIFlCULTTODETERMINEANDPREDICT 7HICH TOOLS CAN THE ECOLOGIST APPLY TO THE PROBLEM OF .)3 !NY SOLUTION MUST DEVELOPFROMASOLIDUNDERSTANDINGOFTHEFOLLOWING HOWPOPULATIONSINTRIN SICALLY BEHAVE HOW POPULATIONS INmUENCE THE BIOTIC AND ABIOTIC SYSTEMS OF WHICHTHEYARECOMPONENTS HOW CONVERSELY ANENVIRONMENTCANINmUENCE A NON INDIGENOUS POPULATION AND HOW .)3 POPULATIONS CAN CHANGE PHENO TYPICALLYANDGENOTYPICALLY INNEWENVIRONMENTS!LTHOUGHALLOFTHESEQUESTIONS FALL SOLIDLY WITHIN THE TRADITION OF ECOLOGICAL RESEARCH THEY DEMAND WITH A STARTLING IMMEDIACY CAPABLE ANSWERS CULLED FROM UNRESOLVED AMBIVALENT AND EVENCONTENTIOUSECOLOGICALDEBATE7HILEECOLOGISTSAREATONCEWELLPOSITIONED TO ADDRESS THE KEY ELEMENTS THAT HAVE ARISEN FROM THE IMPORTANCE OF .)3 OUR ANSWERSARELIKELYTOCARRYWITHTHEMSOMEOFTHESTRUGGLESBORNOFCLASSICTHEORET ICALANDCONCEPTUALDEBATESINECOLOGYANDEVOLUTIONARYBIOLOGY(ERE HOWEVER THESTUDYOF.)3MAYNOTNECESSARILYSUFFERFORTHESECHALLENGES 4HE STUDY OF .)3 WHEN APPROACHED FROM THE REALM OF CONCEPTUAL ECOLOGY CAN ACT AS INTERESTING TESTS OF COMPETING ECOLOGICAL THEORIES 4HIS POTENTIAL HAS LONG BEEN RECOGNIZED AND MORE RECENTLY BEEN PROMOTED ,ODGE $AVIS ETAL 9ET NOTALLECOLOGICALTHEORYISAPPLICABLEORAPPROPRIATEFORTHISTYPE OF TEST .OR WILL THE ANSWERS GAINED FROM ALL APPLICATIONS OF ECOLOGICAL THEORY ASSIST IN IMPROVING OUR UNDERSTANDING INTERVENTION OR PREDICTION ABOUT ACTUAL COLONIZATIONS OF .)3 /NE OF THE KEY GOALS OF THIS BOOK IS TO BETTER RElNE WHAT ECOLOGISTSBELIEVETHESTUDYOF.)3CANDOFORTHElELDOFECOLOGYAND CONVERSELY HOW CONCEPTUAL ECOLOGY CAN ADVANCE OUR ABILITY TO EXPLAIN AND ADDRESS THE CHALLENGES POSED BY .)3 )N THIS CHAPTER WE WILL ORGANIZE SOME OF THE WAYS IN WHICHTHESTUDYOF.)3CANADVANCECONCEPTUALECOLOGYANDVISEVERSA FOCUSING ONRECENTLITERATUREINTHElELDANDTHEWAYSINWHICHTHECHAPTERSOFTHISBOOK lT INTO THAT SCHEME 4HIS CHAPTER WILL ALSO DISCUSS HOW THIS BOOK ESTABLISHES GUIDELINESNOTONLYFORWHATWEMAYLEARNFROM.)3 BUTFORWHATWEAREUNLIKELY TOLEARN!GAIN WITHIMMINENTCHALLENGESANDLIMITEDRESOURCES UNDERSTANDING WHICHSCIENTIlCAPPROACHES THEORETICALANDAPPLIED AREINTRACTABLEORIMPRACTI CAL IS AS IMPORTANT TO ADVANCING THIS lELD AS KNOWING WHICH APPROACHES SHOW PROMISEWHENCONFRONTINGTHISCOMPLEXPROBLEM

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42!#4!",% ).42!#4!",% !.$02!#4)#!,345$)%3 /&")/,/')#!,).6!3)/.3 !LTHOUGH STUDIES ON THE DYNAMICS OF INVASIVE ORGANISMS DEMONSTRATE MANY RESEARCHMETHODOLOGIES THREEAPPROACHESARECRUCIALTOTHEADVANCEMENTOFOUR UNDERSTANDING OF INVASIONS THEY ARE MATHEMATICAL MODELS EXPERIMENTS EITHER MANIPULATIVE OR OBSERVATIONAL AND REVIEWS OR META ANALYSES 4HE STRENGTH DERIVED FROM EXPLORING INVASION DYNAMICS THROUGH MATHEMATICAL MODELING IS THAT SCIENTISTS WITH EXPERTISE IN A VARIETY OF THEORETICAL APPLICATIONS CAN TACKLE THE CHALLENGES OF UNDERSTANDING BIOLOGICAL INVASIONS THROUGH NOVEL TECHNIQUES 3HEA AND #HESSON -ODELING SUGGESTS BOTH POSSIBLE DYNAMICS PROB ABLE lNDINGS AND PERHAPS MORE IMPORTANTLY THE LIMITS TO CERTAIN CONCEPTUAL APPROACHESTOINVASIONS(ARDINGETAL#HAPTER )TISBROADLYACKNOWLEDGED THATINORDERTOBETTERUNDERSTANDINVASIONS EXPERIMENTALAPPROACHESARECRUCIAL 4HEREHASBEENAGROWTHOFSTRONGEXPERIMENTSININVASIONS RANGINGFROMLABO RATORYMICROCOSMS$ICKAND0LATVOET TOlELDMESOCOSMS$UKES TO LARGE SCALE MANIPULATIVE lELD EXPERIMENTS 4ILMAN -ANY OF THE STRENGTHSOFINFERENCESDERIVEDFROMTHESESTUDIES INORDERTOBEBROADLYAPPRECI ATED NEEDTOBEREINCORPORATEDINTOMATHEMATICALMODELS&INALLY META ANALYSES AND REVIEWS PROVIDE A GENERALIZED ASSESSMENT OF THE THEORETICAL AND EMPIRICAL WORK THAT HAS COLLECTED OVER SEVERAL YEARS 4HE SYNTHESIS DERIVED FROM THESE ANALYSESCAN ASWITHTHEMODELS SERVETOINFORM DIRECT ORDELIMITTHEQUESTIONS RESEARCHERSASKABOUTINVASIONS#ADOTTEETAL 4HEDIALECTICDERIVEDFROM THECOMPLEMENTARYAPPROACHESOFSUPPOSITION EXPERIMENTATION ANDASSESSMENT OFFERSTHEMOSTEFlCIENTWAYTOSTUDYINVASIONSANDDRAWBROADERUNDERSTANDINGOF ECOLOGICALPROCESSESTHROUGHTHESTUDYOFINVASIONS!LLTHREEOFTHESEAPPROACHES ARE FEATURED IN THIS BOOK AND IN THE FOLLOWING INTRODUCTION TO THE THEMES OF THIS BOOK WE PAY SPECIAL ATTENTION TO HOW THIS DIALECTIC CAN GUIDE IMPORTANT RESEARCHANDTHINKINGONINVASIONS 4HEBEHAVIOROFPOPULATIONS

%VEN IN MODELS OF POPULATIONS THAT DO NOT INCLUDE ABIOTIC OR INTERSPECIlC ENVI RONMENTAL INTERACTIONS INTRASPECIlC POPULATION DYNAMICS CAN ILLUSTRATE IMPOR TANTPROPERTIESOFINVADINGPOPULATIONSTHROUGHPATTERNSOFINTRINSICPOPULATION GROWTHANDSPREADSEE#ADOTTE ETAL#HAPTER !LTHOUGHANUMBEROFSCALES MAY ULTIMATELY PROVE IMPORTANT WHEN ASSESSING THE ARRIVAL ESTABLISHMENT GROWTH ANDIMPACTOFAN.)3,LORETETAL (AMILTONETAL THEPOPU LATIONSCALEHASLONGPROVIDEDSOMEOFTHECLEARESTINSIGHTSINTOTHEBASICQUESTIONS OFINVASIONDYNAMICS0ETROVSKIIETAL 4HOMSON !LLOFTHEFEATURES THATlGUREPROMINENTLYINPOPULATIONBIOLOGY FROMTHEROLEOFCARRYINGCAPACITY TOMORTALITYANDREPRODUCTION PROVIDEABASELINEUNDERSTANDINGOFHOWAN.)3 CANBEEXPECTEDTOBEHAVEWHENCOLONIZINGANEWAREA!KEYDISTINCTIONWHEN EXPLORINGTHESEINTRINSICPROPERTIESLIESINTHEDIFFERENTEXPECTATIONSOFSTOCHASTIC


VERSUS DETERMINISTIC PROCESSES 1UITE A FEW CHAPTERS IN THIS BOOK IMPLICITLY AND EXPLICITLYADDRESSTHISIMPORTANTDISTINCTION "UCKLEYAND-ETCALF#HAPTER REVIEWTHEROLEOFDENSITYDEPENDENCEINDETER MINING THE POPULATION DENSITIES THAT CAN BE REACHED BY AN INVASIVE POPULATION ANDTHEINmUENCESOFTHOSEDENSITIESONINVASIVESUCCESS4HEYSHOWHOWDENSITY DEPENDENCECANDELIMITDEMOGRAPHICPARAMETERSSUCHASINTRINSICRATEOFINCREASE AND DISPERSAL ABILITY 5SING MICROBIAL MICROCOSMS 7ARREN ET AL #HAPTER SHOWTHATCHANCEEVENTSPLAYAKEYROLEINTHEESTABLISHMENTOFANINVADER)NITIAL DEMOGRAPHICSTOCHASTICITY PROPAGULEPRESSURE ANDTHEINITIALRATEOFINCREASEALL CONTRIBUTETOWHETHERAPOPULATIONISABLETOESTABLISHINACOMMUNITY BUTNOT NECESSARILYPERSISTINTHATCOMMUNITY3PECIES SPECIlCEFFECTSWEREALSOFOUNDTO BE IMPORTANT IN BOTH ESTABLISHMENT AND PERSISTENCE WHICH INDICATES THAT CARE FUL CHARACTERIZATION OF THE DEMOGRAPHIC QUALITIES OF AN INVADING SPECIES MAY BE IMPORTANTTOUNDERSTANDINGITSPOTENTIALIMPACT 7HAT POPULATION SCALE PATTERNS DO LEAD TO PERSISTENCE OVER TIME -URREL #HAPTER TAKESA@PLANT EYEVIEWINUSINGSIMULATIONSTOSHOWHOWTHEDENSITY AND AGGREGATION OF A POPULATION CAN CREATE A @NEIGHBORHOOD EFFECT THAT DETER MINES ULTIMATE POPULATION GROWTH 4HIS APPROACH COULD BE QUITE IMPORTANT IN PLANTINVASIONS ASINTRA SPECIlCCOMPETITIONCANDETERMINEULTIMATEVIABILITYAND SPREADOFAPOPULATION!FTERTHEPOPULATIONISESTABLISHED ITSDISPERSALBECOMES A CRUCIAL ISSUE IN ANTICIPATING THE EXTENT AND IMPACT OF AN INVASION 0UTH AND 0OST ,EWIS ET AL #HAPTER DEMONSTRATE A NOVEL APPROACH TO MODELING DISPERSALTHROUGHTWODIMENSIONS5SINGKERNELMETHODSTOINCORPORATELONG DIS TANCE DISPERSAL INTO MODELS AND TWO DIMENSIONAL MODELS TO CORRECT FOR BIASES IN MORECOMMONLYUSEDONE DIMENSIONALMODELS AMOREACCURATEPREDICTIONOFTHE DISPERSALBEHAVIOROFANINVADINGPOPULATIONCANBEMADE -ETAPOPULATION THEORY ALSO EMPHASIZES THE ROLE OF DISPERSAL IN MAINTAINING .)3 PERSISTENCE OVER TIME (ARDING ET AL #HAPTER SHOW THAT FOR SINGLE .)3 COLONIZING PATCHY ENVIRONMENTS COLONIZATION SUCCESS INTO EMPTY PATCHES MUST BEGREATERTHANEXTINCTIONS4HISIMPLIESTHATSPECIESWITHSTRONGDISPERSALMAYBE PREDISPOSEDTOCOLONIZE#OMBINEDWITHBUFFERINGLIFEHISTORYTRAITS SUCHASPLANTS THATCANSELF POLLINATEORVEGETATIVELYREPRODUCE AGOODDISPERSALMECHANISMCAN LEADTOSUCCESSFULCOLONIZATIONOFAHETEROGENEOUSLANDSCAPE %NVIRONMENTINFLUENCING.)3POPULATIONS

)NTRINSIC POPULATION BEHAVIORS ARE CLEARLY CRUCIAL TO ANY UNDERSTANDING OF THE ESTABLISHMENT AND SPREAD OF .)3 BUT AS WITH MANY ECOLOGICAL STUDIES OF POPU LATIONS THE BEHAVIORS OF THE POPULATION CAN DEPEND ON THE BIOTIC AND ABIOTIC COMPONENTSOFTHEENVIRONMENT,ODGE $UKESAND-OONEY (OLWAY ETAL )NCORPORATINGTHEADDITIONALLEVELOFCOMMUNITYCOMPLEXITYTOPOPU LATIONDYNAMICS HOWEVER CANBEDAUNTINGWHENDETERMININGTHEIMPACTOF.)3 $AVISETAL 4HESTUDYOFTHEESTABLISHMENTANDSPREADOF.)3CANPROVIDE INSIGHT INTO HOW THESE MORE COMPLEX RELATIONSHIPS DEVELOP LENDING IMPORTANT


CASESTUDIESTOTHEANALYSISOFECOLOGICALCOMMUNITIES4HECOMPLEXANDCOMPLICATED DYNAMICSOFTHEENVIRONMENTALSOMEANTHATTHESEADDITIONALCOMPONENTSCANMOVE PROBLEMSFROMLESSREALISTICBUTTRACTABLEPROBLEMSTOINTRACTABLEONES4HEREFORE IT ISIMPORTANTTOUSESTUDIESOFENVIRONMENTALINmUENCESON.)3TODETERMINEWHICH APPROACHESMAYBEAPPROPRIATEANDWHICHANINEFlCIENTUSEOFTIMEANDRESOURCES ! CLASSIC CONCEPT OF HOW AN ENVIRONMENT CAN DICTATE WHETHER OR NOT A SPE CIES CAN PERSIST IS THAT OF THE ECOLOGICAL NICHE 4HE IDEA THAT AN ENVIRONMENT IS PARSEDINTOAlNITESETOFNICHESHASBEENANIMPORTANTONEFORTHEDEVELOPMENT OF INVASIONS BIOLOGY #ADOTTE #HAPTER 6AZQUEZ #HAPTER USES A SERIES OF META ANALYSESTOEXPLOREHOWNICHEBREADTHANDINVASIONSUCCESSRELATE7HEN LOOKING AT FUNDAMENTAL NICHES WHERE SPECIES REQUIREMENTS ARE INDEPENDENT OF COMMUNITY INTERACTIONS VERSUS REALIZED NICHES WHERE THE SUITABILITY OF AN ENVIRONMENTTAKESINTOACCOUNTCOMPETITION THEREALIZEDNICHEULTIMATELYDETER MINES THE SUCCESS OF AN .)3 6AZQUEZ POINTS OUT THAT REALIZED NICHES HOWEVER AREIMPOSSIBLETOMEASUREANDWARNSAGAINSTPURSUINGSTRAIGHTFORWARDINVESTIGA TIONINTONICHE BASEDPREDICTIONSOFPOTENTIAL.)3SUCCESS4HISMARKSAPOWERFUL RECOMMENDATIONFORINVASIONSBIOLOGYASATRADITIONALLINEOFINQUIRYINTOPREDICT ING THE ESTABLISHMENT OF .)3 HAS BEEN THE SUSCEPTIBILITY OF DIFFERENT HABITATS TO INVASIONS(OLWAY ,EVINEAND$!NTONIO )NOTHERCIRCUMSTANCES INVASIONSCANSHEDLIGHTONCONCEPTUALTOPICSTHATARE DIFlCULTTOASSESSINNATURALCOMMUNITIES$UNCANAND&ORSYTH#HAPTER USE HISTORICALRECORDSOFBIRDINVASIONSTOTESTCLASSICHYPOTHESESOFCOMPETITIONAND COMMUNITYSTRUCTURE)NVASIONRECORDSOFFERAUNIQUEWAYOFDISCOVERINGIFINVA SIONSOFBIRDSPECIESINTOCERTAINTYPESOFENVIRONMENTSAREMORELIKELYTOPERSIST 4HEYlNDTHATPRIORITYEFFECTSDOOCCUR ANDTHATDEPENDINGONCIRCUMSTANCES STO CHASTICPROCESSESANDDETERMINISTICPROCESSESSUCHASCOMPETITION CANDETERMINE ULTIMATECOMMUNITYCOMPOSITION3AXAND'AINES#HAPTER SUGGESTTHATSPE CIESRICHCOMMUNITIESARELIKELYTOBEMORESUSCEPTIBLETOINVASIONSBECAUSECON DITIONSAREFAVORABLEFORMANYSPECIES 4HEYARGUE HOWEVER THATTHISISTRUEONLY UPTOACRITICALTHRESHOLDSUCHASHIGHLYSPECIOSETROPICALRAINFORESTS ATWHICH POINT %LTONS %LTON MODEL IN WHICH SPECIES RICH COMMUNITIES HAVE LESS AVAILABLENICHESPACEUNEXPLOITEDBYTHEBESTCOMPETITOR BECOMEAPPLICABLE"OTH 3AX AND 'AINES #HAPTER AND 3MITH AND 3HURIN #HAPTER EXPLAIN THAT HETEROGENEITYWITHINREGIONALSCALESCANMEANTHATMULTIPLEPROCESSESSTOCHASTIC ANDDETERMINISTIC ANDMULTIPLEOUTCOMESINVASIONRESISTANCEANDSUSCEPTIBILITY CAN BE FOUND IN ANY ONE HABITAT 4HIS INDICATES THAT EVEN IN UNSATURATED COM MUNITIESWHEREPRESUMABLYTHEREISAMPLENICHESPACEFORWELL DISPERSEDINVAD ERS INVASIONSUCCESSISCONTINGENTONOTHERFACTORS4HISROLEOFCONTINGENCYAND COMPLEXITY IS BECOMING A COMMON THEME IN BOTH INVASIONS LITERATURE AND THE EMPIRICALSTUDIESOFCOMMUNITYCOMPOSITIONANDASSEMBLY ANDTHEREFOREPOINTS TOANIMPORTANTAREAOFRECIPROCALRESEARCH !NOTHEREXAMPLEOFTHECHALLENGESINHERENTINCOMPLEXCOMMUNITYDYNAMICS ISILLUSTRATEDIN(ARDINGETAL#HAPTER !LTHOUGH ASMENTIONEDABOVE THEY SHOW THAT METAPOPULATIONSWITHOUTCOMPETITIONRELY ON A SIMPLESTRATEGYOF


COLONIZATIONANDBUFFERSFROMEXTINCTION ADDINGEVENONEMORESPECIESINTO THE MODELCANRADICALLYCHANGETHENUMBEROFPOPULATIONPARAMETERSANDLIFE HISTORY TRAITSTHAT MAY ULTIMATELY DICTATE THE SUCCESSFUL ESTABLISHMENT AND PERSISTENCE OFAN.)34HISCOMPLEXITYOFPOTENTIALOUTCOMESINDICATESTHATMETAPOPULATION THEORY ASAPPLIEDTOMULTIPLESPECIESLIVINGINSUBDIVIDEDHABITATSMIGHTBEWELL APPLIEDTO CASE STUDIES EXPERIMENTS AND MANAGEMENT PROBLEMS THAT OFFER SPECIFIC SPECIESCHARACTERISTICSANDROBUSTESTIMATIONOFPOPULATIONPARAMETERS7ITHSUCHA META ANALYSIS ITMAYBEPOSSIBLETODETERMINEWHETHERAMETAPOPULATIONMODEL CANACCURATELYDESCRIBEANDPREDICTCERTAINTYPESOFINVASIONS 5SINGMICROBIALMICROCOSMS 7ARRENETAL#HAPTER REINFORCETHISCONCLU SION)NASERIESOFAMBITIOUSEXPERIMENTSWHEREDIFFERENTSPECIESAREINTRODUCED INTO ESTABLISHED COMMUNITIES THEY SHOW THAT PREDICTING INVASIONS CAN DEPEND ONANUMBEROFCHARACTERISTICSOFTHESPECIESINVOLVEDASWELLASTHECOMMUNITY CHARACTERISTICS 3PECIlCALLY THE INTRINSIC RATE OF INCREASE A SIMPLE POPULATION PARAMETER SHOULD BE THOUGHT OF AS HAVING AS MUCH TO DO WITH THE INTERACTION CONTACTEXPERIENCE BETWEENANINVADERANDACOMMUNITYASINTRINSICPROPERTIES OFTHEINVADINGPOPULATION $EMOGRAPHIC PARAMETERS LIKE THE INTRINSIC RATE OF INCREASE THEMSELVES ARE NOT CONSTANT 4HESE PARAMETERS CAN CHANGE STOCHASTICALLY DUE TO BOTH INTRINSIC DEMOGRAPHICFACTORS SUCHASRANDOMCHANGESINBIRTHORDEATHRATES4HEYCAN ALSO CHANGE DUE TO ENVIRONMENTAL STOCHASTICITY &RECKLETON ET AL #HAPTER DISTINGUISHDEMOGRAPHICVERSUSENVIRONMENTALSTOCHASTICITYATDIFFERENTSTAGESOF ANINVASIONARRIVAL ESTABLISHMENT ANDSPREAD 4HEYSHOWWITHMATHEMATICAL MODELSTHATSTOCHASTICPROCESSESINmUENCETHESESTAGESOFTHEINVASIONINDIFFERENT WAYS AND WITH DIFFERENT CONSEQUENCES 3TOCHASTICITY MAY BE MORE IMPORTANT IN PHASES WITH LOW DENSITIES ARRIVAL AND ESTABLISHMENT WHILE DENSITY DEPENDENT BEHAVIORSMAYHOLDAGREATERINmUENCEONTHESPREADOFALREADYESTABLISHEDPOPU LATIONS !GAIN MODELS LIKE THIS CAN INDICATE WHEN AND HOW TO PROCEED WITH AN EXPERIMENTAL PROGRAM TO TEST STOCHASTIC AND DETERMINISTIC COMPONENTS OF INVA SIONSUCCESS !LTHOUGH DIRECT AGONISTIC INTERACTIONS BETWEEN SPECIES SUCH AS COMPETITION AND PREDATION HAVE LONG BEEN HELD AS CENTRAL TO UNDERSTANDING THE POPULATION STRUCTURE OF COMMUNITIES INDIRECT EFFECTS AND MUTUALISMS HAVE RECENTLY BEEN THRUSTINTOTHEFOREFRONTOFTHINKINGONANUMBEROFCONCEPTUALTHEMESINECOLOGY 7OOTTON ,ORTIE ET AL SUCH AS RICHNESS PRODUCTIVITY POPULATION VIABILITY ANALYSIS AND INVASIONS ,ACH 6AZQUEZ #HAPTER SHOWS IN HISMETA ANALYSESOFNICHEBREATHANDINVASIONSTHATTHEPRESENCEOFMUTUALISTS ANDOTHERNICHECATEGORIESTHATMAYBETRICKYTOMEASURECANHAVEANIMPORTANT INmUENCEONTHEULTIMATEVIABILITYOFAPOPULATIONINANEWHABITAT4HORPEAND #ALLAWAY #HAPTER EXTEND THE DISCUSSION OF MUTUALISMS TO THE LEVEL OF INDI RECTMUTUALISTINTERACTIONSANDFEEDBACKLOOPS'OODEXPERIMENTALEVIDENCEHAS SHOWNTHATPRESENCEOFSOILPATHOGENSDECREASE.)3PLANTSUCCESSINNATIVERANGE AND ABSENCE OF THOSE PATHOGENS INCREASES .)3 SUCCESS IN NEW RANGE &URTHER MUTUALISTINTERACTIONSCANMOREEASILYCREATEPOSITIVEFEEDBACKSINANEWRANGE


ENHANCING PLANT SUCCESS 4HIS CONCEPTUAL APPROACH TO INVASIONS MIGHT BE WELL SUITEDFORAMATHEMATICALSTUDY ASFEEDBACKSAREBOTHCOMMONINNATURE YETDIF lCULTTOTEASEAPARTFROMOTHERCOMMUNITYEFFECTS )NADDITIONTOUSINGANALYSESOFENVIRONMENTALCONTEXTSTOPREDICTWHETHERAN .)3 WILL SUCCESSFULLY ESTABLISH AND PERSIST IN A NOVEL ENVIRONMENT 'ILBERT AND 0ARKER#HAPTER AND3ATAKEETAL#HAPTER ADDRESSHOWTHEENVIRONMENT CAN PREVENT AN INVASION OR EVEN REVERSE AN ALREADY PERSISTENT .)3 'ILBERT AND 0ARKERARGUETHATTHEUNDERSTUDIEDROLETHATPATHOGENSPLAYINPLANTPOPULATION REGULATION CAN HAVE IMPORTANT CONSEQUENCES IN UNDERSTANDING PREDICTING AND MITIGATINGORREVERSINGHIGH DENSITYPERSISTENCEOF.)33ATAKEETAL#HAPTER MODEL@CLASSICMASTSEEDING ANDSHOWTHATWHENSEEDSETISNEGATIVELYCORRELATED INTIMEBUTPOSITIVELYCORRELATEDACROSSSPACEASYSTEMISMOSTRESISTANTTOINVAD INGSEEDPREDATORS 0HENOTYPICANDGENOTYPICCHANGE

!NEWANDEXCITINGTHEMEININVASIONSBIOLOGYADDRESSESHOWPOPULATIONSOF.)3 MAYCHANGEINPHENOTYPICEXPRESSION3CHWEITZERAND,ARSON ORGENOTYPE 3AKAI ET AL DUE TO THE NOVEL ENVIRONMENTS THEY EXPERIENCE IN THEIR NEW RANGE THIS INCLUDES POPULATION CHANGES INHERENT IN A COLONIZING EVENT SUCH AS FOUNDER EFFECTS OR DRIFT 0ALUMBI #OX *UST AS MUTATIONS IN A VIRUS WITHIN HUMAN POPULATIONS CAN MEAN THE DIFFERENCE BETWEEN RARITY AND A PAN DEMIC SOTOOCHANGESIN.)3POPULATIONSCANTURNARAREORISOLATEDPOPULATION INTOAPEST4HISCANALSOBEONEOFTHEMAJORFACTORSINCREATINGCREATETIMELAGS BETWEENTHEARRIVALPHASEOFAN.)3ANDANOUTBREAK-ACKETAL "YERSAND 'OLDWASSER -EMMOTT ET AL .EW METHODS IN GENETICS LIFE HISTORY EVOLUTION ANDCOEVOLUTIONARYTHEORYCANPROVIDEINSIGHTINTOANDDRAWINFERENCE FROMTHEGROWINGEXAMPLESOF.)3POPULATIONSTHATHAVECHANGEDFUNDAMENTALLY SINCETHEIRARRIVALINANEWRANGE %VOLUTIONARYCHANGEIN.)3POPULATIONSCANFOLLOWMANYPOSSIBLEPATHWAYS 3CHIERENBECK AND !ÕNOUCHE #HAPTER EMPHASIZE THAT PRE ADAPTED GENERALIST GENOTYPESWILLFACILITATEINVASIONSUCCESS3UBSTANTIALGENETICVARIATIONCANPRO VIDE THE REQUISITE GENETIC MATERIAL FOR RAPID EVOLUTIONARY RESPONSE TO THE NOVEL ENVIRONMENT AND3HIERENBECKAND!ÕNOUCHE#HAPTER POINTOUTTHATTHEREARE MANY PATHWAYS TO THIS VARIATION HETEROZYGOSITY POLYPLOIDY AND PERHAPS NOW EVEN EXTRA GENOMIC GENETIC INFORMATION ,ALLE ET AL (OWEVER GENERAL GENETICDIVERSITYMAYNOTALONEBEENOUGHTOINmUENCEINVASIONSUCCESS(ERBEN ET AL -ORE IMPORTANTLY HOW LABILE LIFE HISTORY TRAITS ARE PHENOLOGY CLONALORVEGETATIVEREPRODUCTIONINPLANTS MATINGBEHAVIORS ETC MAYMARKTHE IMPORTANT GENETIC DISTINCTION "UCKLEY AND -ETCALF #HAPTER DESCRIBE HOW LIFE HISTORYEVOLUTIONDUETOUNIQUEFORCESATWORKINNOVELENVIRONMENTSDIFFER ENTLIFE HISTORYSTRATEGIES MAYBENElT.)3POPULATIONS 7HILE LIFE HISTORY EVOLUTION MAY BE RESPONSIBLE FOR RARE LARGE OUTBREAKS THIS WOULD BE DIFlCULT TO TEST 4HORPE AND #ALLAWAY #HAPTER EXPLAIN THAT


EVOLUTIONARYRESPONSEOFMICROBIALCOMMUNITIESCANHAPPENSOFASTTHATTHISMAY MUTEORMITIGATEAN.)3FROMLONGTERMDOMINANCETHROUGHPOSITIVESOILFEEDBACK PATHWAYS"ECAUSEOFAPOTENTIALLYRAPIDRESPONSEANDTHESHORTGENERATIONTIMES OFMICROBIALCOMMUNITIES ITMAYBEPOSSIBLETOTESTSOILSYSTEMSFORRAPIDEVOLU TIONARYRESPONSETOENCOURAGINGORMITIGATINGTHESUCCESSFULESTABLISHMENTOFAN .)3 .)3 COLONIZATION ADDITIONALLY MAY PROVIDE IDEAL SYSTEMS TO RESEARCH THE STABILITYOFMICROBIALCOMMUNITIESASWELLASTHEIRRELATIONSHIPTOTHEPLANTSWITH WHICHTHEYINTERACTTHROUGHBELOWGROUNDPATHWAYS7ARDLE 0ATHOGENS WOULDALSOlTTHISMODEL AND'ILBERTAND0ARKER#HAPTER DESCRIBETHECOEVO LUTION OF PLANT PATHOGEN SYSTEMS AND MATERNALLY INHERITED INDUCED RESISTANCE 4HEEVOLUTIONARYRESPONSEOFAN.)3TOTHEBIOTICCOMMUNITYMAYBECRUCIALNOT ONLYINTHEESTABLISHMENT BUTINTHERESULTINGEFFECTONTHENATIVEBIOTA+ONDOH #HAPTER MODELSHOWCONTACTEXPERIENCE THEPREVIOUSEVOLUTIONARYlLTERING FROMPRIORINTERACTIONSBETWEENAN.)3ANDRELATEDNOVELCOMPETITORS PREDATORS ANDPREY CANRESULTINSUCCESSFULINVASION(EDESCRIBESHOWTHECONTACTEXPERI ENCE IN MANY FORMS CAN INmUENCE THE SPECIlC COMPONENTS OF CONTACT BETWEEN THE .)3 AND NOVEL BIOTA AS INFORMATION RETRIEVAL DETECTING THE OTHER SPECIES PROCESSING RECOGNIZING CHARACTERISTICS OF THAT NOVEL SPECIES AND BEHAVIORAL RESPONSEBEINGABLETOPREYUPON ESCAPE ORCOMPETEWITHTHATSPECIES .)3POPULATIONSINFLUENCINGPOPULATIONSANDENVIRONMENT

)T SHOULD BE NOTED THAT EVEN IDENTIFYING AN INVASIVE SPECIES CAN BE PROBLEM ATIC #OLAUTTI AND -AC)SAAC -URPHY ET AL #HAPTER "UT REGARDLESS OF DElNITION THEREISAGENERALUNDERSTANDINGAMONGBIOLOGISTSTHATULTIMATELYANY INVASIVEWILLINSOMEKEYWAYBEDElNEDBYITSINmUENCEONTHEBIOTICANDABIOTIC COMPONENTSOFITSNEWRANGE4HEREMAYBEMILLIONSOF.)3PROPAGULESENTERING COMPLEX ENVIRONMENTS BUT OUR CONCERN FOR THEIR RANGE EXPANSION IS ULTIMATELY AFUNCTIONOFTHEIRIMPACTONOTHERSPECIESINTHEIRNEWRANGE THEWAYSINWHICH THEYAFFECTECOSYSTEMPROCESSES ANDHOWTHESECHANGESMAYPERSISTORINCREASE OVERTIME (ISTORICALLY DOCUMENTED INVASIONS CAN ALSO PROVIDE INSIGHTS INTO THE PATH WAYSTHROUGHWHICHTHECONTEXTOFANDINVADINGORGANISMSCANINmUENCEBOTH PERSISTENCEANDTHECONCOMITANTINmUENCEONNATIVEBIOTA#OURCHAMPAND#AUT #HAPTER USEDMODELSINCORPORATINGDIRECTANDINDIRECTINTERACTIONSTOEXPLAIN INVASIONS AS WELL AS SHOW HOW THE INVASIONS THEMSELVES ILLUSTRATE THE COMPLEX AND SOMETIMES COUNTERINTUITIVE BEHAVIORS OF INTERACTING POPULATIONS #OMPLEX DYNAMICS BETWEEN POPULATIONS MAY ALSO MEAN THAT AFTER AN INVASION IT TAKES MANY GENERATIONS FOR THE EFFECTS OF THE NEW INTERACTIONS TO SHOW THEIR IMPACT &RECKLETONETAL#HAPTER !LTHOUGH DOCUMENTED CHANGES IN NATIVE BIOTA OR ECOSYSTEM FUNCTION MAY BE CLEAR AFTER AN INVASIVE BECOMES A DAMAGING PEST PREDICTING THE ULTIMATE IMPACTOFAN.)3ONNATIVEHABITATSISDIFlCULT!NUMBEROFFACTORS INTRINSICTO THE INVADING POPULATION AND DUE TO THE NOVEL ENVIRONMENT CAN ELICIT COMPLEX


RESPONSESTOTHENON NATIVEPOPULATIONS)NDIRECTEFFECTSONTHEENVIRONMENTARE DIFlCULTTODETECT LETALONEPREDICT YETMAYBEAMONGTHEMORECOMMONANDSERI OUS RESPONSES TO .)3 )NVASIVE PLANTS CAN ALTER THE SOIL NUTRIENT FEEDBACK LOOPS AND RENDER LONG TERM CHANGES TO THE SOIL ENVIRONMENT 4HORPE AND #ALLAWAY #HAPTER -UTUALISMS SUCHASPOLLINATIONSERVICES CANBEDISRUPTEDBYINVA SIVES 4HOUGH THE CONVERSE MAY OCCUR .ON NATIVE BEES HAVE BEEN SHOWN TO INCREASEPOLLINATIONEFlCIENCYOFSOMEPLANTS2ICHARDSONETAL ALTHOUGH THE EFFECT ON NATIVE POLLINATOR COMMUNITIES ADDS ADDITIONAL UNCERTAINTY TO THE DIAGNOSIS OF THESE EFFECTS 'ENERALISM VERSUS SPECIALISM CAN BE CRUCIAL TO THE EXTENTOFINmUENCEANON NATIVESPECIESMAYHAVEINPATHOGEN HOSTRELATIONSHIPS 'ILBERTAND0ARKER #HAPTER POLLINATORSYSTEMS6AZQUEZ #HAPTER AND SOILMUTUALISMS4HORPEAND#ALLAWAY#HAPTER 4HESYMMETRYOFTHESEMUTU ALISTRELATIONSHIPSISOFFURTHERCONSEQUENCE6AZQUEZ #HAPTER WHENINFERRING THEPOTENTIALIMPACTAN.)3MAYHAVEONNOVELSYSTEMS 7HETHER DIRECT OR INDIRECT THE STOCHASTIC NATURE OF POPULATION INTERACTIONS CAN RADICALLY AFFECT THE ULTIMATE CONSEQUENCES OF A PERSISTENT .)3 &RECKLETON et al#HAPTER 7ARRENETAL#HAPTER ESPECIALLYASSYSTEMSMAYCONTAINNON LINEARDYNAMICS!lNALLEVELOFCOMPLEXITYRESULTSFROMTHEMANYAPPLICATIONSOF OURINFERENCETOPOLITICAL SOCIAL ANDECONOMICISSUES)TISBROADLYACCEPTEDTHAT .)3CANAFFECTTHEINHERENTRICHNESSOFNATIVEBIOTA SPECIlCENDANGEREDSPECIES THE ECOSYSTEM FUNCTION OF NATIVE HABITATS AS WELL AS BIOTA OF ECONOMIC IMPOR TANCE )N THEIR REVIEW OF HOW .)3 INmUENCE NOVEL COMMUNITIES -URPHY ET AL #HAPTER FOUNDACORRELATIONBETWEENLEVELOFINVASIVEONTHE3%SCALEANDCOM MUNITYIMPACT THEREWASNOCORRELATIONWITHECONOMICIMPACT4HISMAYTROUBLE OUR ABILITY TO APPLY A LEVEL OF COMMUNITY CHANGE DUE TO AN INVASIVE TO SOME SYSTEMOFSOCIALORECONOMIC@IMPORTANCEOFTHEINVADER

#/.#,53)/. )NVASIONSBIOLOGYISFACEDWITHMANYOFTHESAMESTRUGGLESTHATHAVELONGFACED MAINSTREAMECOLOGY/RGANISMSSHOWANARRAYOFINTRINSICQUALITIESTHATAREBOTH INDICATIVE OF THEIR POPULATION DYNAMICS AS WELL AS RESPONSIBLE FOR THOSE DYNAM ICS 9ET POPULATIONS OF ORGANISMS RESPOND AND INmUENCE THEIR BIOTIC AND ABIOTIC CONTEXTS ANDTHEYADAPTPHENOTYPICALLYANDGENOTYPICALLYTOTHEM4HEPROBLEM OF lLTERING THAT WHICH IS BROADLY IMPORTANT TO POPULATIONS FROM THAT WHICH IS IDIOSYNCRATIC IS HIGHLIGHTED IN THE STUDY OF .)3 7E CERTAINLY NEED TO DEVELOP A GENERALUNDERSTANDINGOFTHEQUALITIESOFPOPULATIONSANDHABITATSTHATCANLEADTO INVASIONPERSISTENCEANDIMPACT YETWEOFTENlNDTHATTHECAUSESOFANYSPECIlC INVASION CAN BE UNIQUE TO THAT SPECIlC SPECIES OR HABITAT ! MAJOR GOAL OF THIS BOOKISTOCAREFULLYASSESSWHENSIMPLICITYISINFORMATIVEEG APOPULATION LEVEL ANALYSISOFDENSITYDEPENDENCE WHENCOMPLEXITYISINSTRUMENTALSUCHASWHEN ABIOTIC FACTORS INmUENCE .)3 PERSISTENCE AND WHEN GENERALIZATION IS NOT LIKELY POSSIBLESUCHASTHEFACTORSTHATMAKEUPTHEREALIZEDNICHEOFAN.)3


/NE OF THE GREATEST CHALLENGES FACING THE STUDY OF INVASIONS BIOLOGY ARISES FROM SPECIES SPECIlC CHARACTERISTICS !S IS OFTEN SHOWN IN THIS BOOK A BETTER UNDERSTANDING OF THE INTERFACE BETWEEN INTRINSIC POPULATION PROPERTIES AND THE STOCHASTICCONTEXTOFAPOPULATIONISLIKELYTOPROVIDEIMPORTANTINSIGHTSINTO.)3 ESTABLISHMENT AND EXPANSION &RUSTRATING MANY STRAIGHTFORWARD PATHS TO INVA SIONPREDICTIONISTHECOMBINATIONOFSTOCHASTICANDDETERMINISTICPROCESSESTHAT INmUENCEPOPULATIONSBEHAVIORS$ENNISETAL -ATHEMATICALMODELSMAY HELP INDICATE WHICH PARAMETERS UNDER WHICH ASSUMPTIONS CAN SHOW A DElNI TIVE INmUENCE ON POPULATION DYNAMICS 4HUS WHEN ENTERING AN OBSERVATIONAL OR MANIPULATIVE EXPERIMENTAL PROGRAM THE THEORETICAL LITERATURE CAN PROVE AN IMPORTANTGUIDETODEVELOPINGHYPOTHESESANDTESTINGTHEM 2EmECTING RECENT CONCEPTUAL ADVANCES IN GENERAL ECOLOGICAL THEORY OFTEN IGNORED PROCESSES SUCH AS MUTUALISMS INTRA SPECIlC COMPETITION AND BELOW GROUNDPROCESSESAREALSOLIKELYTOINmUENCETHEPOTENTIALIMPACTOF.)3#ALLAWAY AND !SCHEHOUG 2ICHARDSON ET AL 0ARKER AND (AUBENSAK #ALLAWAYETAL ANDMARKPOTENTIALPATHWAYSTOBRIDGEWHATAPPEARSTOBE IDIOSYNCRATICTOMOREGENERALIZABLEPATTERNS)NTHESEAREAS THESTUDYOF.)3MAY BE WELL SUITED TO INFORM OUR GREATER UNDERSTANDING OF SUCH COMPLEX AND OFTEN MASKED MECHANISMS IN GENERAL 4HUS NOT ONLY IS THERE A RECIPROCAL INTEREST IN UNDERSTANDINGTRADITIONALPROBLEMSINECOLOGYANDINVASIONSBIOLOGY THESETWO APPROACHES TO NATURAL SYSTEMS SHOULD INTERACT AND INFORM EACH OTHER AS THEY ADVANCEINTECHNIQUES CONCEPTS ANDUNDERSTANDING

2%&%2%.#%3 "YERS * % AND , 'OLDWASSER %XPOSING THE MECHANISM AND TIMING OF IMPACT OF NONINDIGENOUSSPECIESONNATIVESPECIES%COLOGY #ADOTTE -7 "-URRAYAND*,OVETT $OUST5SINGDATABASEANALYSESTOTESTWIDE SPREADECOLOGICALGENERALITIESININVASIONSBIOLOGY"IOLOGICAL)NVASIONSINPRESS #ALLAWAY 2 - AND % 4 !SCHEHOUG )NVASIVE PLANTS VERSUS THEIR NEW AND OLD NEIGHBORS!MECHANISMFOREXOTICINVASION3CIENCE #ALLAWAY 2- '#4HELEN !2ODRIGUEZAND7%(OLBEN3OILBIOTAANDEXOTIC PLANTINVASION.ATURE #OLAUTTI 2)AND(*-AC)SAAC!NEUTRALTERMINOLOGYTODElNE@INVASIVESPECIES $IVERSITYAND$ISTRIBUTIONS $AVIS -! *0'RIMEAND+4HOMPSON&LUCTUATINGRESOURCESINPLANTCOMMUNI TIESAGENERALTHEORYOFINVASIBILITY*OURNALOF%COLOGY $AVIS -! +4HOMPSONAND*0'RIME#HARLES3%LTONANDTHEDISSOCIATIONOF INVASIONECOLOGYFROMTHERESTOFECOLOGY$IVERSITYAND$ISTRIBUTIONS $ENNIS " 2 ! "ESHARNAIS * - #USHING 3 - (ENSON AND 2 & #ONSTANTINO #ANNOISEINDUCECHAOS/)+/3 $ICK * 4 ! AND $ 0LATVOET )NVADING PREDATORY CRUSTACEAN $IKEROGAMMARUS VILLOSUS ELIMINATES BATH NATIVEANDEXOTICSPECIES0ROCEEDINGSOFTHE2OYAL3OCIETYOF ,ONDON3ERIES" "IOLOGICAL3CIENCES


$UKES * 3 3PECIES COMPOSITION AND DIVERSITY AFFECT GRASSLAND SUSCEPTIBILITY AND RESPONSETOINVASION%COLOGICAL!PPLICATIONS $UKES *3AND(!-OONEY$OESGLOBALCHANGEINCREASETHESUCCESSOFBIOLOGICAL INVADERS4RENDSIN%COLOGY%VOLUTION %LTON #34HEECOLOGYOFINVASIONSBYANIMALSANDPLANTS-ETHUENAND#O,4$ ,ONDON 5+ (AMILTON - ! " 2 -URRAY - 7 #ADOTTE ' # -OSE ! # "AKER # * (ARRIS AND $,ICARI,IFE HISTORYCORRELATESOFPLANTINVASIVENESSATREGIONALANDCONTINEN TALSCALES%COLOGY,ETTERS (ERBEN 4 " -ANDAK + "IMOVA AND : -UNZBERGOVA )NVASIBILITY AND SPECIES RICHNESSOFACOMMUNITY!NEUTRALMODELANDASURVEYOFPUBLISHEDDATA%COLOGY (OLWAY $ ! &ACTORS GOVERNING RATE OF INVASION A NATURAL EXPERIMENT USING !RGENTINEANTS/ECOLOGIA (OLWAY $ ! ! 6 3UAREZ AND 4 * #ASE 2OLE OF ABIOTIC FACTORS IN GOVERNING SUSCEPTIBILITYTOINVASION!TESTWITHARGENTINEANTS%COLOGY ,ACH ,)NVASIVEANTS5NWANTEDPARTNERSINANT PLANTINTERACTIONS!NNALSOFTHE -ISSOURI"OTANICAL'ARDEN ,EVINE *-AND#-$!NTONIO%LTONREVISITED!REVIEWOFEVIDENCELINKINGDIVER SITYANDINVASIBILITY/)+/3 ,LORET & & -EDAIL ' "RUNDU AND 0 % (ULME ,OCAL AND REGIONAL ABUNDANCE OF EXOTIC PLANT SPECIES ON -EDITERRANEAN ISLANDS ARE SPECIES TRAITS IMPORTANT 'LOBAL %COLOGYAND"IOGEOGRAPHY ,ODGE $ - "IOLOGICAL )NVASIONS – ,ESSONS FOR %COLOGY 4RENDS IN %COLOGY %VOLUTION ,ORTIE # * 2 7 "ROOKER 0 #HOLER : +IKVIDZE 2 -ICHALET & ) 0UGNAIRE AND 2-#ALLAWAY2ETHINKINGPLANTCOMMUNITYTHEORY/IKOS -ACK 2 . $ 3IMBERLOFF 7 - ,ONSDALE ( %VANS - #LOUT AND & ! "AZZAZ "IOTIC INVASIONS #AUSES EPIDEMIOLOGY GLOBAL CONSEQUENCES AND CONTROL %COLOGICAL !PPLICATIONS -EMMOTT * .-7ASERAND-60RICE4OLERANCEOFPOLLINATIONNETWORKSTOSPE CIESEXTINCTIONS0ROCEEDINGSOFTHE2OYAL3OCIETYOF,ONDON3ERIES" "IOLOGICAL3CIENCES 0ARKER )-AND+!(AUBENSAK#OMPARATIVEPOLLINATORLIMITATIONOFTWONON NATIVESHRUBSDOMUTUALISMSINmUENCEINVASIONS/ECOLOGIA 0ARKER ) - $ 3IMBERLOFF 7 - ,ONSDALE + 'OODELL - 7ONHAM 0 - +AREIVA - ( 7ILLIAMSON " 6ON (OLLE 0 " -OYLE * % "YERS AND , 'OLDWASSER )MPACT TOWARD A FRAMEWORK FOR UNDERSTANDING THE ECOLOGICAL EFFECTS OF INVADERS "IOLOGICAL)NVASIONS 0ETROVSKII 3 !-OROZOVAND",,I2EGIMESOFBIOLOGICALINVASIONINAPREDATOR PREYSYSTEMWITHTHE!LLEEEFFECT"ULLETINOF-ATHEMATICAL"IOLOGY 0UTH , - AND $ - 0OST 3TUDYING INVASION HAVE WE MISSED THE BOAT %COLOGY ,ETTERS


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-7#ADOTTE

7ALDO%MERSONHADALREADYBEENPLEADINGTOTHE!MERICANPUBLICTORETHINKITS UNHEALTHYRELATIONSHIPWITHNATURE%MERSON 4HEIMPACTOFCERTAININVAD ERSWASBECOMINGAPPARENT%IGHTEENTHCENTURYBOTANISTS SUCHAS*OHN"ARTRAM WERE STARTING TO COMMENT ON THE FACT THAT SOME INTRODUCED PLANTS WERE HAVING NEGATIVEIMPACTS ANDWEREDIFlCULTTOCONTROLSEE-ACK (OOKER NOTICEDTHAT%UROPEANSPECIESWEREQUICKLYREPLACINGNATIVESIN.EW:EALAND 3OMEOFTHEEARLIESTCONCERNSABOUTEXOTICSPECIESWEREINTERMSOFTHEMAIN TENANCEOFTHE@NATURAL BASEDONAMORALITYOFAESTHETICSEG /LMSTEAD 3ARGENT BOTH CITED AND DISCUSSED BY 3IMBERLOFF 3OON AFTER A MORE DISTINCTLY !MERICAN PRAGMATIC APPROACH RECOGNIZED THE ECONOMIC AGRICUL TURALANDECOLOGICALEFFECTSBYNON INDIGENOUSSPECIESEG &ITCH (OWARD A )N HIS ADDRESS TO THE !MERICAN !SSOCIATION FOR THE !DVANCEMENT OF 3CIENCE ,ELAND (OWARD SAYS h0OTENTIALLY COSMOPOLITAN FORMS x HAVE BY HUMAN AGENCY BECOME DISPERSED OVER NEARLY ALL OF THE CIVILIZED PARTS OF THE GLOBE WHILETHOUSANDSOFOTHERSPECIESHAVEBEENCARRIEDTHOUSANDSOFMILESFROM THEIRNATIVEHOMES ANDHAVEESTABLISHEDTHEMSELVESANDmOURISHED OFTENWITHA NEWVIGOR INANEWSOILANDWITHANOVELENVIRONMENTv(OWARDA P (OWARD PUBLISHED MORE THAN ARTICLES ON NON NATIVE INSECT PESTS AND THE REALIZED OR POTENTIAL IMPACTS OF INTRODUCED SPECIES EG (OWARD A B (OWARDSPEERANDFRIEND 3TEPHEN&ORBESTHE FATHEROF!MERICANECOLOGYALSOBECAMEPROFESSIONALLYDEDICATEDTOTHEEFFECTS THATINSECTPESTSPOSEDFORAGRICULTURE#ROKER &ORBESWROTEMANYARTICLES ONTHEBIOLOGYANDIMPACTSOFINSECTPESTSEG &ORBES A "Y THE TURN OF THE CENTURY WE HAVE LEGITIMATE NON AESTHETIC CONCERNS ABOUT THE IMPORTATION OF NOVEL SPECIES /F COURSE MUCH OF THIS CONCERN WAS IN TERMSOFAGRICULTURALANDECONOMICCOSTS$URINGTHISTIMEECOLOGYWASDEVELOP INGINTOITSOWNSCIENCE%GERTON -C)NTOSH ANDHOWDIDTHISSCIENCE OFECOLOGYADDRESSTHESECONCERNSABOUTINVASIVESPECIES $URING THIS PERIOD THE DEVELOPMENT OF THE SCIENCE OF ECOLOGY WAS LARGELY A %UROPEANPHENOMENON WITHOUTAUNIQUELY!MERICANSCHOOLUNTILSHORTLYAFTER THETURNOFTHECENTURY-C)NTOSH /FCOURSETHEREWAS&ORBES WHOWROTE SEVERALPAPERSBEFORETHETHCENTURY WHICHWESHOULDCALL@ECOLOGICAL ESPECIALLY HISFAMOUS,AKEASA-ICROCOSMTALKDELIVEREDTOTHE0EORIA3CIENTIlC!SSOCIATION &ORBESB (EREHESTRESSEDTHEINTERACTIONAMONGSPECIESANDABALANCEOF NATUREVIEW BUTWECANNOTCALLTHISA@SCHOOLASLITTLESUBSEQUENTWORKWASDONE SPAWNINGLITTLERESEARCHANDNOTEXTBOOKS&ORBESANDHISCONTEMPORARIES(ENRY #OWLES AND ,ELAND (OWARD COULD BE SAID TO HAVE STARTED APPLIED ECOLOGY )T IS CURIOUS THEN THATONTHEONEHAND&ORBESWORKEDEXTENSIVELYWITHINSECTPESTS AND EXOTIC AGRICULTURAL DISEASES AND YET MAINTAINED A CLOSED SYSTEM BALANCE OF NATURE APPROACH IN HIS ECOLOGICAL WRITINGS 4HE FACT THAT A SINGLE INDIVIDUAL RECOGNIZINGTHEIMPORTANCEOFPESTSANDUNDERSTANDINGECOLOGICALSYSTEMS WOULD KEEPTHESEIDEASDISSOCIATEDISPROPHETICFORTHERESTOFEARLYECOLOGY %COLOGYGREWOUTOFTHEAPPARENTNEEDTOSEPARATECAUSESINWHOLE ORGANISM BIOLOGY 7HEREAS $ARWINS THEORY EXPLAINED THE ULTIMATE CAUSES AND PATTERNS


OFWHYWElNDSPECIESWHEREWEDOEG WHYCACTIAREDIVERSEINDESERTREGIONS AND THE PURPOSE OF THE PANDAS THUMB IT DID NOT INCLUDE A STRONG FRAMEWORK TO ACCOUNT FOR PROXIMATE CAUSES AND PATTERNS EG CYCLIC POPULATION DYNAMICS AND PATTERNS OF ABUNDANCES %ARLY FORAYS INTO THE ULTIMATE CAUSES OF SPECIES DISTRIBUTIONSFEATUREDGEOGRAPHICALANDGEOLOGICALCAUSESOFSPECIESDISTRIBUTIONS EG 7ALLACE 7ALLACE OBSERVED THAT BIOTAS WERE LARGE REGIONAL ENTITIES OFTENWITHFAIRLYDISCRETEBOUNDARIES#OMMONWASTHEIDEAOFBARRIERSTO MOVEMENT WITHALLSPECIESBEINGABLETOMOVETONEWLOCALS BUTRARELYDOINGSO EG (EILPRIN 7RITINGSOFDE#ANDOLLEAND$ARWINCERTAINLYADDRESSISSUES OFPROXIMATEPATTERNS BUTITTOOKASEPARATElELDTOCREATETHEIROWNPROXIMATE EXPLANATIONS 4HE BIOGEOGRAPHER /SCAR $RUDE WAS ABLE TO SEPARATE THESE CAUSES AND PAT TERNS IN HIS -ANUAL DE 'EOGRAPHIE "OTANIQUE (E NOTED THAT THERE WERE TWOFORCESOFCHANGEINSPECIESRANGESANDABUNDANCEGEOLOGICALANDBIOLOGICAL $RUDERIGHTLYTHOUGHTTHATALLULTIMATECHANGEHAPPENEDINhCOURSDELÏVOLUTION GEOLOGIQUEvP THECOURSEOFGEOLOGICALEVOLUTION4HISINCLUDEDADAPTA TION AS WELL ASCONSTANT CHANGE BUT HE ALSO SAW THE ROLES OF THE ORGANISM ENVIRONMENTINTERFACE DISPERSAL ANDCOMPETITION4HEDISTINCTIONBETWEENGEOLOGICAL ANDBIOLOGICALCAUSESWASIMPORTANTFOR$RUDESUNDERSTANDINGOFRAPIDCHANGESIN SPECIESDISTRIBUTIONS$RUDECLASSIlESLIMITSTOSPECIESRANGESASEITHERGEOGRAPHI CAL THAT IS MOUNTAINS OCEANS AND THE LIKE ARISING FROM GEOLOGICAL PROCESSES ANDBIOLOGICAL BYWHICHHEMEANSCHANCEDISPERSALANDTHEAGENCYOFHUMANS h,ESLIMITSDESAIRESSONTPUREMENTGÏOGRAPHIQUES OUBIENRÏSULTENTDELACTION COMBINÏEDESCONDITIONSDEVIEvP $RUDESAYSTHATWITHOUTTHEAIDOFHUMANS GEOGRAPHICAL BARRIERS LIMIT SPECIES SPREAD BUT THAT RARE CHANCE EVENTS STILL PLAY ANIMPORTANTROLEFORRANGEEXPANSION7ITHHUMANAID SPECIESWILLSPREADASFAR ASTHEEXTERNALENVIRONMENTALLOWS$RUDETELLSTHEREADERTHATMOVINGTOANEW LOCATION WHICH MUST BE CLIMATICALLY SIMILAR TO THAT IN A SPECIES NATIVE RANGE ISONLYHALFTHEEQUATION ANDONCEAPLANTHASARRIVED hELLELUTTEAVECSUCCESCON TREUNEPLANTEINDIGÒNETOUT Ì FAITADAPTÏEAUCLIMATvP ITHASTOBESUC CESSFULINTHESTRUGGLEAGAINSTINDIGENOUSPLANTSPERFECTLYADAPTEDTOTHECLIMATE 'IVEN THIS LIMITATION PLANTS STILL COME TO hCOUVRIR DE GRANDES SURFACESv P ANDINCOVERINGTHESELARGEAREAS DISPLACEOTHERSPECIES(EGOESEVENFURTHERTO SAYTHATSOMESPECIESDONOTDOMINATEONEANOTHER ANDCOMPETITIONISINDETERMI NATE)NTHESESPECIESTHERANGESARESETUPBYWHOEVERARRIVESTHERElRST $RUDESACCOUNTSOUNDSVERYMODERN(ISBIOGEOGRAPHYINCORPORATESGEOGRA PHY CHANCE COMMUNITYASSEMBLY ANDLOCALCOMPETITION(EALSOHASASYSTEMOF PROXIMATECAUSESANDPATTERNSTHATREADILYACCOUNTSFORTHEDYNAMICSOFINVASIVE SPECIES (OWEVER IN READING THE CHAPTER ON RANGE EXPANSION IN $RUDE ONEGETSTHEIMPRESSIONTHATHEISTRYINGTOEXPLAINTHEFACTOF.)3SPREADINLIGHTOF LATE NINETEENTHCENTURYKNOWLEDGEOFBIOGEOGRAPHY RATHERTHANTRYINGTOUNDER STANDINVASIONSANDSPECIlCINVADERS4HISISNOTACRITICISM ASHEWASDEVELOPING ASYSTEMOFKNOWLEDGEABOUTTHENATURALWORLD ANDHISEPISTEMOLOGYCALLEDFOR EXPLAININGEXTANTPATTERNSWITHINTHEEXISTINGFRAMEWORK

-7#ADOTTE

!NOTHER %UROPEAN ECOLOGIST %UGENE 7ARMING WROTE AN INmUENTIAL ECOLOGY BOOKBEFORETHETURNOFTHECENTURY4HE%NGLISHTRANSLATIONOFHIS/ECOLOGY OF 0LANTS WAS CONCERNED WITH POPULATION AND COMMUNITY ECOLOGY AND HE TRIED TO DEVELOP A SYSTEM OF ECOLOGICAL UNDERSTANDING 7ARMING WAS VERY MUCHINTERESTEDINTHEPROCESSOFECOLOGICALCHANGE ANDTHISCHANGEINCLUDEDTHE ARRIVAL OF NEW SPECIES (E BELIEVED THAT ECOLOGICAL PROCESSES INCLUDING CHANGE WEREREALIZEDATTHECOMMUNITYLEVEL&OREXAMPLEHEBELIEVEDTHATSUCCESSIONAL CHANGERESULTEDFROMCOMPETITIONAMONGCOMMUNITYTYPES AFFECTEDBYCHANGES IN THE ENVIRONMENT %SSENTIALLY 7ARMINGS CHANGE IS ASSEMBLAGES OF SPECIES MOVINGAMONGEQUILIBRIA BUTWHATWASHISMECHANISMFORTHESECHANGES 7ARMING SAYS THAT THERE ARE TWO TYPES OF COMMUNITY CHANGE lRST IS FROM @CHANGES IN SOIL AND THE OTHER IS CHANGE @WITHOUT NEW SOIL )N THE lRST TYPE OF CHANGE DISTURBANCES BOTH NATURAL AND HUMAN CAUSED ARE IMPORTANT AND ABRUPT3LOWERTYPESOFCHANGEINCLUDEINCREASESORDECREASESINWATERCONTENTOR BYTHEACCUMULATIONOFSOIL4HESECONDTYPEOFCHANGEHAPPENSTHROUGHMIGRA TIONSANDSTRUGGLESAMONGINDIVIDUALSPECIES 4HISSECONDTYPEOFCOMMUNITYCHANGE 7ARMINGSAYS ISATYPICAL hTHESTRUG GLESINQUESTIONARERAREvANDTHATCOUNTRIEShWHOSEVEGETATIONISNOTAPPRECIABLY DISTURBEDBYMANORANIMALS ANDWHICHHASBEENEXPOSEDFORLONGAGESPASTTO IMMIGRATION FROM ADJOINING COUNTRIES IN THIS CASE A CERTAIN EQUILIBRIUM MUST HAVE BEEN ATTAINEDv P 4HIS EQUILIBRIUM VIEW MEANS THAT THE PROBLEM OF INVASIVESPECIESISONEPRIMARILYASSOCIATEDWITHDISTURBANCESWHICHISLARGELY TRUE (OWEVER HIS VIEW MAY HAVE SOME DIFlCULTLY EXPLAINING WHY SOME SPE CIESINVADEINTACTCOMMUNITIES(ECONCEDESTHISPOINTONTHENEXTPAGE hSOME CHANGES IN THE NATURE OF FORESTS MAY HAVE BEEN SIMPLY DUE TO THE ENTRY OF NEW SPECIESvP 7ARMINGDOESMAKEANEMOTIONALPLEATOBEWEARYOFIMPORTINGNEWSPECIES BECAUSEOFTHECOMPETITIONTOWHICHTHEYMAYSUBJECTNATIVEFORMShANEW x COM MUNITY WHICH DID NOT NATURALLY OCCUR BEFORE THE SOIL HAD BEEN DRAWN INTO THE SERVICE OF -AN AND THE SPECIES WHICH NOW OCCUR IN VAST NUMBERS AND FORM A COMMUNITYWITHITSOWNSPECIALSTAMPANDECONOMYvP 7ARMINGSSYSTEMMAKESPREDICTIONSASTOWHATTYPESOFCOMMUNITIESOUGHTTO BEMOREINVADED ANDOURMODERNUNDERSTANDINGOFTHEINVASIONPROCESSWOULD ALSO PREDICT THAT INTACT COMMUNITIES ARE LESS INVADABLE THAN DISTURBED ONES (OWEVER BOTH 7ARMING AND $RUDE WERE NOT EXPLICITLY TRYING TO UNDERSTAND INVASIONS RATHER THEY WERE TRYING TO lT THE FACT THAT WE SEE INVADERS INTO THEIR RESPECTIVE ECOLOGICAL SYSTEMS &OR THEM THERE WAS NO REAL ASSOCIATION BETWEEN DEVELOPING ECOLOGICAL UNDERSTANDING AND ADDRESSING THE PROBLEM OF INVASIVE SPECIES 4HEY FELT THAT IF THEIR RESEARCH PROGRAMMES EXPLAINED THE GENERAL PHENOMENON OF .)3 THEN THEIR ECOLOGY WAS ROBUST 4HE RELATIONSHIP BETWEEN ECOLOGY AND INVADERS WAS LIMITED AND ONE WAY !T MOST INVADERS WERE TESTS OF EARLYECOLOGISTSIDEASORATWORSTPHENOMENANEEDINGEXPLANATION


4(%.!452%/&#(!.'%#,%-%.43!.$4(%!-%2)#!.3#(//, 3HORTLYAFTERTHETURNOFTHECENTURY AN!MERICANSCHOOL EMBODIEDIN&REDERIC #LEMENTS COME TO THE FORE -C)NTOSH ) SAY THAT #LEMENTS EMBODIED THE SCHOOL BECAUSE HE DID ALL THE THINGS THAT MAKE A SUCCESSFUL SCHOOL OF THOUGHT (E INTERACTED WITH A NUMBER OF STUDENTS AND COLLEAGUES HE WROTE NUMEROUS SUCCESSFUL TEXTBOOKS AND MOST IMPORTANTLY HE EMPHASIZED A STRONG HEURISTIC PARADIGMINMUCHOFHISWRITINGNAMELY THENATUREOFECOLOGICALCHANGE #LEMENTS lRST TWO BOOKS REALLY LAID THE GROUNDWORK FOR THIS NEW SCHOOL (IS lRST 2ESEARCH -ETHODS IN %COLOGY DETAILED HOW THE SCIENCE OF ECOLOGY SHOULDBEDONE WHATTECHNIQUESANDRESEARCHTOPICSWEREMOSTFRUITFUL4HISWAS SOONFOLLOWEDBYASECONDBOOK 0LANT0HYSIOLOGYAND%COLOGY WHICHHAD MUCHOVERLAPWITHHISBOOK BUTREINFORCEDWHICHAREASOFRESEARCHWERE MOSTIMPORTANTANDTHEPARADIGMOFPLANTECOLOGY3PECIlCALLY THESEBOOKSHAD ANUNPRECEDENTEDFOCUSONECOLOGICALCHANGE ORWHATBECAMEKNOWNASSUCCES SION)NTUITIVELY SUCHAPARADIGMSEEMSLIKE.)3WOULDBEOFCENTRALCONCERN "OTH BOOKS DElNE INVASION ALMOST IDENTICALLY AS h4HE MOVEMENT OF ONE OR MORE PLANTS FROM ONE AREA INTO ANOTHER AND THEIR ESTABLISHMENT IN THE LATTER P ALSO A VERY SIMILAR QUOTE IN P (E NOTES h)NVASION IS A REGULAR OCCURRENCE BETWEEN ADJACENT FORMATIONS BUT IT ALSO TAKES PLACE INTO REMOTE ONES AS A RESULT OF LONG CARRIAGE BY WIND WATER BIRDS RAILROADS OR VESSELSv P (E TELLS US THAT DISPERSAL IS USUALLY CONSTRAINED BY BARRIERS BUT THAT HUMANS AS AN AGENT OF DISPERSAL ARE ABLE TO TRANSCEND THESE BARRIERS )NVASIONS ARE IMPORTANT FOR A NUMBER OF REASONS &IRST INVASIONS CAN SIGNIlCANTLY AFFECT SPECIES DISTRIBUTIONS 3ECONDLY ECOLOGICAL CHANGE DEPENDS ONINVASIONS#LEMENTSDElNESSUCCESSIONASAhSERIESOFINVASIONSxINTHESAME SPOTv P P /FCOURSE SEVERALFACTORSWORKAGAINSTTHESUCCESSOFANINVASION&IRSTOFALL THEREARETHEWELL KNOWNGEOGRAPHICALBARRIERSTOMIGRATIONMOUNTAINS OCEANS ETC BUT MORE IMPORTANTLY #LEMENTS DETAILS OTHER TYPES OF BARRIERS 4HERE IS AN ABIOTICBARRIERTHESPECIESMUSTlNDITSELFINANENVIRONMENTINWHICHITCAN SURVIVE -ANY BIOLOGICAL FORCES WORK AGAINST SPECIES ESTABLISHMENT INCLUDING PREDATION DISEASE COMPETITION AND HUMANS TRYING TO CONTROL WEEDS !LSO #LEMENTSlNDSTHATWHETHERTHEHABITATISFULLORNOTISOFPARAMOUNTIMPORTANCE TO INVASION SUCCESS AS COMPETITION FROM FULL COMMUNITIES WILL BE TOO SEVERE FOR THECOLONIZERTOSUCCEED 4HIS VIEW OF ECOLOGICAL SUCCESSION IS COMMON IN THE WRITINGS OF #LEMENTS COLLEAGUES AND COLLABORATORS 3HANTZ SAW INVASIONS AS THE PROCESS OF SUCCESSION ANDSUCCESSIONASTHEPROCESSOFCHANGINGFORMATIONSORCOMMUNITY TYPES 4HE IDEA OF SPECIES INVASIONS AS THE FORCE BEHIND SUCCESSION IS ALSO DOMI NANT IN 7EAVER AND #LEMENTS (UMANITYS ROLE IS EXAMINED IN GREATER DETAIL AND THEY NOTICE THAT ANTHROPOGENIC EFFECTS ON COMMUNITY SUCCESSION CAN BE SEVERE AS WE BOTH DISTURB HABITATS AND BRING IN NEW INDIVIDUALS 4HEY NOTETHATTHEMOTOROFSUCCESSIONISNOTDISTURBANCE BUTRATHERBIOTICPROCESSES

-7#ADOTTE

MIGRATIONANDCOMPETITIONANDTHATCLIMAXCOMMUNITIESOFTENRESISTTHESE BIOTIC FACTORS #LEMENTS AND 3HELFORD CLARIlED WHO ARE CALLED INVADERS 3PECIlCALLY INVADERSARETHOSESPECIESTHATDIDNOTPREVIOUSLYEXISTINTHEHABITAT THEY ARE INVADING 0REVIOUSLY #LEMENTS DID NOT EXPLICITLY STIPULATE WHETHER THE INVADERSHADTOBESEPARATESPECIES(ERE#LEMENTSAND3HELFORD MAKENO DISTINCTIONABOUTWHERESPECIESCOMEFROM INTERMSOFTHEIRNATIVEORINTRODUCED STATUS %ARLIER #LEMENTS DID CREATE TERMS TO REmECT SPECIES THAT MIGRATE FROM NEARBY VERSUS THOSE ORIGINATING FURTHER AWAY 9ET NONE OF THESE WORKS EXPLICITLYEXAMINES.)3 JUSTECOLOGICALPROCESSESOFIDEALIZEDSPECIES!GAINLIKE THEOTHEREARLYECOLOGISTS #LEMENTSANDCOLLEAGUESWEREINTERESTEDINESTABLISHING ASTRONGPROGRAMMETHATCOULDPOTENTIALLYEXPLAINTHEOCCURRENCEOF.)3

%80,!).).'30%#)%3/##522%.#%37)4(4(%.)#(% )CONTINUEBYTAKINGABRIEFTOUROFECOLOGYUPTOTHES$URINGTHISPERIOD PRIMARYPUBLICATIONSIE ACADEMICJOURNALARTICLES WEREBECOMINGINCREASINGLY IMPORTANTFORTHEDEVELOPMENTANDDISSEMINATIONOFNEWIDEAS/NEOFTHEMOST IMPORTANT CONCEPTUAL DEVELOPMENTS IN EARLY ECOLOGY WAS THE IDEA OF THE NICHE 4HROUGH UNDERSTANDING A SPECIES NICHE ONE COULD POTENTIALLY UNDERSTAND AND PREDICTWHEREANDWHENSPECIESISFOUND ANDWHICHSPECIESARELIKELYTOREPLACE ONEANOTHER 7ECOULDPROBABLYTRACETHENICHECONCEPTALLTHEWAYBACKTO$ARWIN BUTTHE IDEAOFEXAMININGTHEDISTRIBUTIONOFSPECIESTHROUGHASPECIESSUITEOFENVIRON MENTALNEEDSISCOMMONLYATTRIBUTEDTO'RINNELL 'RINNELLSNICHECONCEPT HASBEENANIMPORTANTTHEMEINTHEDEVELOPMENTOFECOLOGY(ISPREMISEWASTHAT PATTERNSOFSPECIESOCCURRENCEAREBESTUNDERSTOODTHROUGHTHEIRABIOTICANDBIOTIC REQUIREMENTS(UTCHINSON FAMOUSLYUSEDTHISNICHECONCEPTTOADVANCED THENOTIONOFAMULTIDIMENSIONALNICHESPACEDElNINGWHEREEACHSPECIESCOULD POTENTIALLY LIVE (UTCHINSONS CONCEPT COULD POTENTIALLY EXPLAIN WHERE SPECIES COULD LIVE AND THEREFORE WHERE THEY COULD INVADE AS EACH SPECIES POTENTIALLY OCCUPIES A UNIQUE REGION OF THE NTH DIMENSIONAL NICHE HYPERSPACE 4HE DElNI TIONOF@NICHEHASBEENRECOGNIZEDASPROBLEMATIC3IMBERLOFF#ONNERAND 3IMBERLOFF AND OPEN TO VARIOUS INTERPRETATIONS ,EIBOLD #HASE AND ,EIBOLD !NEARLYREINTERPRETATIONWASPROVIDEDBY%LTON WHOSAW THENICHEASASPECIES@STATUSINTHECOMMUNITY4HISINCLUDEDTHEROLEANORGAN ISMPLAYEDANDMOSTIMPORTANTLYITSRELATIONSHIPTOOTHERSPECIESANDESPECIALLY THETROPHICSTATUSOFASPECIES%LTONSINVASIONSBOOK ACTUALLYUSEDBOTH CONCEPTSOFTHENICHETOUNDERSTANDWHENANDWHERE.)3INVADEANDWHICHCOM MUNITIESWEREMORELIKELYTOBEINVADED/NLYRECENTLYHADTHEREBEENANATTEMPT AT RECONCILING THESE TWO MAJOR CONCEPTUALIZATIONS OF THE NICHE CONCEPT ,EIBOLD #HASEAND,EIBOLD 3INCE 'RINNELLS PAPER RESEARCH ON COMPETITION HAS BEEN INTIMATELY ASSOCIATEDWITHTHENICHECONCEPT%LTON LIKE7ARMING THOUGHT


SPECIES RICH COMMUNITIES OUGHT TO BE LESS INVADABLE BECAUSE AVAILABLE NICHES SHOULD BE lLLED AND COMPETITION FOR NICHE SPACE MORE INTENSE #OMPETITION AS A MAJORSTRUCTURINGFORCESURFACEDBEFORE%LTONEG 'AUSE $!NCONA WITH THE FOUNDATION IN WHAT 'AUSE CALLED THE @COMPETITIVE EXCLUSION PRINCIPLE SEE ALSO (ARDIN PROBABLY lRST ARTICULATED BY 'RINNELL 4HECENTRALPREMISEOFTHISPRINCIPLEISTHATh.OTWOSPECIESOFIDENTICALOREVEN CLOSELY SIMILAR BIOLOGICAL PREDILECTIONS CAN LONG OCCUPY THE SAME NICHE x AT THE SAME TIMEv 'RINNELL P )N FACT 'RINNELL USED THIS REASON ING TO ARGUE AGAINST THE PURPOSEFUL INTRODUCTION BY THE STATE OF #LAIFORNIA OF THE(UNGARIANPARTRIDGEFORHUNTING'RINNELLSCONCERNWASTHATTHE(UNGARIAN PARTRIDGE SHARED ITS NICHE WITH THE NATIVE #ALIFORNIA QUAIL AND THAT THE LATTER WOULDLIKELYBECOMPETITIVELYEXCLUDED4HISPREDICTIONWASBASEDONTHEOBSER VATION THAT SPECIES HAVING LARGE NATIVE RANGES USUALLY EXCLUDE SMALLER RANGED COMPETITORS 'RINNELL APPLIED ECOLOGICAL REASONING TO PREDICTING THE OUTCOME OF ASPECIESINTRODUCTION 'AUSE SAW THE VALUE THAT INVASIONS HAVE FOR UNDERSTANDING GENERAL ECOLOGICALPROCESSES4OSTUDYCOMPETITION'AUSECOMMENTEDONTHEIMPORTANCE OF EXPERIMENTATION AND THAT IN NATURAL EXPERIMENTS hTHE MOST FREQUENT ONES CONSISTINTHETRANSPORTATIONOFANIMALSINTOCOUNTRIESNEWTOTHEM WHICHCOM MONLY LEADS TO A GREAT NUMBER OF HIGHLY INTERESTING PROCESSES OF THE STRUGGLE FOREXISTENCEvP /NEEXAMPLEHIGHLIGHTEDBY'AUSEISTHEINTRODUCTIONOF THE%UROPEANCARPINTOEASTERN.ORTH!MERICAINTHESANDHOWIThHASNOW INMANYSTREAMSANDLAKESMULTIPLIEDTOSUCHANEXTENTTHATSEVERALNATIVESPECIES AREFOUNDINGREATLYDIMINISHEDNUMBERvP -UCHUNDERSTANDINGOFTHENATUREOFSPECIESINTERACTIONS ANDESPECIALLYTHOSE THATSTIMULATED'AUSE WASADVANCEDBYTHETHEORETICALMODELSOF,OTKA EG AND6OLTERRAEG 4HEWORKOF,OTKAAND6OLTERRANOTONLY REVOLUTIONIZEDHOWECOLOGISTSTHOUGHTABOUTSPECIESINTERACTIONS BOTHCOMPETI TION AND PREDATION BUT ALSO SHOWED HOW MODELS COULD BE USED TO UNDERSTAND APPLIEDPROBLEMS4HEFAMOUSINSTANCEISTHATTHESON IN LAW 5MBERTO$!NCONA ASKED HIS FATHER IN LAW 6ITO 6OLTERRA IF IT WERE POSSIBLE TO EXPLAIN MATHEMATI CALLY WHY IT SHOULD BE THAT WITH THE CESSATION OF lSHING IN &IUME NEAR 4RIESTE DURING77) PREDATORYSHARKSANDRAYSCAMETOCONSTITUTEAHIGHERMEANPROPOR TIONOFTHECATCHBIOMASSEG $!NCONA(ALLAM /FCOURSE USING HIS PREDATOR PREY MODELS 6OLTERRA WAS ABLE TO EXPLAIN THIS INCREASE IN PREDATOR PROPORTION 6OLTERRA ASSUMED THAT THE HARVESTING PRIOR TO 77) WAS INDISCRIMI NANTANDRESULTEDINAlXEDPROPORTIONOFINDIVIDUALSREMOVED SOTHATTHEPERIODIC EQUILIBRIUM BETWEEN PREDATOR AND PREY DENSITIES SHIFTED TO HAVE A CENTER WITH HIGHER PREY AND LOWER PREDATOR ABUNDANCE WHEN THERE IS DENSITY INDEPENDENT MORTALITY )NTHESAMEVEIN $!NCONA SHOWEDHOW,OTKA 6OLTERRA TYPEFORMULA TIONSCOULDBEUSEDTOUNDERSTANDTHEDYNAMICSOFSPECIESINVASIONS5SINGTHESE TYESOFEQUATIONS $!NCONA SHOWEDTHATANEWINVADERWILLEITHERMOVE TO AN EQUILIBRIUM OF ZERO DENSITY IE UNSUCCESSFUL OR CHANGE THE EQUILIBRIUM

-7#ADOTTE

DYNAMICS OF THE EXTANT COMPETITORS WHICH ESSENTIALLY ALTERS THE DENSITIES OF THE OTHERSPECIES )TISWORTHMENTIONINGTHATTHE,OTKA 6OLTERRAEQUATIONSHAVEBEENCRITICIZED WITHANUMBEROFSHORTCOMINGSRECOGNIZED NAMELYTHEYAREDIFlCULTTOAPPLYIN SPECIlCCIRCUMSTANCESANDTHEINTERACTIONCOEFlCIENTSAREPROBLEMATICTOCOMPUTE (ECK (ALLAM 4HATSAID THEYDOOFFERGREATUSEASHEURISTICDEVICES ANDASAMECHANISMTOPRODUCEQUALITATIVEHYPOTHESES(ECK 4HESETYPES OF MODELS HAVE FOUND USE IN UNDERSTANDING AND PREDICTING THE CONSEQUENCES OF INVASIONSEG #OURCHAMPETAL#OURCHAMPAND#AUT #HAPTER8

5.$%234!.$).'30!4)!,302%!$ /NE MAJOR DEVELOPMENT PRIOR TO %LTONS BOOK BRIDGING ECOLOGY AND INVASIONS BIOLOGY WAS 3KELLAMS USE OF SPATIAL SPREAD MODELS 4HE MAJOR THRUST OF THISRESEARCHWASTHEAPPLICATIONOFMODELSDESCRIBINGTHEDIFFUSIONOFPARTICLESIN APHYSICALSYSTEMTOTHESPREADOFAREPRODUCINGPOPULATIONOVERATWO DIMENSIONAL landscape (Skellam 1951, Kiersteadt and Slobodkin 1953). Skellam (1951) APPLIEDTHESEPHYSICALMODELSTOUNDERSTANDINGANDPOTENTIALLYPREDICTINGPOPULA TIONSPREADACROSSALANDSCAPE"YTHES THERAPIDSPREADOF.)3FROMTHEIR POINTSOFORIGINHADBEENDOCUMENTEDANDTO3KELLAMWEREINNEEDOFMECHANIS TIC EXPLANATION ,IKE $ARWIN 3KELLAM USED .)3 TO SHOW HOW HIS THEORY COULD BE USED TO EXPLAIN SPATIAL SPREAD OF A POPULATION 7HAT BETTER WAY TO STUDY THE DYNAMICSOFASPREADINGPOPULATIONTHENWITHNEWLYARRIVINGSPECIES4HE INTRODUCTIONANDSPREADOFTHEMUSKRAT /NDATRAZIBETHICA INCENTRAL%UROPEWAS AN ILLUSTRATIVE EXAMPLE FOR 3KELLAM 3KELLAM WAS ABLE TO ADD POPULATION GROWTHTERMS EITHEREXPONENTIALORLOGISTIC TOSPREADMODELS!DDINGEXPONEN TIALGROWTH THECHANGEINDENSITYIS ,N , N RN$ ,T ,X WHERENISTHEPOPULATIONDENSITYANDLOCATIONXWITHGROWTHRATERANDDIFFUSIVITY $&OLLOWING+OT THEVELOCITYOFSPREADIS

X R$ T

!DDINGLOGISTICGROWTH THECHANGEINDENSITYIS

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!GAINFOLLOWING+OT THEVELOCITYOFSPREADIS DX R$ DT Skellam’s spatial spread models have been used to understand the spread OF NATURAL POPULATIONS EG /VASKAINEN AND ESPECIALLY FOR THE SPREAD OF POPULATIONSOFINVASIVESPECIESEG (ASTINGS +OTETAL"UCHANAND 0ADILLA

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7(!4()34/294%,,3!"/54%#/,/'9!.$).6!3)/.")/,/'9 ) AM PAINTING THE PICTURE THAT THE NEW SCIENCE OF ECOLOGY IN THE EARLY TH CEN TURY WAS DEVELOPING ITS EPISTEMOLOGICAL DOMAIN AND THE QUESTION IS DID THEY TRYTOUSETHEIRNEWSCIENCETOUNDERSTANDINVASIVEEXOTICS)THINKTHEYDIDNOT 4HESEEARLYECOLOGISTSSEEMEDTOINCORPORATE.)3BECAUSETHEYYIELDEDREAL WORLD OBSERVATIONS WHICHOBEYEDTHEVERYNATURALLAWSTHESEAUTHORSWEREEXPLORING &URTHERMORE .)3WERE INSOMECASES USEDTOSHOWCASETHEIRIDEASABOUTNATURAL LAWSORASNATURALEXPERIMENTS"YANDLARGETHEEARLYECOLOGISTSDIDNOTUSETHEIR CONCEPTUALIDEASTOUNDERSTANDANDPREDICTTHEPROBABLEOUTCOMESOFSPECIESINVA SIONS 4HEY DID NOT OFTEN IMPLEMENT 'AUSES SUGGESTION THAT INVASIONS CONSTITUTENATURALEXPERIMENTSTOUNDERSTANDECOLOGYBETTER /F COURSE THIS REVIEW DOES NOT SCOUR THE LITERATURE FOR EVERY RECORDED IDEA OR EVERYDISCUSSIONOF.)3INVADER2ATHER )HAVEATTEMPTEDTOlNDTHEPROMINENT MODESOFTHINKINGINECOLOGYANDESPECIALLYWITHRESPECTTO.)3INVADERS)HAVE RELIEDEXTENSIVELYONTEXTSASRECORDSOFTHESETRENDS ANDAVALIDCRITICISMISTHAT GENERAL TEXTS DO NOT CAPTURE ALL THE DIVERSITY OF THINKING WITHIN A lELD OF STUDY BOTH SUBTLE AND STARK (OWEVER %GLER IN HIS CRITICISM OF THE EPISTEMOL OGYOF!MERICANPLANTECOLOGYDURINGTHES FOUNDTHATTHEMAJORTEXTSDID LARGELYREPRESENTTHESCHOOLSOFTHOUGHTANDPHILOSOPHIESOF!MERICANECOLOGY $AVIS ET AL ASSOCIATE %LTONS INVASIONS BOOK WITH THE CAUSE OF THEDISSOCIATIONBETWEENECOLOGYANDINVASIONSBIOLOGY)FWETHINKOFECOLOGYAS A SCIENCE OF CASE STUDIES EG 3HRADER &RECHETTE AND -C#OY THEN PER HAPSTHEREWOULDBENODISSOCIATION ANDBYSTUDYINGINDIVIDUALCASESOFSPECIES INVASIONS WE CAN THEN FORM LARGER PICTURES OF WHAT IS HAPPENING IN NATURE 3HRADER &RECHETTE 9ET MUCH OF ECOLOGY IS BASED ON THE PRECEPT THAT THERE ARE FUNDAMENTAL OPERATIONS IN NATURE 4HESE FUNDAMENTAL OPERATIONS ARE APPROXIMATED THROUGH THEORY CONSTRUCTION EXPERIMENTATION AND OBSERVATION 4HE DISSOCIATION SEEN BY $AVIS ET AL IS THAT THESE SCIENTIlC EXERCISES THEORY EXPERIMENT AND OBSERVATION ARE WHAT BOTH INVASIONS BIOLOGISTS AND

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INVASIONECOLOGY PARTICULARLYIN.ORTH!MERICA THROUGHITSEMPHASISONNATIVE ENVIRONMENTSANDNATIVESPECIES "Y THE MID S MORE AND MORE ECOLOGISTS WERE BEGINNING TO THINK ABOUT INVASIONS FROM AN ECOLOGICAL PERSPECTIVE (OWEVER WHAT WAS STILL LACKING WAS ASYNTHESISOFTHISTHINKINGTHATWOULDHELPDElNEAlELDOFINVASIONECOLOGY)N FACT THEGROUNDWORKFORSUCHANEFFORTWASALREADYUNDERWAY)N THE4HIRD )NTERNATIONAL#ONFERENCEON-EDITERRANEAN%COSYSTEMSWASHELDIN3TELLENBOSCH 3OUTH!FRICA ANDINTERESTINBIOLOGICALINVASIONSATTHEMEETINGLEDTOAPROPOSAL TOTHE3#/0%GENERALASSEMBLYIN/TTAWAIN4HISPROPOSALRESULTEDINTHE CREATION IN OF A SCIENTIlC ADVISORY COMMITTEE THAT WAS TO ENCOURAGE AND FACILITATEFOCUSONTHEIMPACTSOFBIOLOGICALINVASIONSONNATURALECOSYSTEMS4HE ADVISORYCOMMITTEEARTICULATEDTHREEQUESTIONSTOGUIDETHE3#/0%INVASIONPRO GRAM WHATFACTORSDETERMINEWHETHERASPECIESWILLBEANINVADERORNOT WHATARETHECHARACTERISTICSOFTHEENVIRONMENTTHATMAKEITEITHERVULNERABLETO ORRESISTANTTOINVASIONS HOWCANTHEKNOWLEDGEGAINEDFROMANSWERINGTHE lRSTTWOQUESTIONSBEUSEDTODEVELOPEFFECTIVEMANAGEMENTSTRATEGIES$EVELOPED WITH THE INTENT OF hBUILDING ON THE CONSIDERABLE KNOWLEDGE BASE AVAILABLE ON INVADERS OF AGRICULTURAL SYSTEMSv THE 3#/0% PROGRAM ON BIOLOGICAL INVASIONS WASCLEARLYCONCEIVEDINTHECONSERVATIONTRADITIONOF%LTON)TISNOCOINCIDENCE THATSCIENTISTSFROM3OUTH!FRICA !USTRALIA .EW:EALAND ANDTHE5NITED3TATES CONTRIBUTED SO SIGNIlCANTLY TO THE 3#/0% INITIATIVE 4HE NATURAL ENVIRONMENTS INTHESECOUNTRIESHADBEENEXPERIENCINGRECENTANDSUBSTANTIALINTRODUCTIONSOF NEWSPECIESFROMOTHERREGIONSOFTHEWORLDANDCONSIDERABLECONSERVATIONCON CERNSWEREBEINGRAISEDINTHESECOUNTRIESREGARDINGTHEIMPACTSOFTHESESPECIES

3OUTH !FRICAN SCIENTISTS HAD BEEN AMONG THE LEADERS IN RECOGNIZING THE CONSER VATION IMPLICATIONS OF INTRODUCED SPECIES EG 7ICHT 4AYLOR AND THEYPUBLISHEDTHElRST3#/0%VOLUMEIN-ACDONALDAND*ARMAN (OWEVER IT WAS NOT UNTIL THE LATTER HALF OF THE DECADE THAT MOST OF THE 3#/0% REGIONAL WORKSHOPS BEGAN PUBLISHING THEIR PROCEEDINGS 4HE .ORTH !MERICAN CONTINGENT PUBLISHED %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII -OONEY AND $RAKE 4HE BOOK WAS ORGANIZED AROUND VARIOUS PATTERNS OFINVASIONS INCLUDING ASSOCIATIONS WITH DIFFERENT TAXONOMIC GROUPS ATTRIBUTES OF INVADERS AND SITE CHARACTERISTICS PROMOTING INVASIONS )N ADDITION A VARIETY OF CASESTUDIESWEREPROVIDED4HISPUBLICATIONWASENTIRELYA5NITED3TATESINITIATIVE WITH BOTH EDITORS AND ALL THE CONTRIBUTORS BEING FROM 53 UNIVERSITIES 4HAT BIO LOGICALINVASIONSHADlNALLYCAPTUREDTHEINTERESTOFPROMINENT.ORTH!MERICAN ECOLOGISTSISEVIDENCEDBYTHECONTRIBUTORSTOTHEBOOK EG 3IMBERLOFF %HRLICH "AZAZZ 2EGAL /RIANS 6ITOUSEK 2OUGHGARDEN %WEL 0IMM AND-OONEY #OINCIDENTALLY THESYMPOSIUMTHATLEDTOTHISVOLUMETOOKPLACEIN!SILOMAR #ALIFORNIA THE SAME SITE OF THE SYMPOSIUM ON THE GENETICS OF COLONIZING SPECIES

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HELD TWENTY YEARS EARLIER 4HE VOLUME CONTAINS AN INTERESTING MIXTURE OF CHAPTERS -OST WERE CLEARLY CONCEIVED AND WRITTEN WITH A CONSERVATION AND ENVIRONMENTALPERSPECTIVE ASWOULDBEEXPECTEDGIVENTHENATUREOFTHE3#/0% PROGRAM (OWEVER SOME CHAPTERS WERE WRITTEN MORE IN THE SPIRIT OF THE !SILOMARSYMPOSIUMANDFOCUSEDMOREONECOLOGICALTHEORY3IMBERLOFFS CHAPTER ON THE BIOGEOGRAPHY OF INSECT INTRODUCTIONS EXAMINED TOPICS SUCH AS ISLAND MAINLAND PATTERNS AND ISSUES OF BIOTIC RESISTANCE PRIMARILY FROM A THEO RETICALPERSPECTIVE!LTHOUGHHEDIDCITE%LTON 3IMBERLOFFDIDNOTTAKEASTRONGLY CONSERVATION APPROACH IN HIS CHAPTER REFERRING PRIMARILY TO @INTRODUCED SPE CIES AND @COLONIZERS RATHER THAN @INVADERS AND @EXOTICS AND SPECIlCALLY RECOM MENDEDTHEhRElNEMENTOFTHEAPPROACHOFMANYOFTHEPAPERSIN4HE'ENETICSOF #OLONIZING 3PECIES "AZZAZ ORGANIZED HIS CHAPTER ON LIFE HISTORIES AROUND THECONCEPTOF@COLONIZINGSPECIESANDALSOMADEEXPLICITREFERENCESTOTHE BOOK-OULTONAND0IMM EXPANDEDONTHEIRPAPERANDSHOWEDHOW BIOLOGICALINVASIONSCANBEUSEDTOTESTECOLOGICALTHEORY !DDITIONALPROCEEDINGSWEREPUBLISHEDFROM3#/0%WORKSHOPSHELDIN3OUTH !FRICA !USTRALIA AND 'REAT "RITAIN EG -ACDONALD ET AL 'ROVES AND "URDON +ORNBERG AND 7ILLIAMSON "EING 3#/0% INITIATIVES THESE PUBLICATIONS WERE ALSO WRITTEN FROM A CONSERVATION PERSPECTIVE (OWEVER COM MENTSBYTHEEDITORSOFTHE!USTRALIANPROCEEDINGSINDICATETHATTHEYRECOGNIZED ANEMERGINGTENSIONTHATWASDEVELOPINGININVASIONECOLOGYASSOMEECOLOGISTS EMBRACED THE CONSERVATION AND STRONG ENVIRONMENTAL EMPHASIS ARTICULATED BY %LTON WHILE OTHERS EXPRESSED CONCERN OVER THE STRONG NORMATIVE NATURE OF THIS APPROACH)NTHE&OREWORDTOTHEPUBLICATION'ROVESAND"URDON THE EDITORS STATED THAT hTHE TERMINOLOGY ASSOCIATED WITH @INVASIONS GENERALLY IS UNSATISFACTORYWITHITSCONNOTATIONSOFAMILITARYOPERATIONx7HEREVERPOSSIBLE WE HAVE TRIED TO ELIMINATE EMOTIVE TERMS SUCH AS @WEEDS @PESTS @EXOTICS AND @ALIENSv)NSTEAD THEEDITORSSTRIVEDTOUTILIZETHEWORD@INTRODUCEDASMUCHAS POSSIBLETHROUGHOUTTHEBOOK !NOTHERIMPORTANTDEVELOPMENTTHATOCCURREDDURINGTHISTIMEPERIODWASTHE FOUNDINGINOFTHE3OCIETYFOR%COLOGICAL2ESTORATION3%2 NOWKNOWNAS 3OCIETYFOR%COLOGICAL2ESTORATION)NTERNATIONAL3%2EMERGEDOUTOFTHERAPIDLY DEVELOPINGINTERESTINRESTORATIONBYINDIVIDUALSANDCONSERVATIONGROUPSINTER ESTED IN MANAGING NATURAL ENVIRONMENTS 5PON ITS FOUNDING 3%2 WAS PRIMAR ILY A .ORTH !MERICAN INITIATIVE AND THE RESTORATION ECOLOGY MOVEMENT THAT IT REPRESENTED AND INSPIRED SHARPLY DISTINGUISHED BETWEEN SPECIES BASED ON THEIR GEOGRAPHY OF ORIGIN WITH NATIVE SPECIES BEING DESIRABLE AND NON NATIVES BEING UNDESIRABLE IN NATURAL ENVIRONMENTS 4HE STARK DICHOTOMY BETWEEN NATIVE AND NON NATIVESPECIESPARTICULARLYCHARACTERIZEDCONSERVATIONANDRESTORATIONEFFORTS INREGIONSLIKE.ORTH!MERICA (AWAII AND.EW:EALAND WHICHHADEXPERIENCED RELATIVELYFEWSPECIESINTRODUCTIONSUNTILTHEPASTFEWCENTURIES4HISDISTINCTION SEEMED TO BE LESS CRUCIAL AMONG CONSERVATIONISTS AND RESTORATIONISTS IN %UROPE WHERE AS5SHERB ACKNOWLEDGED DISTINGUISHINGBETWEENNATIVEANDINTRO DUCEDSPECIESISOFTENPROBLEMATICDUETOTHEMILLENNIAOFHUMANMOVEMENTSAND

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SPECIESINTRODUCTIONSACROSSTHECONTINENT2ESTORATIONECOLOGYANDINVASIONECOL OGYEMERGEDATABOUTTHESAMETIME AND IN.ORTH!MERICA THEYDEVELOPEDAS SISTERDISCIPLINESDURINGTHELATTERS ANDCONTINUEDTOREINFORCEONEANOTHER INSUBSEQUENTYEARS 4HE GROWING RELATIONSHIP BETWEEN INVASION ECOLOGY AND CONSERVATION ECOLOGY DURINGTHISTIMEWASILLUSTRATEDBYTHEDECISIONOFTHEEDITORSOFTHEJOURNAL"IOLOGICAL #ONSERVATION TO DEVOTE A SPECIAL ISSUE TO THIS TOPIC 4ITLED "IOLOGICAL )NVASIONS OF .ATURE2ESERVES THISPUBLICATION5SHERA REPRESENTEDANOTHER3#/0%PROD UCT !LTHOUGH IT WAS BECOMING INCREASINGLY COMMON FOR ECOLOGISTS TO ADOPT THE MOREEXPLICITCONSERVATIONPERSPECTIVEEMPHASIZEDBYTHE3#/0%PROGRAM NOTALL ECOLOGISTSWEREDOINGSO&OREXAMPLE INHISARTICLEONINVASIONWINDOWS *OHNSTONE EXAMINEDHABITATINVASIBILITYMOSTLYFROMATHEORETICALPERSPECTIVE AND HEDIDNOTLINKHISARTICLETOCONSERVATIONCONCERNSREGARDINGINVASIONS 4HE DECADE ENDED WITH THE PUBLICATION OF "IOLOGICAL )NVASIONS ! 'LOBAL 0ERSPECTIVE$RAKEETAL THESYNTHESISREPORTOFTHEVARIOUSREGIONAL3#/0% SYMPOSIAANDWORKSHOPS4HISPUBLICATIONREPRESENTEDTHETHPUBLICATIONINTHE 3#/0% SERIES 4WENTY NINE ECOLOGISTS REPRESENTING SEVEN COUNTRIES 53! 5+ !USTRALIA 3OUTH!FRICA &RANCE $ENMARK )NDIA MANYOFWHOMHADCONTRIBUTED TOTHEVOLUME AUTHOREDCHAPTERSFORTHISPUBLICATION3OMEOFTHEPROMI NENTNON !MERICANCONTRIBUTORS MANYOFWHOMHAVECONTINUEDTOFOCUSMUCH OF THEIR RESEARCH ON BIOLOGICAL INVASIONS UP TO THE PRESENT INCLUDED &RANCESCO DI #ASTRI 0ETER !SHTON $AVID 2ICHARDSON )AN -ACDONALD -ICHAEL 5SHER -ARK7ILLIAMSON 2ICHARD(OBBS -ICHAEL#RAWLEY 2ICHARD'ROVESAND-ARCEL 2EJMANEK2EJMANEKHADMOVEDFROM#ZECHOSLOVAKIATOTHE5NITED3TATESBYTHE TIMETHEBOOKWASPUBLISHED )NDIVIDUALLYFOCUSINGONDIFFERENTTAXAORREGIONSOF THEWORLD CONTRIBUTORSTRIEDTOANSWERTHETHREEQUESTIONSTHATHADBEENPOSEDBY THE3#/0%ADVISORYCOMMITTEEIN)NTHEBOOKSlNALCHAPTER -OONEYAND $RAKE CONCLUDEDTHATALTHOUGHKNOWLEDGEPERMITTEDhGENERICGUIDELINESv FOR ASSESSING THE LIKELIHOOD OF BIOLOGICAL INVASIONS EG DISTURBANCES NORMALLY INCREASEDINVASIBILITY THEYCONCURREDWITHTHECONCLUSIONSREACHEDBYMOSTOFTHE AUTHORSTHATITWASNOTPOSSIBLEATTHATTIMETOMAKEACCURATEPREDICTIONSABOUT INDIVIDUALCASES !LTHOUGH SOME OF THE .ORTH !MERICAN ECOLOGISTS CONTINUED TO USE THE TERMS @INTRODUCTIONAND@INTRODUCEDSPECIESRATHERTHAN@INVASIONSAND@INVADERSIN THEVOLUMEEG 3IMBERLOFFAND0IMM POSSIBLYINDICATINGSOMERESISTANCE TOADOPTINGTHEMOREVALUE BASEDCONSERVATIONAPPROACH ITISINTERESTINGTHATTHE FREQUENCYWITHWHICH!MERICANECOLOGISTSCITED%LTONSBOOKCONTINUEDTO INCREASE)N ONLYTHREEOFTHEELEVEN 53CONTRIBUTORSTOTHE'ENETICS OF #OLONIZING 3PECIES CITED 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS )N THE .ORTH!MERICAN3#/0%VOLUME WHICHWASAUTHOREDENTIRELYBY53ECOLO GISTS OFTHECHAPTERSCITED%LTONSBOOK!NDINTHE3#/0%SYNTHESIS VOLUME OF THE 53 AUTHORED CHAPTERS CITED %LTONS BOOK "Y CONTRAST ONLYOF OFTHECHAPTERSINTHE3#/0%VOLUMEAUTHOREDENTIRELY BYNON 53ECOLOGISTSCITED%LTON4WOOFTHECHAPTERSWEREAUTHOREDBYATLEAST

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ONE53ANDONENON 53AUTHORONEOFTHESECITED%LTONANDTHEOTHERDIDNOT )N THEBOOKSlNALCHAPTER (AL-OONEYAND*AMES$RAKEBOTH53ECOLOGISTS SPECIl CALLYENCOURAGEDTHEREADERSTOCONSULT%LTONSBOOKh4HOSEWISHINGANIN DEPTH TREATMENT OF THE DYNAMICS OF BIOLOGICAL INVASIONS ARE REFERRED TO %LTONS CLASSIC WORK AND TO THE PUBLICATIONS WHICH AROSE OUT OF THE PROGRAMv ;IE THE 3#/0%PROGRAM= 4HESCATTEREDIDEASCONCERNINGBIOLOGICALINVASIONSPUTFORTHBYECOLOGISTSIN THESEVENTIESANDEARLYEIGHTIESlNALLYCOALESCEDINTHEMIDTOLATEEIGHTIES RESULT INGINTHEPUBLICATIONOFANUMBEROFIMPORTANTPAPERSANDEDITEDVOLUMESFROM 4HESE PUBLICATIONS REVIEWED KNOWLEDGE AND THEORY TO THAT POINT IDENTIlED QUESTIONS TO BE ANSWERED AND SET MUCH OF THE DIRECTION FOR FUTURE RESEARCHOFBIOLOGICALINVASIONS)NSHORT INVASIONECOLOGYEMERGEDASARESEARCH SPECIALTY AREA DURING THIS TIME PERIOD AS A DIRECT RESULT OF THESE PUBLICATIONS !LTHOUGH SOMEINVESTIGATORSCONTINUEDTOPURSUEINVASIONECOLOGYMOREINTHE TRADITIONOFTHE!SILOMARSYMPOSIUMONCOLONIZATION IE FOCUSINGPRIMAR ILYONECOLOGICALANDEVOLUTIONARYTHEORY MOREANDMOREECOLOGISTS PARTICULARLY .ORTH!MERICANECOLOGISTS WEREPRESENTINGTHEIRWRITINGSINANEXPLICITLYENVI RONMENTALCONTEXT THEPATHSETFORTHBY%LTONIN

)NVASION ECOLOGY TOOK THE SPOTLIGHT FOLLOWING THE SERIES OF INVASION BOOKS AND ARTICLESPUBLISHEDBETWEENAND"IOLOGICALINVASIONSBECAMEAPOPU LARAREAOFRESEARCHANDANINCREASINGLYCONTROVERSIALTOPICOFDEBATEDURINGTHE SRESULTINGINAmOODOFPUBLICATIONS BOTHSCHOLARLYANDPOPULAR THATCON TINUESTOTHISDAY.ATIONALANDINTERNATIONALECOLOGYMEETINGS ANDSOMEGENERAL SCIENCE MEETINGS EG !!!3 BEGAN TO REGULARLY SCHEDULE SYMPOSIA AND PAPER SESSIONSDEVOTEDTOBIOLOGICALINVASIONSANDINTRODUCEDSPECIESDURINGTHENINE TIES4HElRSTOFSEVENINTERNATIONALCONFERENCESONTHEECOLOGYOFALIENPLANTINVA SIONSWASHELDIN,OUGHBOROUGH 5+IN ANDTHETHCONFERENCEWASHELDIN &ORT,AUDERDALE &LORIDA 53!IN ANDSEVERALOFTHESECONFERENCESRESULTED INPUBLICATIONSOFTHEPROCEEDINGSEG 0YÝEKETAL 3TARlNGERETAL #HILD ET AL 7ITH THE EXCEPTION OF THE SECOND AND SEVENTH CONFERENCES HELDIN4EMPE !RIZONAAND&ORT,AUDERDALE &LORIDA THECONFERENCESTOOKPLACE IN %UROPE WITH %UROPEAN ECOLOGISTS REPRESENTING THE MAJORITY OF PARTICIPANTS 4HUS THISSERIESPROVIDESANEXCELLENTOVERVIEWOFTHERESEARCHANDIDEASCOMING FROM %UROPE AT THIS TIME PARTICULARLY FROM EASTERN %UROPEAN COUNTRIES SUCH AS THE #ZECH 2EPUBLIC WHICH AS STATED ABOVE HAVE HAD A LONG TRADITION OF STUDY INGINVASIONS3OMEOFTHEPROMINENTECOLOGISTSWHOPLAYEDASIGNIlCANTROLEIN THESE CONFERENCES AND PUBLICATIONS INCLUDE 0ETR 0YÝEK AND +AREL 0RACH #ZECH 2EPUBLIC )NGO +OWARIK AND 5WE 3TARlNGER 'ERMANY -ARK 7ILLIAMSON -AX 7ADE AND ,OIS #HILD 5+ 'IUSEPPI "RUNDU )TALY AND *OHN "ROCK AND -ARCEL2EJMANEK53!

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5NLIKE THE TIME PERIODS DESCRIBED ABOVE THE YEARS DO NOT OFFER ANOBVIOUSLISTOFIMPORTANTPUBLICATIONS DUETOTHESHEERNUMBEROFBOOKSAND ARTICLESPRODUCEDDURINGTHISTIME4HUS THEPUBLICATIONSBRIEmYMENTIONEDBELOW CONSTITUTE A VERY SMALL REPRESENTATIVE SUBSET OF THE LARGE NUMBER OF SIGNIlCANT PUBLICATIONSONECOULDHAVEINCLUDED ,ODGE’S 42%% ARTICLE PROVIDED A COMPREHENSIVE OVERVIEW ANDASSESSMENT OF THE lELD OF INVASION ECOLOGY TO THAT POINT #ONSISTENT WITH PRIOR ASSESS MENTS ,ODGE CONCLUDED THAT IT WAS NOT YET POSSIBLE TO ACCURATELY PREDICT THE CONSEQUENCESOFASINGLEINVASIONEVENTANDTHATANYHOPEOFUSEFULPREDICTIONS COULDONLYEMERGEFROMFOCUSEDSTUDIESONPARTICULARSPECIESANDENVIRONMENTS ,ODGES PAPER WAS DISTINCTIVE BECAUSE IT CONTAINED WELL DEVELOPED ASPECTS OF BOTHTHECONCEPTUALAPPROACHESTOBIOLOGICALINVASIONSTHATHADDEVELOPEDDUR ING THE PRECEDING THREE DECADES 7HILE ,ODGE BEGAN HIS PAPER EMPHASIZING THE ENVIRONMENTALIMPACTSOF@EXOTICSPECIES WHICHHAVEhSERIOUSCONSEQUENCESFOR BOTHMANANDNATUREv HEALSOSTRESSEDTHESCIENTIlCOPPORTUNITYTHATINVASIONS PROVIDE hBECAUSE THE CHARACTERISTICS AND ECOLOGICAL IMPACT OF EXOTIC SPECIES MAYPROVIDECLUESTOLONGSTANDINGISSUESINTHESTUDYOFCOMMUNITYASSEMBLYv #ONSISTENT WITH THIS DUAL EMPHASIS ,ODGE CITED BOTH %LTON AND "AKER AND 3TEBBINS IN THE SAME SENTENCE REFERRING TO THEM BOTH AS @CLASSICS 7ILLIAMSONS BOOK "IOLOGICAL )NVASIONS WHICH REVIEWED AND SYNTHESIZED INVASION RESEARCH AND THEORY CONDUCTED AND DEVELOPED DURING THE PRIOR SEV ERAL DECADES MADE A VERY IMPORTANT CONTRIBUTION BY PROVIDING INVESTIGATORS A COMPREHENSIVE AND UP TO DATE OVERVIEW OF THE NEW AND RAPIDLY EVOLVING lELD 7ILLIAMSONS BOOK PRIMARILY FOCUSED ON THE SCIENTIlC ASPECTS OF SPECIES INVA SIONS HOWEVERHEDIDSETTHEBOOKINACLEARCONSERVATIONCONTEXT EMPHASIZING THE MANAGEMENT VALUE OF BETTER SCIENTIlC UNDERSTANDING OF INVASIONS *AMES #ARLTONS NUMEROUS PUBLICATIONS ON THE IMPACTS OF INVASIONS ON MARINE ECO SYSTEMS EG #ARLTON A B PROMPTED MORE MARINE ECOLOGISTS TO CONSIDER THE IMPORTANCE OF BIOLOGICAL INVASIONS 4HE PUBLICATION OF "IOLOGICAL )NVASIONS 4HEORY AND 0RACTICE BY *APANESE ECOLOGISTS 3HIGESADA AND +AWASAKI WHICH REVIEWED MATHEMATICAL MODELS OF SPECIES SPREAD ILLUSTRATED THE EXTENT TO WHICH BIOLOGICAL INVASIONS HAD ATTRACTED THE INTERESTS OF ECOLOGISTS FROMAROUNDTHEWORLD 4HEIMPORTANCEOFUNDERSTANDINGINTERACTIONSWITHSOILMICROBESPOSITIVEAND NEGATIVE ASPARTOFTHEINVASIONPROCESSINPLANTSWASEMPHASIZEDBY+LIRONOMOS AND 2ICHARDSON ET AL EMPHASIZED THE ROLE THAT MUTUALISMS CAN PLAYINTHEINVASIONPROCESS4HEENEMY RELEASEHYPOTHESISRECEIVEDCONSIDERABLE ATTENTIONDURINGTHISTIME ALTHOUGHSTUDIESPRODUCEDCONmICTINGRESULTS+EANE AND#RAWLEY 7ILLIAMSON PROPOSEDTHESINCEOFT CITED@TENS RULE OF BIOLOGICAL INVASIONS WHICH STATES THAT APPROXIMATELY OF IMPORTED SPECIES EXIST IN SOME SENSE OUTSIDE OF CAPTIVITY OF THESE ESTABLISHED SELF SUSTAINING POPULATIONS AND OF THESE BECOME PESTS 2EVIVING THE EMPHASIS ON GENETICSOFCOLONIZINGSPECIESTHATCHARACTERIZEDTHE!SILOMARSYMPOSIUM MANYECOLOGISTSBEGANFOCUSINGONTHEGENETICSOFINTRODUCEDSPECIES RECOGNIZING

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THE IMPORTANCE THAT NEW GENOTYPES MIGHT PLAY IN SPECIES SPREAD %LLSTRAND AND3CHIERENBECK 6ILAETAL $AEHLERAND#ARINO 0YSEËKETAL %WELETAL REVIEWEDTHEBENElTSANDRISKSASSOCIATEDWITHDELIBER ATE SPECIES INTRODUCTIONS AND OUTLINED THE RESEARCH NEEDED TO PROVIDE THE INFOR MATIONREQUIREDTOINCREASETHEFORMERANDLOWERTHELATTER!SINVASIONECOLOGY CONTINUEDTODEVELOPDURINGTHISPERIOD SEVERALSCIENTISTSEXPRESSEDCONCERNTHAT THE lELD WAS NOT WELL CONNECTED WITH OTHER DISCIPLINES AND THAT INVASION ECOL OGYWASNOTBEINGINFORMEDBY NORINFORMING DISCIPLINESSUCHASBIOGEOGRAPHY EVOLUTIONARY BIOLOGY AND ECOLOGICAL SUBDISCIPLINES SUCH AS SUCCESSION ECOLOGY AND WEED ECOLOGY 6ERMEIJ $AVIS ET AL $AVIS ET AL !T THE SAME TIME SOME CONSCIOUS EFFORTS WERE BEING MADE TO BRIDGE THESE GAPS EG "OOTHETAL $URING THE NINETIES ECOLOGISTS CONTINUED THE SEVERAL DECADES LONG EFFORT TO DETERMINE WHETHER INVADERS POSSESSED DISTINCTIVE TRAITS -ANY RESEARCHERS CON CLUDED THAT THERE WAS LITTLE DIFFERENCE BETWEEN THE TRAITS OF INVASIVEAND NON INVASIVE SPECIESEG 4HOMPSONETAL 'OODWINETAL 7ILLIAMSON ALTHOUGH SOME TAXONOMICALLY BASED COMPARATIVE STUDIES DID SHOW DISTINCT DIFFERENCES BETWEEN RESIDENT AND SPREADING INTRODUCED SPECIES EG 2EJMANEK AND2ICHARDSON +OLARAND,ODGE WEREMOREOPTIMISTICTHATTRAITS COULDBEUSEDASPREDICTORSOFINVASIONS CONCLUDINGTHATQUANTITATIVEAPPROACHES (e.g., Daehler and Carino 2000) were making progress and that these approACHESSHOULD“ALLOWUSTOPREDICTPATTERNSOFINVADINGSPECIESMORESUCCESSFULLY” 5NLIKE ,ODGE’S PAPER WHICH EMPHASIZED BOTH THE CONSERVATION AND SCIENTIFIC IMPLICATIONS OF BIOLOGICAL INVASIONS THE 42%% PAPER BY +OLAR AND ,ODGE WASMUCHMORESTRONGLYORGANIZEDAROUNDTHECONSERVATIONANDENVIRONMENTAL CONCERNSABOUTSPECIESINVASIONS &ACTORSTHATCONTRIBUTETOANENVIRONMENTSSUSCEPTIBILITYTOINVASIONINVASI BILITY ONEOFTHEOTHERORGANIZINGTHEMESOFTHE3#/0%INITIATIVESINTHES ALSO CONTINUEDTOBEACENTRALFOCUSOFRESEARCHANDDISCUSSIONDURINGTHESANDTHE EARLY YEARS OF THE NEW CENTURY )N HIS BOOK "IOLOGICAL $IVERSITY (USTON ADDRESSED INVASIBILITY AND EMPHASIZED THE COMBINED IMPORTANCE OF DISTURBANCE AND PRODUCTIVITY ,ONSDALE PRESENTED HIS lNDINGS OF A COMPREHENSIVE REVIEW OF GLOBAL PATTERNS OF PLANT INVASIONS AND FOUND A POSITIVE CORRELATION BETWEENNATIVEANDEXOTICSPECIESATASITE ALTHOUGHHECONCLUDEDTHATITWASDIFl CULTTODISCRIMINATEBETWEENTHERELATIVEIMPORTANCEOFINVASIBILITYANDPROPAGULE PRESSURE$AVISETAL ARGUEDFORATHEORYOFINVASIBILITYBASEDONRESOURCE AVAILABILITY EMPHASIZING THAT INVASIBILITY IS NOT A CONSTANT CHARACTERISTIC OF AN ENVIRONMENT BUT IS AN ATTRIBUTE THAT VARIES OVER TIME AS RESOURCE AVAILABILITY mUCTUATES$AVISAND0ELSOR TESTEDTHISTHEORYINAlELDEXPERIMENTBASED ONTHEINTRODUCTIONOFNATIVESPECIESPRAIRIEFORBS INTOAPLANTCOMMUNITYDOMI NATEDBYINTRODUCEDSPECIES.ORTH!MERICANOLDlELD SHOWINGTHATITISTHEECO LOGICALPROCESSESTHATMATTER NOTTHEGEOGRAPHICORIGINOFTHESPECIESINVOLVED !LTHOUGH MUCH OF THE PROGRESS IN INVASION ECOLOGY DURING THE EIGHTIES AND NINETIESINVOLVEDMOVINGBEYONDPURELYmORISTICSTUDIESOFNATIVEANDINTRODUCED

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ASWITHOTHERINVASIVESPECIES2ICHARDSONETALB 4HEREISSOMEEVIDENCE SUGGESTINGTHATINVASIONSMAYDEPENDON ORBEENHANCEDBY THEESTABLISHMENT OF MUTUALISMS OR FACILITATIVE INTERACTIONS BETWEEN THE INVASIVE PLANT AND OTHER ORGANISMS EITHER INTRODUCED OR NATIVE 2ICHARDSON ET AL B 4HERE ARE MANYEXAMPLESOFINVASIVEWEEDSPECIESTHATAREOBLIGATEOUTCROSSERSANDREQUIRE A POLLINATOR MUTUALIST TO REPRODUCE EG PURPLE LOOSESTRIFE ,YTHRUM SALICARIA ;-AL ET AL = AND #ENTAUREA DIFFUSA AND # MACULOSA ;(ARROD AND 4AYLOR = #ARR REPORTED THAT THE INVASIVE mORA OF 6ICTORIA !USTRALIA IS POLLINATEDBYAVARIETYOFBOTHNATIVEANDINTRODUCEDINSECTSMAINLYHONEYBEES !PISMELLIFERA )NTRODUCED PLANT SPECIES WHICH ALTER SOIL NUTRIENT AVAILABILITY CAN FACILITATE THEINVASIONOFOTHERNON INDIGENOUSSPECIES&OREXAMPLE THE!TLANTICNITROGEN lXINGSHRUB-YRICAFAYAHASINVADEDNITROGEN POORVOLCANICSOILSIN(AWAIIAND PROBABLYFACILITATESFURTHERPLANTINVASIONS6ITOUSEKAND7ALKER ANDSEE 3IMBERLOFF AND 6ON (OLLE FOR OTHER EXAMPLES 4HE INTERACTION BETWEEN PLANTS AND THEIR SOIL COMMUNITY CAN RESULT IN DYNAMIC FEEDBACK %MPIRICAL EVIDENCESUGGESTSANETPOSITIVEFEEDBACKBETWEENPLANTSANDTHEIRSOILCOMMUNI TYINCOMMUNITIESOUTSIDETHEIRNATIVERANGE2EINHARTETAL FOUNDTHATTHE INVASIONOFBLACKCHERRY0RUNUSSEROTINA INTONORTHWESTERN%UROPEWASFACILITAT EDBYFEATURESOFTHESOILCOMMUNITY)NITSNATIVERANGETHESOILCOMMUNITYTHAT DEVELOPSAROUNDBLACKCHERRYINHIBITSTHEGROWTHOFNEARBYCONSPECIlCS WHEREAS THEOPPOSITEOCCURSINTHENON NATIVERANGE#ENTAUREADIFFUSAHASMUCHSTRONGER NEGATIVEEFFECTSONGRASSSPECIESINITSNON NATIVE.ORTH!MERICANRANGETHANIN ITSNATIVE%UROPEANRANGEDUETODIFFERENCESINTHEEFFECTSOFITSROOTEXUDATESAND HOWTHESEAFFECTCOMPETITIONFORRESOURCES#ALLAWAYAND!SCHEHOUG %NVIRONMENTAL RESISTANCE MAY INVOLVE ABIOTIC RESOURCE AVAILABILITY SUITABLE CLIMATICFACTORSORLIGHTINTENSITIES FOREXAMPLE ANDMAYPRECLUDEASPECIESALTO GETHER OR MAY INDUCE A SIGNIlCANT TIME LAG BETWEEN ARRIVAL AND ESTABLISHMENT OFASPECIES6ON(OLLEETAL "LACKBURNAND$UNCAN FOUND USING A GLOBAL DATASET THAT THE SUCCESS OF INTRODUCED BIRDS DEPENDS ON THE SUITABILITY OF THE ABIOTIC ENVIRONMENT FOR THE SPECIES AT THE INTRODUCTION SITE &OR EXAMPLE INTRODUCTIONSUCCESSWASSIGNIlCANTLYGREATERWHENTHEDIFFERENCEBETWEENASPE CIESLATITUDEOFORIGINANDTHELATITUDEOFINTRODUCTIONWASSMALL 4HE @ENEMY RELEASE HYPOTHESIS HAS BEEN USED TO EXPLAIN THE SUCCESS OF SOME SPECIES IN COMMUNITIES OUTSIDE THEIR NATIVE RANGE AND STATES THAT OUTSIDE OF THEIR NATIVE RANGE PLANT SPECIES SHOULD EXPERIENCE A DECREASE IN REGULATION BY HERBIVORESANDOTHERNATURALENEMIES RESULTINGINANINCREASEINABUNDANCEAND DISTRIBUTION 4HE SUCCESS OF BIOLOGICAL CONTROL HAS BEEN USED AS SUPPORT FOR THE ENEMY RELEASE HYPOTHESIS +EANE AND #RAWLEY %MPIRICAL EVIDENCE IN SUPPORT OF THE HYPOTHESIS IS EQUIVOCAL +EANE AND #RAWLEY -ARON AND 6ILÉ HOWEVER INANANALYSISOFPLANTSPECIESNATURALIZEDINTHE53 -ITCHELL AND 0OWER FOUND SPECIES IN THEIR NON NATIVE RANGES HAD ON AVERAGE FEWER FUNGI AND FEWER VIRUS SPECIES THAN IN THE RESPECTIVE NATIVERANGES

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/CCURINHUMANDISTURBEDAREASANDHAVE SPREADTOOCCURINDISTURBEDNATURALAND SEMI NATURALCOMMUNITIES

/PERATIONALLY OURDElNITIONOFNATURALIZEDTHUSLIMITSSPECIESTOOCCURRENCEINMAINLYHUMAN MODIlEDCOMMUNITIESTHISISNOTNECESSARILY THEINTENTOF2ICHARDSONETALSDElNITIONSEETEXTONTHIS

4RANSFORMERS

(ASSPREADTOAREASDISTANTTOTHEPOINT OFINTRODUCTION

0RODUCESREPRODUCTIVEOFFSPRINGINLARGENUMBERS #OMMONANDWIDESPREAD LOWEXTINCTION ATCONSIDERABLEDISTANCEFROMPARENTPLANT PROBABILITY3% 3% FORSPECIESPRIMARILYDISPERSEDBYSEEDM INYEARSFORSPECIESSPREADINGPRIMARILY VEGETATIVELYMYEARS ORANYSPECIES PRIMARILYSPREADBYHUMANS

3%2ANKINGIN/NTARIO

!NALIENPLANT

2EALIZED#RITERIA

)DEALCRITERIA

4ABLE #ONTINUED 0ARAMETER 2ICHARDSONETALA )NVASIVEPLANTS

(4-URPHY ET AL


,ONG DISTANCE DISPERSAL VECTORS INCLUDED WEED CONTAMINATED CROP SEED SOIL OROTHERAGRICULTURALPRODUCTS BOATS CARSANDOTHERVEHICLES WATERFOWL FISH AND IRRIGATIONWATER 2ATES OF SPREAD AS REQUIRED BY 2ICHARDSON ET ALS SCHEME PROVE TO BE ONLY RARELY AVAILABLE ONLY SEVEN OF THE ARTICLES WE SURVEYED REPORTED ANY RATE OF SPREAD&IVEOFTHESEWEREFORSPECIESTHATSPREADPRIMARILYBYVEGETATIVEMEANS ANDNONEHADBEENMEASUREDORESTIMATEDINTHEADVENTIVE/NTARIOENVIRONMENT 7HERE DISPERSAL OF PROPAGULES IS PROMOTED BY ANTHROPOGENIC ACTIVITIES OR OTHER NON STANDARDMEANS RATESOFSPREADCANNOTREASONABLYBEESTIMATEDBYSEEDOR VEGETATIVE PROPAGULE CHARACTERISTICS (IGGINS ET AL !LTHOUGH IN THEORY SPREAD COULD BE MEASURED RELATIVELY OBJECTIVELY USING POPULATION GROWTH AND DISTANCE FROM THE SOURCE UNLESS SUBSTANTIAL HISTORICAL INFORMATION IS AVAILABLE REALRATESOFSPREADAREQUITEDIFlCULTTODETERMINE&URTHERMOREFORMANYOFTHE SPECIES IN OUR DATASET WHICH ARE PRIMARILY AGRICULTURAL WEEDS LONG DISTANCE DISPERSAL MAY OCCUR RELATIVELY REGULARLY THROUGH TRANSPORT IN CONTAMINATED SEED STOCKS OR INFESTED HAY 4HESE METHODS HAVE BEEN CONSIDERED A MAJOR CON TRIBUTORTOSPREADFORMANYSPECIESEG 3ILENEALBA -C.EILL-ELILOTUSSPP 4URKINGTONETAL3ORGHUMHALEPENSE 7ARWICKAND"LACK 4HE .()# DATABASE INCLUDES ESTIMATES OF ABUNDANCE OF EXOTIC PLANTS USING A PROVINCIAL RANKING SYSTEM 3% RANK ;3UB NATIONAL EXOTIC= 7E USED THE PROVIN CIAL3%RANKINGASASURROGATEFORTHEAMOUNTOF@SPREADTHATHADBEENACHIEVED 4HE 3% RANKING IS ESSENTIALLY A DISTRIBUTION AND ABUNDANCE INDICATOR AND SO CARRIESIMPLICATIONSOFEXTINCTIONRISK4HUS3% AND3% RANKEDSPECIESARECON SIDEREDVULNERABLETOEXTINCTION 3%SPECIESHAVEAMEDIUMRISKOFEXTINCTIONAND 3%AND3%HAVE GENERALLY ALOWRISKOFEXTINCTIONSEE-ASTER 4HUS s 3% %XTREMELY RARE IN /NTARIO USUALLY OR FEWER OCCURRENCES IN THE PROV INCE OR VERY FEW REMAINING INDIVIDUALS OFTEN ESPECIALLY VULNERABLE TO EXTIRPATION s 3% 6ERYRAREIN/NTARIOUSUALLYBETWEENANDOCCURRENCESINTHEPROV INCEORWITHMANYINDIVIDUALSINFEWEROCCURRENCESOFTENSUSCEPTIBLETO EXTIRPATION s 3% 2ARETOUNCOMMONIN/NTARIOUSUALLYBETWEENANDOCCURRENCES IN THE PROVINCE MAY HAVE FEWER OCCURRENCES BUT WITH A LARGE NUMBER OF INDIVIDUALS IN SOME POPULATIONS MAY BE SUSCEPTIBLE TO LARGE SCALE DISTURBANCES -OST SPECIES WITH AN 3% RANK ARE ASSIGNED TO THE WATCH LIST UNLESSTHEYHAVEARELATIVELYHIGHGLOBALRANK s 3% #OMMONANDAPPARENTLYSECUREIN/NTARIOUSUALLYWITHMORETHAN OCCURRENCESINTHEPROVINCE s 3% 6ERYCOMMONANDDEMONSTRABLYSECUREIN/NTARIO #OMMUNITY ECOSYSTEMANDECONOMIC@IMPACTS ASPER$AVISAND4HOMPSONS SCHEME WERE QUANTIlED AS FOLLOWS AND SEE 4ABLE &OR COMMUNITY IMPACT SPECIES OCCURRENCE IN ONLY COMMUNITY TYPES ANDOR BOTH GENERALLY HIGHLY HUMAN MODIlED COMMUNITIES WAS SCORED AS POINT OCCURRENCE IN ANY OTHER

&ROMHERBARIUMSPECIMENOR IFNODATEGIVEN DATEISNOTED ASIFTHESPECIESISLISTED IN'LEASON )S/NTARIOWITHINTHENATIVE RANGEOFTHESPECIES 6EGETATIVEORSEED

$ATEOFlRST DOCUMENTED OCCURRENCE IN/NTARIO

.ATIVITYTO/NTARIO

0RIMARYMEANS OFRECRUITMENT

VEGETATIVE SEED

YES NO

$ATE

4ABLE $ATAEXTRACTEDFROMTHE"IOLOGYOF#ANADIAN7EEDSSERIESAND.()#DATABASE TOADDRESSCRITERIAOUTLINEDIN4ABLE !TTRIBUTE $ESCRIPTION 6ARIABLE !BUNDANCE2ANK 3%2ANKING 3%%XTREMELYRAREIN/NTARIOUSUALLYORFEWEROCCURRENCESINTHEPROVINCE ORVERYFEWREMAININGINDIVIDUALSOFTENESPECIALLYVULNERABLETO EXTIRPATION 3%6ERYRAREIN/NTARIOUSUALLYBETWEENANDOCCURRENCESINTHE PROVINCEORWITHMANYINDIVIDUALSINFEWEROCCURRENCESOFTENSUSCEPTIBLE TOEXTIRPATION 3%2ARETOUNCOMMONIN/NTARIOUSUALLYBETWEENANDOCCURRENCES INTHEPROVINCEMAYHAVEFEWEROCCURRENCES BUTWITHALARGENUMBEROF INDIVIDUALSINSOMEPOPULATIONSMAYBESUSCEPTIBLETOLARGE SCALE DISTURBANCES 3%#OMMONANDAPPARENTLYSECUREIN/NTARIOUSUALLYWITHMORETHAN OCCURRENCESINTHEPROVINCE 3%6ERYCOMMONANDDEMONSTRABLYSECUREIN/NTARIO

(4-URPHY ET AL

WIND WATER BIRD ANIMAL GRAVITYORBALLISTIC

0RIMARYMODEOFNATURAL DISPERSALUSUALLYBASEDON ADAPTATIONSOFTHESEEDORFRUIT /THERDOCUMENTED USUALLY HUMAN FACILITATED MEANS OFDISPERSAL $OCUMENTEDOCCURRENCEIN VARIOUSCOMMUNITYTYPES $OCUMENTEDECONOMICIMPACTS

3ECONDARY DISPERSALMODE

#OMMUNITIESINWHICH SPECIESOCCURS

%CONOMICIMPACTS

%COSYSTEMIMPACTS $OCUMENTEDECOSYSTEMIMPACTS FORMSMONOCULTURES DOMINATESAQUATICECOSYSTEMSWITHMAJOREFFECTSON mOW OXYGEN LIGHTETC SIGNIlCANTNITROGENlXER %CONOMIC IMPACTS OTHER THAN THOSE LISTED HERE WERE OCCASIONALLY REPORTED EG MAKES HARVESTING DIFlCULT CHEMICALLY INHIBITS CROP SPECIES HOWEVERTHESEIMPACTSARECLOSELYRELATEDTO ANDALWAYSOCCURREDWITH ANDTHEREFOREWERECONSIDEREDREDUNDANTANDNOT INCLUDEDASSEPARATEIMPACTS

COMPETESWITHCROPORPASTURESPECIES ISTOXICORIRRITANTTOFARMANIMALS ORHUMANS DESTROYSAPPEARANCEOFLAWNSORGARDENS HARBOURSINSECTS ORDISEASEORGANISMSTHATATTACKOTHERPLANTSPECIES INTERFERESWITHWATER INFRASTRUCTURE IMPACTSRECREATIONALAREASBEACHES LAKESETC CONTAMI NATESSEEDSTOCKS INFESTSHAYETC

ROADSIDES GARDENS WASTELANDS OTHERDISTURBEDURBANAREAS GRAZED PASTURE CULTIVATEDlELDS CROPS DISTURBEDNATURALCOMMUNITIES OPEN WOODLAND FORESTMARGINSORCLEARINGS STREAMBANKS SHORELINES AQUATICLAKE STREAM POND RIVERETC

CONTAMINATEDCROPSEEDSORINFESTEDHAY FARMMACHINERYORVEHICLES INSOILORMANURE LIVESTOCKORDOMESTICANIMALS BOATS IRRIGATION WATER HUMANCLOTHINGORFOOTWEAR

6ARIABLE

$ESCRIPTION

4ABLE #ONTINUED !TTRIBUTE 0RIMARYDISPERSAL MODE


(4-URPHY ET AL

MORE @NATURAL COMMUNITY TYPES BROUGHT AN ADDITIONAL POINT 4HUS IF THE SPECIES OCCURRED IN COMMUNITY TYPES AND SEE 4ABLE THE TOTAL SCORE WOULD BE POINTS 4HE TOTAL NUMBER OF POINTS SCORED WAS THEN MULTIPLIED BY THE 3% RANK VALUE &OR EXAMPLE IF THE ABOVE SPECIES WAS RANKED AS 3% THE #OMMUNITY )MPACT 3CORE #)3 WOULD BE ! SIMILAR SYSTEM WAS APPLIED TO ECOSYSTEMIMPACTS%COSYSTEM)MPACT3CORE%)3 &ORECONOMICIMPACT ASPE CIESSCOREDPOINTSIFITWASNOTEDTOHAVEIMPACTSRELATEDTODESCRIPTORS AND SEE4ABLE WHICHINGENERALINVOLVEBOTHCROPPRODUCTIONLOSSESANDCONTROL COSTS AND POINT IF IT WAS NOTED TO HAVE IMPACT IN ANY OTHER CATEGORY WHICH PRIMARILY INVOLVE CONTROL COSTS ONLY 4HAT TOTAL SCORE WAS THEN MULTIPLIED BY THE3%RANKVALUEASABOVE%CONOMIC)MPACT3CORE%CON)3 #RITERIAFORDETERMININGWHETHERTHESCORECORRESPONDEDTOA@GREATOR@SMALL IMPACTARESHOWNIN4ABLE@$4 )FASPECIESWASDETERMINEDTOHAVEAGREAT IMPACTINANYOFTHETHREEIMPACTCATEGORIES THEOVERALLIMPACTWASDETERMINEDAS @GREATINTHELANGUAGEOF$4 )TISDIFlCULTTOREMOVESUBJECTIVITYFROMTHESCOR INGOFIMPACT7ETRIEDSEVERALALTERNATIVESTOTHEABOVESCHEMESANDPRESENTONE OFTHEMHERE7EAPPLIEDANALTERNATIVEMETHODTOCALCULATING#)3IFTHESPECIES OCCURREDONLYINMEDIUMTOHIGHLYHUMAN MODIlEDCOMMUNITIESIE OR ASCOREOFWASAPPLIED ANDASCOREOFWASAPPLIEDTOASPECIESTHATOCCURREDIN ANYNATURALORSEMI NATURALCOMMUNITY4HESCOREWASTHENMULTIPLIEDBYTHE3% RANKVALUE7EALSOMODIlEDTHECRITERIAFORDETERMININGWHETHERTHEIMPACTWAS SMALLORGREAT4HESETWOMODIlCATIONSCOMBINEDRESULTINTHEALTERNATIVE$AVIS AND4HOMPSONCLASSIlCATION$4IN4ABLEANDIN4ABLEINRESULTS 4ABLE #RITERIATOBESATISlEDFORDETERMINATIONOFIMPACTAS@SMALLOR@GREATINTWO ALTERNATIVESCORINGSCHEMESAPPLIEDTO$AVISAND4HOMPSONSCLASSIlCATIONSCHEME )MPACT $4 $4 3MALL 'REAT 3MALL 'REAT

#OMMUNITY#)3 %COSYSTEM%)3 %CONOMIC%CON)3

) )

) )

)N OUR APPLICATION OF 2ICHARDSON ET ALS SCHEME THE 3% RANK VALUE IS THE PRI MARY FACTOR DRIVING THE DISTINCTION BETWEEN INVASIVE AND OTHER ALIEN SPECIES 3%RANKISALSOAKEYFACTORINOURAPPLICATIONOF$AVISAND4HOMPSONSSCHEME INTHEDIVISIONBETWEENGREATANDSMALLIMPACTS!CLOSEASSOCIATIONBETWEEN3% RANKANDTHERAWIMPACTFACTORIE IMPACTSCORESPRIORTOMULTIPLICATIONBY3% RANKVALUE SHOULDRESULTINAGREATEROVERLAPBETWEENTHETWOSCHEMES7EUSED


CORRELATIONANALYSISTODETERMINEHOWTHE3%RANKVALUEWASRELATEDTOTHERAW IMPACT SCORES FOR COMMUNITY AND ECONOMIC IMPACTS ONLY SEVEN SPECIES SCORED ABOVEINTHEECOSYSTEMIMPACTCATEGORYSO%)3WASNOTTESTEDFORASSOCIATION 4O EXAMINE DIFFERENCES BETWEEN GREAT AND SMALL IMPACT SPECIES IN LIFE HISTORY TRAITSWEUSEDCHI SQUAREDCONTINGENCYANALYSISWITH9ATESCORRECTION)FTWO WAY CONTINGENCY TABLES SHOWED NON INDEPENDENCE 0 THE &REEMAN 4UKEY DEVIATE WAS USED TO DETERMINE IF ANY INDIVIDUAL CELL WAS EITHER UNDER OR OVER REPRESENTEDCOMPAREDTOTHEEXPECTEDVALUE,IFE HISTORYVARIABLESFORWHICHDATA WERECOLLECTEDARESHOWNIN4ABLE 4ABLE ,IFE HISTORYTRAITSRECORDEDFOREACHSPECIES ,IFE HISTORYTRAIT 0ARAMETERS 3EEDDORMANCY ,ONGYEARS 3HORTYEARS .ONEKNOWN 0RIMARYPOLLINATIONMODE )NSECT WIND SELF VARIOUS UNKNOWN #LONALORGANPRESENCE 0RESENT ABSENT &LOWERINGSEASON %ARLY MID LATE ALLSEASON &LOWERINGDURATION .UMBEROFMONTHS 3OILMOISTUREPREFERENCE -OIST DRY VARIABLE 3EXHABIT (ERMAPHRODITE MONOECIOUS DIOECIOUS POLYGAMOUS ,IFECYCLE !NNUALANDBIENNIAL PERENNIAL VARIABLE $OMINANTRECRUITMENTMODE 6EGETATIVE SEED VARIABLE

!S WITH MOST MACROECOLOGICAL DATASETS #ADOTTE ET AL OURS HAS ITS LIMITATIONS4HETERM@WEEDINTHE"IOLOGYOF#ANADIAN7EEDSSERIESREFERSTOANY VASCULARPLANTTHATPERPETUATESITSELFINHABITATSWHEREITIShNOTWANTEDv#AVERS AND7ARWICK AMEANINGDIFFERENTFROMTHATCOMMONLYUSEDFOR@WEEDS INTHEECOLOGICALLITERATUREANDWHICHUSUALLYINCLUDESTHATTHESPECIESHASDETECT ABLE ECONOMIC OR ENVIRONMENTAL IMPACTS EG 0YÝEK ET AL 2ICHARDSON ETAL A 4HUS THESE SPECIES SHOULD NOT BE CONSIDERED TO HAVE BEEN ALREADY CLASSIlED AS @WEEDS IN THE TRADITIONAL ECOLOGICAL SENSE RATHER THEY STILL VALIDLY REPRESENTSPECIESINTHERANGEOFCATEGORIESDElNEDBYTHETWOSCHEMES4HESPE CIESINOURLISTAREBIASEDTOWARDSSPECIESOCCURRINGINAGRICULTURALAREASSINCETHE ORIGINALPURPOSEOFTHESERIESWASTOPROVIDEABASISFOREFFECTIVECONTROLMETHODS AND TO MEET THE NEEDS OF REGULATORY AGENCIES IN #ANADA #AVERS AND 7ARWICK (OWEVER THE DATASET DOES INCLUDE A RANGE OF SPECIES OCCURRING IN BOTH NATURALANDAGRICULTURALHABITATSANDINCLUDESBOTHABUNDANT3%AND3% AND RARE3% SPECIES)TISIMPORTANTTONOTETHATWEARENOTATTEMPTINGTOTESTTHE ACCURACY OF EITHER SCHEME IN CLASSIFYING SPECIES INTO CATEGORIES SINCE THERE IS NO @RIGHT ANSWER 2ATHER WE AIM TO DETERMINE IF EITHER SCHEME IS MORE FUNCTIONAL OROPERATIONAL BASEDONTHEDATAAVAILABLEINATYPICALSPECIESDATASET4HUSANY

(4-URPHY ET AL

CONCLUSIONS WE MAKE AS TO WHICH CLASSIlCATION WAS @BETTER REFER ONLY TO WHICH MODEL COULD BE APPLIED MORE USEFULLY GIVEN THE DATA AVAILABLE TO EVALUATE EACH CRITERIONFORCATEGORIZATION

2%35,43 ! TOTAL OF FAMILIES WAS REPRESENTED IN THE DATASET OF SPECIES 4ABLE 4HE !STERACEAE WAS THE ONLY FAMILY REPRESENTED IN ALL 3% RANKS WITH A TOTAL OF SPECIES 0OACEAE WAS NEXT WITH A TOTAL OF SPECIES AND ONLY 3%SPECIESEXTREMELYRARE WERENOTREPRESENTED&ABACEAEWASNEXTWITHNINE SPECIES ALL RANKED 3% 4HERE WERE EIGHT "RASSICACEAE IN 3% 3% AND 3%RANKS 4WENTY TWOOFTHEFAMILIESHADONLYORSPECIESREPRESENT EDINTHEDATASET!STERACEAE &ABACEAEAND"RASSICACEAEAREALLOVER REPRESENTED INOURDATASETCOMPAREDWITHTHEIRREPRESENTATIONINTHEEXOTICmORAOF/NTARIO ANDAMONGNATIVE/NTARIOSPECIESSEE4ABLE !PPLICATIONOFTHE2ICHARDSONETALSCHEMECLASSIlEDOFTHETOTALSPECIES AS INVASIVE AS OPPOSED TO $AVIS AND 4HOMPSON WHERE APPROXIMATELY OF SPECIES WERE CLASSIlED AS INVADERS USING OUR lRST CRITERIA $4 AND USING THE ALTERNATIVE CRITERIA $4 4ABLE !LL BUT ONE OF THE SPECIES CLASSIlED AS INVASIVE BY 2ICHARDSON ET AL WERE ALSO CLASSIlED AS INVASIVE BY BOTH $AVIS AND 4HOMPSONSCHEMES4HEEXCEPTIONWAS(ELIANTHUSTUBEROSUSWHICHWASCLASSIlED ASASUCCESSIONALCOLONIZERINBOTH$4AND$4DUETOITSACTUALLYBEINGCONSID EREDNATIVETO/NTARIO4HEDISTINCTIONDEPENDSUPONCONmICTINGCONCLUSIONSBY EXPERTS!LTHOUGHCONSIDEREDNON NATIVETO/NTARIOBYSEVERALAUTHORS-ORTON AND6ENN;= .EWMASTERETAL;= AND3COGGAN;= MOSTREGIONAL mORASANDmORASFROMNEARBYAREASCONSIDERTHESPECIESNATIVEEG 'LEASONAND #RONQUIST )T IS LIKELY THAT AT SOME TIME IN THE FUTURE THE 3 RANK OF THIS SPECIES WILL BE CHANGED FROM 3% TO 3 INDICATING A NATIVE STATUS RATHER THAN EXOTICINTHEPROVINCE .()# !LLSPECIESRANKEDAS3%WERECLASSIlEDBY 2ICHARDSONETALASCASUALANDBY$4AND$4ASNOVELNON INVASIVECOLONIZERS 4ABLE )NOURAPPLICATIONOFBOTHCLASSIlCATIONS ITWASNOTPOSSIBLEFORAN3% SPECIESTOBEREGARDEDASINVASIVE/FTHE3%SPECIES 2ICHARDSONETALSSCHEME CLASSIlEDASINVADERS COMPAREDWITH$4 AND$4 4ABLE 3%RANKVALUEWASSIGNIlCANTLYCORRELATEDWITHRAWCOMMUNITYIMPACTSCORES $4 R P N$4 R P N HOW EVERTHEREWASNOCORRELATIONBETWEEN3%RANKVALUEANDECONOMICIMPACTSCORE $4 R – P N 4HUS SPECIES WITH GREATER ABUNDANCE TENDEDTOOCCURINMOREOFTHEDElNEDCOMMUNITYTYPES INCLUDINGNATURALAND SEMI NATURAL COMMUNITIES THAN LESS ABUNDANT SPECIES BUT DID NOT NECESSARILY FALLINTOMOREECONOMICIMPACTCATEGORIES)N$4ALL3%SPECIESHADANOVERALL IMPACT OF @GREAT WHEREAS IN $4 THREE 3% SPECIES HAD ONLY @SMALL IMPACT 'REAT ANDSMALL IMPACTSPECIESDIFFEREDONLYINTHEIRPROPORTIONSINTHESEEDDOR MANCYLIFE HISTORYPARAMETERLONG SHORTORNONE $4 r P


4ABLE &AMILYREPRESENTATIONIN3%RANKANDTOTALNUMBEROFFAMILYMEMBERSINTHE DATABASE COMPAREDWITHPROPORTIONOFFAMILYINALLSPECIESLISTEDAS@EXOTICIN/NTARIOAND INALLNATIVESPECIESOF/NTARIO &AMILY !MARANTHACEAE !PIACEAE !STERACEAE "ORAGINACEAE "RASSICACEAE #ANNABACEAE #ARYOPHYLLACEAE #HENOPODIACEAE #LUSIACEAE #ONVOLVULACEAE $IPSACACEAE %UPHORBIACEAE &ABACEAE (ALORAGACEAE ,AMIACEAE ,YTHRACEAE -ALVACEAE /XALIDACEAE 0LANTAGINACEAE 0OACEAE 0OLYGONACEAE 0ORTULACACEAE 0OTAMOGETONACEAE 2ANUNCULACEAE 2OSACEAE 2UBIACEAE 3CROPHULARIACEAE 3OLANACEAE 6IOLACEAE 4OTAL

3%2ANK

4OTAL OF TOTAL DATASET

OF OF FAMILY FAMILY INALL INNATIVES EXOTICS OF OF/NTARIO /NTARIO N N

(4-URPHY ET AL

4ABLE 3UMMARY OF RESULTS OF CLASSIlCATION SCHEMES FOR SPECIES IN EACH 3% RANK REGIONALDISTRIBUTIONANDABUNDANCE $4$AVISAND4HOMPSON 4OTALIN3%CATEGORY

3%

3%

3%

3%

3%

4OTAL

2ICHARDSONETAL s #ASUAL s .ATURALIZED s )NVASIVE

$4 s 3UCCESSIONALCOLONIZER s .OVEL NON INVASIVECOLONIZER s )NVADER

$4 s 3UCCESSIONALCOLONIZER s .OVEL NON INVASIVECOLONIZER s )NVADER

$4GREATIMPACT $4SMALLIMPACT $4GREATIMPACT $4SMALLIMPACT

$4 r P 2ESULTS OF THE &REEMAN 4UKEY DEVIATE TEST INDI CATEDTHATSPECIESWITHASMALLIMPACTWERESIGNIlCANTLYUNDER REPRESENTEDBYTHE PRESENCEOFALONGDORMANCYPERIODANDSPECIESWITHAGREATIMPACTWEREUNDER REPRESENTEDBYPRESENCEOFSHORTANDORNODORMANCYPERIOD!DDITIONALLY GREAT ANDSMALL IMPACTSPECIESDIFFEREDINTHEIRGEOGRAPHICORIGIN$4 r P$4 r P 3PECIESHAVINGASMALLIMPACTWERE UNDER REPRESENTED IN ORIGINATING FROM %URASIA AND WERE OVER REPRESENTED IN ORIGINATINGFROM!SIAPROPERANDTHE-EDITERRANEANAREAOF%UROPE3PECIESWITH AGREATIMPACTWEREOVER REPRESENTEDINORIGINATINGFROM%URASIA


$)3#533)/. $AVIS AND 4HOMPSONS CLASSIlCATION SCHEME WAS CLEARLY LESS DISCRIMINATING IN DETERMININGINVASIVESPECIESINTHISDATASET4HISCOULDBEAMELIORATEDSOMEWHAT BY INCREASING THE SCORE RANGE FOR @SMALL IMPACTS (OWEVER THE ORIGINAL SCORE RANGE FOR %CON)3 ) TAKES INTO ACCOUNT THE FACT THAT AN 3% SPECIES WITH AN IMPACTINONEECONOMICCATEGORYSUCHASTHEMOSTCOMMONCATEGORYn WOULD SCOREA)TMAKESLITTLESENSETOCALLTHISA@SMALLIMPACT(OWEVER EVENWITH THEEXPANDEDRANGEFORSMALLECONOMICIMPACTS$4 THEREAREONLYSEVENSPE CIES THATWOULDBEREASSIGNEDFROMTHE@INVASIVECATEGORYTOTHE@NON INVA SIVECOLONIZERCATEGORY)TISNOTEWORTHYTHAT3%RANKANDTHEECONOMICIMPACT SCOREBEFOREADJUSTINGFORABUNDANCE WERENOTCORRELATED3%SPECIESWEREJUST ASLIKELYTOHAVEANUMBEROFDIFFERENTTYPESOFECONOMICIMPACTSAS3%SPECIES (OWEVER MORE ABUNDANT SPECIES WERE MORE LIKELY TO HAVE SPREAD TO NATURAL OR SEMI NATURALHABITATSTHANLESSABUNDANTSPECIES /N A CASE BY CASE BASIS 2ICHARDSON ET ALS SCHEME WOULD SEEM TO BE MORE PRACTICALLY USEFUL SINCE IT IS IN THEORY LESS SUBJECTIVE 9ET WHEN ATTEMPTING TO CLASSIFY EVEN A RELATIVELY DETAILED AND CONSISTENT DATASET AS WE HAVE DONE THE @SPREADCRITERIONPRESENTSALMOSTASMANYPROBLEMSANDISPERHAPSJUSTASSUBJEC TIVEAS$AVISAND4HOMPSONSIMPACTCRITERION7EAREFORTUNATEWITHTHE/NTARIO DATASETTOHAVETHEDISTRIBUTIONANDABUNDANCERANKINGINFORMATIONTHATCANBE USEDASASURROGATEFORTHE@SPREADCRITERION(OWEVERTHE3%RANKINGSYSTEMHAS SEVERAL LIMITATIONS IN ITS USE AS A SPREAD SURROGATE &IRST IT IS BASED ON CURRENT ABUNDANCEINTHEPROVINCE3% RANKEDSPECIESAREATTHELIMITOFTHEABUNDANCE RANKING BUT SOME MAY HAVE EXHAUSTED THE POTENTIAL RANGE OF SUITABLE HABITATS ANDBENOLONGERCAPABLEOFFURTHERSPREAD WHILEOTHERSMAYNOT3% SPECIES ALTHOUGHNOTCURRENTLYABUNDANT MAYBESPREADINGATAMORERAPIDRATETHAN3% AND3%SPECIES ANDTHISREMAININGPOTENTIALFORRAPIDSPREADISNOTCAPTUREDIN THE3%RANKING4HUSTHESPREADCRITERIONISCOMPLICATEDBYTHETEMPORAL@SNAP SHOTNATUREOFTHEASSESSMENT ! RELATED PROBLEM IS THAT THE 3% RANKING GIVES NO INDICATION AS TO WHERE THE POPULATIONSARELOCATEDRELATIVETOEACHOTHER)NFACT VIRTUALLYALLOFTHE3%SPE CIESINOURDATASETHAVEBEENRECORDEDFROMPOPULATIONSWIDELYDISTANTFROMONE ANOTHERIE KM DETERMINEDTHROUGHAVISUALINSPECTIONOFTHEDISTRIBU TIONMAPS )FWEWERETOBASETHERATE OF SPREADCRITERIONONTHE TIME SINCE INTRODUCTIONOFTHESPECIES ANDTHEAVERAGEDISTANCEBETWEENPERSISTENTPOPULATIONS IN /NTARIO WE WOULD MOST LIKELY PLACE ALL THE SPECIES ON OUR LIST !PPENDIX IN2ICHARDSONETALS@INVASIVECATEGORY4HESPREADCRITERIONFORINVASIVESIE FORSEED DISPERSEDSPECIES MFROMPARENTALPLANTSINYEARS BEGINSTO MAKELITTLESENSEONREGIONALANDLANDSCAPESCALES ESPECIALLYWHENMOSTSPECIES HAVEMODESOFDISPERSALWITHAPOTENTIALTOCARRYPROPAGULESGREATDISTANCESFROM PARENTALINDIVIDUALS 2ICHARDSON ET AL A ESTIMATED THAT OF @INVADERS AS DElNED BYTHEIRCLASSIlCATION WOULDHAVE@HARMFULDETECTABLEENVIRONMENTALORECONOMIC

(4-URPHY ET AL

EFFECTS AND THAT THE REST ARE @BENIGN INVADERS WHOSE ENVIRONMENTAL OR ECONOMIC IMPACTS ARE BEYOND ANY PRACTICAL DETECTION LIMITS "Y OUR ANALYSIS OF THE SPECIES CLASSIlED AS INVASIVE BY 2ICHARDSON ET ALS SCHEME HAVE LARGE ENVIRONMENTAL OR ECONOMIC IMPACTS AND MOREOVER BETWEEN AND OF SPECIES DElNED AS NATURALIZED ALSO HAVE HARMFUL EFFECTS 4HIS IS PERHAPS NOT SURPRISING SINCE OUR CRITERIA FOR NATURALIZATION IN 2ICHARDSON ET ALS SCHEME INCLUDED A REQUIREMENT THAT THE SPECIES HAD NOT YET SPREAD TO NATURAL OR SEMI NATURALHABITATS4HUSWHILECOMMUNITYIMPACTSWEREMINIMIZEDOCCURRENCEIN FEWERCOMMUNITYTYPES ECONOMICIMPACTSFORTHESESPECIESMAYSTILLHAVEBEEN LARGEENOUGHTOGENERATEANOVERALLGREATIMPACT&OREXAMPLE 3%SPECIESTHAT ONLYOCCURINCULTIVATEDlELDSIE 2ICHARDSONETALS@NATURALIZEDSPECIESINOUR ANALYSIS WOULDSTILLHAVESCOREDAGREATIMPACTIFTHEYCOMPETEWITHAGRICULTURAL SPECIES IN THOSE lELDS AND THEREFORE WOULD HAVE BEEN CLASSIlED AS INVADERS IN $ 4S SCHEME )T SHOULD BE NOTED THAT THE DISTINCTION BETWEEN NATURALIZED AND INVASIVE SPECIES WE USED HERE MAY NOT STRICTLY REPRESENT THE INTENTION OF 2ICHARDSON ET AL 3INCE 2ICHARDSON ET AL SUGGEST NATURALIZED PLANTS HAVE NOT OVERCOMEBARRIERSTODISPERSAL WELIMITEDNATURALIZEDSPECIESTOOCCURRENCEONLY INHUMAN MODIlEDCOMMUNITIES2ICHARDSONETALSDElNITIONISUNCLEARINTHIS RESPECT THEY NOTED h.ATURALIZED PLANTSxDO NOT NECESSARILY INVADE NATURAL SEMI NATURALORHUMAN MADEECOSYSTEMSv #ADOTTEETAL HAVESTUDIEDTHERELATIONSHIPBETWEEN3%RANKSANDLIFE HISTORY ATTRIBUTES IN /NTARIOS EXOTIC mORA N 4HEIR RESULTS SHOWED THAT COMMONEXOTICSWEREMORELIKELYTOHAVEACLONALORGAN ALONGERmOWERINGPERIOD ANDA%URASIANORIGIN7EFOUNDTHAT INTERMSOFLIFE HISTORYTRAITS LARGE IMPACT SPECIESDIFFEREDFROMSMALL IMPACTONESINTHELIKELIHOODOFHAVINGALENGTHYSEED DORMANCYPERIOD#ADOTTEETALFOUNDTHEVARIABLEMOSTSTRONGLYASSOCIATEDWITH INVASIVENESSANDHIGHER3% RANK WASORIGININ%URASIAAND%UROPE 3IMILARLY INOURANALYSIS SPECIESHAVINGGREATIMPACTCAMEDISPROPORTIONATELYOFTENFROM %URASIA 4HIS SUPPORTS #ADOTTE ET AL IN THAT SPECIES NATIVE ELSEWHERE IN .ORTH !MERICA WERE NOT MORE LIKELY TO HAVE A GREAT IMPACT IN /NTARIO HOWEVER OUR SAMPLESIZEINTHISCATEGORY;SPECIES=WASSMALL #ADOTTEETALSUGGESTSEVERAL REASONS WHY %URASIAN SPECIES MAY BE MORE SUCCESSFUL IN /NTARIO 3PECIES FROM %URASIAMAYBELESSPHYLOGENETICALLYRELATEDTOSPECIESFROM.ORTH!MERICAAND MAY BE MORE LIKELY TO HAVE EVOLVED ECOLOGICAL NOVELTIES IN LINE WITH $ARWINS NATURALIZATION HYPOTHESIS ;$ARWIN = !LTERNATIVELY THE ENEMY RELEASE HYPOTHESISMAYBERESPONSIBLE ORTHEMATCHINGOFPROVENANCEIE COMINGFROM ACOMPARABLECLIMATICZONE COULDBEANOTHERPOSSIBLEFACTOR 7E CONCLUDE THAT NEITHER FRAMEWORK IS ESPECIALLY USEFUL IN THEIR PRESENT FOR MULATIONSFORCLASSIFYINGREGIONALORLARGER EXOTICmORAS IE LISTSOFKNOWNNON NATIVESPECIES4HESEARCHFOROPERATIONALDElNITIONSOFTERMINOLOGYININVASIONS ECOLOGYREMAINSELUSIVE2ELEVANTINFORMATIONISSIMPLYNOTAVAILABLEANDTHEUSE OFSURROGATESFORCRITERIASUCHAS@SPREADAND@IMPACTARELIKELYTOINTRODUCEJUST AS MUCH SUBJECTIVITY INCONSISTENCY AND CONFUSION IN THE LITERATURE AS ALREADY EXISTS &AILURE TO OPERATIONALISE DElNITIONS USED IN CLASSIFYING EXOTICmORADATASETS


WILL LIKELY CONTINUE TO LEAD TO AMBIGUOUS GENERALIZATIONS AND PREDICTIONS .OTWITHSTANDINGTHISAMBIGUITY COMPARATIVESTUDIESOFINVASIVEmORASHAVEPRO VIDEDNEWINSIGHTSINTHEUNDERSTANDINGOFGENERALPATTERNSOFPLANTINVASIONAND THE VALUE OF THESE STUDIES IS NOT TO BE DIMINISHED 2ATHER WHEN CLASSIFYING LISTS OFmORATHECRITERIAUSEDTOASSIGNEACHSPECIESTOACATEGORYSHOULDBEEXPLICITLY STATEDSOTHATRESEARCHERSCANCOMPARESPECIESBASEDONLIKECRITERIARATHERTHAN THECATEGORYITSELF WHICHMAYHAVEBEENDERIVEDFROMUNLIKEDATA!S0YÝEKETAL CONCLUDEINTHEIRRECENTPAPERONTHETREATMENTOFINVASIONSTERMINOLOGY INREGIONALmORAS STATEMENTSPRECEDEDBY@PROBABLYOR@POSSIBLYMAYBETEMPO RARILYTHEMOSTHONESTWAYOFCLASSIFYINGSOMETAXA #OLAUTTI AND -AC)SAAC RECENTLY PROPOSED A SUPPLEMENTARY LEXICON TO CURRENT TERMINOLOGY IN INVASIONS ECOLOGY 4HEIR FRAMEWORK ATTEMPTED TO ELIMI NATETHENEEDFORUNIVERSALDElNITIONSOFCURRENTTERMSBYUSINGOPERATIONALTERMS WITHNOAPRIORIMEANINGIE ASSTAGES INAPROCESS BASEDMODEL4HEFRAMEWORK ISBASEDONCURRENTMODELSTHATENVISIONPROCESSESINIMMIGRATIONANDNATURALIZA TIONASASERIESOFCONSECUTIVESTAGES4HEGOALOFTHEFRAMEWORKISTOSUPPLEMENT AMBIGUOUSTERMSWITHTHESTAGE BASEDTERMINOLOGY3UCHAFRAMEWORKISLOGICAL ANDINTUITIVELYAPPEALINGANDWOULDLIKELYLEADTOSOMECONSISTENCYININDIVIDUAL POPULATION BASED STUDIES OF INVASIVE SPECIES AS WOULD THAT OF 2ICHARDSON ET AL ;A= (OWEVER ITISALSOUNLIKELYTOBEUSEFULFORCLASSIFYINGLISTSOFALIENSPE CIES FOR COMPARATIVE PURPOSES SINCE THE SAME DATA LIMITATIONS WOULD APPLY AS DESCRIBEDABOVEFOR2ICHARDSONETALAND$AVISAND4HOMPSONSSCHEMES

!02/0/3%$-/$)&)#!4)/.4/#522%.4#/.#%045!,&2!-%7/2+3 &/24(%).6!3)/.302/#%33 #OLAUTTIAND-AC)SAAC NOTEDTHATTERMINOLOGYUSEDTODESCRIBEINTRODUCED SPECIESAREMISNOMERS INTHESENSETHATINTRODUCED NATURALIZEDORINVASIVESPECIES ETCAREOFCOURSEINTRODUCED NATURALIZEDORINVASIVEPOPULATIONS!FOCUSONINVA SIONSATAPOPULATIONLEVELRATHERTHANASPECIESLEVELHASIMPORTANTIMPLICATIONS FOR THE DEVELOPMENT OF INVASIONS ECOLOGY )NDEED IT MAKES LITTLE SENSE TO ASSIGN CATEGORICALPROPERTIESTOA@SPECIES2ATHER DEMOGRAPHICATTRIBUTESOFTHEADVEN TIVEPOPULATIONANDOFANYMETAPOPULATIONOROTHERREGIONALLYCONNECTEDGROUP SEE-URPHYAND,OVETT $OUST NEEDTOBECHARACTERIZED ASTHEATTRIBUTESOF LONGEVITY FECUNDITYANDMORTALITYRATESARETHEKEYDETERMINANTSOFANINVADERS STATUS WITHIN THE ECOLOGICAL CONTINUUM REPRESENTING THE INVASION PROCESS AND EXTENDINGACROSSTHEARCFROMIMMIGRATIONTONATURALIZATION&URTHERMOREWHEN ITDOESHAPPEN CLASSIlCATIONSHOULDOCCURATADElNEDTEMPORALORSPATIALSCALE AS POPULATIONS OF SPECIES WILL APPEAR TO BE IN DIFFERENT PLACES ON THE CONTINUUM DEPENDINGONTHESCALEOFTHEASSESSMENT 4HE@BLINKINGLIGHTSMETAPHOROFMETAPOPULATIONEXTINCTIONANDCOLONIZATIONS MAYBEUSEFULINTHEINVASIONSPROCESSTOO!METAPOPULATIONDESCRIBESA@POPU LATION CONSISTING OF A NUMBER OF LOCAL POPULATIONS IN THE SAME SENSE IN WHICH

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A LOCAL POPULATION IS A POPULATION CONSISTING OF MANY INDIVIDUALS !CCORDING TO THE ,EVINS CLASSICAL METAPOPULATION CONCEPT ALL LOCAL POPULATIONS HAVE A SUBSTANTIAL PROBABILITY OF EXTINCTION AND THEREFORE LONG TERM PERSISTENCE OF A SPECIES IS REGULATED AT THE REGIONAL OR METAPOPULATION LEVEL (ANSKI -ETAPOPULATIONTHEORYPROPOSESTHATTHEREGIONALPOPULATIONPERSISTSASTHERESULT OFABALANCEBETWEENLOCALPOPULATIONEXTINCTIONINPATCHESANDPATCHMIGRATIONS LEADINGTOCOLONIZATION4HEKEYTOPOPULATIONPROCESSESLIESINUNDERSTANDINGTHE SHIFTINGMOSAICOFPATCHOCCUPANCYASOPPOSEDTODETAILSOFWITHIN PATCHEVENTS +AREIVA AND 7ENNERGREN &RECKLETON AND 7ATKINSON DESCRIBE OTHER REGIONAL ENSEMBLES OF PLANT POPULATION DYNAMICS AT LARGE SCALES )N THE FOLLOWING WE VISUALIZE 2ICHARDSON ET ALS CATEGORIES OF ALIEN SPECIES PLUS AN ADDITIONAL CATEGORY @SPREADING POPULATIONS BETWEEN NATURALIZED AND INVASIVE STAGES AND THE BARRIERS THEY SURMOUNT THROUGH THE INVASIONS PROCESS INAPOPULATION BASEDCONTEXT4HEFOURCATEGORIESOFPOPULATIONSCANBEDESCRIBED IN TERMS OF THE METAPOPULATION PARAMETERS OF EXTINCTION AND COLONIZATION AS SHOWNIN4ABLE 4ABLE -ETAPOPULATION CONDITIONS FOR POPULATION THROUGH THE INVASION PROCESS EEXTINCTIONCCOLONIZATION #ATEGORY3TAGE -ETAPOPULATIONDYNAMICS #ASUAL EC .ATURALIZED EC 3PREADING EC )NVASIVE EC

#ASUAL

!DVENTIVE INDIVIDUALS APPEAR AND MAY BE INTRODUCED ON MULTIPLE OCCASIONS BEFOREAPOPULATION@TAKESORESTABLISHES4HERECURRENTBUTEPHEMERALINTRODUC TIONSGENERATETHESTATUSOF@CASUALi.e., the iNTRODUCEDSPECIESISATTHEEARLYSTAGE OF BEING AN INTERMITTENT MEMBER OF THE NEW mORA 4HE POPULATION MAY @BLINK OFF AND ON AGAIN AS IT FAILS TO SUSTAIN ITSELF OVER LONGER PERIODS BUT OCCASIONALLY PERSISTSORBECOMESRE ESTABLISHEDBECAUSEOFREPEATEDINTRODUCTIONSFROMSOURCE POPULATIONSOUTSIDETHEADVENTIVEAREA4HESEPOPULATIONSESTABLISHBECAUSESOME INDIVIDUALS OF THE SPECIES HAVE SURMOUNTED A MAJOR GEOGRAPHICAL BARRIER LONG DISTANCEBARRIER!OF&IG .ATURALIZED

%VENTUALLY A CASUAL POPULATION MAY BLINK ON AND REMAIN ON FOR AN EXTENDED PERIOD4HE lRSTLOCAL POPULATION MEETSCRITERIASETFORSTEADY STATEMAINTENANCE


ASUSTAINABLEPOPULATION 4HISCORRESPONDSTOTHECONCEPTIN0OPULATION6IABILITY !NALYSISOFAN-60MINIMUMVIABLEPOPULATION THENUMBEROFINDIVIDUALSTHAT ENSURES A POPULATIONS PERSISTENCE ;3HAFFER = )N THE VOCABULARY OF INVA SIONS THIS CAN BE TERMED @NATURALIZATION !T THAT POINT THE FOUNDER POPULATION HASBECOMERESILIENTTOENVIRONMENTALANDDEMOGRAPHICSTOCHASTICITIES ANDTHE PROBABILITY OF CHANCE EXTINCTION HAS DECREASED $EMOGRAPHIC ATTRIBUTES OF THIS POPULATION INCLUDE A SIGNIlCANT BREEDING POPULATION FOR PLANTS AN ESTABLISHED SEEDBANKISABENElTSOTHATYEAR TO YEARVARIATIONSINFECUNDITYARENOTDIRECTLY EVIDENTINRECRUITMENT)NADDITION INDIVIDUALSLIKELYDEVELOPFACILITATIVEASSOCIA TIONS SUCH AS POLLINATION SEED DISPERSAL AND PERHAPS MYCORRHIZAL ASSOCIATIONS )NDIVIDUALS IN THESE POPULATIONS HAVE OVERCOME BARRIERS TO SURVIVAL IN ENVIRON MENTALCONDITIONSBARRIER"IN&IG ATTHESITEOFINTRODUCTIONSOILANDCLIMATE FOR EXAMPLE AS WELL AS BARRIERS TO THE PREVENTION OF CONSISTENT AND LONG TERM GENERATION OF RECRUITS TO THE POPULATION MATING SYSTEM COMPATIBILITY FERTILITY FECUNDITYANDOTHERREPRODUCTIVEBARRIERSBARRIER#IN&IG 3PREADINGMETAPOPULATION OROTHERREGIONALENTITY

@3PREADINGPOPULATIONSCANBEVISUALIZEDASINCLUDINGAPOPULATIONWITHALIGHT PERMANENTLY ON THE NATURALIZED POPULATION SURROUNDED BY ADJACENT POPULA TIONS THAT MAY BLINK ON AND OFF LIKE CASUAL POPULATIONS BUT THE NATURALIZED POPULATIONISTHESOURCE RATHERTHANTHESOURCEBEINGFROMBEYONDTHEADVENTIVE AREA 4HISSTAGEINVOLVESTHERELATIVELYSHORT DISTANCEDISPERSALOFPROPAGULESTO ADJACENTSUITABLESITESTHEREBYOVERCOMINGBARRIER$IN&IG 3PREADFROMTHE INITIALNATURALIZEDPOPULATIONTOOTHERSUITABLESITESREQUIRESSUFlCIENTDISPERSALBY PROPAGULES ANDORSUFlCIENTLANDSCAPECONNECTIVITYBETWEENSUITABLESITESSUCH THAT LOCAL EXTINCTIONS MAY BE REPLACED BY RECOLONIZATIONS FROM NEARBY NATURAL IZED POPULATIONS IF NOT FROM THEIR OWN SEED BANK 4HE DISCOVERY OF CONTIGUOUS POPULATIONSOFDIFFERINGSIZEAROUNDANOLDERONEISWELLDOCUMENTEDINTHEHER BARIUM COLLECTIONS USED TO DEVELOP THE DISTRIBUTION MAPS OF THE SPECIES STUDIED INTHE"IOLOGYOF#ANADIAN7EEDSSERIES 4HISOCCURSWHENINITIALLONG DISTANCE DISPERSALEG INTOANEWPARTOFTHEPROVINCE ORWATERSHED ISFOLLOWEDBYSUB SEQUENTOUTBREAKSOFPOPULATIONSINTHEGENERALAREAASSUITABLEHABITATBECOMES OCCUPIED 4HIS CORRESPONDS TO THE STAGE WE TERM LANDSCAPE @SPREADING &IG 4HESE POPULATIONS HAVE OVERCOME BARRIERS TO RELATIVELY SHORT DISTANCE DISPERSAL INTHEIMMEDIATEAREABARRIER$IN&IG ANDENVIRONMENTALCONDITIONSATADJA CENTHUMAN MODIlED AREASBARRIER%IN&IG ASSUMINGAVAILABILITYOFSUITABLE DISTURBED SITES 3PREADING POPULATIONS ARE SELF SUSTAINING WITHOUT INPUT FROM SOURCESOUTSIDETHEADVENTIVEREGIONBUTMAYBERECOLONIZEDFROMNEARBYSITESIF LOCALEXTINCTIONOCCURS

(4-URPHY ET AL

)NVASIVEMETAPOPULATIONOROTHERREGIONALENTITY

4HEIMAGEOFTHESPREADINGPOPULATIONSATLEASTONEPERMANENTLY@ONLIGHTSUR ROUNDEDBYNUMEROUSBLINKINGLIGHTS ISREPEATEDINMANYPARTSOFTHEADVENTIVE RANGE 3PREADING POPULATIONS BECOME THEMSELVES THE PRIMARY SOURCE FOR NEW CASUAL NATURALIZEDANDSPREADINGPOPULATIONSTHOUGHSOMEMAYALSOCONTINUE TOBECOMEESTABLISHEDTHROUGHSEPARATEDISPERSALEVENTSFROMTHEORIGINALSOURCE REGION 4HESE POPULATIONS HAVE OVERCOME BARRIERS TO LONG DISTANCE DISPERSAL IN THEADVENTIVEENVIRONMENT 3OMERESEARCHERSALSOCONSIDERTHATABIOTICANDBIOTICBARRIERSTOESTABLISHMENT INNATURALHABITATSNEEDSTOBEOVERCOMEATTHISSTAGEOFTHEINVASIONSPROCESSOTH ERS CONSIDER THAT THIS BARRIER MAY BE OVERCOME BY NATURALIZED POPULATIONS SEE 2ICHARDSON ET AL ;A= &ROM AN ECOLOGICAL STANDPOINT THE MORE IMPORTANT DEVELOPMENTOCCURSWHEREINVASIVEPOPULATIONSSPREADTONATURALENVIRONMENTS (OWEVERFROMAMANAGEMENTANDECONOMICPOINTOFVIEW INVASIVEPOPULATIONS THAT ONLY OCCUR IN FOR EXAMPLE AGRICULTURAL SETTINGS ARE EQUALLY AS IMPORTANT 4HUSMETAPOPULATIONSOFTHEINTRODUCEDSPECIESSHOULDNOTHAVETOOCCURINNATU RALHABITAT TOBEREGARDEDASINVASIVE7EDOTHINKITISUSEFULINOURFRAMEWORK HOWEVER TODISTINGUISHECOLOGICALLYINVASIVEPOPULATIONSFROM INVASIVEPOPULA TIONS IN DISTURBED HABITATS )N TERMS OF THE MAJOR ECOLOGICAL IMPACTS OF INVASIVE SPECIESONBIODIVERSITY ITMAYBEIMPORTANTTOUNDERSTANDHOWSPECIESTHATARE CAPABLEOFINVADINGNATURALHABITATSDIFFERFROMTHOSETHATREMAININDISTURBEDOR AGRICULTURALCOMMUNITIESANDHAVEPRIMARILYECONOMICIMPACTS

0/05,!4)/.6)!"),)49!.!,93)306! 4/42!#+0/05,!4)/.3 /&./. .!4)6%30%#)%3 0OPULATION VIABILITY ANALYSIS HAS BEEN USED TRADITIONALLY TO ESTIMATE THE RISK OR TIME TO EXTINCTION FOR AN ENDANGERED SPECIES AND COULD EQUALLY BE APPLIED TO PREDICT THE POTENTIAL FOR ESTABLISHMENT GROWTH OR PERSISTENCE IN NON NATIVE SPECIES 06! EVALUATES THE LIKELIHOOD THAT A GIVEN SPECIES WILL PERSIST FOR A GIVEN TIME INTO THE FUTURE 4HE GOAL OF 06! IS OFTEN CONSERVATION OR MANAGE MENT OF RARE OR ENDANGERED SPECIES THIS INCLUDES IDENTIFYING THREATS TO SPECIES PERSISTENCE AND APPLYING THEORETICAL CONCEPTS OF POPULATION AND METAPOPULA TIONECOLOGYTOIMPROVESURVIVORSHIPSEEEG "ROOKETAL !K AKAYAAND 3JÚGREN 'ULVE -ORRISAND$OAK SUMMARIZEDTHREEGENERALLEVELSOFCOMPLEXITYAVAIL ABLE FOR 06! THAT INCORPORATE MULTI SITE DATA !LL RELY ON USE OF MATRICES TO CHARACTERIZE POPULATION STATUS OVER TIME 4HE SIMPLEST APPROACH IS TO TRACK THE NUMBER OF POPULATIONS SENSU METAPOPULATION AND OTHER REGIONAL ENTITIES THAT IS TO ESTIMATE THE PRESENCE OR ABSENCE OF POPULATIONS IN LOCAL SITES OF SUITABLE HABITAT )T IS RELATIVELY EASY TO ENUMERATE SITES WHERE AN INTRODUCED SPECIES IS REPORTED!SECOND COUNT BASEDCENSUS APPROACHISAMOREUSEFULFORMOF06!


BUTESTIMATESOFMIGRATIONRATES ANDMEAN VARIANCEANDCOVARIANCEINPOPULA TION GROWTH RATES ARE NECESSARY TO DEVELOP SUCH MODELS -OST USEFUL OF ALL BUT ALSO MORE DATA DEMANDING IS A 06! MODEL INCLUDING DEMOGRAPHIC ANALYSIS AT EACH SITE BASED ON FOR EXAMPLE KNOWLEDGE OF BIRTH AND DEATH RATES AND RATES OFINDIVIDUALTRANSITIONSTHROUGHSIZE ORAGECLASSESTHATGOVERNFECUNDITYRATES 3UCHINFORMATIONWOULDALLOWCONSTRUCTIONOFAMULTI SITEMATRIXMODEL WHICH COULDMOREACCURATELYPREDICTTHEFATEOFTHEINTRODUCEDSPECIES 7HILE COUNT BASED AND DEMOGRAPHY BASED 06! PROVIDE MORE ROBUST RESULTS OURANALYSISHEREHASSHOWNTHATTHISLEVELOFSPECIES SPECIlCINFORMATIONISOFTEN UNAVAILABLE AND MAY BE INSUFlCIENT TO ESTIMATE THE PARAMETERS OF THE MODEL (OWEVER TRACKINGPRESENCEORABSENCEOFANON NATIVESPECIESINSUITABLEHABI TATISSUFlCIENTTOESTIMATETHEPARAMETERSOFTHESIMPLEST06!MODELS0ATCH /CCUPANCY -ODELS 0/- !K AKAYA AND 3JÚGREN 'ULVE 3UCH MODELS AS WITH ALL @PATCH MODELS OF METAPOPULATION DYNAMICS (ANSKI ASSUME THAT LOCAL DYNAMICS OCCUR RAPIDLY IN COMPARISON TO METAPOPULATION DYNAMICS IE CHANGES IN POPULATION SIZES OF LOCAL POPULATIONS TAKE PLACE MORE RAPIDLY THAN COLONIZATIONS OF CURRENTLY EMPTY HABITAT PATCHES 7ITH THIS ASSUMPTION IT IS REASONABLE TO FOCUS ENTIRELY ON THE PRESENCE OR ABSENCE OF THE SPECIES OF INTERESTINTHEAVAILABLEHABITATPATCHES'IVENTHIS THEPERSISTENCEOFTHESPECIES CANBEMODELEDBYEXAMININGTHEPROBABILITYOFEXTINCTIONOFANOCCUPIEDPATCH ANDTHEPROBABILITYOFCOLONIZATIONOFANEMPTYPATCH 3IMPLE 0/-S ARE BASED ON CLASSICAL METAPOPULATION MODELS SENSU ,EVINS AND THUS TREAT HABITAT PATCHES AS IF THEY WERE IDENTICAL AND MOVEMENT BETWEENALLPAIRSOFPATCHESISEQUALLYLIKELY(ANSKIAND'YLLENBERG (ANSKI 2ECENTLY MORE DATA INTENSIVE AND SPATIALLY EXPLICIT MODELS HAVE BEEN CREATEDSEEEG (ANSKI -OILANEN 7ECONSTRUCTEDASIMPLE0/- BASED SOFTWARE MODULE THAT DEMONSTRATES THE USEFULNESS OF 06! FOR MODELING CONTRASTINGLEVELSOFINVASIVENESSINEXOTICSPECIES4HEMODELUSESTWOINPUTSTHE PROBABILITYTHATANOCCUPIEDPATCHWILLBECOMEVACANTDUETOLOCALEXTINCTIONAND THEPROBABILITYOFANUNOCCUPIEDPATCHBECOMINGOCCUPIEDBYMIGRANTSFROMAN OCCUPIEDPATCHINEACHTIMESTEPORITERATION3UCHVALUESMAYBEESTIMATEDFROM ASERIESOF@SNAPSHOTSOFTHEPRESENCEORABSENCEOFASPECIESTHROUGHTIMEAND WITHPARTICULARLIFEHISTORYCHARACTERISTICSINmUENCINGCOLONIZATIONABILITY 'OTELLI AND4AYLORA B ESTIMATEDSUCHPROBABILITIESFORlSHASSEMBLAGESUSINGTHE PROBABILITYOFCOLONIZATIONASTHENUMBEROFUNOCCUPIEDSITESINYEART THATWERE OCCUPIEDINYEART DIVIDEDBYTHENUMBEROFSITESTHATWERECENSUSEDINYEAR T 3IMILARLY THEPROBABILITYOFEXTINCTIONCANBEESTIMATEDASTHENUMBEROFSITES OCCUPIEDINYEART THATWEREUNOCCUPIEDINYEART DIVIDEDBYTHENUMBER OFSITESOCCUPIEDINYEART 5SING A COMBINATION OF PROBABILITY LEVELS FOR EXTINCTION HIGH MEDIUM AND LOW 0EXT VALUES OF AND RESPECTIVELY AND THREE FOR THE PROB ABILITYOFCOLONIZATIONHIGH MEDIUMANDLOW0COLVALUESOF AND RESPECTIVELY CLEAR CONSISTENT OUTCOMES EMERGED %ACH WAS PLOTTED FOR RAN DOMITERATIONSTOGENERATEPLOTSTHATCORRESPONDTOTHEFOURCATEGORIESOFNON NATIVE

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POPULATIONSOFSPECIES4HEVALUESUSEDTOPARAMETERIZETHISMODELWEREBASEDON A RANGE OF EXTINCTION AND COLONIZATION ESTIMATES GIVEN FOR A VARIETY OF ORGANISMS SEEEG 7AHLBERGETAL -OILANENETAL -OILANEN 'OTELLIAND 4AYLORA B 3IMULATIONSWERERUNINARANDOMLANDSCAPE WITHAVAIL ABLEPATCHES INITIALLYWITHASINGLEPATCHOCCUPIEDREPRESENTINGANINTRODUCTION )NEACHCASETHEREWEREITERATIONS IE SEPARATEINTRODUCTIONS 4ABLE SUMMARIZES THE SIMULATION OUTPUT AND &IG DEPICTS THE CHANGE IN PROPORTIONOFPATCHESOCCUPIEDOVERTIME FOREACHSCENARIO4HEMODELSPROVIDE AN EFFECTIVE FRAMEWORK FOR GENERALIZATION WE CAN STATE THAT WHERE 0COL ) 0EXT THE SPECIES IS CASUAL TO NATURALIZED 7HERE 0COL 0EXT THE SPECIES IS SPREADING ITISONLYWHERE 0COL0EXT THATTHESPECIESISLIKELYTOBECOMEINVASIVE4HISGEN ERALIZATIONSUGGESTSTHATMOSTINTRODUCTIONSSHOULDRESULTINCASUALORNATURALIZED POPULATIONSOFSPECIESOFTHEOUTCOMES WITHONLYBEINGSPREADINGAND INVASIVE )NDEPENDENTOF0COL IF0EXTISHIGHTHENTHESPECIESISMERELYCASUAL%VENIFTHE SPECIESHASLOW0COLANDAMEDIUM0EXT ITWILLOCCURASACASUAL0OPULATIONSMAY BLINKOFFANDONAGAINBUTFAILTOSUSTAINTHEMSELVESOVERLONGERPERIODSONLY OCCASIONALLYPERSISTING3IMULATIONSSHOWEDTHATONAVERAGE WITHLOWCOLONIZA TIONRATEANDMEDIUMEXTINCTIONRATEALLPOPULATIONSBLINKEDOFFAFTER ITERA TIONSHOWEVER TWOOUTLIERPOPULATIONSPERSISTEDFORTHEFULLRUNS.ATURALIZED SPECIESWERETHOSEWITHANEQUIVALENTEQUALLYWEAKORSTRONG 0COLAND0EXTTHAT ISHAVINGLOW0COLAND0EXTLOW LOW ORMEDIUM0COLAND0EXTMEDIUM MEDIUM 7HILE MOST OF THE INTRODUCTIONS ENDED IN EXTINCTION LOW LOW AND MEDIUM MEDIUM PERSISTEDFORALLITERATIONS 3PREADINGSPECIESWOULDHAVEAPROPORTIONATELYGREATERPROBABILITYOF0COLAND 0EXTHIGH MEDIUMORMEDIUM LOW )NVASIVESPECIESAREDISTINGUISHEDBYHAVING AHIGH0COLANDALOW0EXT7ENOTETHESEEXEMPLARSREPRESENTANECOLOGICALCON TINUUMFROMCASUALTOINVASIVE)TISINTERESTINGTHATTHECURVESHAVEDISTINCTIVE SHAPES &OR EXAMPLE ALTHOUGH SPREADING SPECIES MAY REACH COMPARABLE LEVELS OFOCCUPANCYASINVASIVESSEE&IGSB ANDF SPREADINGSPECIESSHOWATIMELAG ASSOCIATEDWITHPROLONGEDLOWSITEOCCUPANCY RESULTINGINAGREATERRISKOFhINVA SIONFAILUREv !NY INTRODUCTION HAD THE POSSIBILITY OF FAILURE %VEN THE INVASIVE SPECIES IN OURSIMULATIONFAILEDTOESTABLISHSIXPERCENTOFTHETIMEFOLLOWINGINTRODUCTION )NDEED AS NOTED EARLIER THE LITERATURE SUGGESTS THAT MOST INTRODUCTIONS FAIL TO ESTABLISH AND EVEN THOSE THAT SUCCESSFULLY ESTABLISH AND PERSIST MAY HAVE HAD MANYPREVIOUSFAILEDATTEMPTS)TISIMPORTANTTONOTETHATEVENWHENPOPULATIONS HAVEBECOMEINVASIVE THEPROCESSISNOTSTATIC2ATHER POPULATIONSMAYSTILLBE VULNERABLETODEMOGRAPHICANDENVIRONMENTALFACTORSACTINGTOINCREASEEXTINC TION AND DECREASE COLONIZATION RATES 7E HAVE OBSERVED DRAMATIC CHANGES OVER THE PAST lFTEEN YEARS IN SOUTHWESTERN /NTARIO POPULATIONS OF PURPLE LOOSESTRIFE ,YTHRUM SALICARIA SEE TOO -AL ET AL &OLLOWING A SURGE OF COLONIZATIONS OVERTHEPAST DECADES ANDABUNDANTLARGELOCALPOPULATIONS MANYOFTHESE HAVEGONEEXTINCTORBECOMEEXTREMELYDIMINISHEDINRECENTYEARS

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(4-URPHY ET AL

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(4-URPHY ET AL

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4HEIMPORTANCEOFEXOGENOUSFACTORSFORDENSITYDEPENDENTPOPULATIONREGULA TIONISPARTICULARLYWELLILLUSTRATEDBYARECENTANALYSISOFTHEDYNAMICSOFRAGWORT 3ENECIOJACOBAEA, ANDITSSPECIALISTHERBIVORETHECINNABARMOTH 4YRIAJACOBAEAE ,"ONSALL ETAL ,ONGTERM*YEARS TIMESERIESFORBOTHSPECIESEXIST FOR TWO SITES ONE IN 3ILWOOD 5+ AND THE OTHER IN -EIJENDEL 4HE .ETHERLANDS )N3ILWOODRAGWORTPOPULATIONS ONLYDIRECTDENSITYDEPENDENCEIE THEINmUENCE OF PLANT DENSITY IN THE PREVIOUS YEAR WAS DETECTED WHEREAS IN -EIJENDEL BOTH DIRECTYEARPREVIOUS ANDDELAYEDTWOYEARSPREVIOUS DENSITYDEPENDENCEWAS DETECTED LEADINGTOQUALITATIVELYDIFFERENTDYNAMICSATTHETWOSITES0OPULATIONS ARE RELATIVELY STABLE IN 3ILWOOD BUT EXHIBIT OSCILLATIONS IN -EIJENDEL 4HE DRIVER FOR THE DIFFERENCES IN DYNAMICS BETWEEN THE SITES MAY BE DIFFERENCES IN RECRUIT MENT2ECRUITMENTISMICRO SITELIMITEDAT3ILWOODBUTNOTAT-EIJENDEL IMPLYING STRONGDENSITYDEPENDENCEOPERATINGATTHESEEDLINGSTAGEIN3ILWOODPOPULATIONS 3ENECIOJACOBAEAISNATIVETO%UROPEANDINTRODUCEDTO!USTRALASIA THE!MERICAS AND3OUTH!FRICA(ARPERAND7OOD 4HISSTUDYISALANDMARKFORECOLO GISTSWORKINGONINVASIVES ASTHEVARIABILITYINTHEQUALITATIVEDYNAMICSOFTHIS SPECIESWITHINITSNATIVERANGEALONESHOULDLEADUSTOASKQUESTIONSOFATTEMPTS TOEXTRAPOLATEMODELOREXPERIMENTALRESULTSFROMNATIVETOEXOTICECOSYSTEMSIN THEABSENCEOFDATAFROMTHEEXOTICHABITAT)TSHOULDALSOENCOURAGEUSTOMOVE ONFROMDOCUMENTINGTRAITDIFFERENCESBETWEENSPECIESINTHEIRNATIVEANDEXOTIC RANGES 3IEMANN AND 2OGERS "UCKLEY ET AL B 3IEMANN AND 2OGERS TO INVESTIGATING THE POPULATION DYNAMIC CONSEQUENCES OF THOSE TRAIT DIFFERENCES AND THEIR INTERACTION WITH HABITAT DIFFERENCES )N ADDITION CONTEXT DEPENDENCY OF THIS SORT MIGHT RESULT IN DENSITY DEPENDENCE BEING OVERLOOKED IF THESYSTEMSTUDIEDINCLUDESHABITATHETEROGENEITY&OREXAMPLE INASTUDYOFREEF lSH 3HIMA AND /SENBERG FOUND THAT THE STRENGTH OF DENSITY DEPENDENT MORTALITY DEPENDED ON SITE QUALITY AND A FAILURE TO TAKE HETEROGENEITY IN SITE QUALITYINTOACCOUNTCOULDHAVELEADTOTHECONCLUSIONTHATDENSITYDEPENDENCE WAS UNIMPORTANT 3HIMA /SENBERG REFER TO THE PATTERNS OBSERVED AS hCRYPTIC DENSITYDEPENDENCEv 7ITHINAPOPULATION DIFFERENCESBETWEENINDIVIDUALSORSTAGESWILLALSOAFFECT DENSITY DEPENDENCE AND RESULTING DYNAMICS &OR EXAMPLE POPULATION DENSITY AND ASYMMETRIC COMPETITION CAN INCREASE THE DIFFERENTIAL IN SIZE BETWEEN LEVELS IN HIERARCHIES OF PLANT POPULATIONS 7EINER AND THIS CAN CREATE DIFFER ENCESBETWEENINDIVIDUALRESPONSESTODIFFERENTDENSITIESOFDIFFERENTSTAGES3IMPLE MODELSLIKETHE(ASSELLMODELSHOWNABOVEDONOTADDRESSTHIS(OWEVER WECAN INCORPORATESUCHDIFFERENCESBYUSINGMODELSWITHAGEORSTAGESTRUCTURE"ENTON ET AL AND #AMERON AND "ENTON USE EXPERIMENTALLY MANIPULATED SOILMITEPOPULATIONSANDMODELSTOEXPLORETHEINTERACTIONOFDENSITYDEPENDENCE AND ENVIRONMENTAL VARIABILITY ON THE OUTCOME OF HARVESTING DIFFERENT STAGES 4HEYFOUNDTHATHARVESTINGDIFFERENTSTAGESREDUCINGSURVIVALOFEGGS JUVENILES ORADULTS HADDIFFERENTIMPACTSONTHEMEANPOPULATIONSIZEANDITSVARIANCEIN EACH STAGE )N A VARIABLE ENVIRONMENT THEY FOUND THAT REMOVAL OF OF EGGS ACTUALLY RESULTED IN AN INCREASE IN MEAN POPULATION SIZE WHEREAS REMOVAL OF


CORRESPONDING PROPORTIONS OF JUVENILES AND ADULTS LED TO A DECREASE IN MEAN POPULATION SIZE 4HIS WOULD APPEAR TO BE A RESULT OF DENSITY DEPENDENCE ACTING DIFFERENTLY IN DIFFERENT STAGES 4HEY LIKEN REMOVAL OF EGGS TO THINNING SEEDLINGS THIS RELEASES THE SURVIVORS FROM DENSITY DEPENDENT SUPPRESSION AND IF DENSITY DEPENDENCEISSTRONGENOUGHCANLEADTOANINCREASEINOVERALLPOPULATIONSIZE 4HE EFFECTS OF EGG REMOVAL MAY HAVE BEEN MORE PRONOUNCED IN THE VARIABLE ENVIRONMENTBECAUSEOFTHEALTERNATINGPERIODSOFSTRONGANDWEAKCOMPETITION FORRESOURCES4HESAMECOUNTER INTUITIVERESULTHARVESTINGLEADINGTOINCREASED POPULATIONSIZE CANOCCURINACONSTANTENVIRONMENTWHEREDENSITYDEPENDENCE ISVERYSTRONGOROVER COMPENSATINGEG "UCKLEYETAL /FRELEVANCETOTHE MANAGEMENTOFINVASIVESIS"ENTONETALS CONCLUSIONTHATDENSITYINDE PENDENTMODELSFAILEDTOPREDICTTHENEGATIVEELASTICITYOFSURVIVALATTHEEGGSTAGE THEREFOREMANAGEMENTMODELSWHICHDONOTINCLUDEDENSITYDEPENDENCE WHEREIT ISKNOWNTOBEIMPORTANT RUNTHERISKOFGIVINGTHEWRONGANSWER )NCORPORATINGTHEADDEDSTRUCTUREFROMINDIVIDUALVARIATIONTOMODELSISOFTEN IMPORTANTWITHTHISADDEDCOMPLEXITYHOWEVER GREATERCARESHOULDBETAKENTO CHOOSE THE APPROPRIATE MODEL &OX AND +ENDALL ILLUSTRATE THAT FAILURE TO MODELINDIVIDUALVARIABILITYCORRECTLYASSYSTEMATICVARIATIONAMONGINDIVIDUALS RATHERTHANRANDOMVARIATION MAYLEADTOINACCURATEPREDICTIONS4HEYCONCLUDE hALMOST ALL POPULATION VIABILITY ANALYSES 06!S OVER ESTIMATE THE IMPORTANCE OF DEMOGRAPHIC STOCHASTICITY AND THEREFORE THE RISK OF EXTINCTIONv -URRELL #HAPTER PRESENTSAMODELLINGFRAMEWORKTHATTAKESACCOUNTOFLOCALINTERAC TIONS THE hPLANTS EYE VIEWv OF ITS NEIGHBOURHOOD DENSITY WHICH EVEN WITHOUT SPATIALORTEMPORALHETEROGENEITYLEADSTOINVASIONDYNAMICSQUITEDIFFERENTFROM THOSE PREDICTED BY MEAN lELD APPROXIMATIONS WHICH TAKE OVERALL DENSITY INTO ACCOUNT .EW TOOLS WHICH ALLOW US TO TAKE ACCOUNT OF VARIATION IN RESOURCES AT DIFFERENT SPATIO TEMPORAL SCALES AND HOW PLANTS RESPOND TO VARIABLE RESOURCES AND CLUSTERING ALLOW BOTH INCREASINGLY ACCURATE PREDICTIONS OF DYNAMICS AND A BETTER UNDERSTANDING OF THE SCALE AND MECHANISMS INVOLVED IN DENSITY DEPEN DENTRESPONSES 3O FAR WE HAVE ONLY ADDRESSED NEGATIVE EFFECTS OF DENSITY DEPENDENCE ON lT NESS OR POPULATION GROWTH HOWEVER DENSITY DEPENDENCE CAN ALSO OPERATE POSI TIVELY7HEREANYCOMPONENTOFlTNESSINCREASESASDENSITYORNUMBERSINCREASE THISISKNOWNASAN!LLEEEFFECT THISMAYTRANSLATEINTODEMOGRAPHIC!LLEEEFFECTS WHERE POPULATION GROWTH RATE DECLINES WITH DECREASING DENSITY DEPENDING ON THESTRENGTHOFNEGATIVEDENSITYDEPENDENCEINTHECOMPONENTOFlTNESSINQUES TION3TEPHENSETAL !NEXAMPLEOFACOMPONENT!LLEEEFFECTISTHATTHERE MIGHTBEAGREATERPROBABILITYOFlNDINGAMATEINALARGERPOPULATION&ORINSECT POLLINATED PLANTS SEED SET MAY DEPEND ON THERE BEING NEARBY CON SPECIlCS 0ARKER AND 0ARKER AND (AUBENSAK GIVE EXAMPLES OF POLLINA TOR LIMITATION IN THE INVASIVE 3COTCH BROOM #YTISUS SCOPARIUS !N IMPORTANT CONSEQUENCE OF THE !LLEE EFFECT FOR INVASIONS IS THAT ISOLATED PLANTS OR ISOLATED POPULATIONS CAN EXPERIENCE A SLOWER POPULATION GROWTH RATE RELATIVE TO LARGER POPULATIONS4HISMAYBEPARTICULARLYIMPORTANTDURINGTHEESTABLISHMENTPHASE


OFINVASIVESPECIES ORDETERMINEWHATLEVELOFCONTROLWILLLEADTOERADICATIONOR SLOWERPOPULATIONGROWTH-ANYINVASIVESPECIESEXPERIENCEAhLAGTIMEvBETWEEN INITIALCOLONIZATIONANDRAPIDPOPULATIONGROWTH4HISMIGHTSIMPLYBEDUETOTHE LAG PHASE IN AN EXPONENTIAL GROWTH CURVE BUT IT COULD ALSO INDICATE THE ACTION OF STRONG OR WEAK !LLEE EFFECTS 4HE DISTINCTION BETWEEN STRONG AND WEAK !LLEE EFFECTSISANIMPORTANTONEANDISOUTLINEDIN7ANGAND+OT $EMOGRAPHIC !LLEEEFFECTSOCCURWHENTHEPOPULATIONGROWTHRATEATSOMESETOFLOWDENSITIES IS SLOWER THAN POPULATION GROWTH RATE AT HIGHER DENSITIES 3TRONG DEMOGRAPHIC !LLEE EFFECTS OCCUR WHEN POPULATION GROWTH RATE AT LOW DENSITY IS NEGATIVE )FSTRONG!LLEEEFFECTSWEREOPERATINGDURINGTHEESTABLISHMENTPHASEOFANINVA SIVE SPECIES THE POPULATION WOULD NEED TO REACH A THRESHOLD SIZE BEFORE BEING ABLE TO SPREAD RAPIDLY 4HIS COULD BE ACHIEVED THROUGH ONE LARGE INITIAL RELEASE OR THROUGH REPEATED INVASIONS EQUIVALENT TO A RESCUE EFFECT IN META POPULATION MODELS!MARASEKARE %QUALLY THATPOPULATIONCOULDBEDRIVENTOEXTINC TIONBYREDUCINGITBELOWTHETHRESHOLD7EAKDEMOGRAPHIC!LLEEEFFECTSRESULTIN APOPULATIONTHATGROWSMORESLOWLYATLOWDENSITIESTHANITDOESATHIGHDENSITIES BUTTHATGROWTHISALWAYSPOSITIVESOATHRESHOLDDOESNOTEXIST!CONSEQUENCE OFTHEOPERATIONOFWEAK!LLEEEFFECTSWOULDBETHATTHELAGPHASEOFANINVASION WOULDBELONGERTHANPREDICTEDBYANEXPONENTIALGROWTHCURVE !LLEE EFFECTS CAN BE IMPORTANT DURING INVASIVE SPECIES EXPANSION $AVIS ET AL DEMONSTRATETHISFOR3PARTINAALTERNImORA WHICHhSETSVERYLITTLEVIABLESEED AT THE LEADING EDGES OF AN INVASION IN 7ILLAPA "AY 7ASHINGTON 53! WHERE IT WASINTRODUCEDCYEARSAGOv3PARTINAALTERNImORAHASTWODISPERSALMECHA NISMS SHORT DISTANCE SPREAD FROM RHIZOMATOUS GROWTH IN EXISTING PLANTS AND LONGDISTANCESPREADVIASEEDS,ONGDISTANCESPREADFROMTHELEADINGEDGEOFTHE POPULATION IS LIMITED HOWEVER BY A LACK OF VIABLE SEED UNTIL THE POPULATION HAS lLLEDINTHROUGHRHIZOMATOUSGROWTHORGERMINATIONOFOTHERSEEDSDISPERSEDFROM EXISTING DENSE POPULATIONS 7EAK !LLEE EFFECTS SUCH THOSE FOUND IN THE INVASIVE 3ALTERNImORANOTONLYAFFECTPOPULATIONGROWTHRATESATLOWDENSITY EQUILIBRIUM DENSITIESANDSTABILITY&OWLERAND2UXTON BUTTHEIRINCLUSIONINMODELSOF SPREADCANALTERSPREADVELOCITIES4HEIMPACTOFWEAK!LLEEEFFECTSONEQUILIBRIA STABILITYANDSPREADVELOCITIESHASONLYBEENADDRESSEDRELATIVELYRECENTLY PREVI OUSLY ONLY STRONG !LLEE EFFECTS HAD BEEN CONSIDERED IN ANY DETAIL &OR INTEGRO DIFFERENCEEQUATION)$% MODELSOFSPREAD +OTETAL SHOWEDTHATSTRONG !LLEE EFFECTS CAN TURN ACCELERATING INVASIONS INTO CONSTANT SPEED INVASIONS AND 7ANG ET AL SUGGEST USING NUMERICAL SOLUTIONS THAT INCLUDING WEAK !LLEEEFFECTSCANALSOSLOWDOWNINVASIONSFROMACCELERATINGTOCONSTANTSPEEDS 7ANG ET AL ALSO SHOW THAT !LLEE EFFECTS DETERMINE THE DIRECTION OF A TRAVELLING WAVE SOLUTION OF )$% MODELS WHERE THE DIRECTION OF THE TRAVELLING WAVE SOLUTION DETERMINES WHETHER AN INVASION WILL SUCCEED OR NOT 4RADITIONAL REACTION DIFFUSION MODELS OF SPREAD HAVE ALSO BEEN INVESTIGATED WITH REGARD TO THEINCLUSIONOF!LLEEEFFECTS AGAINSHOWINGTHAT!LLEEEFFECTSSLOWDOWNSPREAD #RUICKSHANKETAL ANDEVENTHATANINVASIONCANONLYSUCCEEDONCEACER TAINCRITICALAREAISOCCUPIED,EWISAND+AREIVA


7HETHER DENSITY DEPENDENCE ACTS NEGATIVELY OR THROUGH !LLEE EFFECTS IT WILL HAVEIMPLICATIONSFORPOPULATIONSTABILITY4HISISTRUEEVENINTHESIMPLESTMOD ELSSEETHE(ASSELLMODELABOVEFORNEGATIVEDENSITYDEPENDENCEAND3CHEURING WHOSHOWSTHAT!LLEEEFFECTSPROMOTESTABILITYINSIMPLEMODELS )NTEREST IN DENSITY DEPENDENCE OFTEN STEMS FROM THE SEARCH FOR MECHANISMS EITHER PRO MOTING STABILITY IN PLANT POPULATIONS OR DESTABILISING POPULATIONS -OST PLANT POPULATIONSAREBELIEVEDTOEXHIBITSTABLEDYNAMICSDUETOSTABILIZINGFEATURESOF THEIRLIFE HISTORIESSUCHASSOILSEEDBANKS7ATKINSON 0ACALAAND3ILANDER *ARRY ET AL PHENOTYPIC PLASTICITY AND ASYMMETRIC COMPETITION 0ALMBLAD 7EINER 0ACALA AND 7EINER 3ILVERTOWN SMALLSIZETHRESHOLDSFORREPRODUCTION2EESAND#RAWLEY ANDSELF THINNING 7ATKINSON 7ATKINSON AND $AVY $ESTABILIZING PROCESSES INCLUDE OVER COMPENSATING DENSITY DEPENDENT FECUNDITY 4HRALL ET AL TIME LAGS CAUSED BY MATERNAL EFFECTS #RONE LARGE SIZE THRESHOLDS FOR REPRODUCTION 4HRALLETAL ANDDELAYEDmOWERINGATHIGHDENSITY"UCKLEYETAL #YCLICORCHAOTICDYNAMICSCANRESULTFROMANOVER COMPENSATINGDENSITYDEPEN DENT RESPONSE COMBINED WITH A HIGH lNITE RATE OF POPULATION GROWTH FROM LOW DENSITIES/VER COMPENSATINGDENSITYDEPENDENCEOCCURSvWHENTHEPROPORTIONAL DECLINEINPARAMETERVALUEWITHINCREASINGDENSITYEXCEEDSTHECHANGEINDENSITYv &RECKLETONAND7ATKINSON -ECHANISMSGIVINGRISETOOVER COMPENSATING DENSITY DEPENDENCE ARE RARE IN PLANT SYSTEMS AND THEREFORE UNSTABLE DYNAMICS SUCHASCYCLESORCHAOSAREEQUALLYRARE#HAOTICDYNAMICSINANNUALPLANTSYS TEMSAREREVIEWEDBY&RECKLETON7ATKINSON ANDTHEREISLITTLEEVIDENCE FORCHAOTICDYNAMICSINOTHERPLANTLIFE HISTORIES2EESAND#RAWLEY (OWEVER 2EESETAL HAVESHOWNTHATmOWERINGDYNAMICSCLOSETOCHAOTIC OCCURINAMAST SEEDINGTUSSOCKGRASS #HIONOCHLOAPALLENS POSSIBLYASANEVOLU TIONARYRESPONSETOATTACKBYSEEDANDmOWERFEEDERS 3TABILITY IS AN IMPORTANT ISSUE FOR POPULATIONS OF INVASIVES FOR A NUMBER OF REASONSKNOWINGWHETHERAPOPULATIONISLIKELYTOBESTABLEOREXHIBITCYCLESMAY ALLOW PREDICTION OF LEVELS OF IMPACT LIKELY TO OCCUR STABILITY MAY ALSO AFFECT THE SUCCESSOFBIOCONTROLPROGRAMS&ORPLANTSPECIESWITHLONG LIVEDSEEDBANKSITIS IMPORTANT TO MAINTAIN POPULATIONS OF A BIOCONTROL AGENT IN THE SYSTEM IN ORDER TOCONTROLPOPULATIONSARISINGFROMTHESEEDBANKATALATERDATE ORCONTINUOUS RE INTRODUCTIONOFTHEBIOCONTROLAGENTISNECESSARY7HENCHOOSINGABIOCONTROL AGENT THEREFORE IT MAY BE BETTER TO CHOOSE AN AGENT WHICH MAINTAINS THE PLANT POPULATIONATALOWSTABLELEVELRATHERTHANONEWHICHDRIVESTHEABOVEGROUND POPULATION TO EXTINCTION CAUSING ITS OWN EXTINCTION AND THE SUBSEQUENT RESUR GENCEOFTHEINVASIVEPLANT%VENIFTHEHERBIVOREDOESNOTCAUSEPLANTEXTINCTION DIRECTLY UNSTABLECYCLESCANRESULTINAHIGHERPROBABILITYOFSTOCHASTICEXTINCTION OFTHEPLANTPOPULATION"UCKLEYETAL USEANEXPERIMENTALLYPARAMETER ISED PLANT HERBIVORE MODEL TO SHOW THAT DENSITY DEPENDENCE IN BOTH PLANT AND HERBIVORE POPULATIONS CONTRIBUTE TO STABILITY IN THE SYSTEM BUT THAT THE FORM OF DENSITYDEPENDENCEINTHEHERBIVORE INCOMBINATIONWITHHIGHATTACKRATES CAN DESTABILISETHEDYNAMICS3TUDYINGTHEFORMOFDENSITYDEPENDENCEEGSCRAMBLE


OR CONTEST IN POTENTIAL AGENTS MAY THEREFORE GIVE US SOME IDEA OF WHICH AGENTS WOULDBEMOSTAPPROPRIATETOINTRODUCEINSYSTEMSLIKETHISABIOCONTROLAGENTCOM BININGSTRONGSCRAMBLECOMPETITIONWITHAHIGHATTACKRATEMAYNOTBEAGOODCHOICE 4HE EXACT WAY IN WHICH DENSITY DEPENDENT PROCESSES AFFECT STABILITY CAN BE SUBTLE $ENSITY DEPENDENCE MAY OCCUR AT SEVERAL LIFE HISTORY STAGES WITHIN A SPECIES AND WHICH STAGE IT ACTS ON CAN BE OF CRITICAL IMPORTANCE TO ITS EFFECT FOR POPULATIONSTABILITY&OREXAMPLE "UCKLEYANDCOLLEAGUES FOUNDEVIDENCE FOR DENSITY DEPENDENT SURVIVAL mOWERING AND FECUNDITY IN THE INVASIVE ANNUAL 4RIPLEUROSPERMUM PERFORATUM 4HESE DIFFERENT OCCURRENCES HAD DIFFERENT IMPLICA TIONSFORPOPULATIONSTABILITY$ENSITYDEPENDENCEINSURVIVALANDFECUNDITYWAS STABILISING WHEREASDENSITYDEPENDENCEINmOWERINGLEDTOINSTABILITYINFACULTA TIVEBIENNIALSYSTEMSSEE&IGFORDENSITYDEPENDENTmOWERINGPROBABILITYAND &IGFORMODELSTABILITY (OWEVER DENSITYDEPENDENTmOWERINGALSOMEANSTHAT INTHISFACULTATIVEBIENNIAL DELAYEDmOWERINGISFAVOUREDATHIGHDENSITIES4HIS LEADSTOASYMMETRICCOMPETITIONBETWEENLARGEROVER WINTEREDROSETTESANDNEW SEEDLINGSINTHEFOLLOWINGYEAR WHICHISGENERALLYASTABILISINGFORCEASTHELARGER ROSETTES ARE MORE COMPETITIVE WITH SEEDLINGS 3O DENSITY DEPENDENCE NOT ONLY AFFECTSTHEDYNAMICSINTHISPREDOMINANTLYANNUALSYSTEM BUTALSOPLAYSAPART IN DETERMINING THE LIFE HISTORY STRATEGY ADOPTED BY THE PLANT AND THE TIMING OF DENSITYDEPENDENCEISIMPORTANTFORBOTHOFTHESEOUTCOMES 4HIS EXAMPLE ALSO ILLUSTRATES HOW THE TIMING OF DENSITY DEPENDENCE CAN BE CRITICAL FOR DECISIONS RELATING TO MANAGEMENT OF INVASIVE SPECIES -ANAGEMENT STRATEGIESGENERALLYRESULTINEXOGENOUSMORTALITY THROUGHMOWING FOREXAMPLE $UE TO OVER COMPENSATING DENSITY DEPENDENCE IN 4 PERFORATUM THE TIMING OF EXOGENOUS MORTALITY AFFECTS THE EQUILIBRIUM SEED DENSITY DRAMATICALLY )F EXOG ENOUS MORTALITY OCCURS EARLY IN THE LIFE CYCLE FREEING THE FEW SURVIVING PLANTS FROMDENSITYDEPENDENTDEPRESSIONOFSEEDPRODUCTION SEEDOUTPUTCANACTUALLY INCREASE EXACERBATINGTHEWEEDPROBLEMINTHELONG TERM"UCKLEYETAL 'ENERALLY IF DENSITY DEPENDENCE IS IMPORTANT FOR POPULATION REGULATION THE REMOVALOFSEEDS SEEDLINGSORPLANTSBEFOREDENSITYDEPENDENCEOCCURSISUNLIKELY TOLEADTOSUCCESSFULCONTROL4HISISOFTENRELEVANTWHENCONSIDERINGBIOCONTROL AGENTS!SPOINTEDOUTBY!LEXANDERAND3CHRAG SEEDPREDATORSORSEEDLING PATHOGENSCANHAVEASTRONGEFFECTONSEEDLINGNUMBERS%DWARDSAND#RAWLEY !LEXANDER AND -IHAIL #UMMINGS AND !LEXANDER BUT NOT NECESSARILY IMPACT ON lNAL REPRODUCTIVE OUTPUT OF A PATCH DUE TO SUBSEQUENT DENSITY DEPENDENT PROCESSES 7HERE SEED INPUT IS REDUCED LOW DENSITY SEEDLING POPULATIONS ARE PRODUCED WHICH MAY HAVE LOWER RATES OF INTRASPECIlC COMPETI TION AND THUS HIGHER PER CAPITA SEED PRODUCTION COMPENSATING FULLY OR TO SOME EXTENTFORTHEINITIALSEEDORSEEDLINGLOSS4HECASEOF!CACIANILOTICAILLUSTRATESTHIS POINT!CACIANILOTICA ANINVASIVESHRUBORSMALLTREEISDISPERSEDBYCATTLE WHICH EAT SEEDS AND DEPOSIT THEM IN COW PATS 4HE SEEDLINGS ARE THEREFORE AGGREGATED INSMALLPATCHESANDSELF THINNINGENSURESTHATNOMORETHANAPPROXIMATELYONE SEEDLING SURVIVES TO ADULTHOOD +RITICOS ET AL AND +RITICOS ET AL ESTIMATE THAT THE INTRODUCTION OF A SEED EATING BIOCONTROL AGENT IS THEREFORE


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UNLIKELYTOAFFECTADULTPOPULATIONSIZESUNLESSTHENUMBEROFSEEDSPERCOWPATIS REDUCEDDRAMATICALLY TOTWOORLESS 3EVERAL AUTHORS HAVE CALLED FOR A THOROUGH UNDERSTANDING OF THE OCCURRENCE AND EFFECTS OF DENSITY DEPENDENCE AT DIFFERENT STAGES -ORTIMER ET AL 7ATKINSON ET AL 'ILLMAN ET AL !S SHOWN BY THE EXAMPLES GIVEN ABOVE THISISESPECIALLYRELEVANTFORWEEDSPECIESWHEREDENSITYISMANIPULATEDAT ONEORMORESPECIlCSTAGESFORCONTROLPURPOSES )NVIEWOFTHESERESULTSITISOBVIOUSTHATMODELSSEEKINGTOPREDICTTHEEFFECTS OF CONTROL STRATEGIES AT DIFFERENT STAGES SHOULD INCORPORATE DENSITY DEPENDENCE )NASUSTAINABLEHARVESTINGSTUDY&RECKLETONETAL POINTOUTTHATTHEUSE OF DENSITY INDEPENDENT MATRIX MODELS WHERE THE TRANSITION PROBABILITIES ARECAL CULATED WHEN THE POPULATION IS CLOSE TO EQUILIBRIUM h CLOSE TO COULD GIVE MISLEADING RESULTS WHEN USED TO PREDICT POPULATION INCREASE FROM LOW DENSITY 4HEYCALLFOREXPLICITINCORPORATIONOFDENSITYDEPENDENCEINHARVESTINGMODELS ANDTHESAMECALLSHOULDBEMADEFORCONTROLMODELSOFINVASIVESWHEREDENSITY DEPENDENCEISKNOWNORSUSPECTEDTOBEIMPORTANT !THOROUGHUNDERSTANDINGOFTHEOCCURRENCEANDEFFECTSOFDENSITYDEPENDENCE WOULDALSOGREATLYCONTRIBUTETOINVESTIGATIONSINTOSELECTIONPRESSURESANDEVO LUTION )NVASIVE PLANTS CAN BE EXCELLENT MODEL SYSTEMS FOR THE DEVELOPMENT OF MODELS OF LIFE HISTORY EVOLUTION 0LANTS IN THE EXOTIC RANGE MAY BE UNDER DIFFER ENTSELECTIONPRESSURESDUETOENEMYRELEASEORCOMPETITIVERELEASE#ONTRASTING MODELS PREDICTING EVOLUTIONARILY STABLE STRATEGIES IN EACH ENVIRONMENT COULD BE DEVELOPED 4HIS APPROACH WOULD COMPLEMENT OBSERVATIONAL AND EXPERIMENTAL STUDIESAIMEDATDETECTINGEVOLUTIONARYCHANGEBETWEENINVASIVESINTHEIRNATIVE AND EXOTIC HABITATS "LOSSEY AND .ÚTZOLD 7ILLIS ET AL 3IEMANNAND2OGERS (ISTORICALLY WHENEXPLORINGLIFEHISTORYSTRATEGIES INVESTIGATORSIGNOREDDENSI TYDEPENDENCE ANDSIMPLYUSEDR FROMTHE%ULER ,OTKAEQUATION TODElNElTNESS 3TEARNS (OWEVER ITBECAMEAPPARENTTHATDENSITYDEPENDENCECOULDNOT BEIGNORED BECAUSEINADENSITYDEPENDENTSITUATION THElTNESSOFONESTRATEGY WILLDEPENDONTHEACTIONSOFOTHERSTRATEGIES'RANTAND"ENTON "ECAUSE OFTHIS THEEVOLUTIONARYSTABLESTRATEGY%33 ISBESTDETERMINEDBYUSINGTHEINVA SIONEXPONENT ORTHERATEOFINCREASEOFARAREMUTANTINTOANhENVIRONMENTv SETBYARESIDENTSTRATEGY ANDCHARACTERISEDBYTHERESIDENTSDENSITY)F THEN THEINVADERISSUCCESSFUL4HE%33ISSIMPLYTHESTRATEGYTHATCANNOTBEINVADED BYANYOTHER5SINGTHISFRAMEWORK -YLIUSAND$IEKMANN SHOWEDTHAT IN A CONSTANT ENVIRONMENT THE %33 MAY SOMETIMES BE THE STRATEGY AT WHICH A RELATIVELYSIMPLEFUNCTIONISMAXIMISED(OWEVER WHICHFUNCTIONISAPPROPRIATE ISDETERMINEDBYWHENDENSITYDEPENDENCEACTSINTHELIFECYCLE)FDENSITYDEPEN DENCE ACTS SO THAT ONLY THE EXPECTED LIFETIME OFFSPRING PRODUCTION IS REDUCED THENANAPPROPRIATElTNESSMEASUREISLIFETIMEREPRODUCTIVESUCCESS OR2)FDEN SITYDEPENDENCEAFFECTSONLYTHEPROBABILITYPERUNITTIMEOFDYING THENPOPULA TIONRATEOFINCREASE h ISAPPROPRIATE4HETWOMAYPROVIDEDIFFERENTPREDICTIONS SOITISIMPORTANTTOUSETHEAPPROPRIATEMEASURE


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2%&%2%.#%3 !LEXANDER ( - AND * $ -IHAIL 3EEDLING DISEASE IN AN ANNUAL LEGUME CONSE QUENCES FOR SEEDLING MORTALITY PLANT SIZE AND POPULATION SEED PRODUCTION /ECOLOGIA !LEXANDER (-AND!-3CHRAG2OLEOFSOILSEEDBANKSANDNEWLYDISPERSEDSEEDS INPOPULATIONDYNAMICSOFTHEANNUALSUNmOWER (ELIANTHUSANNUUS*OURNALOF%COLOGY !MARASEKARE 0)NTERACTIONSBETWEENLOCALDYNAMICSANDDISPERSAL)NSIGHTSFROM SINGLESPECIESMODELS4HEORETICAL0OPULATION"IOLOGY "ENTON 4' 4##AMERONAND!'RANT0OPULATIONRESPONSESTOPERTURBATIONS PREDICTIONSANDRESPONSESFROMLABORATORYMITEPOPULATIONS*OURNALOF!NIMAL%COLOGY "LOSSEY " AND 2 .ÚTZOLD %VOLUTION OF INCREASED COMPETITIVE ABILITY IN INVASIVE NONINDIGENOUSPLANTSAHYPOTHESIS*OURNALOF%COLOGY "ONSALL -" %VANDER-EIJDENAND-*#RAWLEY#ONTRASTINGDYNAMICSINTHE SAME PLANT HERBIVORE INTERACTION 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES "UCKLEY 9 - $ 4 "RIESE AND - 2EES A $EMOGRAPHY AND MANAGEMENT OF THE INVASIVE PLANT SPECIES (YPERICUM PERFORATUM ) 5SING MULTI LEVEL MIXED EFFECTS MODELS FOR CHARACTERIZING GROWTH SURVIVAL AND FECUNDITY IN A LONG TERM DATA SET *OURNAL OF !PPLIED%COLOGY "UCKLEY 9 - 0 $OWNEY 3 6 &OWLER 2 , (ILL * -EMMOTT ( .ORAMBUENA - 0ITCAIRN 2'3HAW !73HEPPARD #7INKS 27ITTENBERGAND-2EESB!RE INVASIVESBIGGER!GLOBALSTUDYOFSEEDSIZEVARIATIONINTWOINVASIVESHRUBS%COLOGY "UCKLEY 9- (,(INZ $-ATTHIESAND-2EES)NTERACTIONSBETWEENDENSITY DEPENDENT PROCESSES POPULATION DYNAMICS AND CONTROL OF AN INVASIVE PLANT SPECIES 4RIPLEUROSPERMUMPERFORATUMSCENTLESSCHAMOMILE %COLOGY,ETTERS "UCKLEY 9- -2EES !73HEPPARDAND-*3MYTH3TABLECOEXISTENCEOFAN INVASIVE PLANT AND BIOCONTROL AGENT A PARAMETERISED COUPLED PLANT HERBIVORE MODEL *OURNALOF!PPLIED%COLOGY #AMERON 4 # AND 4 ' "ENTON 3TAGE STRUCTURED HARVESTING AND ITS EFFECTS AN EMPIRICALINVESTIGATIONUSINGSOILMITES*OURNALOF!NIMAL%COLOGY #ASWELL ( -ATRIX POPULATION MODELS CONSTRUCTION ANALYSIS AND INTERPRETATION NDEDITION3INAUER!SSOCIATES )NC 3UNDERLAND -ASSACHUSETTS #RONE %%0ARENTALENVIRONMENTALEFFECTSANDCYCLICALDYNAMICSINPLANTPOPULA TIONS4HE!MERICAN.ATURALIST #RUICKSHANK ) 73#'URNEYAND!26EITCH4HECHARACTERISTICSOFEPIDEMICS ANDINVASIONSWITHTHRESHOLDS4HEORETICAL0OPULATION"IOLOGY #UMMINGS #,AND(-!LEXANDER0OPULATIONECOLOGYOFWILDSUNmOWERSEFFECTS OFSEEDDENSITYANDPOST DISPERSALVERTEBRATESEEDPREDATION/ECOLOGIA $AVIS (' #-4AYLOR *##IVILLEAND$23TRONG!N!LLEEEFFECTATTHEFRONTOF APLANTINVASION3PARTINAINA0ACIlCESTUARY*OURNALOF%COLOGY


%ASTERLING -2 30%LLNERAND0-$IXON3IZE SPECIlCSENSITIVITY!PPLYINGA NEWSTRUCTUREDPOPULATIONMODEL%COLOGY %DWARDS '2AND-*#RAWLEY2ODENTSEEDPREDATIONANDSEEDLINGRECRUITMENT INMESICGRASSLAND/ECOLOGIA &OWLER 36AND'$2UXTON0OPULATIONDYNAMICCONSEQUENCESOF!LLEEEFFECTS *OURNALOF4HEORETICAL"IOLOGY &OX '!AND"%+ENDALL$EMOGRAPHICSTOCHASTICITYANDTHEVARIANCEREDUCTION EFFECT%COLOGY &RECKLETON 20 $-3ILVA-ATOS -,!"OVIAND!27ATKINSON0REDICTING THE IMPACTS OF HARVESTING USING STRUCTURED POPULATION MODELS THE IMPORTANCE OF DENSITY DEPENDENCE AND TIMING OF HARVEST FOR A TROPICAL PALM TREE *OURNAL OF !PPLIED %COLOGY &RECKLETON 2 0 AND ! 2 7ATKINSON !RE WEED POPULATION DYNAMICS CHAOTIC *OURNALOF!PPLIED%COLOGY 'ILLMAN - * - "ULLOCK * 3ILVERTOWN AND " #LEAR (ILL ! DENSITY DEPENDENT MODELOF#IRSIUMVULGAREPOPULATIONDYNAMICSUSINGlELD ESTIMATEDPARAMETERVALUES /ECOLOGIA 'RANT !AND4'"ENTON%LASTICITYANALYSISFORDENSITYDEPENDENTPOPULATIONSIN STOCHASTICENVIRONMENTS%COLOGY (ARPER *,AND7!7OOD"IOLOGICAL&LORAOFTHE"RITISH)SLES3ENECIOJACOBAEA, *OURNALOF%COLOGY (ASSELL -0$ENSITY DEPENDENCEINSINGLE SPECIESPOPULATIONS*OURNALOF!NIMAL %COLOGY *ARRY - - +HALADI - (OSSAERT -C+EY AND $ -C+EY -ODELING THE POPULA TION DYNAMICS OF ANNUAL PLANTS WITH SEED BANK AND DENSITY DEPENDENT EFFECTS !CTA "IOTHEORETICA +EANE 2 - AND - * #RAWLEY %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS4RENDSIN%COLOGY%VOLUTION +OT - - ! ,EWIS AND 0 VAN DEN $RIESSCHE $ISPERSAL DATA AND THE SPREAD OF INVADINGORGANISMS%COLOGY +REBS # * 4WO COMPLEMENTARY PARADIGMS FOR ANALYSING POPULATION DYNAMICS 0HILOSOPHICAL4RANSACTIONSOFTHE2OYAL3OCIETYOF,ONDON3ERIES" "IOLOGICAL3CIENCES +RITICOS $ * "ROWN ) 2ADFORD AND - .ICHOLAS 0LANT POPULATION ECOLOGY AND BIOLOGICALCONTROL!CACIANILOTICAASACASESTUDY"IOLOGICAL#ONTROL +RITICOS $* *2"ROWN '&-AYWALD )$2ADFORD $-.ICHOLAS 273UTHERSTAND 37!DKINS30!N$8APROCESS BASEDPOPULATIONDYNAMICSMODELTOEXPLORE MANAGEMENTANDCLIMATECHANGEIMPACTSONANINVASIVEALIENPLANT !CACIANILOTICA %COLOGICALMODELLING ,EWIS -!AND0+AREIVA!LLEEDYNAMICSANDTHESPREADOFINVADINGORGANISMS 4HEORETICAL0OPULATION"IOLOGY -ETCALF * # + % 2OSE AND - 2EES %VOLUTIONARY DEMOGRAPHY OF MONOCARPIC PERENNIALS4RENDSIN%COLOGY%VOLUTION


-ORTIMER !- **3UTTONAND0'OULD/NROBUSTWEEDPOPULATIONMODELS7EED 2ESEARCH -YLIUS 3$AND/$IEKMANN/NEVOLUTIONARILYSTABLELIFEHISTORIESANDTHENEED TOBESPECIlCABOUTDENSITYDEPENDENCE/IKOS 0ACALA 3 7 AND * ! 3ILANDER &IELD TESTS OF NEIGHBORHOOD POPULATION DYNAMIC MODELSOFTWOANNUALWEEDSPECIES%COLOGICAL-ONOGRAPHS 0ACALA 3 7 AND * 7EINER %FFECTS OF COMPETITIVE ASYMMETRY ON A LOCAL DENSITY MODELOFPLANTINTERFERENCE*OURNALOF4HEORETICAL"IOLOGY 0ALMBLAD )'#OMPETITIONINEXPERIMENTALSTUDIESONPOPULATIONSOFWEEDSWITH PARTICULAREMPHASISONTHEREGULATIONOFPOPULATIONSIZE%COLOGY 0ARKER )-0OLLINATORLIMITATIONOF#YTISUSSCOPARIUS3COTCHBROOM ANINVASIVE EXOTICSHRUB%COLOGY 0ARKER )-AND+!(AUBENSAK#OMPARATIVEPOLLINATORLIMITATIONOFTWONON NATIVESHRUBSDOMUTUALISMSINmUENCEINVASIONS/ECOLOGIA 0AYNTER 1 0 / $OWNEY AND ! 7 3HEPPARD !GE STRUCTURE AND GROWTH OF THE WOODY LEGUME WEED #YTISUS SCOPARIUS IN NATIVE AND EXOTIC HABITATS IMPLICATIONS FOR CONTROL*OURNALOF!PPLIED%COLOGY 0IMENTEL $ , ,ACH 2 :UNIGA AND $ -ORRISON %NVIRONMENTAL AND ECONOMIC COSTSOFNONINDIGENOUSSPECIESINTHE5NITED3TATES"IOSCIENCE 2EES - AND - * #RAWLEY 'ROWTH REPRODUCTION AND POPULATION DYNAMICS &UNCTIONAL%COLOGY 2EES - AND - * #RAWLEY $O PLANT POPULATIONS CYCLE &UNCTIONAL %COLOGY 2EES - $+ELLYAND/."JORNSTAD3NOWTUSSOCKS CHAOSANDTHEEVOLUTIONOF MASTSEEDING4HE!MERICAN.ATURALIST 2EES -AND+%2OSE%VOLUTIONOFmOWERINGSTRATEGIESIN/ENOTHERAGLAZIOVIANA ANINTEGRALPROJECTIONMODELAPPROACH0ROCEEDINGSOFTHE2OYAL3OCIETY,ONDON3ERIES " 3CHEURING )!LLEEEFFECTINCREASESTHEDYNAMICALSTABILITYOFPOPULATIONS*OURNALOF 4HEORETICAL"IOLOGY 3HIMA *3AND#7/SENBERG#RYPTICDENSITYDEPENDENCEEFFECTSOFCOVARIATION BETWEENDENSITYANDSITEQUALITYINREEFlSH%COLOGY 3IBLY 2-AND*(ONE0OPULATIONGROWTHRATEANDITSDETERMINANTSANOVERVIEW 0HILOSOPHICAL4RANSACTIONSOFTHE2OYAL3OCIETYOF,ONDON3ERIES" "IOLOGICAL3CIENCES 3IEMANN %AND7%2OGERS'ENETICDIFFERENCESINGROWTHOFANINVASIVETREESPE CIES%COLOGY,ETTERS 3IEMANN %AND7%2OGERS2EDUCEDRESISTANCEOFINVASIVEVARIETIESOFTHEALIEN TREE3APIUMSEBIFERUMTOAGENERALISTHERBIVORE/ECOLOGIA 3ILVERTOWN *-ODULARITY REPRODUCTIVETHRESHOLDSANDPLANTPOPULATIONDYNAMICS &UNCTIONAL%COLOGY 3TEARNS 3#4HEEVOLUTIONOFLIFEHISTORIES/XFORD5NIVERSITY0RESS /XFORD 3TEPHENS 0! 7*3UTHERLANDAND2&RECKLETON7HATISTHE!LLEEEFFECT/IKOS


4HRALL 0( 370ACALAAND*!3ILANDER/SCILLATORYDYNAMICSINPOPULATIONSOF ANANNUALWEEDSPECIES!BUTILONTHEOPHRASTI*OURNALOF%COLOGY 4URCHIN 00OPULATIONREGULATIONASYNTHETICVIEW/IKOS 7ANG -( -+OTAND-'.EUBERT)NTEGRODIFFERENCEEQUATIONS !LLEEEFFECTS ANDINVASIONS*OURNALOF-ATHEMATICAL"IOLOGY 7ATKINSON ! 2 $ENSITY DEPENDENCE IN SINGLE SPECIES POPULATIONS OF PLANTS *OURNALOF4HEORETICAL"IOLOGY 7ATKINSON !2AND!*$AVY0OPULATIONBIOLOGYOFSALT MARSHANDSANDDUNE ANNUALS6EGETATIO 7ATKINSON ! 2 7 - ,ONSDALE AND - ( !NDREW -ODELLING THE POPULATION DYNAMICSOFANANNUALPLANT3ORGHUMINTRANSINTHEWET DRYTROPICS*OURNALOF%COLOGY 7EINER * 3IZE HIERARCHIES IN EXPERIMENTAL POPULATIONS OF ANNUAL PLANTS %COLOGY 7ILLIS !* *-EMMOTTAND2)&ORRESTER)STHEREEVIDENCEFORTHEPOST INVASION EVOLUTIONOFVIGOURAMONGINVASIVEPLANTSPECIES%COLOGY,ETTERS 7ILLIS ! * - " 4HOMAS AND * ( ,AWTON )S THE INCREASED VIGOUR OF INVASIVE WEEDS EXPLAINED BY A TRADE OFF BETWEEN GROWTH AND HERBIVORE RESISTANCE /ECOLOGIA

#HAPTERSIX

3TOCHASTICITY NONLINEARITY ANDINSTABILITYINBIOLOGICAL INVASIONS 20&RECKLETON 0-$OWLINGAND.+$ULVY

).42/$5#4)/. #OMPARED WITH OTHER SCIENCES ECOLOGY HAS FEW GENERAL THEORIES THAT CAN BE APPLIEDTOPREDICTTHEDYNAMICSOFITSSYSTEMSFROMlRSTPRINCIPLES4HISISPERHAPS NOT SURPRISING GIVEN THE HUGE VARIABILITY OF ECOLOGICAL SYSTEMS ! NUMBER OF BROADINSIGHTSHAVEEMERGED HOWEVER ANDONEOFTHEMOSTIMPORTANTOFTHESEIS THAT PREDICTING THE DYNAMICS OF ECOLOGICAL SYSTEMS REQUIRES THAT WE UNDERSTAND THE INTERPLAY OF TWO KINDS OF PROCESSES STOCHASTIC AND DETERMINISTIC ,EWONTIN AND #OHEN -AY ,ANDE ET AL 4HIS CONCLUSION IS ESSENTIALLY A CONSENSUS RESULTING FROM A GREAT DEAL OF DEBATE IN THE ECOLOGICAL LITERATURE DATING BACK TO THE S EG !NDREWARTHA AND "IRCH .ICHOLSON (ASSELL7HITE 0REDICTING BIOLOGICAL INVASIONS IS AN EXTREMELY IMPORTANT APPLIED ECOLOGI CAL PROBLEM BECAUSE INVASIVE SPECIES ARE ECONOMICALLY ENORMOUSLY SIGNIlCANT IN AGRICULTURAL AND CONSERVATION TERMS AND METHODS FOR PREDICTING THE EFFECTS OF CONTROL MEASURES ARE URGENTLY REQUIRED "YERS ET AL /NE OF THE MOST IMPORTANT APPROACHES TO STUDYING BIOLOGICAL INVASIONS IS THROUGH POPULATION MODELLING 0OPULATION MODELS MAY TAKE A RANGE OF FORMS INCLUDING SIMPLE -7#ADOTTE ETAL (EDS) #ONCEPTUALECOLOGYANDINVASIONBIOLOGY – ¥3PRINGER0RINTEDINTHE.ETHERLANDS

20&RECKLETON 0-$OWLINGAND.+$ULVY

MATHEMATICAL MODELS (ASSELL -AY -AY ET AL -AYNARD 3MITH 7ATKINSON STATISTICALMODELS"UCKLEYETALA B ANDCOMPLEX SIMULATIONS 0ACALA ET AL 4HESE MODELS CAN BE USED IN A RANGE OF WAYS FROM MAKING HIGHLY SPECIlC PREDICTIONS ABOUT THE DYNAMICS OF SPECIES IN GIVEN AREAS THROUGHTOGENERALANALYSESAIMEDATDEVELOPINGAGENERALUNDERSTANDING OFTHEPROCESSESDETERMININGINVASIONSUCCESS 5NFORTUNATELYPOPULATIONMODELSAREFREQUENTLYEQUATEDWITHANEQUILIBRIUM ORDETERMINISTICOUTLOOKONPOPULATIONDYNAMICS WHICHISFREQUENTLYCRITICISED (OWEVER EVEN SIMPLE MODELS MAY FREQUENTLY YIELD RATHER COMPLEX OUTCOMES -AYAND/STER &ORINSTANCE ASIMPLELOGISTICMODELOFPOPULATIONGROWTH MIGHTBEEXPECTEDTOYIELDASTRAIGHTFORWARDOUTCOME NAMELYTHESMOOTHGROWTH OF A POPULATION TO ITS CARRYING CAPACITY 7HEN IMPLEMENTED AS A DISCRETE TIME MODEL HOWEVER THE OUTCOME MAY BE FAR MORE COMPLEX AND CHAOTIC DYNAMICS MAY BE POSSIBLE &ROM THE POINT OF VIEW OF PREDICTING POPULATION DYNAMICS THIS RAISEDTHEPOSSIBILITYTHATCOMPLETELYDETERMINISTICSYSTEMSMAYYIELDUNPREDICT ABLECHANGESINPOPULATIONNUMBERS4HEEARLYSALSOSAWANINCREASINGREC OGNITIONTHATVARIOUSFORMSOFINTERACTIONSANDINTERVENTIONCOULDYIELDUNSTABLE POPULATIONDYNAMICS-AY &OREXAMPLEHUNTING HARVESTINGORPREDATION COULD POTENTIALLY DESTABILISE POPULATION DYNAMICS TO THE EXTENT THAT OTHERWISE STABLEPOPULATIONSMIGHTBECOMEEXTINCT GIVENAPERTURBATIONTOTHESYSTEM ! lNAL ELEMENT THAT IS IMPORTANT IN PREDICTING POPULATION CHANGE IS THE STO CHASTIC COMPONENT OF POPULATION CHANGE 3TOCHASTICITY RESULTS FROM RANDOM VARIATIONS IN THE ENVIRONMENT OR FROM RANDOM VARIATION BETWEEN INDIVIDUALS 4HETHEORYFORSTOCHASTICPOPULATIONDYNAMICSHASALONGHISTORY#OHEN ,EWONTINAND#OHEN4ULJAPURKAR ANDTHEREHAVEBEENNUMEROUS RECENTDEVELOPMENTSOFTHIS,ANDEETAL 4HEMAJORCONCLUSIONFROMTHIS WORK HAS BEEN THAT THE EFFECTS OF STOCHASTICITY ON POPULATION DYNAMICS MAY BE COMPLEX0REDICTINGTHEIMPACTSOFSTOCHASTICITYISNOTASTRAIGHTFORWARDASMAK ING SOME PARAMETERS OF MODELS RANDOM VARIABLES OR OF CALCULATING AN AVERAGE OF SOME FORM 2ATHER STOCHASTICITY MAY IMPACT IN A PROFOUND AND A QUALITATIVE MANNERONPOPULATIONDYNAMICS 4HE PROBLEM OF PREDICTING AND MANAGING POPULATIONS OF INVASIVE SPECIES REQUIRES THAT WE ARE ABLE TO UNDERSTAND THE IMPACTS OF THE FACTORS DETAILED ABOVE ON SEVERAL PHASES OF THE INVASION PROCESS 4HE ELEMENTS OF POPULATION DYNAMICS OF INVASION CAN BE CONCEPTUALLY VIEWED AS CONSISTING OF THREE PHASES ARRIVAL ESTABLISHMENT AND SPREAD $OBSON AND -AY 7ILLIAMSON 4HE PROCESSES DESCRIBED ABOVE MIGHT BE EXPECTED TO PLAY DIFFERENT ROLES DEPEND ING ON WHICH OF THIS PHASES THE INVADING POPULATION IS IN )N THE ARRIVAL AND ESTABLISHMENTPHASES POPULATIONSAREGROWINGFROMLOWDENSITIESANDEXPANDING INTONEWHABITAT)NTHISPHASESTOCHASTICFACTORSMAYARGUABLYBEIMPORTANT AND LIMITINGFACTORSLESSSO)NCONTRAST FOLLOWINGSUCCESSFULESTABLISHMENTANDDURING THESPREADPHASEPOPULATIONSMAYBEATMUCHHIGHERDENSITIESANDFACTORSSUCHAS DENSITY DEPENDENCE MAY DOMINATE POPULATION CHANGES #ORRESPONDINGLY THESE DIFFERENCES IN DYNAMICS MAY INmUENCE CONTROL STRATEGIES 4AYLOR AND (ASTINGS

3TOCHASTICITY NONLINEARITYANDINSTABILITYINBIOLOGICALINVASIONS

-OREOVER WHEN FACTORS SUCH AS !LLEE EFFECTS OPERATE THE DETERMINISTIC COMPONENTOFDYNAMICSMAYBESIGNIlCANTATLOWDENSITIESANDINmUENCEPOPULA TIONPERSISTENCE4HEKEYTASKFORPOPULATIONMODELLINGISTOWORKOUTHOWTHESE VARIOUSFACTORSINTERACTWITHEACHOTHER 4HISCHAPTERISORGANISEDINTOTHREESECTIONS)NTHElRSTSECTIONWEREVIEWTHE PRINCIPLESOFSIMPLESTOCHASTICMODELSANDHOWTHEYMAYBEAPPLIEDTOINVASIONS 7ETHENEXAMINETHEDETERMINISTICCOUNTERPARTSOFTHESEMODELS ANDTHEPROB LEMS THESE PRESENT &INALLY WE BRIEmY REVIEW TWO STUDIES THAT EXHIBIT UNSTABLE DYNAMICSANDSPECULATEONTHEGENERALITYOFTHESE 34/#(!34)#0/05,!4)/.$9.!-)#3!.$4(%34!"),)49 /&0/05,!4)/.3 )T IS USEFUL TO RECOGNISE TWO SOURCES OF STOCHASTICITY IN POPULATION DYNAMICS %NGENETAL SINCETHESOURCEOFSTOCHASTICITYISIMPORTANTINUNDERSTAND INGITSEFFECTSONPOPULATIONDYNAMICS%NVIRONMENTALSTOCHASTICITYRESULTSFROM RANDOM VARIATIONS IN DEMOGRAPHIC RATES AS A CONSEQUENCE OF VARIATION IN ENVI RONMENTALCONDITIONS FOREXAMPLERESULTINGFROMTHEEFFECTSOFWEATHER!SECOND SOURCEOFSTOCHASTICITYISDEMOGRAPHICSTOCHASTICITY5NDERDEMOGRAPHICSTOCHAS TICITYTHEEXPECTEDCONTRIBUTIONOFEACHINDIVIDUALTOTHENEXTGENERATIONISALSO INDEPENDENT OF THE STATE OF THE POPULATION IN THE PREVIOUS GENERATION HOWEVER THE VARIANCE ABOUT THIS EXPECTATION DOES DEPEND ON THE STATE OF THE POPULATION AS DISTINCT FROM AN !LLEE EFFECT IN WHICH THE EXPECTATION DEPENDS ON DENSITY 3TEPHENSETAL 3IMPLESTOCHASTICPOPULATIONGROWTH

4HESIMPLESTMODELFORPOPULATIONDYNAMICSISONEINWHICHTHEEXPECTEDRATESOF DEATHANDFECUNDITYAREASSUMEDTOBECONSTANT ANDVARYRANDOMLYABOUTTHESE MEANS)FTHENETRATEOFPOPULATIONCHANGEINYEARTIS hT AND.T AND.T AREPOPULATIONSIZESINSUCCESSIVEYEARS THENTHEDYNAMICSOFSUCHAPOPULATION CANBEMODELLEDAS .T hT .T

&ORASPECIESTOBECAPABLEOFINVASION THEEXPECTEDVALUEOF.T4 .T MUST BEGREATERTHANONEAS4BECOMESLARGE)NACONSTANTENVIRONMENTTHISREQUIRES THATTHEVALUEOFhMUSTBEGREATERTHANUNITY)NANENVIRONMENTINWHICHTHERE ISSTOCHASTICITYTHECONDITIONONhISNOTASSTRAIGHTFORWARD BUTDEPENDSONTHE DISTRIBUTION OF h ABOUT ITS MEAN !CCORDING TO EQUATION POPULATION SIZE AT TIME T 4 IS A NON LINEAR FUNCTION OF hT hTxhT4 4HIS MEANS THAT THE DISTRI BUTION OF h HAS TO BE UNDERSTOOD IN ORDER TO PREDICT LONG TERM DYNAMICS -ORE COMPLEXEFFECTSSUCHASTHEAUTOCORRELATIONSBETWEENPOPULATIONGROWTHRATESIN SUCCESSIVE YEARS MAY ALSO COME INTO PLAY AND FURTHER COMPLICATE PREDICTIONS OF


POPULATIONPERSISTENCE(EINOETAL !LTHOUGHTHEPOSSIBILITIESARECOMPLEX TWO SIMPLE EXAMPLES ILLUSTRATE SOME OF THE MAIN FEATURES OF STOCHASTIC MODELS 4HEMAINCONCLUSIONATTHEENDOFTHISSECTIONISTHATTHEOUTCOMEOFSTOCHASTIC MODELSCANBEMORECOMPLEXTHANONEMIGHTlRSTIMAGINE %NVIRONMENTALSTOCHASTICITY

&IRSTLY ASSUMETHAThISLOG NORMALLYDISTRIBUTED ASMAYBETHECASEINPOPULA TIONS SUBJECT TO ENVIRONMENTAL STOCHASTICITY )N THAT CASE EQUATION MAY BE WRITTENAS WHEREN>LOG. NT NT LOG;hT =

4HIS IS LINEAR IN N WITH THE CONSEQUENCE THAT THE ARITHMETIC MEAN OF LOG h PREDICTSTHELONGTERMPOPULATIONTRAJECTORY)TISEASYTOSHOWTHATTHEEXPECTED VALUEOFNT4 ISNORMALLYDISTRIBUTEDWITHMEANN 4LOGh ANDVARIANCE 4 VAR ;LOGh = IF THE LAMBDAS ARE INDEPENDENT AND NORMALLY DISTRIBUTED &IG A SHOWSEXAMPLESOFASERIESOFPOPULATIONSGROWINGINTHISWAY AND&IGCSHOWS THEDISTRIBUTIONOFPOPULATIONSIZESAFTERAPERIODOFPOPULATIONGROWTH !SNOTEDABOVE PREDICTINGTHEOUTCOMEOFSTOCHASTICITYREQUIRESTHATTHEEFFECTS OF STOCHASTICITY ON POPULATION GROWTH ARE UNDERSTOOD IN DETAIL &OR INSTANCE IF THE DISTRIBUTION OF POPULATION GROWTH RATES IS NOT LOG NORMAL OR IF SUCCESSIVE POPULATION GROWTH RATES ARE NOT INDEPENDENT THEN THE RESULTS IN THE PREVIOUS PARAGRAPHDONOTHOLDEXACTLY)NSUCHCASESSTOCHASTICCALCULUSHASTOBEUSEDIN ORDERTODETERMINETHEAPPROPRIATEMETHODOFTRANSFORMINGPOPULATIONDENSITIES INORDERTOPREDICTPERSISTENCEEG ,ANDE $EMOGRAPHICSTOCHASTICITY

4HE SECOND EXAMPLE IS A POPULATION SUBJECT TO DEMOGRAPHIC STOCHASTICITY -AY ,ANDE ,ANDE ET AL $EMOGRAPHIC STOCHASTICITY RESULTS IN VARIABILITYINWHICHTHEVARIANCEDECLINESWITHTHENUMBEROFINDIVIDUALSINTHE POPULATION m $ VARh . OR AS A HYPERBOLIC FUNCTION OF DENSITY IF . IS THE AVERAGE NUMBER OF INDIVIDUALS PERUNITAREA ANDINDIVIDUALSAREASSUMEDTOBERANDOMLYDISTRIBUTED&RECKLETON UNPUB m $ VARh D. 7HEN COMBINED WITH ENVIRONMENTAL VARIABILITY WHICH HAS VARIANCE m% THEVARIANCEINPOPULATIONGROWTHRATEINTHISMODELIS


m $ VARh m % .

%XAMPLESOFPOPULATIONSGROWINGACCORDINGTOTHISMODELARESHOWNIN&IGB 4HE MOST IMPORTANT FEATURE OF THIS MODEL IS THAT IF DENSITY FALLS BELOW A CRITICAL THRESHOLD £ ¥ . m$ ³hnnm%³ ¤ ¦ THENEXTINCTIONISHIGHLYLIKELY,ANDEETAL 4HERESULTOFTHISISABIMODAL DISTRIBUTIONOFPOPULATIONSIZES ASSHOWNIN&IGD COMPAREDWITHTHENORMAL DISTRIBUTIONIN&IGC

&IG 3OURCESOFSTOCHASTICITYANDEFFECTSONPOPULATIONGROWTHAC ANDPOPULATIONSIZE BD 0OPULATIONGROWTHWASDENSITY INDEPENDENTWITHSTOCHASTICITYEITHERENVIRONMENTAL AC ORENVIRONMENTALANDDEMOGRAPHICBD

)N THE MODEL WITH ENVIRONMENTAL STOCHASTICITY ONLY POPULATIONS ARE ABLE TO INVADE IF THE POPULATION GROWTH RATE E XCEEDS A CRITICAL VALUE4HEGREATERTHE


DIF FERENCEBETWEENTHELONG TERMAVERAGEANDTHISCRITICALVALUE THEMORELIKELYA SPECIESISTOINVADE/NTHEOTHERHAND IFAPOPULATIONISSUBJECTTODEMOGRAPHIC STOCHASTICITY POPULATIONS MUST EXCEED A CRITICAL DENSITY BEFORE INVASION CAN OCCUR 4HEREFORE THE TWO FORMS OF STOCHASTICITY HAVE RATHER DIFFERENT IMPLICA TIONS FOR POPULATION DYNAMICS AND PREDICTING INVASION REQUIRES THAT BOTH OF THESE SOURCES OF STOCHASTICITY ARE UNDERSTOOD IN DETAIL )N NON INVASIVE SPECIES ESTIMATESOFDEMOGRAPHICANDENVIRONMENTALSTOCHASTICITYFROMBIRDPOPULATIONS SUGGESTTHATBOTHSOURCESMAYBEEXTREMELYSIGNIlCANT ANDHENCETHATTHETWO FORMSNEEDTOBEMEASUREDSEPARATELY3AETHERETAL )MPLICATIONSOFSTOCHASTICMODELSFORMODELLINGINVASIONS

4HE MAIN CONCLUSION FROM THE EXAMPLE MODELS OUTLINED ABOVE IS THAT IN A STO CHASTICENVIRONMENTTHELONG TERMPOPULATIONGROWTHISNOTALINEARFUNCTIONOF THEAVERAGEPOPULATIONGROWTHRATES#OHEN,EWONTINAND#OHEN 4ULJAPURKAR .OT ONLY IS IT IMPORTANT TO ESTIMATE THE AMOUNT OF VARI ABILITY IN POPULATION GROWTH RATES &RECKLETON AND 7ATKINSON BUT ALSO TO DISENTANGLE THE RELATIVE ROLES OF DEMOGRAPHIC AND ENVIRONMENTAL VARIATION 4HIS REQUIRES THAT TEMPORALLY REPLICATED MEASURES OF POPULATION GROWTH OR THE COMPONENTSOFPOPULATIONGROWTH AREAVAILABLE7ITHOUTSUCHINFORMATIONITIS NOTPOSSIBLETOPREDICTWHICHSPECIESARECAPABLEOFINVADINGANDWHICHARENOT OR CONDITIONS UNDER WHICH A GIVEN SPECIES WILL BECOME INVASIVE OR NOT OR TO DERIVEREALISTICMODELS 5NFORTUNATELYSUCHINFORMATIONISRARELYAVAILABLEFORMANYINVASIVESPECIES OFTEN BECAUSE INVASIVE SPECIES HAVE RECENTLY BEEN INTRODUCED TO NOVEL ENVIRON MENTS #ONSEQUENTLY LONG TERM DATASETS TEND TO BE RARE 5NDER SUCH CIRCUM STANCESTHEREARETWOCHOICESFORTHEMODELLER EITHERTOGIVEUP ORTOTRYTOMAKE DOWITHWHATEVERINFORMATIONISAVAILABLE!SANEXAMPLEOFTHELATTER2EESAND 0AYNTER DEVELOPED A MODEL FOR THE DYNAMICS AND CONTROL OF INVASIVE POPULATIONSOF3COTCH"ROOM4HISMODELWASPARAMETERISEDUSINGASEVERALDATA SOURCESFROMBOTHTHENATIVEANDEXOTICRANGEOFTHESPECIES ASWELLASANUNDER STANDING OF ITS BASIC AUTECOLOGY )T SEEMS LIKELY HOWEVER THAT MANY EXISTING MODELSARECOMPROMISEDTOSOMEEXTENTINTHEIRPREDICTIVEABILITYTHROUGHALACK OFDATAONSTOCHASTICVARIATIONINKEYPARAMETERS 2ECENTWORKHASSUGGESTEDTHATTHEDEMOGRAPHICANDENVIRONMENTALCOMPO NENTSOFPOPULATIONGROWTHMAYBERELATEDTOLIFEHISTORYTRAITSINBIRDS3AETHER ETAL &OREXAMPLE DEMOGRAPHICSTOCHASTICITYTENDSTOBELARGERIN SPECIESWITHGREATERADULTSURVIVAL AGEATMATURITYANDGENERATIONTIMES3AETHER ET AL 3IMILARLY THE EXPECTED TIME TO EXTINCTION OF POPULATIONS INCREASED WITHDECREASINGCLUTCHSIZE4HESERESULTSAREIMPORTANTBECAUSETHEYSHOWTHAT ITISPOSSIBLETOGENERALIZEABOUTHOWSENSITIVEPOPULATIONSARETODIFFERENTFORMS OFVARIABILITY BASEDONLIFE HISTORYTRAITS4ODATETHEREHAVEBEENNOCOMPARABLE ANALYSESOFTHEDEMOGRAPHICSOFPOPULATIONDURINGTHEINITIALSTAGESOFINVASION HOWEVERSUCHANALYSISCOULDBEENORMOUSLYREVEALING


$%4%2-).)34)#0/05,!4)/.$9.!-)#3 )FLEFTUNCHECKED THESYSTEMDElNEDBYEQUATION WILLULTIMATELYBECOMEEXTINCT ,EWONTIN #OHEN )F THE VALUE OF h IS GREATER THAN ONE THE EXPECTED MEANPOPULATIONSIZEAS4BECOMESLARGEISINlNITEALTHOUGH COUNTERINTUITIVELY THEPROBABILITYOFEXTINCTIONREMAINSEQUALTOONE ALBEITWITHAVERYLONGEXPECTED TIME TO EXTINCTION 4HIS BEHAVIOUR DOES NOT SIT WELL WITH ECOLOGICAL INTUITION #OMMON OBSERVATION APPEARS TO INDICATE THAT THE DYNAMICS OF MANY SPECIES ARE RELATIVELY INVARIANT 3OME INVASIVE SPECIES DO EXHIBIT INTRINSICALLY COMPLEX POPULATIONDYNAMICBEHAVIOUR PARTICULARLYTHEVIRUSESTHATCAUSEDISEASESSUCH AS MEASLES AND mU %ARN ET AL #YCLIC DYNAMICS ARE REASONABLY COMMON IN A RANGE OF TAXA +ENDALL ET AL 'INZBURG #OLYVAN HOWEVER THESE TEND TO BE EXTRINSICALLY DRIVEN OR THE CONSEQUENCE OF SPECIES INTERACTIONS SUCHASPREDATOR PREYDYNAMICS RATHERTHANINTRINSICPROPERTIESOFPOPULATIONS ! GREAT DEAL OF EFFORT HAS BEEN EXPENDED ON UNDERSTANDING lRSTLY WHY POPU LATIONS DO NOT SIMPLY BOOM OR BUST IN ACCORD WITH THE MOST SIMPLE DENSITY INDEPENDENT MODELS AND SECONDLY WHY DIFFERENT SYSTEMS EXHIBIT ALTERNATIVE KINDSOFPOPULATIONDYNAMICS $ENSITY DEPENDENCE

$ENSITY DEPENDENCEOCCURSWHENANYVITALRATECHANGESSYSTEMATICALLYWITHDEN SITY3TRICTLYSPEAKINGTHISCOULDINCLUDEARANGEOFPOPULATIONLEVELPHENOMENA 2OYAMA BUTTYPICALLYTHISDElNITIONISTAKENTOIMPLYTHATSOMEPERCAPITA RATE SUCH AS MORTALITY OR FECUNDITY VARIES SYSTEMATICALLY WITH DENSITY $ENSITY DEPENDENCEOFTHISSORTMAYRESULTFROMARANGEOFECOLOGICALPROCESSES4HEMOST COMMONLY RECOGNISED FORM IS NEGATIVE DENSITY DEPENDENCE WHICH RESULTS FROM DIRECTCOMPETITIONFORRESOURCES.ICHOLSON SUCHASFOOD SHELTERORMATES -OREINDIRECTLY DENSITY DEPENDENCEMAYARISEFROMTHEIMPACTOFOTHERSPECIES FOR INSTANCE PREDATORS OR PARASITES WHICH MAY INCREASE MORTALITY RATES AT HIGH PREYORHOSTDENSITIESRESPECTIVELY !S NOTED ABOVE DENSITY INDEPENDENT MODELS SUGGEST THAT DENSITY DEPENDENCE SHOULD BE HIGHLY PREVALENT BECAUSE IN THE ABSENCE OF DENSITY DEPENDENCE POPULATIONS ARE LIKELY TO EITHER EXPAND WITHOUT LIMIT OR BECOME EXTINCT $ESPITE THIS MANYMODELSFORPOPULATIONDYNAMICSIGNOREDENSITY DEPENDENCE ANDTHIS CAN SEVERELY COMPROMISE MODEL PREDICTIONS EG SEE &RECKLETON ET AL 4HISPROBLEMMAYBEESPECIALLYACUTEFORINVASIVESPECIESWHICHMIGHTBEEXPECT EDTOHAVEAHIGHAVERAGEVALUEOFh ANDHENCEBECAPABLEOFRAPIDLYGROWINGTO HIGHDENSITIES)NTHEINITIALSTAGESOFANINVASIONTHESTOCHASTICFACTORSTHATDETER MINEhSEEMLIKELYTOPLAYAKEYROLEINDETERMININGINVASIONSUCCESS(OWEVER AS SHOWN BELOW FOLLOWING SUCCESSFUL INVASION THE ULTIMATE SIZE REACHED BY THE INVADER POPULATION WILL BE IN LARGE PART DETERMINED BY THE FORM NATURE ANDSTRENGTHOFDENSITY DEPENDENCE


-ODELSFORDENSITY DEPENDENTPOPULATIONGROWTH

!SUITEOFMODELSHAVEBEENEMPLOYEDTOMODELTHEDYNAMICSOFSPECIESGROWING INADENSITY DEPENDENTFASHION4HEBESTKNOWNOFTHESEISTHELOGISTICMODEL HERE THEDISCRETETIMEVERSION .T .T R.T n.+

)NTHISFORMTHELOGISTICMODELISAPOORMODELFORDESCRIBINGECOLOGICALDYNAM ICS4HEREAREANUMBEROFPROBLEMSWITHTHISMODEL INCLUDINGTHEEQUILIBRIUMIS INDEPENDENTOFTHElNITERATEOFINCREASE DENSITY DEPENDENCEISLINEAR ANDSTABIL ITYBEHAVIOURISDETERMINEDSOLELYBYTHEMAXIMUMRATEOFINCREASE RSEEBELOW $ESPITETHIS THELOGISTICMODELISWIDELYEMPLOYEDINTHEORETICALMODELLING PROB ABLYBECAUSEITISANALYTICALLYVERYCONVENIENTTOWORKWITH -OREREALISTICMODELSHAVEBEENSUGGESTED INCLUDINGMODIlCATIONSTOTHELOGIS TICINORDERTOMAKEITMOREREALISTICEG THETHETA LOGISTICOF,ANDEETAL /NEPARTICULARLYUSEFULMODELISTHATOF(ASSELL .T h.T ;A.T =nB

4HIS MODEL HAS TWO PARAMETERS THAT MODEL DIFFERENT ASPECTS OF THE DENSITY DEPENDENT RESPONSE A DETERMINES THE DENSITY AT WHICH THE PER CAPITA EFFECTS OF DENSITY DEPENDENCEBECOMESIGNIlCANT WHILSTBVARIESTHERATEOFCHANGEINPOPU LATIONGROWTHRATEASDENSITYBECOMESHIGHANDMAYBERELATEDTOTHENATUREOF COMPETITIONCONTESTVERSUSSCRAMBLE(ASSELL ORTHEEFlCIENCYWITHWHICH RESOURCESARECONVERTEDINTOPOPULATIONGROWTH&IRBANKAND7ATKINSON &RECKLETONAND7ATKINSON 4HEEQUILIBRIUMOFTHISMODELISGIVENBY .È hBn A

4HE IMPORTANT ADVANCE OVER THE LOGISTIC MODEL IS THAT THE EQUILIBRIUM IS A COMPOUND OF THREE MODEL PARAMETERS )NCREASING THE lNITE RATE OF INCREASE OR DECREASING A LEADS TO INCREASES IN POPULATION DENSITY 4HESE EFFECTS ARE THEN MODULATEDBYB WHICHALSODETERMINESTHESTABILITYPROPERTIESOFTHEMODEL )T SEEMS LIKELY THAT THE THREE PARAMETERS MAY BE RELATED TO EACH OTHER AT A NUMBER OF SCALES 7ITHIN POPULATIONS TEMPORAL VARIABILITY IN THE ENVIRONMENT MAY LEAD TO VARIATION IN ANY OF THE PARAMETERS !S POINTED OUT BY #HESSON AND (UNTLEY UNDERSTANDING HOW THE EFFECTS OF STOCHASTICITY INTERACT WITHTHESTRENGTHOFCOMPETITIONISTHEKEYTOPREDICTINGTHEOUTCOMEOFCOMPETI TIONINSTOCHASTICENVIRONMENTS)NTHEMODELABOVE THEPROBLEMISTOUNDERSTAND HOWTHEPARAMETERSAANDhCOVARYWITHEACHOTHER)FhANDAAREINDEPENDENT THEN POPULATION GROWTH RATES ARE TERMED ADDITIVE &IG A WITH THE CONSE QUENCETHATSTOCHASTICENVIRONMENTALEFFECTSIMPACTDIRECTLYONPOPULATIONSIZES &IG C )N CONTRAST SUB ADDITIVE POPULATION GROWTH RATES OCCUR WHEN h AND


&IG )NTERACTIONS BETWEEN DENSITY DEPENDENCE AND STOCHASTICITY ,INES REPRESENT POPULATION GROWTH UNDER DIFFERENT ENVIRONMENTAL CONDITIONS A !DDITIVE POPULATION GROWTH RATES B SUB ADDITIVE POPULATION GROWTH RATES C A POPULATION SUBJECT TO STO CHASTICITY AND ADDITIVE POPULATION GROWTH D A POPULATION SUBJECT TO STOCHASTICITY AND SUB ADDITIVEPOPULATIONGROWTH

A ARE CORRELATED WITH EACH OTHER &IG A )N SUCH POPULATIONS THE STRENGTH OF COMPETITIONCHANGESSOASTOBUFFERPOPULATIONGROWTHFROMSTOCHASTICENVIRON MENTAL CHANGES 4HE CONSEQUENCE IS THAT POPULATIONS SUBJECT TO SUB ADDITIVE POPULATION GROWTH ARE BUFFERED AGAINST ENVIRONMENTAL CHANGE &IG D SHOWS A POPULATION SUBJECT TO PERTURBATIONS IDENTICAL TO THOSE IN &IG C HOWEVER THE SUB ADDITIVEPOPULATIONGROWTHRATESCLEARLYHAVEANIMPORTANTBUFFERINGEFFECT &ROMTHEPOINTOFVIEWOFPREDICTINGTHEDYNAMICSOFINVASIVESPECIES THEPAT TERNSSHOWNIN&IGS AANDBHAVETWOIMPORTANTCONSEQUENCES &IRST THEFORMOF DENSITY DEPENDENCEANDADDITIVITYINmUENCESTHEEFFECTSOFSTOCHASTICITY3ECOND THE FORM OF ADDITIVITY CAN INmUENCE THE EFFECTS OF CHANGES TO MANAGEMENT &OR INSTANCE IF POPULATION GROWTH RATES ARE SUB ADDITIVE THEN REDUCTIONS IN h


RESULTING FROM ATTEMPTS AT CONTROL OR ERADICATION WILL BE COMPENSATED FOR BY REDUCTIONINTHESTRENGTHOFDENSITY DEPENDENCE YIELDINGNONETEFFECTONPOPULA TIONNUMBERS4HUS ITISNOTSUFlCIENTSIMPLYTODOCUMENTTHEEFFECTSOFSTOCHAS TICITYORDENSITY DEPENDENCEINISOLATION BUTTHEINTERACTIONBETWEENTHESEALSO NEEDSTOBEUNDERSTOOD)NPRACTICETHISISVERYDIFlCULTASTHISREQUIRESTHATTHE FORMOFDENSITY DEPENDENCEISMEASUREDUNDERARANGEOFENVIRONMENTALCONDI TIONS WHICHISHIGHLYDATAINTENSIVE .ON LINEARDYNAMICSANDSTABILITY

!SNOTEDABOVE INTHEMID SITWASFOUNDTHATSIMPLEECOLOGICALMODELSCOULD YIELD UNEXPECTEDLY COMPLICATED PATTERNS OF POPULATION DYNAMICS -AY -AYAND/STER&IGA B )NSHORT INMODELSFORDENSITY DEPENDENT POPULATIONGROWTHFORORGANISMSWITHDISCRETEGENERATIONS DENSITY DEPENDENCE ATHIGHDENSITYMAYOVERCOMPENSATEFORCHANGESINDENSITY WITHTHERESULTTHAT INCREASES IN POPULATION SIZE ABOVE THE DETERMINISTIC EQUILIBRIUM TEND TO BE FOL LOWED BY DISPROPORTIONATELY LARGE DECREASES 4HE CONSEQUENCE OF THIS IS CYCLIC DYNAMICS ORMORECOMPLEXBEHAVIOURSUCHASLIMITCYCLESANDCHAOS5NDERSUCH CIRCUMSTANCESPOPULATIONSEXHIBITSUSTAINEDmUCTUATIONSINPOPULATIONSIZETHAT AREAPPARENTLYRANDOMANDSUPERlCIALLYSIMILARTOTHEmUCTUATIONSINPOPULATION SIZESTHATARESEENINREALPOPULATIONS %XTENSIVEATTEMPTSHAVEBEENMADETOlNDEXAMPLESOFPOPULATIONEXHIBITING CHAOTIC DYNAMICS (OWEVER FEW EXAMPLES EXIST )N FACT IN SOME CASES THERE ARE GOODREASONSTOEXPECTTHATCHAOTICDYNAMICSARERATHERUNLIKELY)NPLANTS FOR EXAMPLE THEABSENCEOFREPRODUCTIVETHRESHOLDS THEPRESENCEOFASEEDBANK AND ASYMMETRIC COMPETITION LEADING TO COMPENSATING DENSITY RESPONSES ALL LEAD TO GENERALLYSTABLEPOPULATIONDYNAMICS2EESAND#RAWLEY &RECKLETON AND 7ATKINSON )MPORTANTLY THIS MULTIPLICITY OF STABILITY GENERATING MECHANISMS MEANS THAT EVEN WHEN ONE CONDITION FOR INSTABILITY HOLDS OTHERS TEND TO CANCEL THIS OUT EG "UCKLEY ET AL -OREOVER GENERAL REVIEWS OF THE STABILITY PROPERTIES OF NATURAL POPULATIONS APPEAR TO SHOW THAT MOST SINGLE SPECIES POPULATIONS SHOW STABLE DYNAMICS (ASSELL ET AL ,ONSDALE &RECKLETONAND7ATKINSON !SNOTEDABOVE INTHEMAJORITYOFDOCUMENTED CASESCYCLICDYNAMICSTENDTOBEDRIVENBYEXOGENOUSFACTORS ORINTERACTIONSWITH OTHERSPECIESEG SEE+ENDALLETAL 0OSITIVEDENSITY DEPENDENCEANDINSTABILITY

4HEMODELSDESCRIBEDABOVEEMPHASISETHENEGATIVEEFFECTSOFDENSITY DEPENDENCE ON POPULATION GROWTH RATES (OWEVER RECENT REVIEWS HAVE POINTED OUT THAT NOT ALL DENSITY DEPENDENT EFFECTS ON POPULATION GROWTH ARE OF THIS FORM 3TEPHENS AND3UTHERLAND3TEPHENSETAL 0OSITIVEDENSITY DEPENDENCERATHER CONFUSINGLYTERMEDhINVERSEvDENSITY DEPENDENCEBYSOMEAUTHORS ISMOSTWELL KNOWNTHROUGH!LLEEEFFECTS!LLEEEFFECTSARISEMOSTCOMMONLYINSOCIALSPECIES


&IG 3TABLE AND UNSTABLE EQUILIBRIA RESULTING FROM !LLEE EFFECTS 4HE RELATIONSHIP BETWEENPOPULATIONGROWTHRATEANDDENSITYISHUMPED7HERETHECURVECUTSTHELINEOF ZEROPOPULATIONGROWTHRATETHEREISANEQUILIBRIUM!SINDICATEDBYTHEARROWS THEUPPER EQUILIBRIUMISSTABLE WHEREASTHELOWERONEISUNSTABLE

WHERE COOPERATION BETWEEN INDIVIDUALS BREAKS DOWN AT LOW DENSITIES LEADING TO A DECLINE IN SOME ASPECTS OF lTNESS WITH DECREASING DENSITIES )N THE EXTREME SUCH COMPONENT !LLEE EFFECTS WHICH AFFECT ONE COMPONENT OF lTNESS MAY BE MANIFEST AT THE LEVEL OF POPULATION GROWTH LEADING TO DEMOGRAPHIC !LLEE EFFECTS IE ARESOIMPORTANTTHATTHEYIMPINGEONRATESOFPOPULATIONCHANGE3TEPHENS AND 3UTHERLAND 4HE IMPORTANCE OF !LLEE EFFECTS IN POPULATION GROWTH IS THATTHESECANLEADTOATHRESHOLDDENSITYBELOWWHICHPOPULATIONSCANNOTPERSIST SEE&IG 4HISISOFCOURSEHIGHLYSIGNIlCANTFORTHEDYNAMICSOFINVASIVESPECIES SINCEINVASIONSREQUIRETHATSPECIESARECAPABLEOFARRIVINGINNEWENVIRONMENTS ATLOWDENSITIESANDTHENSUBSEQUENTLYINCREASING4HISCANHAVEIMPORTANTIMPLI CATIONSFORRATESOFSPATIALSPREAD,EWISAND+AREIVA ASWELLASRESPONSES OFPOPULATIONSTOSTOCHASTICVARIABILITY ,IEBHOLD AND "ASCOMPTE EXPLORED THE CONSEQUENCES OF !LLEE EFFECTS ANDSTOCHASTICITYFORTHECONTROLOFINVASIVESPECIES4HEMOSTIMPORTANTOUTCOME OF!LLEEEFFECTSINTHEIRMODELSWASTHAT!LLEEEFFECTSCANINmUENCETHEOUTCOMES OFERADICATIONPROGRAMMES&REQUENTLYITISFOUNDTHATCLOSETOERADICATION IS REQUIRED FOR CONTROL PROGRAMMES TO BE EFFECTIVE "ECAUSE SUCH HIGH LEVELS OF CONTROL ARE GENERALLY DIFlCULT TO ACHIEVE THIS MAY PROHIBIT ATTEMPTS AT CONTROL (OWEVER !LLEE EFFECTS MAY LEAD TO EXTINCTION THRESHOLDS AT LOW DENSITIES WITH


THE RESULT THAT LOWER RATES OF CONTROL MAY YIELD ERADICATION ,IEBHOLD AND "ASCOMPTE STUDIED POPULATIONS OF THE 'YPSY -OTH ,YMANTIA DISPER IN WHICHTHEYFOUNDTHATERADICATIONCOULDBEACHIEVEDWITHCMORTALITYINA MODELFORTHEPOPULATIONWHICHINCLUDEDAN!LLEEEFFECT WHEREASINTHEABSENCE OF THE !LLEE EFFECT CLOSE TO MORTALITY WOULD BE REQUIRED )N THE CASE STUDY BELOW WE DESCRIBE IN MORE DETAIL A SYSTEM IN WHICH !LLEE EFFECTS ARE EXTREMELY IMPORTANTINEXPLAININGINVASIONS -ULTISPECIESINTERACTIONS

4HE MAIN FOCUS ON THIS REVIEW SO FAR HAS BEEN ON SINGLE SPECIES DYNAMICS (OWEVER INTERACTIONS BETWEEN SPECIES CAN AFFECT THE STABILITY OF POPULATION DYNAMICS)NDEEDMOSTSPECIESDONOTLIVEINISOLATION SOTHISPOSSIBILITYMAYBE QUITECOMMON ANDWEREVIEWTWOEXAMPLESBELOW )N AN INmUENTIAL PAPER -AY SUGGESTED THAT INSTABILITY MAY BE A COM MON PROPERTY OF MANY FORMS OF ECOLOGICAL SYSTEMS (E SHOWED THAT THE SAME MODELLINGFRAMEWORKCOULDBEAPPLIEDTOPREDATOR PREY HARVESTEDANDORINDEED ANY CONSUMER RESOURCE SYSTEM 4HIS EFFECT ARISES AS A CONSEQUENCE OF THE FUNC TIONRESPONSEOFTHECONSUMER7HENCONSUMERSAREATLOWDENSITIESTHERATEOF CONSUMPTION OF RESOURCES INCREASES WITH INCREASING RESOURCE DENSITY WITH THE CONSEQUENCE THAT THE RATE OF RESOURCE LOSS IS POSITIVELY RELATED TO RESOURCE DEN SITY!TLOWDENSITIESCONSUMERSCANPOTENTIALLYERADICATETHEIRRESOURCESATLOW DENSITIES "Y CONTRAST AT HIGH RESOURCE DENSITIES RESOURCES BECOME SATURAT ING AND EFFECTIVELY THE RATE OF RESOURCE LOSS TO CONSUMERS IS NEGATIVELY RELATED TO RESOURCE DENSITY AT HIGH DENSITIES OF RESOURCES 4HIS DUAL BEHAVIOUR LEADS TO THE POTENTIAL FOR TWO EQUILIBRIA ONE AT LOW RESOURCE DENSITIES THE OTHER AT HIGH RESOURCEDENSITIES)FITEXISTSTHEEQUILIBRIUMATLOWDENSITIESISTYPICALLYUNSTABLE 2ECENTLY'ASCOIGNEAND,IPCIUS HAVEEXTENDEDTHISFRAMEWORKTOCONSIDER THEAGGREGATIVERESPONSESOFRESOURCESANDHAVEEMPHASISEDTHATSUCHBEHAVIOUR HASBEENLARGELYIGNOREDINTHEAPPLIEDANDCONSERVATIONLITERATURE ANDSHOWTHAT THEREAREAGROWINGNUMBEROFSYSTEMSTHATIMPLICATESUCHAMECHANISM #OMPETITIVEINTERACTIONSMAYALSOYIELDINSTABILITIES INTWOSOMEWHATDIFFERENT WAYS&IRST SIMPLEMODELSFORTHEDYNAMICSOFTWOCOMPETINGSPECIESSHOWTHAT THREEDISTINCTOUTCOMESMAYOCCURI ONESPECIESORANOTHEREXCLUDESTHEOTHER II THECOMPETINGSPECIESSETTLEATASTABLEJOINTEQUILIBRIUMIII THEREISAJOINT EQUILIBRIUM BUTWHICHISUNSTABLE SOTHATPERTURBATIONSFROMTHEJOINTEQUILIB RIUMLEADTOTHESYSTEMBECOMINGDOMINATEDBYONESPECIESORANOTHER4HISLATTER UNSTABLECONDITIONMAYARISEIFTHEPERCAPITAEFFECTSOFINTER SPECIlCCOMPETITION ARE GREATER THAN THE PER CAPITA EFFECTS OF INTRA SPECIlC COMPETITION )N THE CASE STUDIESBELOW WEDETAILSUCHANEXAMPLE 3ECOND COMPETITIVE INTERACTIONS MAY YIELD UNSTABLE DYNAMICS WHEN MULTI SPECIESSYSTEMSININTERACTIONSARESTRONGARESUBJECTEDTOPERTURBATIONS4ILMAN ETAL 4HEREASONFORTHISISTHATINSUCHAMIXTURETHEDYNAMICSOFANYSIN GLESPECIESAREACOMPLEXFUNCTIONOFTHEDENSITIESOFALLTHESPECIES#ONSEQUENTLY


THERESPONSEOFTHESYSTEMTOPERTURBATIONMAYBECOMPLEX ANDPERTURBATIONMAY LEAD TO COMPLEX INTERMEDIATE OR TRANSIENT DYNAMICS 4HE SIGNIlCANCE OF THIS IS THATFOLLOWINGACHANGE SUCHASTHEINVASIONOFANEWSPECIES THEENTIRESYSTEM MAYTAKEMANYGENERATIONSTORETURNTOEQUILIBRIUM

#!3%345$)%3 4HEPREVIOUSSECTIONSHAVEEMPHASISEDTHATPREDICTINGTHEDYNAMICSOFINVASIVE SPECIESMAYREQUIRETHATASUITEOFPROCESSESAREDIS ENTANGLED4HESEINCLUDETHE EFFECTSOFSTOCHASTICITY ASWELLASTHESTRENGTHSOFINTRA ANDINTER SPECIlCINTERAC TIONS IN THE WIDEST SENSE &OR INVASIVE SPECIES THE KEY QUESTIONS ARE HOW THESE PROCESSES AFFECT THE INVASION OF POPULATIONS INTO NEW ENVIRONMENTS AS WELL AS HOWTHEYDETERMINEPOPULATIONSIZEANDTHEOUTCOMEOFCONTROLSTRATEGIES )N THIS SECTION WE REVIEW IN DETAIL TWO CASE STUDIES OF INVASIVE SPECIES WHICH HAVEBEENSTUDIESUSINGSIMPLEMODELLINGAPPROACHES.ECESSARILYITISIMPOSSIBLE TOCONSIDERALLOFTHEPROCESSESDESCRIBEDABOVE4HElRSTEXAMPLEILLUSTRATESTHE KEYROLETHATEXTREMESTOCHASTICITYMAYPLAYINDETERMININGINVASIONSUCCESS AND HOW THIS MAY BE MODULATED BY THE EFFECTS OF COMPETITION 4HE SECOND EXAMPLE SHOWSTHEEFFECTOFPERTURBATIONONAPREDATOR PREYSYSTEMWITHANINSTABILITY 6ULPIABROMOIDESIN!USTRALIANPASTURESTHEINTERPLAYOFSTOCHASTICITY ANDINSTABILITY

4HIS EXAMPLE SHOWS HOW INSTABILITY AND STOCHASTICTY SIMULTANEOUSLY PLAY ROLES IN DETERMINING WHETHER A SPECIES INVADES A SYSTEM 6 BROMOIDES IS A WINTER ANNUALWHICHORIGINATESFROMTHE-EDITERRANEAN ANDHASBECOMEAPROBLEMIN ANNUALPASTURESYSTEMSIN!USTRALIA)NCONTRASTIN3PAINAND0ORTUGAL WHEREIT OCCURS NATURALLY IN PASTURES 6 BROMOIDES IS NOT REGARDED AS A PROBLEM SPECIES 6 BROMOIDES WAS PROBABLY INTRODUCED TO !USTRALIA AS A CONTAMINANT OF SEED OR FORAGE 3EVERAL SPECIES OF THE GENUS 6ULPIA WERE INTRODUCED TO !USTRALIA 7E STUDIEDTHEINVASIONDYNAMICSOFANNUALPASTURESIN.37 INWHICH6BROMOIDES ISTHECOMMONESTOFTHESPECIESANDOCCURSINCOFTHEPASTURESWHERETHE GENUSISPRESENT$OWLING 'IVENTHATTHE6ULPIAGENUSISWELLESTABLISHED IN!USTRALIA THECURRENTPROBLEMISTODETERMINEWHATFACTORSENABLETHEPERSIS TENCEANDSPREADOFTHESPECIES 6BROMOIDESISAPROBLEMBECAUSE ALTHOUGHINTHEEARLYSTAGESOFTHEGROWING SEASONITMAYPROVIDESOMEUSEFULFORAGEFORLIVE STOCK THEFORAGEPRODUCEDLATE IN THE SEASON IS OF VERY LOW NUTRITIONAL VALUE AND BECAUSE THE SEEDS PRODUCED BY THE WEED BECOME TANGLED IN THE WOOL OF SHEEP AND MAY EVEN CAUSE PHYSICAL INJURIES TO LIVE STOCK ,ONG TERM MANAGEMENT OF 6ULPIA IS DIFlCULT IN PASTURES THAT ARE DOMINATED BY ANNUALS IE IN WHICH THE PERENNIAL COMPONENT IS LOW 4HEPROBLEMOFCONTROLLING6ULPIAISCOMPOUNDEDBYTHEHIGHSEEDPRODUCTIONOF THESPECIESWHICHALLOWSFASTPOPULATIONRECOVERYINTHEYEARSFOLLOWINGHERBICIDE


APPLICATION ASWELLASHIGHRATESOFCOMPENSATORYGROWTHOFSURVIVORSFOLLOWING HERBICIDALCONTROL$OWLINGETAL 4HE MAIN QUESTIONS THAT ARE IMPORTANT IN UNDERSTANDING THE DYNAMICS OF 6BROMOIDES ASWELLASINPREDICTINGTHEEFFECTSOFMANAGEMENT AREI HOWDO INTERACTIONS WITHIN AND BETWEEN SPECIES AFFECT LONG TERM DYNAMICS II (OW ARE POPULATION DYNAMICS AND LONG TERM PERSISTENCE AFFECTED BY STOCHASTICITY &RECKLETONETAL DEVELOPEDAMODELTOPREDICTTHEDYNAMICSOFTHISSPECIES INAMULTI SPECIESPASTUREMIXTUREINORDERTOADDRESSTHESEQUESTIONS 4HEPOPULATIONDYNAMICSOF6BROMOIDESWERESTUDIEDINA YEARlELDEXPERI MENT CONDUCTED BETWEEN AND !RTIlCIAL PASTURES WERE ESTABLISHED COMPRISING THREE SPECIES 6 BROMOIDES TOGETHER WITH TWO @DESIRABLE SPECIES 4RIFOLIUM SUBTERRANEUM A LEGUME AND ,OLIUM RIGIDUM ANOTHER GRASS 0ASTURES WERE SET UP ORIGINALLY WITH LOW MEDIUM AND HIGH DENSITIES OF 4RIFOLIUM LOW OR ZERO DENSITIES OF ,OLIUM AND LOW OR HIGH DENSITIES OF 6ULPIA 4HESE ARTIlCIAL PAS TURESWEREALLOWEDTOGROWUNTILSPRING WHENHALFOFTHEPLOTSWERESPRAYED WITHHERBICIDEINORDERTOCREATEAFURTHERDENSITYDIFFERENTIALOF6ULPIA4HEYEAR WASADROUGHTYEAR ANDWEESTIMATEDTHATDROUGHTSOFTHISSEVERITY OCCUREVERYYEARSORSO&RECKLETONETAL 7EUSEDTHEDATAFROMTHISEXPERIMENTTOPARAMETERISEAMODELPREDICTINGTHE NUMBERSNUMBERSOFMATUREPLANTS. ANDSEEDSINTHESEEDBANK3 OFEACHOF THETHREESPECIES IE n .IxT hI.IT ³-_IJ.JT ³ iI3IT J

n 3IxT hI.IT ³-_IJ.JT ³ iI3IT J hANDhMEASURETHEPERCAPITARATEOFCHANGEINNUMBERSOFMATUREPLANTSAND SEEDS RESPECTIVELY OWING TO SEED PRODUCTION AT THE VEGETATIVE STAGE p AND p RESPECTIVELY MEASURE THE RECRUITMENT OF PLANTS FROM AND PERSISTENCE OF SEEDS WITHINTHESEEDBANKCOMPETITIONBETWEENANYPAIROFSPECIESIANDJISMEASURED BYAPARAMETER_IJ WHICHISTHEPERCAPITAREDUCTIONINPOPULATIONGROWTH.OTE THAT WHEN I AND J ARE DIFFERENT _IJ REFERS TO INTER SPECIlC COMPETITION IE COM PETITION BETWEEN SPECIES BUT WHEN I J _ MEASURES INTRA SPECIlC COMPETITION IE COMPETITION WITHIN THE SPECIES &OR THE THREE SPECIES MIXTURE THEREFORE THEREARENINEIE × COMPETITIONCOEFlCIENTS !NALYSISOFTHElTTEDMODELINDICATEDACLEARDIVISIONWITHINTHISSIMPLECOM MUNITY&IRST COMPETITIONBETWEEN4RIFOLIUMANDTHETWOGRASSESWASVERYWEAK INDEED AND THERE WAS VERY LITTLE INmUENCE OF THE 4RIFOLIUM ON THE DYNAMICS OF EITHER OF THE GRASSES OR OF THE GRASSES ON THE 4RIFOLIUM 4HIS IS PERHAPS UNSUR


PRISING AS LEGUMES AND GRASSES REPRESENT RATHER DIFFERENT FUNCTIONAL GROUPS /N THE OTHER HAND COMPETITION BETWEEN THE TWO GRASSES WAS VERY STRONG AND THEY INmUENCED EACH OTHERS DYNAMICS PROFOUNDLY 3INCE NEITHER OF THE GRASSES POSSESS VERY PERSISTENT SEEDBANKS IN CONTRAST TO THE 4RIFOLIUM THEDYNAMICSOF THESETWOSPECIESCANBEMORESIMPLYMODELLEDBYASIMPLE SPECIESMODEL .,T h,.,T _,,.,T _,6.6T n .6T h6.6T _66.6T _6,.,T n

4HE DYNAMICS OF THIS SYSTEM MAY BE ANALYSED USING A SIMPLE PHASE PLANE ANALYSIS &IG 4HE lTTED COMPETITION COEFlCIENTS FOR EQUATIONS HAD THE PROPERTY THAT IN BOTH MODELS THE INTER SPECIlC COEFlCIENTS WERE LARGER THAN THE INTRA SPECIlC COEFlCIENTS !S A CONSEQUENCE THE EQUILIBRIUM FOR THE TWO SPECIES ISPREDICTEDTOBEUNSTABLE&IGA 4HEUNSTABLEEQUILIBRIUMHASANIMPORTANT CONSEQUENCEFORTHEINVASIONOF6ULPIA6ULPIAISONLYABLETOINVADECOMMUNITIES WHENTHEDENSITYOF,OLIUMISLOW%XAMPLESOFTHEPREDICTEDDYNAMICSARESHOWN IN&IGBANDC6ULPIAISUNABLETOINVADEAHIGHDENSITYOF,OLIUM&IGB ITIS ABLETOINVADEALOWDENSITY&IGC !TlRSTSIGHTITAPPEARSTHATTHEINVASIONOF6ULPIAINTOPASTURESMAYBEDIFlCULT BECAUSEITNEEDSTOEXCEEDACRITICALDENSITYINORDERTOINVADE)FTHEENVIRONMENT WERECONSTANT THENTHISWOULDBETHECASE)NREALITY HOWEVER THEENVIRONMENT ISNOTCONSTANT!SNOTEDABOVE PERIODICALLYSEVEREDROUGHTSOCCUR4HESEGREATLY FACILITATE THE INVASION OF 6ULPIA BECAUSE THESE DROUGHTS REDUCE THE DENSITIES OF ALLSPECIESTOLOWLEVELS&OLLOWINGDROUGHTTHElNITERATEOFINCREASEOF6ULPIAIS MUCHGREATERTHANTHATOF,OLIUMh6 WHILSTh, #ONSEQUENTLY6ULPIA POPULATIONSRESPONDMUCHFASTERFOLLOWINGDROUGHTSTHANDO,OLIUMPOPULATIONS ANDHENCETHEINVASIONOF6ULPIAISFACILITATED7EESTIMATEDTHATSEVEREDROUGHTS OCCURRINGWITHAFREQUENCYOFEVERYINTOINYEARSWOULDGREATLYFACILI TATETHEINVASIONOF6ULPIA3UGGESTIVELY ANECDOTALEVIDENCESUGGESTSTHAT6ULPIA BECAME NOTICED AS A PROBLEM FOLLOWING SEVERE DROUGHTS IN THE EARLY S ALTHOUGHWEHAVENOQUANTITATIVEDATAWITHWHICHTOSUPPORTTHISCONTENTION )NSUMMARY UNDERSTANDINGTHEINVASIONOF 6ULPIAINTOPASTURES ANDITSPER SISTENCE REQUIRES THAT WE NOT ONLY UNDERSTAND THE DETAILS OF COMPETITION WITH OTHERSPECIES BUTALSOTHEEFFECTSOFLONG TERMSTOCHASTICITY3TOCHASTICITYPLAYSA KEYROLEBECAUSETHEUNSTABLEEQUILIBRIUMWOULDMAKEINVASIONOF6ULPIAUNLIKELY FROM LOW DENSITIES INTO ESTABLISHED PASTURES (OWEVER THE EFFECTS OF COMPETITION BECOMEMODULATEDBYPERIODICDROUGHTSMAKINGINVASIONFARMORELIKELY )NSTABILITYANDOUTBREAKSTHECROWNOFTHORNSSTARFISH

4HE SECOND EXAMPLE ILLUSTRATES HOW !LLEE EFFECTS RESULTING FROM PREDATOR PREY INTERACTIONSCANLEADTOUNSTABLEPOPULATIONDYNAMICS ANDCONSEQUENTLYDETER MINEWHETHERINVASIONSAREPOSSIBLEORNOT4HEREHASBEENAGREATDEALOFRECENT


&IG A 0HASE PLANE DIAGRAM SHOWING UNSTABLE INTERACTIONS IN MIXTURES OF ,OLIUM AND 6ULPIA B C &REQUENCY DEPENDENT INVASIONS OF COMMUNITIES BY EITHER ,OLIUM lLLEDCIRCLES OR6ULPIAOPENCIRCLES THEINVADERDEPENDSONTHERELATIVEINITIALDENSITIES OF THE TWO SPECIES 4HE DYNAMICS OF THE THIRD SPECIES 4RIFOLIUM SQUARES ARE ESSENTIALLY NEUTRALWITHRESPECTTOTHEOTHERTWOSPECIES

INTEREST IN SUCH SYSTEMS REVIEWED BY 'ASCOIGNE AND ,IPCIUS INSPIRED MAINLY BY THE RESULTS OF SIMPLE MODELS )N BRIEF PREDATORS CAN GENERATE !LLEE EFFECTS IN THE POPULATION DYNAMICS OF THEIR PREY AS A CONSEQUENCE OF THEIR FUNC TIONAL AND NUMERICAL RESPONSES 4HIS HAPPENS IN SYSTEMS WHERE THE DYNAMICS OF THE PREY POPULATION ARE DRIVEN MAINLY BY PREDATION AND WHEN PREY HAVE NO REFUGES SPATIAL OR TEMPORAL FROM THE EFFECTS OF PREDATION !LLEE EFFECTS ARISE IN SUCHSYSTEMSWHENPREDATORSHONEINONPREYATLOWDENSITIES SOTHATLOWDENSITY POPULATIONSOFPREYTENDTOHAVENEGATIVEPOPULATIONGROWTHRATES 3UCHPREDATORINDUCED!LLEEEFFECTSARESIGNIlCANTFORINVASIVESPECIESBECAUSE THEPOTENTIALEXISTSFORPREDATORSTOERADICATEUNWANTEDINVASIVEPREYBYREDUCING


THEMTOLOWDENSITIES!LTERNATIVELYIFPREYPOPULATIONSCANBEREDUCEDBYCONTROL MEASURES THE POTENTIAL EXITS FOR PREDATORS TO LEAD TO THE ULTIMATE EXTINCTION OF THE PREY #ONVERSELY HOWEVER THE POSSIBILITY EXISTS THAT PREY POPULATIONS MAY BEHELDINCHECKBYPREDATORS WHICHMAINTAINNEGATIVEPREYPOPULATIONGROWTH RATESFROMLOWDENSITIES BUTTHATPERTURBATIONTOEITHERPOPULATIONMAYLEADTO THEPREYPOPULATIONESCAPINGPREDATORCONTROL 4HESYSTEMWEWORKEDWITHCONSISTSOFA LEVELFOODWEBINVOLVINGPREDATORY lSHES THEINVASIVECORAL EATINGCROWN OF THORNSSTARlSH!CANTHASTERPLANCI AND REEF BUILDINGCORALS$ULVYETAL 4HECROWN OF THORNSSTARlSHFEEDSUPON LIVE CORALS CAUSING THE LARGEST KNOWN PEST RELATED DISTURBANCES ON )NDO 0ACIlC CORAL REEFS AND IT IS REGARDED AS A MAJOR MANAGEMENT PROBLEM 3EVERAL MECHA NISMS INCLUDINGHYDROGRAPHY HURRICANEDISTURBANCE NUTRIENTINPUTSANDPREDA TORREMOVAL HAVEBEENSUGGESTEDASPOTENTIALCAUSESOFSTARlSHINVASIONS 7ESTUDIEDASERIESOFOCEANICISLANDSVARYINGINSIZEANDHUMANPOPULA TION&OREACHISLANDANINDEXOFHUMANlSHINGINTENSITYWASESTIMATED!TEACH OFTHESITESDENSITIESOFPREDATORYlSHES STARlSHANDBARRIERREEFCOMMUNITIESWERE SURVEYED BY DIVERS 3URVEYING WAS CONDUCTED IN SUCCESSIVE YEARS 7E WISHED TO TEST THE HYPOTHESIS THAT STARlSH POPULATIONS OUTBREAK AND INVADE REEFS WHEN PERTURBATIONSTOTHEIRPREDATORSREMOVETHEPREDATORCONTROLAND MOREOVER THAT PREDATORSARERESPONSIBLEFORGENERATINGAN!LLEEEFFECTINSTARlSHPOPULATIONS 7EDIDNOTHAVESUFlCIENTLYDETAILEDDATATOBEABLETOPARAMETERISEAFULLPOPU LATIONMODEL(OWEVERWEWERESTILLABLETOUSEAMODELINGFRAMEWORKTOANALYSE THE DYNAMICS OF THIS SYSTEM &OR THE STARlSH WE CALCULATED PER CAPITA RATES OF POPULATIONCHANGE .T n.T n.T FOREACHISLAND4OTESTTHEHYPOTHESIS THAT PREDATORS WERE RESPONSIBLE FOR GENERATING !LLEE EFFECTS IN STARlSH POPULA TIONSWEPLOTTEDTHEPERCAPITARATEOFPOPULATIONCHANGEAGAINSTSTARlSHDENSITY ANDPREDATORDENSITY ASWELLASTOLOOKATHOWPREDATORDENSITIESAREAFFECTEDBY HUMANlSHINGPRESSURE &IRST WEFOUNDTHATPREDATORYlSHESWERELESSABUNDANTATTHEMOSTINTEN SIVELYlSHEDSITESASTHELEASTlSHEDSITES4HISINDICATESTHATTHEREISANENORMOUS RANGEOFVARIATIONINTHEPREDATORYlSHINGPRESSUREINTHISSYSTEM'IVENTHIS THE DATA ON RATES OF POPULATION GROWTH OF THE STARlSH &IG SUGGEST THAT PREDATOR REMOVAL BY SUBSISTENCE EXPLOITATION MAY BE SUFlCIENT TO ALLOW OUTBREAKS OF THE CROWN OF THORNS!SSHOWNIN&IGA THERELATIONSHIPBETWEENPER CAPITARATEOF POPULATIONCHANGEANDSTARlSHDENSITYISHUMPED ASWOULDBEEXPECTEDIFPOPULA TIONSWERESUBJECTTOAN!LLEEEFFECT4HEDATAAPPEARTOINDICATETHATTHEREARETWO EQUILIBRIA ONEATLOWDENSITIES THEOTHERATHIGHDENSITIES4HELOWEREQUILIBRIUM WILL BE UNSTABLE )N A VARIABLE ENVIRONMENT LOW DENSITY POPULATIONS WILL EITHER OUTBREAK ORWILLBECOMEEXTINCT 4HATTHE!LLEEEFFECTSHOWNIN&IGAACTUALLYRESULTSFROMTHEEFFECTSOFPREDA TORS IS CONlRMED IN &IG B !S SHOWN THERE IS A NEGATIVE RELATIONSHIP BETWEEN THERATEOFCHANGEINSTARlSHDENSITYANDPREDATORDENSITY CONlRMINGTHATSTAR lSH POPULATION DYNAMICS ARE DRIVEN BY PREDATION THUS FULlLLING THE CONDITIONS REQUIREDFORPREDATOR INDUCEDINSTABILITY


&IG 4HE RELATIONSHIP BETWEEN AVERAGE STARlSH DENSITY AND PER CAPITA POPULATION GROWTHOFSTARlSHANDA AVERAGESTARlSHDENSITY B AVERAGEDENSITYOFPREDATORYlSHES $ATAARETAKENFROMISLANDS PRESENTEDIN$ULVYETAL

)NSUMMARYTHISSYSTEMSUGGESTSTHATINVASIONOFTHECROWNOFTHORNSSTARlSH MAYBEGOVERNEDBYUNDERLYINGUNSTABLEDYNAMICSANDHOWTHISINTERACTSWITH VARIATIONS IN THE DENSITIES OF PREDATORS )N THIS CASE STUDY VARIATION IN PREDA TOR DENSITY WAS SPATIAL AND THE CONSEQUENCE OF DIFFERENCES IN lSHING INTENSITY AMONG ISLANDS )N OTHER SYSTEMS VARIATION COULD BE THE RESULT OF OTHER FACTORS SUCH AS HABITAT LOSS OR CLIMATIC EFFECTS 7HAT THIS EXAMPLE ILLUSTRATES HOWEVER


ISTHATPREDICTINGSUCHEFFECTSWILLREQUIREADETAILEDUNDERSTANDINGOFTHENATURE OFPOPULATIONSTABILITY

#/.#,5$).'2%-!2+3 %XCEPT IN THE UNLIKELY EVENT THAT POPULATION DYNAMICS ARE COMPLETELY DENSITY INDEPENDENT THE LONG TERM DYNAMICS OF POPULATIONS WILL BE DETERMINED BY THE EFFECTS OF VARIOUS FORMS OF INTRA AND INTER SPECIlC INTERACTIONS )N ADDITION TO THIS THE EFFECTS OF DENSITY INDEPENDENT STOCHASTICITY MAY BE COMPLEX PARTICU LARLY WHEN POPULATIONS ARE FORCED TO LOW DENSITIES 4HIS MEANS THAT FORECASTING THE OUTCOME OF INVASION MAY BE COMPLEX AND REQUIRES A DETAILED UNDERSTAND INGOFTHESTRUCTUREOFTHESYSTEMINQUESTION3IMPLEPOPULATIONMODELSCANBE AN EXTREMELY VALUABLE GUIDE IN ANALYSING SUCH PROBLEMS BOTH IN THEORY AND INPRACTICE

2%&%2%.#%3 !NDREWARTHA ( ' AND "IRCH , # 4HE DISTRIBUTION AND ABUNDANCE OF ANIMALS 5NIVERSITYOF#HICAGO0RESS #HICAGO "UCKLEY 9- "RIESE $4AND2EES -A $EMOGRAPHYANDMANAGEMENTOFTHE INVASIVEPLANTSPECIES(YPERICUMPERFORATUM)5SINGMULTI LEVELMIXED EFFECTSMODELS FOR CHARACTERIZING GROWTH SURVIVAL AND FECUNDITY IN A LONG TERM DATA SET *OURNAL OF !PPLIED%COLOGY "UCKLEY 9 - "RIESE $ 4 AND 2EES - B $EMOGRAPHY AND MANAGEMENT OF THEINVASIVEPLANTSPECIES(YPERICUMPERFORATUM))#ONSTRUCTIONANDUSEOFANINDI VIDUAL BASED MODEL TO PREDICT POPULATION DYNAMICS AND THE EFFECTS OF MANAGEMENT STRATEGIES*OURNALOF!PPLIED%COLOGY "YERS * % 2EICHARD 3 2ANDALL * - 0ARKER ) - 3MITH # 3 ,ONSDALE 7 - !TKINSON )!% 3EASTEDT 42 7ILLIAMSON - #HORNESKY %AND(AYES $ $IRECTING RESEARCH TO REDUCE THE IMPACT OF NON INDIGENOUS SPECIES #ONSERVATION "IOLOGY #HESSON 0,AND(UNTLY . #OMMUNITYCONSEQUENCESOFLIFE HISTORYTRAITSINA VARIABLEENVIRONMENT!NN:OOL&ENNICI #HESSON 0 , AND (UNTLY . 3HORT TERM INSTABILITIES AND LONG TERM COMMUNITY DYNAMICS4RENDSIN%COLOGYAND%VOLUTION #OHEN $ /PTIMIZINGREPRODUCTIONINRANDOMLYVARYINGENVIRONMENTS*OURNALOF 4HEORETICAL"IOLOGY $OBSON ! 0 AND 2 - -AY 0ATTERNS OF )NVASIONS BY 0ATHOGENS AND 0ARASITES 4HE %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW9ORK $OWLING 0 - 4HE ECOLOGY OF 6ULPIA 0LANT 0ROTECTION 1UARTELY 3UPPLEMENT


$OWLING 0 - 6ERBEEK " ,EMERLE $ AND ,EYS ! 2 2APID REGENERATION OF 6ULPIA6ULPIABROMOIDES INPASTURES)N0ROCEEDINGSTH!SIAN 0ACIlC7EED3OCIETY #ONFERENCE PP 4OSUKUBA *APAN $UFFY * % "IODIVERSITY LOSS TROPHIC SKEW AND ECOSYSTEM FUNCTIONING %COLOGY ,ETTERS $ULVY . + &RECKLETON 2 0 AND 0OLUNIN . 6 # #ORAL REEF CASCADES AND THEINDIRECTEFFECTSOFPREDATORREMOVALBYEXPLOITATION%COLOGY,ETTERS %ARN $*$ 2OHANI 0AND'RENFELL "4 0ERSISTENCE CHAOSANDSYNCHRONYIN ECOLOGYANDEPIDEMIOLOGY0ROCEEDINGSOFTHE2OYAL3OCIETY 3ERIES" %NGEN 3 "AKKE AND ! )SLAM $EMOGRAPHIC AND ENVIRONMENTAL STOCHASTIC ITYnCONCEPTSANDDElNITIONS"IOMETRICS n &IRBANK ,'AND7ATKINSON !2 !MODELOFINTERFERENCEWITHINPLANTPOPULA TIONS*OURNALOF4HEORETICAL"IOLOGY &RECKLETON 20AND7ATKINSON !2 (OWDOESTEMPORALVARIABILITYAFFECTPREDIC TIONSOFWEEDPOPULATIONNUMBERS*OURNALOF!PPLIED%COLOGY &RECKLETON 2 0 AND 7ATKINSON ! 2 !SYMMETRIC COMPETITION BETWEEN PLANT SPECIES&UNCIONAL%COLOGY &RECKLETON 20AND7ATKINSON !2 !REWEEDPOPULATIONSCHAOTIC*OURNALOF !PPLIED%COLOGY &RECKLETON 20 7ATKINSON !2 $OWLING 0-AND,EYS !2 $ETERMINANTS OFTHEABUNDANCEOFINVASIVEANNUALWEEDSCOMMUNITYSTRUCTUREANDNON EQUILIBRIUM DYNAMICS0ROCEEDINGSOFTHE2OYAL3OCIETY3ERIES" &RECKLETON 20 3ILVA-ATOS $- "OVI -,!AND7ATKINSON !2 0ROBLEMS WITH PREDICTING THE IMPACTS OF HARVESTING USING STRUCTURED POPULATION MODELS AN EXAMPLEBASEDONTROPICALTREES*OURNALOF!PPLIED%COLOGY 'ASCOIGNE * # AND ,IPCIUS 2 . !LLEE EFFECTS DRIVEN BY PREDATION *OURNAL OF !PPLIED%COLOGY 'INZBURG ,2AND#OLYVAN - %COLOGICALORBITSHOWPLANETSMOVEANDPOPULA TIONSGROW/XFORD5NIVERSITY0RESS /XFORD (ASSELL -0 $ENSITY DEPENDENCEINSINGLESPECIESPOPULATIONS*OURNALOF!NIMAL %COLOGY (ASSELL -0 $ETECTINGDENSITYDEPENDENCE4RENDSIN%COLOGYAND%VOLUTION (ASSELL - 0 ,AWTON * ( AND -AY 2 - 0ATTERNS OF DYNAMICAL BEHAVIOUR IN SINGLE SPECIESPOPULATIONS*OURNALOF!NIMAL%COLOGY (EINO - 2IPA * AND +AITALA 6 %XTINCTION RISK UNDER COLOURED ENVIRONMENTAL NOISE%COGRAPHY +ENDALL "% ETAL7HYDOPOPULATIONSCYCLE!SYNTHESISOFSTATISTICALANDMECHANISTIC MODELLINGAPPROCHES%COLOGY ,ANDE 2 $EMOGRAPHICSTOCHASTICITYAND!LLEEEFFECTONASCALEWITHISOTROPICNOISE /IKOS ,ANDE 2 %NGEN 3 AND3AETHER " % 3TOCHASTICPOPULATIONDYNAMICSINECOLOGY ANDCONSERVATION/XFORD5NIVSERSITY0RESS /XFORD


,EWIS -!AND+AREIVA 0 !LLEEDYNAMICSANDTHESPREADOFINVADINGORGANISMS 4HEORETICAL0OPULATION"IOLOGY ,EWONTIN 2#AND#OHEN $ /NPOPULATIONGROWTHINARANDOMLYVARYINGENVI RONMENT0ROCEEDINGSOFTHE.ATIONAL!CADEMYOF3CIENCES53! ,IEBHOLD !AND"ASCOMPTE * 4HE!LLEEEFFECT STOCHASTICDYNAMICSANDTHEERADI CATIONOFINVASIVESPECIES %COLOGY,ETTERS ,ONSDALE 7 - 4HE BALANCE OF WEED POPULATIONS )N &RONTIERS OF 0OPULATION %COLOGYEDS 2"&LOYDAND!73HEPPARD #3)2/0UBLISHING -ELBOURNE -AY 2 - 3TABILITY AND COMPLEXITY IN MODEL ECOSYSTEMS 0RINCETON 5NIVERSITY 0RESS 0RINCETON .EW*ERSEY -AY 2- 4HRESHOLDSANDBREAKPOINTSINECOSYSTEMSWITHAMULTIPLICITYOFSTABLE STATES.ATURE -AY 2 - -ODELS FOR TWO INTERACTING POPULATIONS )N 4HEORETICAL%COLOGY ED 2--AY PP "LACKWELL3CIENTIlC0UBLICATIONS /XFORD -AY 2 - #ONWAY ' 2 (ASSELL - 0 AND 3OUTHWOOD 4 2 % 4IME DELAYS DENSITY DEPENDENCE AND SINGLE SPECIES OSCILLATIONS *OURNAL OF !NIMAL %COLOGY -AY 2-AND/STER '& "IFURCATIONSANDDYNAMICCOMLEXITYINSIMPLEECOLOGICAL MODELS!MERICAN.ATURALIST -AYNARD3MITH * -ODELSINECOLOGY#AMBRIDGE5NIVERSITY0RESS #AMBRIDGE .ICHOLSON ! * !N OUTLINE OF THE DYNAMICS OF ANIMAL POPULATIONS !USTRALIAN *OURNALOF:OOLOGY 0ACALA 3 7 #ANHAM # $ 3APONARA * 3ILANDER * ! +OBE 2 + AND 2IBBENS % &OREST MODELS DElNED BY lELD MEASUREMENTS ESTIMATION ERROR ANALYSIS AND DYNAMICS%COLOGICAL-ONOGRAPHS 2EES - AND #RAWLEY - * 'ROWTH REPRODUCTION AND POPULATION DYNAMICS &UNCTIONAL%COLOGY 2EES - AND #RAWLEY - * $O PLANT POPULATIONS CYCLE &UNCTIONAL %COLOGY 2EES -AND0AYNTER 1 "IOLOGICAL#ONTROLOF3COTCH"ROOMMODELLINGTHEDETER MINANTSOFABUNDANCEANDTHEPOTENTIALIMPACTOFINTRODUCEDINSECTHERBIVORES*OURNAL OF!PPLIED%COLOGY 2OYAMA 4 !NALYTICAL0OPULATION$YNAMICS#HAPMAN(ALL ,ONDON 3CHEFFER - AND #ARPENTER 3 #ATASTROPHIC REGIME SHIFTS IN ECOSYSTEMS LINKING THEORYTOOBSERVATION4RENDSIN%COLOGYAND%VOLUTION 3AETHER " % ETAL ,IFE HISTORYVARIATIONPREDICTSTHEEFFECTSOFDEMOGRAPHICSTOHCAS TICITYONAVIANPOPULATIONDYNAMICS!MERICAN.ATURALIST 3AETHER " % ETAL 4IMETOEXTINCTIONOFBIRDPOPULATIONS%COLOGYINPRESS 3TEPHENS 0!AND3UTHERLAND 7* #ONSEQUENCESOFTHE!LLEEEFFECTFORBEHAV IOUR ECOLOGYANDCONSERVATION4RENDSIN%COLOGYAND%VOLUTION 3TEPHENS 0 ! 3UTHERLAND 7 * AND &RECKLETON 2 0 7HAT IS THE !LLEE EFFECT /IKOS 4AYLOR #-AND(ASTINGS ! &INDINGOPTIMALCONTROLSTRATEGIESFORINVASIVESPE CIES A DENSITY STRUCTURED MODEL FOR 3PARTINA ALTERNImORA *OURNAL OF !PPLIED %COLOGY


4ILMAN $ -AY 2- ,EHMAN #,AND.OWAK -! (ABITATDESTRUCTIONAND THEEXTINCTIONDEBT.ATURE 4ULJAPURKAR 3 0OPULATION DYNAMICS IN VARIABLE ENVIRONMENTS 3PRINGER .EW 9ORK 7ATKINSON ! 2 $ENSITY DEPENDENCE IN SINGLE SPECIES POPULATIONS OF PLANTS *OURNALOF4HEORETICAL"IOLOGY 7HITE 4#2 /PPOSINGPARADIGMSREGULATIONORLIMITATIONOFPOPULATIONS/IKOS 7ILLIAMSON - "IOLOGICAL)NVASIONS#HAPMAN(ALL ,ONDON 5+

#HAPTERSEVEN

,OCALINTERACTIONSAND INVASIONDYNAMICS POPULATIONGROWTHINSPACE ANDTIME $*-URRELL

).42/$5#4)/. 4HE STUDY OF BIOLOGICAL INVASIONS IS ESSENTIALLY THE STUDY OF POPULATION GROWTH IN BOTH SPACE AND TIME .OT ONLY ARE WE INTERESTED IN THE POPULATION SIZE OF AN INVADER BUTALSOITSRATEOFSPREADACROSSALANDSCAPEORREGION(ENCETHEORETI CALMODELSOFINVASIONSVERYOFTENINCORPORATESOMEFORMOFSPATIALHETEROGENEITY 3KELLAM "OERLIJSTAND(OGEWEG (ASSELLETAL +OTETAL +EELINGETAL ,EWIS ,EWISAND0ACALA 2IETKERKETAL "ROADLYSPEAKING THEREARETWOCLASSESOFSPATIALHETEROGENEITYTHESO CALLED ENDOGENOUSORSELF INDUCEDSPATIALHETEROGENEITYTYPEI ANDEXOGENOUSHETERO GENEITYTYPEII 4YPEI HETEROGENEITYISCAUSEDBYINTERACTIONSBETWEENINDIVID UALSORPOPULATIONS ANDLEADSTOWHATISSOMETIMESCALLEDSELF ORGANISEDSPATIAL PATTERNS "OERLIJST AND (OGEWEG (ASSELL ET AL +EELING ET AL 2IETKERKETAL &OREXAMPLE INMONOCULTURESOFPINES INTENSECOMPETITION BETWEENCLOSENEIGHBOURSLEADSTOANEVENSPACINGOFADULTTREES+ENKEL -7#ADOTTE ETAL (EDS) #ONCEPTUALECOLOGYANDINVASIONBIOLOGY – ¥3PRINGER0RINTEDINTHE.ETHERLANDS

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!NOTHER EXAMPLE SHOWS HOW IMPORTANT 2 CAN BE TO THE INVASION DYNAMICS ANDHOWITCANREVERSESOMEOFTHECONCLUSIONSOFTHENON SPATIALLOGISTICMODEL &IG #ONSIDER IMAGINARY SPECIES LABELLED AND RESPECTIVELY IF R R IE SPECIESHASAHIGHERINTRINSICRATEOFGROWTHTHANSPECIES BUT22AND IF INTERACTIONS AND DISPERSAL ARE LOCALISED IN SPACE THEN IT IS POSSIBLE FOR SPECIES TO BE THE BETTER INVADER BOTH IN TERMS OF SPEED OF INVASION AND EQUILIBRIUM DENSITY 3IMILAR RESULTS COULD EASILY BE PRODUCED FOR SPECIES WITH DIFFERENT SCALESOFDISPERSAL ANDTHISSENDSTHEMESSAGETHATKNOWING RMAYNOTBESUFl CIENTINDETERMININGWHETHERASPECIESCANINVADEORNOT4HESERESULTSALLPOINT TO THE FACT THAT A HIGH REPRODUCTIVE NUMBER 2 IS ADVANTAGEOUS FOR AN INVADER IN HOMOGENEOUS SPACE BUT OTHER RESULTS "OLKER SHOW THAT LOW VALUES FOR 2 CAN BE BENElCIAL IF THERE IS SPATIAL VARIATION IN THE EXTERNAL ENVIRONMENT TYPEII SPATIALHETEROGENEITY

&IG !N EXAMPLE SHOWING HOW 2 MAY REVERSE A MAIN CONCLUSION OF THE NON SPATIAL LOGISTICMODEL3PECIESBROKENLINES HASAHIGHVALUEFORRBUTALOW2NUMBER3PECIES SOLID LINES HAS A LOWER VALUE FOR R BUT A HIGHER 2 NUMBER )N THE NON SPATIAL MODEL THICK LINES SPECIES IS THE BETTER INVADER AND HAS A HIGHER DENSITY AT EQUILIBRIUM 7HENINTERACTIONSANDDISPERSALARELOCALISEDINSPACETHINLINES THISRESULTISREVERSED NOW THE SPECIES HAS THE FASTER INVASION RATE AND HIGHER DENSITY AT EQUILIBRIUM &OR SPECIES B D GIVING R 2 AND FOR SPECIES B D GIVING R 2 /THER PARAMETERS ARE IDENTICAL FOR BOTH SPECIES AND ARED SWSM

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&INALPOPULATIONSIZE

3O FAR WE HAVE CONCENTRATED ON THE TRANSIENT DYNAMICS BUT NEIGHBOURHOOD INTERACTIONS AND LOCAL DISPERSAL CAN ALSO GREATLY AFFECT THE lNAL POPULATION SIZE ,AWETAL %THERIDGE )FNEIGHBOURHOODINTERACTIONSARESUFlCIENTLY LARGE SCALETHENTHEPOSITIONOFINDIVIDUALSACROSSTHELANDSCAPEISOFLITTLEIMPOR TANCEINDETERMININGTHECOMPETITIVEINTERACTIONS)NSUCHCASESTHERESULTSOFTHE MEAN lELD MODEL ARE ASYMPTOTICALLY APPROACHED &IG 4HIS IS IN CONTRAST TO THECASEWHEREDISPERSALISLARGE SCALE)FINTERACTIONSARELOCALISEDINSPACESMALL VALUEFORSW THENMANYOFFSPRINGCANESCAPEFROMCOMPETINGWITHTHEIRPARENT 4HISLEADSTOASPATIALLYSEGREGATEDPOPULATIONWHEREMOSTINDIVIDUALSEXPERIENCE A RELATIVELY COMPETITOR FREE NEIGHBOURHOOD AND HENCE THE lNAL POPULATION SIZE ISMUCHLARGERTHANTHATUNDERMEAN lELDCONDITIONS/NTHEOTHERHANDIFBOTH DISPERSAL AND INTERACTIONS ARE SHORT RANGE SMALL VALUES FOR SM AND SW THEN THE COMPETITIVENEIGHBOURHOODISPERCEIVEDASBEINGCROWDEDWITHTHERESULTTHATTHE lNAL DENSITY IS MUCH LOWER THAN THE MEAN lELD EXPECTATION )N EXTREME CASES WHERE BOTH INTERACTIONS AND DISPERSAL OCCUR OVER SHORT SPATIAL SCALES THEN SELF DRIVENEXTINCTIONOCCURS&IG &IGS AND,AWETAL 3ELF DRIVEN EXTINCTION MIGHT AT lRST THOUGHT SEEM ONLY AN INTERESTING MATH EMATICALARTEFACTANDOFNOCONCERNTOINVASIONECOLOGYAFTERALLIFANORGANISMS DISPERSALISSOSHORT RANGEHOWCOULDITPERSISTATANOTHERLOCATIONANDSENDOUT EMMIGRANTS(OWEVER ITISENTIRELYPOSSIBLEFORASPECIESDISPERSALKERNELTODIFFER BETWEEN ITS NATURAL AND EXOTIC HABITATS -ANY PLANTS RELY ON SECONDARY DISPER SAL OF SEEDS BY ANIMALS !NDRESEN "OHNING 'AESE ET AL (OSHIZAKI ET AL -ILTON AND $EAN 'ORDON AND VAN DER 6ALK 'UITIAN ETAL AND IFINANEWENVIRONMENTTHESECONDARYDISPERSERSARENOTPRESENT THE DISPERSAL KERNEL IS LIKELY TO BE MUCH SHORTER AND HENCE SELF DRIVEN EXTINC TIONISMUCHMORELIKELY!NOTHERFEATUREOFTHEPRESENCEOFSPATIALAGGREGATION OFCONSPECIlCSISTHATWHENLOOKINGATTHEINVASIONDYNAMICSOFASPECIESINTOA COMMUNITYITISNOLONGERPOSSIBLETOIGNORETHEEFFECTOFINTRASPECIlCCOMPETITION AS HAS TRADITIONALLY BEEN THE CASE -ORTONET AL -ORTON AND ,AW

→ &IG %QUILIBRIUMVALUESFORA .ANDB # ASAFUNCTIONOFTHESPATIALSCALEOFTHE INTERACTIONKERNELANDDISPERSALKERNEL4HERESULTSAREOBTAINEDBYNUMERICALLYINTEGRATING THEDETERMINISTICAPPROXIMATION AND UNTILTHECHANGEIN.OVERANINTEGRATIONSTEP FALLSBELOW/THERPARAMETERSAREHELDCONSTANTAREBDD &OR COMPARISON THIS SET OF PARAMETERS NON SPATIAL LOGISTIC MODEL GIVES AN EQUILIBRIUM DENSITYOF


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4HIS IS BECAUSE EVEN THOUGH GLOBALLY THE INVADING SPECIES IS AT A LOW DENSITY LOCALLY THE INVADER STILL @SEES A HIGH DENSITY OF CONSPECIlCS THANKS TO THE LOCAL NATUREOFDISPERSALANDCOMPETITION"OLKERAND0ACALA -URRELLETAL -URRELLAND,AW 4HESERESULTSALLPOINTTOTHEIMPORTANCEOFTHERELATIVESCALESOFDISPERSALAND NEIGHBOURHOODINTERACTIONSTOBOTHTHETRANSIENTDYNAMICSANDlNALPOPULATION DENSITY"OLKERAND0ACALA %LLNER ,AWETAL &ORMANYANIMAL SPECIESTHEINTERACTIONKERNELISLIKELYTOBEOVERAMUCHSHORTERDISTANCETHANTHE DISPERSALKERNEL(OWEVERFORPLANTSANDOTHERSEDENTARYORGANISMSTHISMAYNOT BETHECASE ANDITISENTIRELYPOSSIBLETHATTHEEFFECTSOFDENSITYMAYBEFELTOVER RELATIVELYLARGESPATIALSCALES0ETERS %COLOGISTSHAVEPUTMUCHEFFORTINTO MEASURINGDISPERSALRATESANDDISTANCES#LOBERTETAL "ULLOCKETAL ,EVINE AND -URRELL BUT RATHER LESS IS KNOWN ABOUT THE SHAPES AND SIZES OFINTERACTIONKERNELS0URVESAND,AW #LEARLYMODELSOFTHISTYPESHOW THATTHEINTERACTIONKERNELSAREPOTENTIALLYVERYIMPORTANTINDETERMININGINVA SIONDYNAMICS

,).+34//4(%2-/$%,3 !S HAS BEEN SUGGESTED AT VARIOUS POINTS IN THIS CHAPTER THE MODELS DESCRIBED ANDANALYSEDHEREARECLOSELYRELATEDTOANUMBEROFOTHERSPATIALMODELS9OUNG ETAL SHOWEDTHATAPOPULATIONOFDISCRETEINDIVIDUALSINHABITINGALAND SCAPE AND WITH LOCAL DISPERSAL AND POST BIRTH MOVEMENT WILL QUICKLY AGGREGATE EVEN WITHOUT ANY DENSITY DEPENDENT PROCESSES 4HE MODELS ABOVE HAVE SHOWN THAT INCORPORATING LOCAL DENSITY DEPENDENT PROCESSES CAN LEAD TO ANY OF THE MAINCLASSESOFSPATIALSTRUCTUREAGGREGATIONSEGREGATIONORRANDOMPATTERNING &URTHERTHEDYNAMICALSYSTEM AND COLLAPSESTOTHEMODELOF9OUNGETAL WHEND ANDTHESPATIALPATTERNISNOWDESCRIBEDBYONLYTHREEPAIRSOF TERMSA C TWOOFWHICHARECONCERNEDWITHBIRTHSANDONLYONEOFWHICHIS CONCERNEDWITHTHELOSSOFPAIRS)TCANBEEASILYSEENTHATINTHElRSTINSTANCETHE BIRTHTERMSWILLOUTWEIGHTHEDEATHTERMANDSOAGGREGATIONSOFINDIVIDUALSWILL DEVELOP(OWEVER ITISNOTCLEARTHATTHEAGGREGATIONSWILLEVERSTOP ALTHOUGHTHE RATEOFCHANGEWILLSLOWOVERTIME 4HE THETA LOGISTIC MODEL 'ILPIN AND !YAYLA HAS BEEN USED WITH SOME SUCCESS TO MODEL THE POPULATION DYNAMICS OF A NUMBER OF SPECIES 3AETHER AND %NGEN 3AETHER ET AL A 3AETHER ET AL B 4HE MAIN BASIS FOR THE THETA LOGISTIC MODEL IS THAT THE MAXIMUM RATE OF POPULATION GROWTH MAY BE ACHIEVED AT DENSITIES OTHER THAN HALF THE CARRYING CAPACITY 4URCHIN 4HESPATIALVERSIONOFTHELOGISTICMODELALSOSHOWSTHISFEATURE,AWETAL ANDMAYTHEREFOREACTASAMECHANISTICFOUNDATIONFORTHETHETA LOGISTICMODELS 7HEN INTERACTIONS ARE LOCALISED IN SPACE HOW CROWDED THE NEIGHBOURHOOD IS DETERMINES WHEN THE MAXIMUM GROWTH RATE IS ACHIEVED 7HEN BOTH DISPERSAL AND INTERACTIONS OCCUR OVER SHORT SCALES THE NEIGHBOURHOOD QUICKLY BECOMES


CROWDED EVENIFTHEOVERALLDENSITYISLOW ANDTHISLEADSTOTHEMAXIMUMGROWTH RATEOCCURRINGATLESSTHANHALFTHElNALDENSITY/NTHEOTHERHAND IFDISPERSAL ISLONG RANGEBUTINTERACTIONSARESHORT SCALE THEINDIVIDUALSTENDNOTTOEXPERI ENCEMANYNEIGHBOURSUNTILTHEOVERALLDENSITYISMUCHHIGHER SOTHEMAXIMUM POPULATIONGROWTHRATETENDSTOOCCURATDENSITIESTHATAREHIGHERTHANTHEHALF THElNALPOPULATIONDENSITY,AWETAL 4HISCHAPTERHASFOCUSEDONAMODELFORCOMPETITIONINVESTIGATINGTHEINVASION DYNAMICSOFASINGLESPECIES-ANYECONOMICALLYIMPORTANTINVASIONSAREBYPARA SITESPATHOGENSANDTHEORETICALMODELSHAVEBEENUSEDTOINVESTIGATETHEEFFECTSOF LOCALSPATIALSTRUCTUREONINVASIONDYNAMICSOFTHEPESTPATHOGEN"OLKER +EELING )N A SUSCEPTIBLE INFECTED RECOVERED 3)2 HOST PATHOGEN MODEL WITH LOCAL DISPERSAL OF THE PATHOGEN +EELING SHOWS HOW THE REPRODUC TIVERATIOREQUIREDFORINVASIONINANETWORKWITHLOCALANDlNITECONNECTIONSIS ALWAYS LARGER THAN THE MEAN lELD CASE 'ENERALLY SPEAKING THE AGGREGATION OF HOSTSISGOODATSLOWINGTHERATEOFSPREADOFAPESTPATHOGENIFITSDISPERSALISFAIRLY SHORT RANGE ANDTHISHASIMPORTANTIMPLICATIONSFOREVOLUTIONOFVIRULENCE"OOTS AND3ASAKI "OOTSETAL

#/.#,53)/.3 )NVASIONSAREESSENTIALLYTHESTUDYOFPOPULATIONGROWTHINSPACEANDTIME"OTH DISPERSAL AND COMPETITIVE INTERACTIONS TEND TO BE LOCALISED IN SPACE AND ACTING TOGETHER THEY MAY PRODUCE STRONG SPATIAL STRUCTURES THAT FEED BACK ONTO POPU LATION DYNAMICS AND SO GREATLY AFFECT THE INVASION DYNAMICS 4HIS CHAPTER HAS INVESTIGATED THE EFFECTS OF LOCAL INTERACTIONS AND LOCAL DISPERSAL ON POPULATION GROWTHUSINGSPATIALEXTENSIONSOFTHECLASSICALLOGISTICEQUATION&ROMASTOCHAS TICINDIVIDUAL BASEDMODELADETERMINISTICAPPROXIMATIONHASBEENDERIVEDWHICH GREATLYAIDSTHEANALYSISOFTHEMODEL!NUMBEROFQUALITATIVEANDQUANTITATIVE PATTERNSEMERGE POPULATIONGROWTHMAYBEEITHERFASTERORSLOWERTHANTHE CLASSICALMODEL THERATIOOFDENSITYINDEPENDENTBIRTHSTODENSITYINDEPENDENT DEATHS2 CANGREATLYAFFECTTHEPROBABILITYANDSPEEDOFINVASIONASWELLASTHE lNALPOPULATIONSIZE POPULATIONGROWTHMAYBELINEARRATHERTHANTHEFAMIL IAR SIGMOID SHAPE DETERMINISTIC EXTINCTION MAY OCCUR PURELY DUE TO PARENT OFFSPRINGCOMPETITIONMEANINGTHATINTRASPECIlCCOMPETITIONCANNOTBEIGNOREDIN THE ANALYSIS OF INVASIONS AND THAT COUNTER INTUITIVELY POPULATIONS WITH THE LOWEST EQUILIBRIUM DENSITY MAY TAKE THE LONGEST TO REACH THIS STATE !LL OF THESE PROPERTIESAREDEPENDENTNOTONLYONTHEABSOLUTESPATIALSCALESOFNEIGHBOURHOOD INTERACTIONS AND LOCAL DISPERSAL BUT ALSO THEIR RELATIVE SCALES )T HAS LONG BEEN KNOWN THAT DISPERSAL IS IMPORTANT FOR THE INVASIVE ABILITY OF A SPECIES BUT THESE RESULTSALSOSHOWTHAT2MAYBEJUSTASIMPORTANTASTHEINTRINSICGROWTHRATE R INDETERMININGPOPULATIONGROWTH

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!#+./7,%$'%-%.43 4HE WORK PRESENTED HERE OWES A GREAT DEAL TO 2ICHARD ,AW AND 5LF $IECKMANN WHO SOLVED MANY OF THE DIFlCULT INITIAL PROBLEMS TO DO WITH DERIVING THE DETER MINISTIC APPROXIMATION AND WHO HELPED AND ENCOURAGED ME TO THINK LONG AND HARDABOUTTHEPROBLEMOFMOMENTCLOSURES)WOULDALSOLIKETOTHANK"EN"OLKER #ALVIN$YTHAM $ANIEL,LAMBI AND$REW0URVESFORVARIOUSHELPFULANDINFORMA TIVEDISCUSSIONSALONGTHEWAY ANDTO-ARC#ADOTTE 2ENE3ALINAS *ESSICA-ETCALF AND 9VONNE "UCKLEY FOR COMMENTS ON EARLIER DRAFTS OF THIS CHAPTER 4HIS WORK WASPARTLYSUPPORTEDBYTHE.ATURAL%NVIRONMENT2ESEARCH#OUNCILANDALSOTHE #ENTRAL3CIENCE,ABORATORY$%&2! )MPERIAL#OLLEGE0ARALLEL#OMPUTING#ENTRE )#0# KINDLYDONATEDCOMPUTERPROCESSORTIMETHATHELPEDTOGENERATESOMEOF THERESULTSREPORTEDINTHElGURES

!00%.$)8 4HEPRESENCEOFTHETHIRDMOMENTINTHEDYNAMICSFORTHESECONDMOMENTSMEANS THATTHEDYNAMICALSYSTEMISNOTYETCLOSED)NPRINCIPLEITISPOSSIBLETODERIVETHE DYNAMICS OF THE THIRD MOMENTS BUT APART FROM CAUSING A HEADACHE DUE TO THE NUMBEROFTERMSINVOLVEDTHEYWOULDTHEMSELVESBEFUNCTIONSOFFOURTHMOMENTS QUADDENSITIES (OWTODEALWITHTHISMOMENTHIERARCHYISTHECENTRALPROBLEM TO THIS TECHNIQUE #LASSICAL THEORY EFFECTIVELY TRUNCATES AT THE lRST MOMENT BY ASSUMINGTHATTHEREISNOSPATIALSTRUCTURE BUTTHISONLYDEALSWITHALIMITINGCASE OF THE )"- SEE BELOW ! BETTER SOLUTION IS TO CLOSE THE HIERARCHY AT THE SECOND MOMENTSBYREPLACINGTHETHIRDMOMENTSBYATERMTHATISAFUNCTIONOFTHElRST ANDSECONDMOMENTS2ECENTWORKHASSUGGESTEDAFORMOFSECONDORDERMOMENT CLOSURE THAT GIVES GOOD APPROXIMATIONS TO THE )"- FOR A WIDE RANGE OF SPATIAL STRUCTURES,AWETAL -URRELLAND,AW -URRELLETAL ANDITIS USEDHERE #j #j #j #jnj #j #jnj n. 4j j . . .

!

4HIS CLOSURE DOES HOWEVER MEAN THAT ANALYTICAL SOLUTIONS TO THE DYNAMICAL SYSTEMAREVERYHARDTOACHIEVE ANDSOTHEANALYSISOFTHEDYNAMICALSYSTEMPRO CEEDSBYNUMERICALMETHODS

2%&%2%.#%3 !NDRESEN %3EEDDISPERSALBYMONKEYSANDTHEFATEOFDISPERSEDSEEDSINA0ERUVIAN RAINFOREST"IOTROPICA "OERLIJST - #AND 0 (OGEWEG 3PIRAL 7AVE 3TRUCTURE IN 0RE "IOTIC %VOLUTION n (YPERCYCLES3TABLEAGAINST0ARASITES0HYSICA$


"OHNING 'AESE + "('AESEAND3"2ABEMANANTSOA)MPORTANCEOFPRIMARY AND SECONDARY SEED DISPERSAL IN THE -ALAGASY TREE #OMMIPHORA GUILLAUMINI %COLOGY "OLKER "AND370ACALA5SINGMOMENTEQUATIONSTOUNDERSTANDSTOCHASTICALLY DRIVENSPATIALPATTERNFORMATIONINECOLOGICALSYSTEMS4HEORETICAL0OPULATION"IOLOGY "OLKER " - !NALYTIC MODELS FOR THE PATCHY SPREAD OF PLANT DISEASE "ULLETIN OF -ATHEMATICAL"IOLOGY "OLKER "-#OMBININGENDOGENOUSANDEXOGENOUSSPATIALVARIABILITYINANALYTICAL POPULATIONMODELS4HEORETICAL0OPULATION"IOLOGY "OLKER " - AND 3 7 0ACALA 3PATIAL MOMENT EQUATIONS FOR PLANT COMPETITION 5NDERSTANDING SPATIAL STRATEGIES AND THE ADVANTAGES OF SHORT DISPERSAL !MERICAN .ATURALIST "OLKER "- 370ACALAAND#.EUHAUSER3PATIALDYNAMICSINMODELPLANTCOM MUNITIES7HATDOWEREALLYKNOW!MERICAN.ATURALIST "OOTS - 0*(UDSONAND!3ASAKI,ARGESHIFTSINPATHOGENVIRULENCERELATETO HOSTPOPULATIONSTRUCTURE3CIENCE "OOTS - AND ! 3ASAKI @3MALL WORLDS AND THE EVOLUTION OF VIRULENCE INFECTION OCCURSLOCALLYANDATADISTANCE0ROCEEDINGSOFTHE2OYAL3OCIETYOF,ONDON3ERIES" "IOLOGICAL3CIENCES "ROWN * ( AND ,OMOLINO - 6 "IOGEOGRAPHY 3INAUER !SSOCIATES 3UNDERLAND -! "ULLOCK *- 2%+ENWARDAND23(AILS EDITORS$ISPERSALECOLOGY"LACKWELL /XFORD #ASWELL ( 2 ,ENSINK AND - ' .EUBERT $EMOGRAPHY AND DISPERSAL ,IFE TABLE RESPONSEEXPERIMENTSFORINVASIONSPEED%COLOGY #LOBERT * % $ANCHIN ! ! $HONDT AND * $ .ICHOLS EDITORS $ISPERSAL /XFORD 5NIVERSITY0RESS /XFORD #ODY -,AND*-/VERTON3HORT TERMEVOLUTIONOFREDUCEDDISPERSALINISLAND PLANTPOPULATIONS*OURNALOF%COLOGY #RESSIE .!#3TATISTICSFORSPATIALDATA7ILEY .EW9ORK $ARLINGTON 0* *R#ARABIDAEOFMOUNTAINSANDISLANDSDATAONTHEEVOLUTIONOF ISOLATEDFAUNAS ANDONATROPHYOFWINGS%COLOGICAL-ONOGRAPHS $IECKMANN 5 AND 2 ,AW 2ELAXATION PROJECTIONS AND THE METHOD OF MOMENTS 0AGES IN 5 $IECKMANN 2 ,AW AND * ! * -ETZ EDITORS 4HE 'EOMETRY OF ECOLOGICAL INTERACTIONS SIMPLIFYING SPATIAL COMPLEXITY #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE $IGGLE 0*3TATISTICALANALYSISOFSPATIALPOINTPATTERNS!CADEMIC0RESS ,ONDON %LLNER 300AIRAPPROXIMATIONFORLATTICEMODELSWITHMULTIPLEINTERACTIONSCALES *OURNALOF4HEORETICAL"IOLOGY %THERIDGE !-3URVIVALANDEXTINCTIONINALOCALLYREGULATEDPOPULATION!NNALSOF !PPLIED0ROBABILITY

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3AETHER " % 3 %NGEN 2 ,ANDE # "OTH AND - % 6ISSER B $ENSITY DEPENDENCE AND STOCHASTIC VARIATION IN A NEWLY ESTABLISHED POPULATION OF A SMALL SONGBIRD /IKOS 3KELLAM *'2ANDOMDISPERSALINTHEORETICALPOPULATIONS"IOMETRIKA 4RAVIS *-*AND#$YTHAM$ISPERSALEVOLUTIONDURINGINVASIONS%VOLUTIONARY %COLOGY2ESEARCH 4URCHIN 0#OMPLEXPOPULATIONDYNAMICS0RINCETON5NIVERSITY0RESS 0RINCETON 6EIT 2 2 AND - ! ,EWIS $ISPERSAL POPULATION GROWTH AND THE !LLEE EFFECT $YNAMICSOFTHEHOUSElNCHINVASIONOFEASTERN.ORTH!MERICA!MERICAN.ATURALIST 7ITH + ! 4HE LANDSCAPE ECOLOGY OF INVASIVE SPREAD #ONSERVATION "IOLOGY 7HITTAKER 2*)SLAND"IOGEOGRAPHY%COLOGY %VOLUTIONAND#ONSERVATION/XFORD 5NIVERSITY0RESS /XFORD 9OUNG 7 2 ! * 2OBERTS AND ' 3TUHNE 2EPRODUCTIVE PAIR CORRELATIONS AND THECLUSTERINGOFORGANISMS.ATURE

#HAPTEREIGHT

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!PREDICTIONOFTHISSORTREQUIRESMODELSFORPOPULATIONSPREAD!SOUTLINEDBELOW SUCHMODELSHAVEALONGANDDISTINGUISHEDHISTORYINQUANTITATIVEECOLOGY 7HEREAS EARLY MATHEMATICAL MODELS FOR POPULATION SPREAD WERE PRIMAR ILYCONCEPTUALANDQUALITATIVEINNATURE ANEWGENERATIONOFREALISTICMODELSIS EMERGING4HESENEWMODELSARETIEDDIRECTLYTOTHEDEMOGRAPHYANDDISPERSALOF INDIVIDUALS(OWEVER THEREARENEWCHALLENGESINTHELINKINGOFTHESEMODELSTO THEBIOLOGICALPROCESSES !SWEWILLILLUSTRATEINTHISCHAPTER SPREADRATEPREDICTIONSAREVERYSENSITIVETO ASSUMPTIONSABOUTLONG DISTANCEDISPERSAL!RETHEREROBUSTMETHODSFORESTIMAT INGSPREADRATES4HISISONEQUESTIONWEWILLADDRESS &URTHERMOREALMOSTALLMATHEMATICALMODELSASSUMETHATTHESPREADOCCURSIN ONESPATIALDIMENSION ALONGALINE4HISISNOTBECAUSEMATHEMATICIANSHAVENOT NOTICEDTHATMOSTPOPULATIONSPREADTAKESPLACEINTWODIMENSIONSEXCEPTCASES LIKE DISPERSAL ALONG A COASTLINE OR RIVER 2ATHER IT IS BECAUSE THE MAIN QUALITA TIVEFEATURESOFINVASIONSAREAPPARENTINONE DIMENSIONALMODELS ALTHOUGH AS WEWILLSHOW THEQUANTITATIVERESULTSINSPECIlCCASESCANDEPENDVERYMUCHON THE THE DIMENSIONALITY OF THE DISPERSAL DATA AND OF THE MODEL USED FOR ANALYSIS )NPARTICULAR WEWILLSHOWTHATTHENAIVEAPPLICATIONOFONEDIMENSIONALMODELS TOTWODIMENSIONALDISPERSALDATAWILLPRODUCEASYSTEMATICBIASSOMETIMESPOSI TIVE SOMETIMESNEGATIVE INSPREADRATEESTIMATES)NTHISCHAPTERWEWILLOUTLINE NEWlTTINGMETHODSFORAVOIDINGTHESEBIASES

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(ERENX T ISTHELOCALPOPULATIONDENSITY lISTHEINTRINSICGROWTHRATE gIS THECARRYINGCAPACITY $ISTHEDISCUSIONCOElCIENT XISTHEONE DIMENSIONALSPACE COORDINATEANDTISTIME4HERATEOFSPREADOFAPOPULATIONOBEYINGTHISEQUATION ASYMPTOTICALLY APPROACHES C 3l$ FOR LARGE TIMES +OLMOGOROV ET AL !RONSONAND7EINBERGER &IG 7HEREASTHESPREADRATEPREDICTIONSARE ONALANDSCAPESCALE THEPARAMETERSRAND$CANBEMEASUREDONTHEINDIVIDUAL LEVEL USINGLIFETABLEANALYSIS ANDMARK RECAPTURE&URTHERMORE COMPARISONSOF HISTORICALLY OBSERVED INVASIVE SPREAD RATES WITH THE ASYMPTOTIC SPREAD RATE FOR MULAHAVEHELDUPFORAWIDEVARIETYOFSPECIES!NDOWETAL MAKINGTHE INTERPLAYBETWEENINVASIONTHEORYANDSPREADDATAAMODERN DAYSUCCESSSTORYIN QUANTITATIVEECOLOGY3HIGESADAAND+AWASAKI

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&IG 0OPULATION SPREAD FOR &ISHERS EQUATION ! TYPICAL SOLUTION OF &ISHERS EQUATION ILLUSTRATESGROWTHANDSPREADINONE DIMENSIONALLINEARSPACE!TLEFT THESOLUTIONIS PLOTTEDFOREQUALLY SPACEDTIMEINTERVALS!TRIGHT THEGRAYAREADENOTESTHEREGIONINSPACE WHERETHEPOPULATIONISLARGERTHANATHRESHOLDLEVELN4HEBOUNDARIESOFTHISAREA HAVESLOPESEQUALTOTHEASYMPTOTICSPREADRATEC 3l$&ORTHISlGURE l g $ ANDNX COS/X FOR\X\)"ASEDON.EUBERTAND0ARKER

! MAJOR PROBLEM WITH &ISHERS MODEL IS THAT IT IMPOSES ONE PARTICULAR FORM OF DISPERSAL 4HE ASSUMPTION OF DIFFUSION IN EQUATION WHICH IMPLIES NORMALLY DISTRIBUTED DISPERSAL PROPAGULES IS OFTEN VIOLATED WHEN DISPERSAL IS MEASURED FOR BIOLOGICAL POPULATIONS ,EWIS 7HILE THERE IS TREMENDOUS VARIABILITYINSUCHDISPERSALDATA THEREISASTRONGTENDENCYFORTHEDISTRIBUTIONOF DISPERSALDISTANCESTOBELEPTOKURTIC WITHALARGERNUMBEROFDISTANCESNEARTHE CENTERANDINTHETAILSTHANINANORMALDISTRIBUTIONWITHCOMPARABLEVARIANCE 4HEEFFECTOFTHELONG DISTANCEDISPERSERS ASDESCRIBEDBYTHETAILSOFTHEDISTRIBU TIONOFDISTANCES ISDRAMATIC#ASWELLETAL 0REDICTIONSFORINVASIONRATES CANSPEEDUPBYANORDEROFMAGNITUDEORMOREWHENTHELONG DISTANCEDISPERSERS AREINCLUDED+OT ,EWIS ANDVANDEN$RIESSCHE 7HENTHEDISPERSALDISTRIBUTIONISFARFROMNORMAL THEPARTIALDIFFERENTIALEQUA TIONMODEL NOLONGERSUCCES)TISTHENNECESSARYTODElNEADISPERSALKERNEL KX Y INONESPATIALDIMENSION WHICHDESCRIBESTHEPROBABILITYTHATAPROPAGULE THAT STARTS AT Y MOVES TO THE INTERVAL X X DX BY KX Y DX 4HE UNITS FOR THE DISPERSALKERNELKAREPERUNITLENGTH4HESPATIALREGIONOFINTERESTISTHEINTERVAL 1nú ú 7HENMODELLINGINVASIONS WETYPICALLYASSUME úISARBITRARILYLARGE )N THE ABSENCE OF IMMIGRATION FROM OUTSIDE 1 EVERY DISPERSER MUST ORIGINATE ATSOMEOTHERPOINTIN SOTHAT Gú KX Y DY Hnú

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)N A HOMOGENEOUS HABITAT DISPERSAL BETWEEN TWO LOCATIONS WILL ONLY DEPEND UPON UPON THE RELATIVE LOCATIONS OF THE START AND lNISH POINTS )N THIS CASE TO WHICH WE WILL RESTRICT OUR ATTENTION FOR THE REMAINDER OF THE CHAPTER WE WRITE KX Y KX n Y 3HIGESADA +AWASAKI AND 4ERAMOTO EXAMINE INVASIONS IN HETEROGENEOUS ENVIRONMENTS 4O INCLUDE POPULATION DYNAMICS POPULATIONGROWTHFROMONEGENERATIONTOTHENEXTCANBEDESCRIBEDWITHANON LINEARFUNCTION NTdNT NTGNT

WHEREGDElNESTHEPERCAPITAGROWTHRATEASAFUNCTIONOFLOCALPOPULATIONDENSITY NT .ON OVERLAPPING GENERATIONS ARE ASSUMED BUT HERE AND IN THE SUBSEQUENT ANALYSIS THE ASSUMPTION CAN BE RELAXED TO INCLUDE MODELS WITH STAGE STRUCTURE SEE.EUBERTAND#ASWELL FORDETAILS 4HE NONSPATIAL POPULATION MODEL IS THEN MODIlED TO ALLOW FOR DISPER SAL BETWEEN REPRODUCTION EVENTS )F WE DESIGNATE THE POPULATION DENSITY AT LOCATIONXANDTIMETBYNTX THESEMODELSTAKETHEFORMOFASCALARINTEGRODIFFER ENCEEQUATION Gú NTX dNTY KXnY DY Hnú

%ARLYANALYSESOFPOPULATIONSPREADUSINGINTEGRODIFFERENCEEQUATIONSAPPEARED IN THE MATHEMATICAL LITERATURE PRIMARILY IN THE CONTEXT OF GENETICS 7EINBERGER ,UI A B 7EINBERGER ,UI A B (OWEVER INTEGRODIFFERENCE EQUATIONS AND GENERALIZATIONS OF THEM ARENOW BEING USED BY A GROWING LIST OF ECOLOGISTS TO INVESTIGATE THE SPREAD RATE OF ECOLOGICAL POPULATIONS +OT !LLEN ET AL !LLEN ET AL +OT ETAL 6EIT AND ,EWIS ,EWIS (ARTAND'ARDNER#LARKETAL #LARK (IGGINS AND 2ICHARDSON .EUBERT AND #ASWELL .EUBERT ET AL 4AKASU ET AL 7OOLCOCK AND #OUSENS 7ITH 3CHOlELD #ASWELL ET AL #LARK ET AL -ARCHANT .EUBERTAND0ARKER0OWELLAND:IMMERMANN !MONGTHERESULTSOF THESEINVESTIGATIONSARETWOKEYlNDINGS&IRST INTEGRODIFFERENCEMODELSPRODUCE ARICHERSETOFINVASIONDYNAMICSTHANCANBEGENERATEDBYTHEREACTION DIFFUSION EQUATION INCLUDING FOREXAMPLE THEPOSSIBILITYOFACCELERATINGSPREAD+OT ETAL 3ECOND THESHAPEOFTHEDISPERSALKERNELESPECIALLYTHESHAPEOFTHE TAILSWHICHDETERMINETHEPROBABILITYOFLONG DISTANCEDISPERSALPLAYSACRUCIAL ROLEINDETERMININGTHERATEOFSPREAD 4HE EFFECTOF LONG DISTANCEDISPERSALONSPREADRATESWASHIGHLIGHTEDBY+OT ETAL WHOlTDISPERSALKERNELSTOADATASETDESCRIBINGTHEDISPLACEMENTOF OF GENETICALLY MARKED $ROSOPHILA $OBZHANSKY AND 7RIGHT AND PREDIC TIONS FOR THE CORRESPONDING ASYMPTOTIC SPREAD RATE WERE LINKED TO THE SHAPES OF


THE KERNELS 4HESE PREDICTED SPREAD RATES VARIED OVER AN ORDER OF MAGNITUDE DEPENDINGUPONTHEFATNESSOFTHETAILSOFTHERELATEDDISPERSALKERNELSSEE&IG

&IG &ITTED FUNCTIONS TO $ PSEUDOOBSCURA DISPERSAL DATA PROVIDE INGREDIENTS FOR AN INTEGRODIFFERENCE MODEL FOR INSECT SPREAD 4HE LEFT PANELS SHOW AVERAGE NUMBER OF INSECTS CAUGHT PER TRAP PER DAY IN $OBZHANSKY AND 7RIGHTS EXPERIMENTS )T WAS ASSUMEDTHATDISPERSALWASEQUALLYLIKELYINBOTHDIRECTIONS SOTHEDISPERSALKERNELSWERE KX GX GnX WHEREGISTHElTTEDFUNCTION4HERIGHTPANELSHOWSSIMULATIONSOF THE INTEGRODIFFERENCE EQUATIONS 3IMULATIONSASSUME"EVERTON (OLTPOPULATIONDYNAMICS FORFN WITHAGEOMETRICGROWTHRATEOF h4HECARRYINGCAPACITYWASSCALEDTOEQUAL ONE %ACH INTEGRODIFFERENCE WAS ITERATED FOR GENERATIONS "ASED ON +OT ET AL (EREISISASSUMEDTHATALLREPRODUCTIONANDDISPERSALOCCURSALONGAONE DIMENSIONALSTRIP OFSUITABLEHABITAT4HESPREADRATECANBECALCULATEDBYDIVIDINGTHETOTALDISTANCEMOVED BYTHEPOPULATIONFRONTBYTHEGENERATIONSTAKENTOMOVETHEDISTANCE

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4HE ISSUE OF LONG DISTANCE DISPERSAL HOWEVER GOES BEYOND THE CHOICE OF A PARAMETRICDISPERSALDISTRIBUTIONTODESCRIBEASETOFDATA)TCANALSOREmECTREAL BIOLOGICAL PROCESSES &OR EXAMPLE .EUBERT AND #ASWELL COMPUTED THE SPREADRATEFORTHEHERBACEOUSPLANT$IPSACUSSYLVESTRISBASEDONDATAFROMASEED TRAP EXPERIMENT 7ERNER 4EASEL SEEDS ARE KNOWN TO mOAT BUT DISPERSAL BY STREAMS OR RIVERS WAS OBVIOUSLY NOT MEASURED BY THE SEED TRAP EXPERIMENT .EUBERTAND#ASWELLCALCULATEDTHEASYMPTOTICSPREADRATERESULTINGFROMHYPO THETICALMIXTURESOFTHESEEDTRAPDATAANDDISPERSALBYWATERWITHALONGERMEAN DISTANCE4HEYFOUNDTHATLONG DISTANCEDISPERSALOFEVENONESEEDINAMILLIONWAS ENOUGHTOMAKETHESPREADRATEDEPENDENTONTHEWATERDISPERSALALONE3IMILARLY THE SEEDS OF THE TROPICAL PLANT #ALATHEA OVANDENSIS ARE DISPERSED BY AT LEAST FOUR SPECIESOFANT EACHWITHITSOWNTYPICALDISPERSALDISTANCE(ORVITZAND3CHEMSKE .EUBERTAND#ASWELLFOUNDTHATOVEROFTHEASYMPTOTICSPREADRATE WAS ACCOUNTED FOR BY THE ANT SPECIES WITH THE LONGEST DISPERSAL DISTANCE EVEN THOUGHITDISPERSEDONLYOFTHESEEDS #LASSICALMODELSFORPOPULATIONSPREADLIKE AND CONSIDERTHECASEWHERE THE SPATIAL DOMAIN IS ONE DIMENSIONAL AND LINEAR AND A SMALL BEACHHEAD OF INDIVIDUALSISINTRODUCEDLOCALLY4HISISONLYDIRECTLYAPPLICABLETOCASESSUCHAS POPULATIONSPREADALONGAROADSIDE COASTLINE,UBINAAND,EVIN ORARIVER 3PEIRSAND'URNEY0ACHEPSKYETAL ,ATER WE WILL INTRODUCE MODELS THAT DESCRIBE DISPERSAL IN TWO SPATIAL DIMEN SIONS 4HESE MODELS PRODUCE ASYMPTOTIC SPREAD RATE PREDICTIONS THAT CAN DIFFER IN DIFFERENT DIRECTIONS IF THE DISPERSAL KERNEL IS NOT RADIALLY SYMMETRIC )N BOTH ONEANDTWODIMENSIONS THEDISPERSALKERNELPLAYSACRUCIALROLEINDETERMINING THE ASYMPTOTIC RATE OF SPREAD 4HERE ARE MANY METHODS FOR ESTIMATING DISPERSAL KERNELS ANDFORESTIMATINGTHEPROPERTIESOFTHOSEKERNELSTHATENTERINTOTHEFOR MULAE FOR SPREAD RATE FROM DATA SEE FOR EXAMPLE 3ILVERMAN 7E WILL DISCUSSSOMEOFTHESEMETHODSLATERINTHECHAPTER&IRST WEDISCUSSSOMEOFTHE KINDSOFDISPERSALDATATHATARETYPICALLYCOLLECTEDANDORPUBLISHED

$)30%23!,+%2.%,3)./.%!.$47/$)-%.3)/.3 7E lRST CONSIDER FORMS IN WHICH DATA ARE COLLECTED 4HESE FALL LOOSELY INTO TWO KINDS DISPERSAL DATA AND DENSITY DATA $ISPERSAL DATA DESCRIBE THE LOCATION OF DISPERSERS RELATIVE TO THE PARENTS 4HESE DATA COME FROM FOLLOWING INDIVIDUAL DISPERSERS EG BANDING AND RECAPTURE OF BIRDS MARK AND RECAPTURE OF SEEDS USING COLORING ANDOR RADIO TAGGING AND IS RECORDED AS EITHER DISPLACEMENTS OR DISPLACEMENTDISTANCES)NCONTRAST DENSITYDATADESCRIBETHEDENSITYOFDISPERS ERS NUMBER PER UNIT AREA OBSERVED AT A GIVEN POINT TYPICALLY AS A FUNCTION OF DISTANCEFROMANATALSITEORSOURCEOFDISPERSERS4HESEDATACOMEFROMSEEDTRAPS PHEREMONETRAPSFORINSECTSANDSOFORTH )FWEASSUMETHATTHEPOPULATIONLIVESALONGAONE DIMENSIONALSTRIPOFSUITABLE HABITAT ALONGWHICHALLDISPERSALANDREPRODUCTIONOCCURS THEONE DIMENSIONAL


DISPERSALKERNELNUMBEROFDISPERSERSPERUNITLENGTH ISNEEDEDINEQUATION 4HISKERNELCANBElTTEDEITHERDIRECTLYFROMTHEONE DIMENSIONALDISPERSALDATAOR FROMTHEDENSITYDATANUMBEROFDISPERSERSPERUNITAREA MULTIPLIEDBYTHEWIDTH OFTHESTRIP4HECONSTRAINTTHATTHEKERNELMUSTBESCALEDTOINTEGRATETOEQUA TION MEANSTHATTHEKERNELKWILLACTUALLYBEINDEPENDENTOFTHEWIDTHOFTHE STRIPMULTIPLICATIONISONLYDONEFORMALLYTOENSURETHECORRECTUNITSFORK )F WE ASSUME THAT THE POPULATION LIVES IN A TWO DIMENSIONAL HABITAT IT IS lRST NECESSARY TO EXTEND THE DElNITION OF DISPERSAL TO TWO SPATIAL DIMENSIONS (EREDISPERSALISBETWEENPOINTSX;X X=4ANDY;Y Y=4INTWODIMENSIONAL SPACE 4HE THE TWO DIMENSIONAL DISPERSAL KERNEL +X Y DESCRIBES THE PROBABIL ITYOFAPROPAGULEWHICHSTARTSATYMOVINGTOTHERECTANGLEWITHCORNERSXAND XDXBY+X Y DXDX4HESPATIALREGIONOFINTERESTISGIVENBY1)NTHECASE OF INVASIONS THIS IS TYPICALLY ASSUMED TO BE ARBITRARILY LARGE )N THE ABSENCE OF IMMIGRATIONFROMOUTSIDE1 EVERYDISPERSERMUSTORIGINATEATSOMEOTHERPOINT IN1 SOTHAT G +X Y DY H1 )FTHEKERNEL+X Y DEPENDSONLYUPONTHERELATIVELOCATIONSOFTHESTARTANDlNISH POINTSWEWRITE+X Y +XnY 4O UNDERSTAND THE DIFFERENCE BETWEEN ONE AND TWO DIMENSIONAL DISPERSAL KERNELS WE CONSIDER THE CASE WHERE THE DISPERSAL IS ISOTROPIC IDENTICAL IN ALL DIRECTIONS )NTHISCASETHETWODIMENSIONALDISPERSALKERNEL+CANBEWRITTENAS AFUNCTIONOFTHEDISPERSALRADIUSR\XnY\)NALINEARONE DIMENSIONALENVIRON MENT THESCALEDDISTRIBUTIONOFDENSITIESDISPERSERSPERUNITLENGTH ANDADISTRI BUTION OF DISTANCES THAT THE DISPERSERS TRAVEL FROM THE PARENT ARE THE SAME AND AREGIVENBYTHEKERNELK)NATWO DIMENSIONALENVIRONMENT THESCALEDDISTRIBU TIONOFDENSITIESDISPERSERSPERUNITAREA GIVENBY+R ANDTHEDISTRIBUTIONOF DISTANCESTHATDISPERSERSTRAVELFROMFROMTHEPARENTDISPERSERSPERUNITLENGTH GIVENBY+É /R+R ARENOTTHESAME BECAUSETHEREISMOREAREAAVAILABLEAT DISTANCESFURTHERFROMTHEPARENT

0/05,!4)/.302%!$).!/.% $)-%.3)/.!,,).%!2%.6)2/.-%.4 4HE$OBZHANSKYAND7RIGHTINSECTDATAWERECOLLECTEDFROMTRAPSPLACEDALONG LINEARTRANSECTSRADIATINGFROMAPOINTSOURCE4HUSTHETRAPSGIVEARELATIVEMEA SUREOFTHEDENSITYOFDISPERSERSNUMBERPERUNITAREA ASAFUNCTIONOFDISTANCE

4HROUGHOUTTHISCHAPTER WEWILLUSEBOLDFACE2OMANCHARACTERSSUCHASUANDVTOREPRE SENTVECTORS(ERE \U\3U U DENOTESTHELENGTHOFTHEVECTORU ANDUqVUV UV\U\\V\COSeDENOTESTHE@DOTPRODUCTORPROJECTIONOFONEVECTORONTOTHEOTHER WHEREeISTHEANGLEBETWEENUANDV

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FROM THE RELEASE SITE 4HE MOST REASONABLE ASSUMPTION IS THAT THE TRANSECT DATA DESCRIBETHERADIALDROP OFFINSETTLEDINSECTDENSITYINATWO DIMENSIONALHABITAT NEXT SECTION (OWEVER FOR THE SAKE OF ILLUSTRATION IN THIS PAPER WE lRST CON SIDERTHEASSUMPTIONTHATTHEINSECTSANDTRANSECTSAREFOUNDALONGAONE DIMEN SIONALSTRIPOFSUITABLEHABITAT ALONGWHICHALLDISPERSALANDREPRODUCTIONOCCURS NEXT SECTION 4HIS IS A STANDARD ASSUMPTION IN POPULATION SPREAD MODELS AND ISTHEASSUMPTIONMADEINTHEORIGINALANALYSISOFTHEINSECTSPREADRATESIN+OT ET AL !S WE WILL SHOW THE DIFFERENT ASSUMPTIONS ABOUT THE HABITAT AND DISPERSALGIVERISETOQUITEDIFFERENTSPREADRATEESTIMATES 4HEORY

!STHEINTRODUCEDBEACHHEADOFINDIVIDUALSGROWSANDDISPERSESWEEXPECTGROWTH OF THE RANGE BOUNDARY WITHTIME&IGURE SHOWS A TYPICAL PROGRESSION!PLOTOF RANGEBOUNDARYVERSUSTIMEGIVESLINESWHOSESLOPEEVENTUALLYBECOMECONSTANT 4HEEVENTUALSLOPEOFTHESELINESTHEASYMPTOTICRATEOFSPREADOFTHEINVASION HENCEFORTH REFERRED TO SIMPLY AS SPREAD RATE CAN BE PREDICTED USING MATH EMATICALTHEORYWHICHRELATESTHESLOPETOMODELPARAMETERS)NTHISSECTIONWE OUTLINETHETHEORY )T IS lRST NECESSARY TO MAKE SOME ASSUMPTIONS ABOUT THE GROWTH DYNAMICS 4HE SIMPLEST POPULATION DYNAMICS EXHIBIT NO OVERCOMPENSATION OR !LLEE EFFECT 4HISASSUMPTIONTRANSLATESINTOAGROWTHFUNCTIONdIN THATISMONOTONICALLY INCREASINGWITHMAXIMUMPERCAPITAGROWTHRATESATLOWESTPOPULATIONLEVELS 4HE ASSUMPTION THAT THE MAXIMUM PER CAPITA GROWTH RATE h OCCURS AT THE LOWEST POSSIBLE DENSITY MEANS h G * GN FOR N ! GROWING POPULATION REQUIRESh!SDESCRIBEDABOVE LOCALINTRODUCTIONOFINDIVIDUALS COUPLEDWITH AGROWTHRATEhANDADISPERSALKERNELKZ ZXnY IN MEANSTHEPOPULA TIONSPREADSASITGROWSANDDISPERSES&IG 7EINBERGER SHOWEDTHAT UNDER THE ABOVE ASSUMPTIONS ON GROWTH DYNAMICS THE POPULATION SPREADS TO THE RIGHT AT A RATE WHICH APPROACHES SPEED C AS THE TIME SINCE INTRODUCTION INCREASES WHERE CMIN LN;h-S = S S AND-S ISTHEMOMENTGENERATINGFUNCTIONFORTHEDISPERSALKERNELKZ G' -S KZ EXPSZ DZ Hn'

4HE PARAMETER S CAN BE UNDERSTOOD AS A MEASURE OF THE STEEPNESS OF THE WAVE N | EXPnSZ AT THE LEADING EDGE OF THE RIGHTWARD SPREADING POPULATION 4O lND THESPEEDOFTHELEFTWARDSPREADINGFRONT ONESHOULDUSETHEMOMENTGENERATING FUNCTIONFORKnZ INEQUATION


4HUSTHEPOPULATIONSPREADRATEDEPENDSONLYUPONTWOFEATURESTHEGEOMETRIC GROWTHRATEOFTHEPOPULATIONh ANDTHESHAPEOFTHEDISPERSALKERNELK4HESPEED FOR&ISHERSEQUATION C3l$ CANBEREGAINEDFROMEQUATIONS BYTHE CHOICEOFK.$ ANDlLOGh $ETAILSAREGIVENIN+OTETAL )NPRACTICE CALCULATIONOFTHESPREADRATEMUSTBEDONENUMERICALLY EITHERBY USING A STANDARD MINIMIZATION ROUTINE OR BY SOLVING THE DOUBLE ROOT CONDITION EQUATIONS EXPSC h-S ANDCEXPSC h-S FORTHEWAVESPEEDCANDWAVE STEEPNESSS&ORASIMPLEEXAMPLE WRITTENIN-APLECODESEETHE!PPENDIX (ERE IT IS ASSUMED THAT THE KERNEL K IS EXPONENTIALLY BOUNDED SO THAT THE MOMENT GENERATING FUNCTION CAN BE CALCULATED 7HEN THE KERNEL K HAS TAILS THAT ARE FATTER THAN EXPONENTIAL THERE IS NO ASYMPTOTIC RATE OF SPREAD THE SPREAD RATE CONTINUES TO INCREASE WITH INCREASING TIME +OT ET AL &IG THIRDPANELFROMTHETOP )NTHISSITUATION ANALTERNATIVEDElNITIONOFSPREADRATE BASED ON THE CHANGE IN LOCATION OF THE FURTHEST FORWARD INDIVIDUAL IN THE POPU LATION FROM GENERATION TO GENERATION FURTHEST FORWARD VELOCITY IS APPROPRIATE #LARK ,EWIS AND(ORVATH SEE$ISCUSSION 7HENTHEGROWTHRATEhISKNOWN BUTTHEDISPERSALKERNELISUNKNOWN ESTI MATESFORPOPULATIONSPREADRATESUSINGEQUATION CANVARYWIDELY DEPENDING UPONTHEPARAMETRICFORMOFTHEKERNELCHOSEN ASWITHTHESIMULATIONSSHOWNIN &IG 7HENAPPROPRIATEDATAAREAVAILABLE THISPROBLEMCANBEADDRESSEDBYMEANS OF A NONPARAMETRIC ESTIMATOR FOR THE MOMENT GENERATING FUNCTION WHICH MAKES NO ASSUMPTION ABOUT THE FORM OF THE UNDERLYING KERNEL )N THIS CASE THE MOMENT GENERATING FUNCTION IS ESTIMATED FROM RAW ONE DIMENSIONAL LINEAR DIS PERSALDISPLACEMENTDATA ZxZ. . -%S -EXPSZI . I

4HESUPERSCRIPTISUSEDTOINDICATEANEMPIRICALESTIMATEOFTHEMOMENTGENERAT INGFUNCTION#LARK (ORVATH AND,EWIS (ERETHEDISPERSALMEASUREMENTS ARISEFROMTRACKINGASERIESOFINDIVIDUALS!SADISPLACEMENT XIGIVESTHEDISTANCE ANDDIRECTIONTHATTHE I THINDIVIDUALMOVES"YCONVENTION LEFTWARDMOVEMENTS AREASSIGNEDNEGATIVEVALUES)TISASSUMEDTHATTHETRACKINGEFFORTANDTRACKING EFlCIENCYREMAINCONSTANTOVERTHEENTIRELINEARONE DIMENSIONALDISPERSALREGION &UJIWARAETAL CONSIDERTHEEFFECTSOFCHANGESINSAMPLINGEFFORTORDETEC TIONPROBABILITY )NTHECASEWHEREZxZ.ARENONNEGATIVE DISTANCES RATHERTHAN DISPLACEMENTS THEASSUMPTIONOFASYMMETRICDISPERSALKERNELWHEREBYINDIVIDU ALSAREASLIKELYTOMOVETOTHELEFTASTOTHERIGHT LEADSTO . -%S -COSHSZI . I


3UBSTITUTION OF -%S INSTEAD OF -S IN LEADS TO AN EMPIRICALLY ESTIMATED WAVE SPEED C% 4HIS EMPIRICALLY ESTIMATED WAVE SPEED HAS MANY NICE PROPERTIES #LARKETAL &OREXAMPLEITISUNBIASEDC% CONVERGESTOTOTHETRUEPOPU LATION SPREAD RATE C AS . A ' 4HIS IS NOT GENERALLY THE CASE WHEN PARAMETRIC KERNELSARElTTEDTOTHEDISPERSALDATA)NTHATCASE THETRUEPOPULATIONDISPERSAL KERNELISNOTKNOWN ANDDIFFERENTlTTEDKERNELSCANGIVEVERYDIFFERENTWAVESPEED PREDICTIONS 7HENTHENUMBEROFDATAPOINTS.ISlNITE EACHEMPIRICALLYESTIMATEDWAVE SPEED WILL BE DIFFERENT AS IT WILL DEPEND ON THE PRECISE DATA SET USED (OWEVER THE DISTRIBUTION OF THE EMPIRICAL WAVE SPEED C% ABOUT THE TRUE WAVE SPEED C IS APPROXIMATELY 'AUSSIAN AND THE VARIANCE OF THE 'AUSSIAN APPROACHES ZERO AS . APPROACHES INlNITY #LARK ET AL !LTHOUGH THERE IS NO CLOSED FORM EXPRESSION FOR THE VARIANCE IT CAN BE ESTIMATED USING BOOTSTRAPPING METHODS #LARKETAL 7HENTHEDATACOLLECTIONORRECORDINGMETHODSDONOTPROVIDE DISPERSAL DATA BUT HISTOGRAM DENSITY DATA ARE AVAILABLE IT MAY BE NECESSARY TOUSESUCHAHISTOGRAMASANESTIMATORFORTHEKERNEL ¨ 4 K(Z © I ª

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AND SUBSTITUTION OF -(S INSTEAD OF -S IN LEADS TO A @HISTOGRAM ESTIMATOR FOR THE WAVE SPEED C( $UE TO THE ARBITRARY NATURE OF LOCATION OF THE HISTOGRAM BINS ITCANBESHOWNTHATTHEHISTOGRAMESTIMATORDOESNOTPROVIDEANUNBIASED ESTIMATORFORTHETRUESPEEDC(OWEVER INTHEABSENCEOFOTHERDATA THISHISTO GRAMESTIMATORISAUSEFULALTERNATIVETOTHEEMPIRICALESTIMATORGIVENABOVEAND INPRACTICE GIVESVERYSIMILARRESULTS!STHESIZESOFTHEBINSjInjIn APPROACHES ZEROTHETWOESTIMATORSAREIDENTICAL)NTHECASEWHERETHEHISTOGRAMDATAISFOR DISTANCESASOPPOSEDTODISPLACEMENTS THEASSUMPTIONOFASYMMETRICREDISTRIBU TIONKERNELCAUSES TOBEMODIlEDTO , -(S - 4ISINHSjI nSINHSjIn S I


7E NOW APPLY THE HISTOGRAM SPREAD RATE ESTIMATE AND TO THE $OBZHANSKYAND7RIGHT DATA UNDERTHEASSUMPTIONTHATTHEINSECTSAND TRANSECTSAREFOUNDALONGAONE DIMENSIONALSTRIPOFSUITABLEHABITAT ALONGWHICH ALL DISPERSAL AND REPRODUCTION OCCURS SEE DISCUSSION IN -ODELING "ACKGROUND 4HISESTIMATE WHICHUSESTHEDATASHOWNIN&IG GIVESASPREADRATEOF KM PER YEAR 4HIS IS HIGHER THAN THE SPREAD RATE PREDICTION MADE BY USING THE EXPONENTIAL AND 'AUSSIAN KERNELS IN &IG BUT IS SUBSTANTIALLY LOWER THAN THE PREDICTION MADE BY THE FAT TAILED KERNEL !S WITH THE EMPIRICAL ESTIMATOR BOOT STRAPPINGGIVESTHEDISTRIBUTIONOFWAVESPEEDS FROMWHICHCONlDENCEINTERVALS CANBECALCULATED&IG

&IG "OOTSTRAPPING GIVES A RANGE OF POSSIBLE VALUES FOR THE HISTOGRAM WAVE SPEED 4HE HISTOGRAM WAVE SPEED ESTIMATOR EQUATIONS AND IS APPLIED TO A HISTOGRAM BASED ON THE TOTAL NUMBER OF INSECTS CAUGHT PER TRAP STARTING AT DISTANCE ZERO lNISHING ATDISTANCEKM WITHINTER TRAPSPACINGOFKMWERE AND"OOTSTRAPPINGWASDONEBYRE SAMPLING FROM THE DISPERSAL DISTANCES WITH REPLACEMENT TO PRODUCE NEW DATA SETS 4HE WAVE SPEED WAS CALCULATED FOR EACH OF THESE NEW DATA SETS AND THE DISTRIBUTION OF SPEEDS IS SHOWN HERE .INETY PER CENT OF THE SPEEDS FELL IN THE RANGE KMYEAR KMYEAR #OMPARETHEESTIMATEHEREWITHTHESPREADRATESSIMULATEDIN&IG


0/05,!4)/.302%!$).47/$)-%.3)/.3 )NVASION IN TWO SPATIAL DIMENSIONS INVOLVES LOCAL INTRODUCTION AT A BEACHHEAD FOLLOWEDBYGROWTHANDSPREADINSPACE(ERETHEPROCESSCANBEDIVIDEDINTOTHREE STAGESTHEINITIALESTABLISHMENT THEEARLYRADIALEXPANSIONUNTILWELLESTABLISHED INSPACE ANDTHELATERSPREADOFTHEESTABLISHEDPOPULATION&IG !LTHOUGHEACH OFTHESETHREESTAGESISOFINTERESTBIOLOGICALLY THEFOCUSOFTHISCHAPTERISONANA LYZINGTHELATERSPREADOFANESTABLISHEDPOPULATION!TTHISSTAGEWECANAPPROXI MATETHEINVADINGFRONTBYAPLANARFRONT MOVINGWITHAWELL DElNEDSPEED 4HECALCULATIONOFSPREADINTWODIMENSIONSREQUIRESAUNITVECTORU;UU=4 DESCRIBINGTHEDIRECTION PERPENDICULARTOTHEWAVEFRONT INWHICHTHESPREADIS BEINGCONSIDERED&IG 4HEASYMPTOTICSPREADRATEINTHEDIRECTIONUISGIVEN BY CUMIN LN;h-US = S S

&IG !SKETCHOFTHETHREESTAGESOFPOPULATIONSPREADINAHOMOGENEOUSENVIRONMENT 3HADEDAREASINDICATEINVADEDHABITAT!STIMEPROGRESSES THEINITIALhBEACHHEADvGROWS ANDBECOMESMOREELLIPTICALLYSHAPED&ORLONGTIMES THEINVASIONFRONTISAPPROXIMATELY PLANARINALLDIRECTIONS4HESPEEDINTHEDIRECTIONU PERPENDICULARTOTHEFRONT ISFOUND USINGTHEMARGINALDISPERSALKERNELINTHATDIRECTIONKUU CFEQUATION 4HEMARGINAL KERNEL IN TURN IS FOUND BY INTEGRATING THE ORIGINAL DIMENSIONAL DISTRIBUTION OVER THEDIRECTIONV


WHERE-US ISTHE @DIRECTIONALMOMENTGENERATINGFUNCTION THEMOMENTGENER ATING FUNCTION OF + EVALUATED IN THE DIRECTION OF U !PPENDIX 4WO APPROACHES FOR CALCULATION OF THE DIRECTIONAL MOMENT GENERATING FUNCTION ARE GIVEN IN THE THE !PPENDIX )N GENERAL THE PLANAR SPREAD RATE CU WILL DEPEND ON THE DIRECTION U (OWEVER WHEN THE DISPERSAL KERNEL IS DIRECTIONALLY ISOTROPIC IS IDENTICAL IN ALL DIRECTIONS THE PLANAR SPREAD RATE WILL ALSO BE ISOTROPIC 7E NOW CONSIDER THECASEWITHDIRECTIONALISOTROPY SOTHAT+Z ZXnY CANBEREWRITTENAS+R R3Z Z .OTETHAT+R ISATWO DIMENSIONALDENSITYFUNCTIONWHICHDENOTES THE RELATIVE NUMBER OF SEEDS PER UNIT AREA FALLING AT DISTANCE R FROM THE SOURCE 4HEAREAUNDER+R ISEQUALTOONE G/ G' +R RDRDe Hn' Hn' !RELATEDKERNELDENOTESTHENUMBEROFSEEDSPERUNITLENGTHFALLINGADISTANCER FROMTHESOURCE4HISRELATEDKERNELISFOUNDBYMULTIPLYING+R BYTHEPERIMETER OF A CIRCLE OF RADIUS R TO ACCOUNT FOR THE FACT THAT AT LARGER RADII THERE IS MORE AVAILABLEAREAFORSEEDS TOFALL +ÉR /R+R )F THEDATAHAVEBEEN COLLECTED IN THISFORM ASIMPLERESCALINGBY/RWILLTRANSFORM+É TO+ 7ENOWCONSIDERHOWTOCALCULATETHEPLANARSPREADRATESEEEQUATION WHEN THE KERNEL IS RADIALLY SYMMETRIC 7E ILLUSTRATE THE TWO OPTIONS THAT ARE GIVEN IN THE !PPENDIX FOR CALCULATING THE DIRECTIONAL MOMENT GENERATING FUNC TIONFORTHISCASE(EREWECONSIDERAWAVESPREADINGINTHEX DIRECTIONSOTHAT U ; =4 %VALUATE THE MARGINAL DISTRIBUTION OF + BY INTEGRATING OVER THE Z DIRECTION TO YIELD A ONE DIMENSIONAL DISPERSAL KERNEL THAT DESCRIBES DISPERSAL IN THE Z DIRECTION G' +UZ +3Z Z DZ Hn'

ANDTHENCALCULATETHEDIRECTIONALMOMENTGENERATINGFUNCTION-UOFTHEKER NELKUZ ANDTHUSTHESPEEDCU SEEEQUATIONS AND FORDETAILS 4HIS METHOD EFFECTIVELY REDUCES THE TWO DIMENSIONAL SPREAD PROBLEM TO ONE SPATIAL DIMENSION BY lRST TAKING THE MARGINAL DISTRIBUTION OF THE DISPERSAL KERNEL ANDTHENPROCEEDINGASWITHTHEONEDIMENSIONALCASE4HISAPPROACH ISCONCEPTUALLYSTRAIGHTFORWARD BUTMANYMARGINALDISTRIBUTIONSCANNOTBE CALCULATEDANALYTICALLY EVENFORSIMPLEKERNELS %VALUATE THE MOMENT GENERATING FUNCTION IN THE Z DIRECTION SEE EQUATION DIRECTLYAS G' G' -US +R EXPSZ DZDZ Hn'Hn'


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ANDTHENUSETHISTOCALCULATEOFTHESPEEDCU (ERE) ISTHEMODIlED"ESSEL FUNCTIONOFTHElRSTKINDANDZEROTHORDER!BRAMOWIZAND3TEGUN 7HEN THERE ARE RAW ONE DIMENSIONAL RADIAL DISPERSAL DISTANCE DATA RxR. THENTHEEMPIRICALMOMENTGENERATINGFORTHEPLANARWAVESPEEDCALCULATION BECOMES . -U%S - )SRI . I ANDSUBSTITUTIONINTO GIVESTHEEMPIRICALESTIMATORFORTHEPLANARWAVESPEED (ERETHERIMEASUREMENTSARISEFROMTRACKINGASERIESOFINDIVIDUALSASTHEYDIS PERSE)TISASSUMEDTHATTHETRACKINGEFFORTPERUNITAREAANDTRACKINGEFlCIENCY PERUNITAREAREMAINSCONSTANTOVERTHEENTIREDISPERSALAREA'IVENAHISTOGRAM OFRADIALDENSITYDATA ¨ 4 IF l )RlI +(R © I In OTHERWISE ª WHERE ) I ) , THE CONSTRAINT THAT THE AREA UNDER THE HISTOGRAM INTEGRATES TO ONE MEANS

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)F THE HISTOGRAM IS MEASURED IN TERMS OF THE RELATIVE NUMBER OF DISPERSERS THAT MOVE A DISTANCE R RATHER THAN THE RELATIVE DENSITY IT IS NECESSARY TO RESCALE THE KERNELBY/R n ASABOVE 4HE DIRECTIONAL MOMENT GENERATING FUNCTION FOR THE HISTOGRAM COMES FROM SUBSTITUTING INTO TOOBTAIN / , -U(S - 4IlI)SlI nlIn)SlIn S I


COMPARE WITH AND SUBSTITUTION INTO GIVES THE PLANAR WAVE SPEED (ERE)ISTHEMODIlED"ESSELFUNCTIONOFTHElRSTKINDANDlRSTORDER!BRAMOWIZ AND3TEGUN &ORTHESAKEOFILLUSTRATION WEEARLIERCONSIDEREDTHECASEWHERETHE$OBZHANSKY AND 7RIGHT DATA DESCRIBED INSECT MOVEMENT ALONG LINEAR TRANSECTS OF AVAILABLE HABITAT !CCORDINGLY THE HISTOGRAM ESTIMATOR FOR THE SPREAD RATE FOR THE SITUA TION SHOWN IN &IG WAS CALCULATED USING EQUATIONS AND AS KM PERYEAR 4O COMPARE THE DIFFERENCE BETWEEN THE RESULTS OF THIS SECTION AND OUR EARLIER RESULTS WEREVISITTHE$OBZHANSKYAND7RIGHTDATA UNDERTHEMOREREASONABLE ASSUMPTION THAT THE TRANSECT DATA DESCRIBE THE RADIAL DROP OFF IN SETTLED INSECT DENSITYINATWO DIMENSIONALHABITAT)NTHISCASETHEHISTOGRAMESTIMATORFORTHE PLANAR SPREAD RATE IS CALCULATED FROM EQUATIONS AND AS KM PER YEAR HIGHERTHANTHEPREVIOUSESTIMATE 2EPEATINGTHECOMPARISONOFSPREADRATESFORDIFFERENThSSHOWSTHATTHESPREAD RATE ASSUMING RADIAL DISPERSAL AND GROWTH IN THE TWO DIMENSIONAL HABITAT ISSIGNIlCANTLYHIGHERTHANTHESPREADRATE ASSUMINGGROWTHANDDISPERSALINA LINEARONE DIMENSIONALHABITAT SEE4ABLE 4HISDIFFERENCEISMOSTPRONOUNCED FORALOWGROWTHRATESh4HISORDERINGOFSPREADRATES$SPEEDLARGERTHAN$ SPEED 4ABLE APPEARS ONLY FOR DENSITY DATA NOT DISPERSAL DATA )N FACT IF THE ORIGINAL DATA DESCRIBE DISPERSAL THEN IT CAN BE SHOWN THAT THE ORDERING WILL BE REVERSED WITHTHE$SPEEDBASEDONGROWTHANDDISPERSALINALINEARONE DIMEN SIONALHABITAT EG EQUATIONAND LARGERTHAN$SPEEDBASEDONRADIALDISPER SALANGROWTHINATWO DIMENSIONALHABITAT EG EQUATIONAND

4ABLE 3PREADRATESFORVARYINGGROWTHRATESh$ISPERSALDATAAREASGIVENBYTHELEFT PANELSIN&IG)NCOLUMNLABELED$ITISASSUMEDTHATTHEGROWTHANDDISPERSALOCCURIN A$LINEARHABITAT3PREADRATESARECALCULATEDUSINGEQUATIONS AND )NCOLUMN LABELED$ITISASSUMEDTHATTHEDISPERSALISRADIAL ANDTHATGROWTHANDDISPERSALOCCUR IN A $ HABITAT (ERE THE PLANAR SPREAD RATE IS CALCULATED FROM EQUATIONS AND 4HELASTCOLUMNSHOWSTHERATIOOFTHESECONDTOTHElRSTCOLUMNSENTRIES4HEDIFFERENCE BETWEENTHESPREADRATESISMOSTPRONOUNCEDFORLOWGROWTHRATES h

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-/.4%#!2,/-%4(/$3 4HE SIMPLEST ESTIMATOR OF THE MOMENT GENERATING FUNCTION IS THE EMPIRICAL ESTIMATOR CALCULATED FROM ONE DIMENSIONAL DISPLACEMENT DATA EQUATION )TISNOTONLYSIMPLETOIMPLEMENTNUMERICALLY BUTINMANYCASESISAPPEALINGLY NONPARAMETRIC)TISSOMETIMESUSEFULTOGENERATEAPPROPRIATE $DISPLACEMENT DATA FROM SOME OTHER FORM USING -ONTE #ARLO METHODS 4HE RESULTING DIS PLACEMENTS CAN THEN BE USED AS INPUT TO THE EMPIRICAL ESTIMATOR &OR EXAMPLE #ASWELL ET AL ANALYZED THE INVASION RATES OF SEVERAL SPECIES OF %UROPEAN BIRDS USINGDISPERSALDATACOMPILEDBYVANDEN"OSCHETAL 4HEDISPER SAL DATA WERE OBTAINED IN THE FORM OF HISTOGRAMS OF DISPLACEMENT DISTANCES NOT DENSITIES4HUS THEY WERE INTERPRETED ASGIVINGASETOFDISTANCES INTWO DIMENSIONALSPACE MOVEDBYASETOF MARKEDINDIVIDUALS /BTAININGTHEAPPROPRIATE ONE DIMENSIONAL DISPERSAL KERNEL REQUIRES THE MARGINAL DISTRIBUTION OF THE TWO DIMENSIONAL DISTRIBUTION OF DISPLACEMENTS 4HIS WAS OBTAINED BY GENERATING A LARGE NUMBER OF RANDOM DISPLACEMENT DISTANCES FROM THE HISTOGRAM ASSUMING A UNIFORM DISTRIBUTION OF DISPLACEMENT DISTANCE WITHIN EACH HISTOGRAM BIN !SSUMING TWO DIMENSIONAL ISOTROPY EACH OF THESE DISTANCES WAS ASSIGNED A DIRECTIONUNIFORMLYDISTRIBUTEDBETWEENAND/4HISPRODUCEDASETOFARTIlCIAL DIMENSIONALDISPLACEMENTDATA THEDISTANCECOMPONENTOFWHICHMATCHESTHE REPORTEDHISTOGRAM4HEMARGINALIZEDDISTRIBUTIONWASEASILYGENERATEDBYTAKING THE Z COMPONENT OF EACH OF THE POINTS 4HE RESULTING SET OF DISTANCES WAS THEN INPUT TO THE EMPIRICAL MOMENT GENERATING FUNCTION TO PRODUCE AN ESTIMATE OF WAVESPEED 4HIS -ONTE #ARLO METHOD IS APPROPRIATE BECAUSE WE KNOW MATHEMATICALLY THAT PROVIDING THE DISPERSAL KERNEL IS EXPONENTIALLY BOUNDED THE EMPIRICAL ESTIMATORFORTHEWAVESPEEDISUNBIASEDIE APPROACHESTHETRUEWAVESPEEDAS .A' $ETAILSONCONVERGENCECANBEFOUNDIN#LARKETAL

$)3#533)/. 4HE FOCUS OF THIS PAPER IS METHODS TO RELIABLY CONNECT POPULATION SPREAD RATE THEORYTOBIOLOGICALDATA4HEREARETWOFEATURESTHATWEFOCUSONI SENSITIVITYOF SPREADRATEESTIMATESTOMODELASSUMPTIONSABOUTLONG DISTANCEDISPERSAL ANDII MODELlTTINGISSUESTHATARISEFROMlTTINGTWO DIMENSIONALDISPERSALDATATOONE DIMENSIONAL MODELS 4HE EMPIRICAL AND HISTOGRAM ESTIMATORS PROVIDE A METHOD TOBYPASSASSUMPTIONSABOUTLONGDISTANCEDISPERSAL4HESEAREREALLY@WHATYOU SEEISWHATYOUGETESTIMATORS)NDEED FORMALLYSUBSTITUTINGTHEOBSERVEDSUMOF POINTDISPERSALJUMPSKZ -.I bZnZI INTOEQUATION LEADSTOTHEEMPIRI CAL MOMENT GENERATING FUNCTION 7HEREAS THE ABOVE SUM OF DELTA FUNCTIONS PROVIDESAPOORESTIMATORFORTHEKERNEL THEPROCESSLEADSTOTHEEMPIRICALMOMENT GENERATINGFUNCTIONANDAGOODESTIMATEFORTHESPREADRATE WHICHISTHEQUANTITY OFINTEREST4HEHISTOGRAMESTIMATORBEHAVESINAMANNERWHICHISSIMILARTOTHE


EMPIRICALESTIMATOR ALTHOUGHTHELOCATIONOFBINSCANPRODUCESMALLBIASESINTHE SPREADRATEESTIMATE 7ERECOMMENDTHATTHEEMPIRICALANDHISTOGRAMSPREADRATEESTIMATORSSHOULD BEABASICTOOLFORANYMODELINGEXERCISEWHICHINVOLVESSPREADRATESWHERELONG DISTANCEDISPERSALPLAYSAROLE&ITTEDPARAMETRICDISPERSALKERNELSMAYBEPREFER ABLEWHENTHEREISREASONTOBELIEVETHATEXTRAPOLATIONOFTHEDISPERSALFUNCTION BEYOND THE FURTHEST OBSERVED DISPERSAL DISTANCE CAN BE JUSTIlED (OWEVER EVEN INTHISCASE ITISUSEFULTOCOMPARESPREADRATERESULTSFROMTHEPARAMETRIClTTED KERNELWITHTHEEMPIRICALORHISTOGRAMSPREADRATES4HEDIFFERENCEBETWEENTHE SPREAD RATES WILL HIGHLIGHT THE IMPLICATIONS OF ASSUMPTIONS ABOUT LONG DISTANCE DISPERSALDISTANCESTHATGOINTOTHEPARAMETRICKERNEL 4HENEWMODELlTTINGISSUEWEFOCUSONISTHECORRECTMETHODTOCALCULATEPLA NARPOPULATIONSPREADFROMRADIALLYSYMMETRICDISPERSALDATA.AIVELYlTTINGTHE LINEAR ONE DIMENSIONAL DISPERSAL KERNEL TO THE RADIALLY SYMMETRIC DISPERSAL DATA WILLGIVETHEWRONGSPREADRATEWHENTHEONE DIMENSIONALSPREADMODELISUSED BIASEDDOWNWARDFORDENSITYDATA ANDUPWARDFORDISPERSALDATA )N A LINEAR ONE DIMENSIONAL ENVIRONMENT THE SCALED DISTRIBUTION OF DENSITIES DISPERSERS PER UNIT LENGTH AND A DISTRIBUTION OF DISTANCES THAT THE DISPERSERS TRAVELFROMTHEPARENTARETHESAMEANDAREGIVENBYTHEKERNELK)NATWO DIMEN SIONALENVIRONMENT THESCALEDDISTRIBUTIONOFDENSITIESDISPERSERSPERUNITAREA GIVEN BY + AND THE DISTRIBUTION OF DISTANCES THAT DISPERSERS TRAVEL FROM FROM THE PARENT GIVEN BY +É /R+R ARE NOT THE SAME BECAUSE THERE IS MORE AREA AVAILABLEATDISTANCESFURTHERFROMTHEPARENT4HECORRECTMETHODFORCALCULATING THE SPREAD IN THE TWO DIMENSIONAL ENVIRONMENT INVOLVES A DIRECTIONAL MOMENT GENERATINGFUNCTIONOFTHETWO DIMENSIONALDISPERSALKERNEL4HISISFOUNDEITHER BY EVALUATING THE MOMENT GENERATING FUNCTION OF THE MARGINAL DISTRIBUTION OF THEDISPERSALKERNEL+R ORBYUSING+ÉR INAMODIlEDMOMENTGENERATINGFUNC TIONCALCULATION 4O SEE THE DIFFERENCE BETWEEN THE LINEAR ONE DIMENSIONAL HISTOGRAM DENSITY KERNEL AND THE MARGINAL DISTRIBUTION OF ITS RADIALLY SYMMETRIC ANALOG WE CAN COMPUTE THE MARGINAL DISTRIBUTION OF THE RADIALLY SYMMETRIC HISTOGRAM DENSITY KERNEL DIRECTLY ¨ , K(U Z ©-I dIndI 3lI nZ ª

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4HETWOKERNELSK(Z ANDK(UZ ARESHOWNIN&IG!SCANBESEENFROM THE RESULTS IN 4ABLE THE INCREASE IN NUMBER OF LONG DISTANCE DISPERSERS IN THE MARGINALDISTRIBUTIONSPEEDSUPTHESPREADRATESIGNIlCANTLY 4HECORRECTFORMULAEFORCALCULATINGSPREADRATESAREGIVENIN4ABLESAND 4OTHEBESTOFOURKNOWLEDGE THESEFORMULAEHAVENOTBEENWIDELYDEVELOPEDOR DISCUSSEDELSEWHEREINTHELITERATURE)TISOURHOPETHATTHESETABLES ALONGWITH THEDISCUSSIONINTHECHAPTERWILLFORMAUSERSGUIDETOCALCULATINGSPREADRATES


&IG (ISTOGRAM DISPERSAL KERNEL EQUATION FOR$OBZHANSKY AND 7RIGHTS $ROSOPHILA DISPERSAL DATA UNDER THE ASSUMPTION THAT DISPERSAL OCCURS IN A LINEAR ONE DIMENSIONAL HABITAT GREY -ARGINAL DISTRIBUTION EQUATION OF HISTOGRAM DISPERSAL KERNEL EQUATION UNDER THE ASSUMPTION THAT DISPERSAL OCCURS IN A TWO DIMENSIONAL HABITATANDISRADIALLYSYMMETRIC


FOR DISCRETE TIME MODELS AND IN TURN WILL LEAD TO A CLOSER CONNECTION BETWEEN ECOLOGICALTHEORYANDDATA 7HENTHEDISPERSALDATACOMEFROMA@FAT TAILEDKERNELKERNELWITHNOMOMENT GENERATING FUNCTION THEORY PREDICTS A CONSTANTLY ACCELERATING WAVE WITH AN ASYMPTOTICALLY INlNITE SPEED (OWEVER THE SPREAD RATES BASED ON THE EMPIRICAL MOMENT GENERATING FUNCTION EG EQUATION OR THE HISTOGRAM MOMENT GEN ERATING FUNCTION EG EQUATION ARE lNITE 4HIS IS BECAUSE THE THESE SPREAD RATES ARE CALCULATED FROM A lNITE NUMBER OF DISPERSAL OBSERVATIONS OR ON DENSI TIESMEASUREDOVERAlNITEREGION(EREADDITIONALSAMPLINGEFFORTMAYlNDRARE LONG DISTANCEDISPERSERSORMAYMEASURENONZERODENSITIESOFDISPERSERSFARFROM THEIRNATALSOURCE ANDTHUSTHESPREADRATEESTIMATECANINCREASEWITHSAMPLING EFFORT7HENTHEREISGOODREASONTOBELIEVETHATTHEDISPERSALKERNELISFAT TAILED OR NEARLY FAT TAILED A MORE APPROPRIATE MEASURE OF SPREAD RATE IS THE @FURTHEST FORWARD VELOCITY #LARK ,EWIS AND (ORVATH WHICH REMAINS BOUNDED ! MORE GENERAL DISCUSSION OF UNCERTAINTY IN SPREAD RATES ASSOCIATED WITH LONG DISTANCEDISPERSALISGIVENIN#LARKETAL

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4HEDIRECTIONALMOMENTGENERATINGFUNCTION

4HEDIRECTIONALMOMENTGENERATINGFUNCTIONIS G' G' -US +Z EXPSZ DZDZ Hn' Hn'

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-ANY POLYPLOID SPECIES ARE WELL ADAPTED SUCCESSFUL WEEDY SPECIES WHICH REIN FORCESTHEIDEATHATPOLYPLOIDYMAYHAVEPREDISPOSEDSPECIESTOBECOMEINVADERS "ROWNAND-ARSHALL "ARRETTAND2ICHARDSON )NTERESTINGLY NEWLY FORMEDPOLYPLOIDSAREFREQUENTLYINVASIVESPECIES WHICHSUGGESTSTHATPOLYPLOIDY CONFERSANIMMEDIATEECOLOGICALAPTITUDETOINVADENEWHABITATS)NVASIVESPECIES OFRECENTORIGINAREEXCELLENTMODELSYSTEMSTOINVESTIGATETHEEARLYEVOLUTIONARY MECHANISMS ASSOCIATED WITH INVASIVENESS AND PROVIDE THE UNIQUE OPPORTUNITY TO COMPARE THE NEW LINEAGE TO ITS PARENTS THAT ARE GENERALLY IDENTIlED AND STILL EXTANT 4HE ALLOPOLYPLOIDS 3PARTINA ANGLICA CORDGRASS !ÕNOUCHE ET AL A 4RAGOPOGONMIRUSAND4MISCELLUSGOATSBEARD 3OLTISETAL 3ENECIOCAMB RENSIS7ELSHRAGWORT AND3EBORACENCIS!BBOTTAND,OWE AND#ARDAMINE SCHULZIIBITTERCRESS 5RBANSKAETAL FORMEDDURINGTHELAST YEARS HAVEWELL DOCUMENTEDORIGINS HAVESPREADRAPIDLY ANDDISPLAYALARGERECOLOGI CALAMPLITUDETHANTHEIRPROGENITORS4HESESPECIESAREEITHERPERENNIALSORANNU ALS BIENNIALSANDDISPLAYVARIOUSBREEDINGORPOLLINATIONSYSTEMS 'ENOMEDUPLICATIONMAYHAVEDIFFERENTIMPACTSONFERTILITYANDMODESOFINHER ITANCETHATISDEPENDENTONCHROMOSOMEBEHAVIORANDGENETICSEGREGATION)TIS GENERALLYPREDICTEDTHATDUPLICATIONOFTHESAMEGENOMEWITHINSPECIESIE STRICT AUTOPOLYPLOIDY WILL RESULT IN RANDOM PAIRING POLYSOMIC INHERITANCE AT DUPLI CATED LOCI IRREGULAR MEIOSIS AND THUS LIMITED FERTILITY WHEREAS THE DUPLICATION OFMOREDIFFERENTIATEDHOMOEOLOGOUS GENOMESIE ALLOPOLYPLOIDY WILLRESULTIN PREFERENTIAL CHROMOSOME PAIRING BIVALENTS REGULAR MEIOSIS HIGH FERTILITY AND DISOMICINHERITANCE$A3ILVAAND3OBRAL )NFACT AUTOPOLYPLOIDSANDALLO POLYPLOIDSOCCURONACONTINUUMINNATURE ASTHEONGOINGEVOLUTIONARYPROCESS RESULTS IN MORE OR LESS DIVERGENT PARENTAL POPULATIONS OF THE POLYPLOID 3TEBBINS 7ENDELAND$OYLE -OREOVER CHROMOSOMEPAIRINGMAYBEAFFECTED BYVARIOUSGENETICANDGENOMICFACTORSANDVARYWITHTHEAGEOFTHEPOLYPLOIDIT ISTHENRECOMMENDEDTODISTINGUISHBETWEENTHEMODEOFFORMATIONOFAPOLYPLOID SPECIESANDITSMODEOFCHROMOSOMALSEGREGATION/TTOAND7HITTON 2ECENT RESEARCH HAS RESULTED IN A PARTICULARLY DYNAMIC VISION OF POLYPLOID GENOMESOVERBOTHASHORT ANDLONG TERMEVOLUTIONARYTIMESCALE7ENDEL 3OLTISAND3OLTIS 4HEDEVELOPMENTOFMOLECULARMARKERSANDPARTICULARLY THECOMBINEDUSEOFMATERNALLY INHERITEDCYTOPLASMICMARKERSWITHBIPARENTALLY INHERITED NUCLEAR MARKERS HAS ALLOWED THE DETECTION OF MULTIPLE AND RECURRENT ORIGINSOFPOLYPLOIDSPECIES3OLTISAND3OLTIS !SMULTIPLE SEQUENCEDATAS ETSARENOWAVAILABLEFORPHYLOGENETICANALYSES ITISPOSSIBLETODETECTRECURRENT ANDBI DIRECTIONALRETICULATEEVOLUTIONEVENINOLDPOLYPLOIDLINEAGESEG 'LYCINE $OYLEETAL WHERETHEYOTHERWISEWOULDHAVEBEENUNDETECTED 4HEPROCESSOFRECURRENTPOLYPLOIDFORMATIONWITHRETICULATEGENEmOWMAYIN VOLVE VARIOUS PARENTAL GENOTYPES AND INCREASES THE LEVEL OF GENETIC DIVERSITY AVAILABLE TO NEWLY FORMED SPECIES 3CHIERENBECK ET AL &OR INSTANCE AT LEAST LINEAGES OF SEPARATE ORIGINS FOR THE ALLOTETRAPLOID 4RAGOPOGON MISCELLUS AND FOR 4 MIRUS HAVE BEEN DOCUMENTED IN THE 0ALOUSE ACCORDING TO VARIOUS MORPHOLOGICALANDMOLECULARALLOZYMES CHLOROPLASTANDNUCLEAR$.! LINESOF


EVIDENCE REVIEWED IN 3OLTIS ET AL THESE RECURRENT ORIGINS INVOLVE EITHER ONLY ONE DIPLOID SPECIES AS THE MATERNAL PARENT EG 4 PORRIFOLIUS FOR THE ALLO TETRAPLOID 4 MIRUS OR ALTERNATIVELY BOTH THE PARENTAL SPECIES 4 PORRIFOLIUS AND 4DUBIUSIN RECIPROCAL CROSSES E.g. FOR THE ALLOTETRAPLOID 4 MISCELLUS 4HIS HAS RESULTEDINVARIOUSGENOTYPESANDDRAMATICmORALDIFFERENCESINTHEALLOPOLYPLOID POPULATIONS THAT ARE PROGRESSIVELY REPLACING DIPLOIDS AS PREVALENT WEEDS3OLTIS ETAL 3IMILARLY TWOSEPARATEORIGINSHAVEBEENDOCUMENTEDIN.ORTH7ALES AND 3COTLAND FOR THE RUDERAL ALLOHEXAPLOID 3ENECIO CAMBRENSIS THAT ORIGINATED IN "RITAIN DURING THE PAST YEARS REVIEWED IN !BBOTT AND ,OWE /NE OF THE MOST COMPLEX EXAMPLES OF MULTIPLE ALLOPOLYPLOID ORIGINS IS REPRESENTED BY THEPOLYPLOIDAGAMICCOMPLEX!NTENNARIAROSEAPUSSYTOES THATHASFORMEDFROM MULTIPLECROSSESINVOLVINGVARIOUSDIPLOIDTAXAOCCURRINGINSPECIlCHABITATSOFTHE 2OCKY-OUNTAINS"AYER 4HEPOLYPLOIDLINEAGESOFTHIShCOMPILOSPECIESv ARE GAMETOPHYTIC APOMICTS THAT DISPLAY LARGER ECOLOGICAL AMPLITUDE THAN THEIR DIPLOIDPROGENITORS .OTALLSUCCESSFULALLOPOLYPLOIDSHAVEMULTIPLEORIGINS)NCONTRASTTO4RAGOPOGON SPP 3ENCECIO CAMBRENSIS AND !NTENNARIA ROSEA THE INVASIVE SALTMARSH SPECIES 3PARTINA ANGLICA HAS UNDERGONE A SEVERE GENETIC BOTTLENECK AT THE TIME OF ITS FORMATION IN THE "AY OF 3OUTHAMPTON 5+ 4HIS DODECAPLOID SPECIES FORMED AFTER CHROMOSOME DOUBLING OF THE lRST GENERATION HYBRID 3PARTINA X TOWNSENDII THATHASRESULTEDFROMHYBRIDIZATIONBETWEENTHEINTRODUCED%AST !MERICANHEXA PLOID 3PARTINA ALTERNImORA AND THE NATIVE HEXAPLOID 3PARTINA MARITIMA 2AYBOULD ETAL "OTHPARENTALSPECIESLACKGENETICDIVERSITYINTHEHYBRIDIZATIONSITE A LIMITED NUMBER OF 3 ALTERNImORA GENOTYPES HAVE BEEN INTRODUCED IN 7ESTERN %UROPE "AUMEL ET AL WHEREAS A STRIKING LACK OF MOLECULAR VARIATION IS ENCOUNTERED IN POPULATIONS OF THE NATIVE 3 MARITIMA 9ANNIC ET AL %UROPEAN POPULATIONS OF 3 ANGLICA ARE MOSTLY COMPOSED OF ONE MAJOR MULTILO CUS GENOTYPE THAT HAS FORMED IN 3OUTHAMPTON AND THAT IS IDENTICAL TO THE lRST GENERATIONHYBRID3XTOWNSENDII"AUMELETALA #HLOROPLAST$.! ANALYSISHASREVEALEDALLPOPULATIONSOF3ANGLICAINWESTERN%UROPEDISPLAYIDEN TICALPLASTOMETO3ALTERNImORAWHICHISTHENCONSIDEREDASTHEMATERNALGENOME DONOR&ERRISETAL"AUMELETAL 3PARTINAANGLICAHASRAPIDLYINVADED THE "RITISH SALTMARSHES SINCE ITS FORMATION 4HOMPSON AND IT HAS BEEN NATURALLY OR DELIBERATELY INTRODUCED IN VARIOUS CONTINENTS SUCH AS #HINA OR !USTRALIA WHEREITISNOWCONSIDEREDASASERIOUSTHREATTONATIVEmORAANDFAUNA !ÕNOUCHEETALAANDREFERENCESTHEREIN !LTHOUGHITHASLIMITEDINTER INDI VIDUALGENETICDIVERSITY 3ANGLICACONTAINSTWOWELL DIFFERENTIATEDHOMOELOGOUS GENOMESINHERITEDFROMITSHEXAPLOIDPARENTS WHICHPROVIDESlXEDHETEROZYGOS ITYATHOMOEOLOGOUSLOCI"AUMELETALB!ÕNOUCHEETALB 3PARTINA IS AN IDEAL SYSTEM IN WHICH TO EXPLORE THE GENETIC AND GENOMIC CONSEQUENCES OF HYBRIDIZATION AND GENE DUPLICATION IN SUCCESSFUL INVASIVE SPECIES ALTHOUGH PREVIOUS ATTEMPTS OF RE SYNTHESIZING EXPERIMENTALLY THE ALLOPOLYPLOID HAVE FAILED TIMESINCESPECIESFORMATIONANDTHEPARENTALSPECIESAREKNOWNITISPOS SIBLETODIFFERENTIATEBETWEENTHEEFFECTSOFHYBRIDIZATIONIN3XTOWNSENDII AND


GENOMEDUPLICATIONIN3ANGLICAPOPULATIONS MOREOVER TWONATURALREPLICATES OF HYBRIDIZATION EVENTS BETWEEN 3 MARTIMA AND 3 ALTERNImORA ARE AVAILABLE IN 3XTOWSENDIIAND3XNEYRAUTIIANOTHERHYBRIDTHATHASFORMEDATTHESAMEPERIOD INSOUTHEWEST&RANCE WITHNOGENOMEDOUBLING"AUMELETAL 4HEIMMEDIATECONSEQUENCEOFPOLYPLOIDYISAGREATERINTRA INDIVIDUALGENETIC DIVERSITY AND HETEROZYGOSITY AT DUPLICATED LOCI THAN IN DIPLOIDS THAT RESULTS IN INCREASEDBIOCHEMICALDIVERSITY2OOSEAND'OTTLIEB ANDCONFERSAGREATER TOLERANCE TO ENVIRONMENT VARIATION AND MAY PROMOTE SUCCESSFUL COLONIZATION "ROWNAND-ARSHALL 'ENEDUPLICATIONSRESULTINGFROMPOLYPLOIDYAREALSO BELIEVED TO HAVE A BUFFERING EFFECT AGAINST DELETERIOUS MUTATIONS /HNO ,YNCHAND#ONERY ,AWTON 2AUH !DDITIONALLY POLYPLOIDSOFHYBRID ORIGINALLOPOLYPLOIDS MAYBENElTFROMHIGHERlTNESSDUETOHETEROSIS3IMILARLY TRAITS WHICH RESULT IN THE hGIGASv EFFECT OR A GENERAL INCREASE IN MORPHOLOGICAL CHARACTERISTICS DE 6RIES ARE ASSOCIATED WITH BOTH POLYPLOIDY AND INVA SIVE PLANT SPECIES "AKER 2IESEBERG ET AL (YPERICUM PERFORATUM 3T*OHNSWORT ATETRAPLOIDTHOUGHTTOBEOFALLOPOLYPLOIDORIGIN HASHIGHREPRO DUCTIVEPLASTICITY-ATZKEETAL BUTREPRODUCESMOSTCOMMONLYVIAFACULTA TIVEAPOMIXIS&IELDCOLLECTIONSOF(PERFORATUMIN!USTRALIAFOUNDALACKOFWITHIN POPULATION VARIATION -AYO AND ,ANGRIDGE BUT HIGH INTERPOPULATIONAL GENETIC DIVERSITY (YPERICUM PERFORATUM HAS HIGH LEVELS OF HYPERICIN A CHEMICAL THAT CAUSES PHOTOSENSITIZATION AND REDUCED HERBIVORY THAT ARE HYPOTHESIZED TO BEADIRECTRESULTOFALLOPOLYPLOIDIZATION-AYOAND,ANGRIDGE )NTRODUCED INTO .ORTH !MERICAN IN THE S THE ALLOPOLYPLOID AND NEARLY MONOMORPHIC 3ETARIAFABERIGIANTFOXTAIL ISNOWPRESENTTHROUGHOUTTHEDISTURBEDAREASONTHE CONTINENT0OHL (AmIGERAND3CHOLZ $EKKER NAMED THE ALLOPOLYPLOIZATION OF 3 FABERI THE hWEED SPECIATION EVENTv AS THE POLYPLOID HAS HIGHER lTNESS IN AGRICULTURAL SYSTEMS THAN ITS DIPLOID ANCESTORS /NE OF THE WORLDS WORST WEEDS IS THE POLYPLOID 3ORGHUM HALEPENSE *OHNSON GRASS APRODUCTOFHYBRIDIZATIONBETWEENTHECULTIVAR3BICOLORANDTHEWILD3PROPIN QUUM ANDWHICHRESPONDSWELLTOCULTIVATIONANDISEXTREMELYPERNICIOUSTODUE THERHIZOMATOUSGROWTHHABIT0ATERSON !GROWINGBODYOFEVIDENCECONTINUESTOACCUMULATEINREGARDTOTHEDYNAMIC AND PLASTIC NATURE OF POLYPLOID GENOMES THAT WOULD EXPLAIN THEIR EVOLUTIONARY SUCCESS !LLOPOLYPLOID GENOMES ARE PARTICULARLY DYNAMIC AT BOTH THE STRUCTURAL ANDEXPRESSIONLEVELSOVERTHELONG ANDALSOSHORT TERMEVOLUTIONARYTIMESCALE REVIEWEDIN7ENDEL ,IUAND7ENDEL /SBORNETAL 3IGNIlCANT ADVANCES IN REVEALING THE OCCURRENCE AND NATURE OF THE EARLY EVOLUTIONARY CHANGES IN POLYPLOID GENOMES ARE POSSIBLE DUE TO EXPERIMENTALLY RESYNTHESIZED ALLOPOLYPLOIDS INVOLVING WELL KNOWN MODEL SYSTEMS SUCH AS "RASSICA OILSEED RAPE !RABIDOPSIS 'OSSYPIUMCOTTON OR4RITICUM !EGILOPSWHEAT 4HESEMODEL SYSTEMSALLOWTHEEXPLORATIONOFALLOPOLYPLOIDMATERIALOFKNOWNORIGINWITHTHE COMPARISONOFTHEIRACTUALPARENTALGENOTYPES ACONDITIONRARELYMETFORMOSTNAT URALALLOPOLYPLOIDS2APIDANDBIASEDSTRUCTURALCHANGESHAVEBEENENCOUNTERED IN THE lRST GENERATIONS FOLLOWING POLYPLOIDIZATION IN "RASSICA 3ONG ET AL


AND WHEAT &ELDMAN ET AL ,IU ET AL A B /ZKAN ET AL (OWEVER ,IU ET AL DID NOT lND CONSISTENT STRUCTURAL CHANGES IN NEWLY SYNTHESIZED ALLOPOLYPLOID 'OSSYPIUM 6ARIOUS EVOLUTIONARY MECHANISMS APPEAR TOAFFECTALLOPOLYPLOIDGENOMESOVERALONGERTERMANDINCLUDETHEINDEPENDENT EVOLUTION OF DUPLICATED GENES IN ALLOTETRAPLOID COTTON THAT FORMED ONE TO TWO MILLIONYEARSAGO#RONNETAL 3ENCHINAETAL INTERACTIONBETWEEN THE HOMOELOGOUS SUBGENOMES FOR REPETITIVE SEQUENCES VIA CONCERTED EVOLUTION e.g.,'OSSYPIUM 7ENDELETAL .ICOTIANATOBACCO 6OLKOV ORSPREAD OFTRANSPOSABLEELEMENTS:HAOETAL 4HEFATEOFDUPLICATEDHOMOEOLOGOUS GENESHASBEENPARTICULARLYWELL INVESTIGATEDINTHE'OSSYPIUMSYSTEMBY*ONATHAN 7ENDEL AND HIS COLLEAGUES EG !$( GENES 3MALL AND 7ENDEL -9" GENES #EDRONI ET AL AND REVEALS VARIOUS EVOLUTIONARY PATTERNS INCLUDINGCOPYNUMBERLABILITY PSEUDOGENIZATION GENEELIMINATION ORACCELERAT EDRATEOFNUCLEOTIDESUBSTITUTIONEG FOR!$( #GENES (OWEVER ARECENTANALY SISOFNUCLEARGENES3ENCHINAETAL INDICATEDTHATPOLYPLOIDYLEDTOAN OVERALLMODESTENHANCEMENTINRATESOFNUCLEOTIDESUBSTITUTIONIN'OSSYPIUM 7HEN COMPARED TO RESYNTHESIZED ALLOPOLYPLOIDS NATURALLY NASCENT ALLOPOLY PLOIDSDISPLAYDIFFERENTPATTERNSOFGENOMEEVOLUTIONVARIOUSLEVELSOFCONCERTED EVOLUTION SEEM TO HAVE AFFECTED R$.! SEQUENCES OF THE YOUNG ALLOPOLYPLOID POPULATIONS IN 4RAGOPOGON 3OLTIS ET AL WHEREAS NO HOMOGENIZATION OF THE PARENTAL SEQUENCES IS OBSERVED IN 3PARTINA ANGLICA !ÕNOUCHE ET AL A )NTHELATTERSYSTEM NOMAJORCHANGEOFTHEPARENTALGENOMESAREOBSERVEDFOR VARIOUS MULTILOCUS MARKERS )332S 2!0$S !&,0S ALTHOUGH SOME PREFERENTIAL LOSSOFMATERNALFROM3ALTERNImORA !&,0FRAGMENTSAREOBSERVEDIN3xTOWNSEN DIIAND3ANGLICA!ÕNOUCHEETALB 3ALMON!ETALUNPUBLISHED !TRANS POSONDISPLAYANALYSISINDICATESNOBURSTOFRETRO ELEMENTACTIVATIONIN3ANGLICA "AUMELETALA ANDSUGGESTSTHATDIFFERENTBIOLOGICALSYSTEMSRESPONDVARI OUSLY TO POLYPLOIDY ,IU ET AL )N SPITE OF THE STRUCTURAL GENOMIC STASIS ENCOUNTEREDFORMOSTOFTHEMARKERSINVESTIGATEDTODATE 3PARTINAANGLICAPOPULA TIONSEXHIBITCONSISTENTMORPHOLOGICALPLASTICITY4HOMPSON ANDSUGGEST APROBABLEFUNCTIONALPLASTICITYINTHEEXPRESSIONOFTHEDUPLICATEDLOCI!ÕNOUCHE ETALA 2ECENT STUDIES HAVE POINTED OUT THAT THERE IS MODULATED EXPRESSION OF DUPLI CATEDLOCIINPOLYPLOIDS#OMAI 3HAKEDETAL +ASHKUSHETAL +ASHKUSHETAL (EETAL !DAMSETAL 4HESEEXPRESSIONCHANG ES MAY INVOLVE VARIOUS MECHANISMS INCLUDING INCREASED VARIATION IN DOSAGE REGULATEDGENEEXPRESSION ALTEREDREGULATORYNETWORKS ANDGENETICOREPIGENETIC CHANGES 2IDDLE AND "IRCHLER /SBORN ET AL )N WHEAT POLYPLOIDY WASACCOMPANIEDBYTRANSCRIPTIONALACTIVATIONOFRETROELEMENTSTHATLEDTONOVEL EXPRESSIONPATTERNS+ASHKUSHETAL,EVYAND&ELDMAN %XPRESSION CHANGES MAY HAVE PROFOUND IMPACT ON lTNESS WHEN THEY RESULT IN VARIABLE PHENOTYPES 'ENE SILENCING RESULTED IN PHENOTYPIC VARIATION AND INSTABILITY IN EXPERIMENTALLY RESYNTHESIZED !RABIDOPSIS ALLOTETRAPLOIDS THAT DISPLAYED CONSIDER ABLE VARIATION IN MORPHOLOGY mOWERING TIME AND FERTILITY #OMAI ET AL


.OVEL mOWERING TIME VARIATION WAS ALSO OBSERVED IN RESYNTHESIZED ALLOPOLYPLOID "RASSICANAPUS3CHRANZAND/SBORN %XPRESSIONOFHOMOEOLOGOUSGENE PAIRSWASANALYSEDBY!DAMSETAL INNATURALTO MYROLD ANDSYN THETIC ALLOTETRAPLOID 'OSSYPIUM 4HE DUPLICATED GENES SHOWED UNEQUAL LEVELS OF EXPRESSION AND ORGAN SPECIlC RECIPROCAL SILENCING SUGGESTING A PARTITIONING OF THEANCESTRALFUNCTIONSASBOTHIMMEDIATEINSYNTHETICPOLYPLOIDS ANDLONG TERM INNATURALPOLYPLOIDS RESPONSESTOPOLYPLOIDIZATION)NRECENTLYFORMEDNATURAL ALLOPOLYPLOIDS SUCHEXPRESSIONCHANGESAPPEARTOTAKEPLACEALSO ASREVEALEDBY C$.!!&,0INVESTIGATIONSIN4RAGOPOGONWHEREABOUTOFTHEGENESEXAMINED INTHEALLOPOLYPLOIDSHAVEBEENSILENCEDANDANADDITIONALEXHIBITNOVELGENE EXPRESSIONRELATIVETOTHEIRDIPLOIDPARENTS3OLTISETAL %PIGENETICCHANGESASSOCIATEDWITHINVASIVEABILITY

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POLYPLOID WHEAT OF THE LOCI INVESTIGATED USING -ETHYLATION 3ENTITIVE !&,0 -3!0 WERE FOUND METHYLATED 3HAKED ET AL AND TRANSCRIPTIONAL ACTI VATION OF RETROTRANSPOSONS WAS SHOWN TO ALTER THE EXPRESSION OF ADJACENT GENES +ASHKUSHETAL,EVYAND&ELDMAN !LTHOUGHNOCHANGESINMETH YLATION PATTERNS WERE OBSERVED IN NEWLY SYNTHESIZED 'OSSYPIUM ALLOPOLYPLOIDS ,IUETAL THEORGAN SPECIlCANDRECIPROCALGENESILENCINGFOUNDBY!DAMS ETAL ISINTERPRETEDASRESULTINGFROMEPIGENETICREGULATIONTHROUGHMECHA NISMSTHATHAVEYETTOBEELUCIDATED!DAMSAND7ENDEL 3PARTINA ANGLICA IS TO OUR KNOWLEDGE THE lRST INVASIVE SPECIES THAT HAS BEEN INVESTIGATEDINTHECONTEXTOFEPIGENETICGENEEXPRESSION!ÕNOUCHEETALB 3ALMON ET AL HAVE ATTEMPTED TO DIFFERENTIATE BETWEEN THE GENOMIC CON SEQUENCES THAT RESULT FROM HYBRIDIZATION AND THOSE THAT RESULT FROM GENOME DUPLICATION 4HIS WAS MADE POSSIBLE BY THE COMPARISON OF THE ALLOPOLYPLOID TO THE NATURAL & HYBRID SPECIES 3 X TOWNSENDII THE PROGENITOR OF 3 ANGLICA AND 3 X NEYRAUTII THE OTHER HYBRID THAT HAS FORMED INDEPENDENTLY IN SOUTHWEST &RANCE "AUMEL ET AL -3!0 DATA ANALYSIS REVEALED CONSISTENT METHYLA TIONCHANGESTHATCONTRASTWITHTHESTRUCTURALADDITIVITYOFTHEPARENTALGENOMES MENTIONEDABOVE-OSTMETHYLATIONCHANGESWEREFOUNDINBOTH3XTOWNSENDII AND3XNEYRAUTII WHICHINDICATESTHEREPRODUCIBILITYOFTHECHANGESINTHETWO DIFFERENTHYBRIDISATIONEVENTS4HEMETHYLATIONALTERATIONSFOUNDIN3ANGLICAWERE ALREADYPRESENTORINITIATEDIN3XTOWNENDII SUGGESTINGTHATEPIGENETICCHANGES WERETRIGGEREDBYHYBRIDIZATIONRATHERTHANBYGENOMEDUPLICATION4HEEXTENTOF SUCHCHANGESANDTHEIRVARIABILITYWHENPLANTSAREFACINGDIFFERENTENVIRONMENTAL CONDITIONSNEEDTOBEEXPLOREDATTHEPOPULATIONLEVEL ANDTHESEQUENCESTHATARE EPIGENETICALLYAFFECTEDHAVETOBEIDENTIlED )N THE CONTEXT OF RAPID EXPANSION OF INVASIVE SPECIES THAT EXPLORE NEW HABI TATS EPIGENETICPROCESSESAREOFMAJORINTERESTASTHEYDElNITELYINmUENCElTNESS "ECAUSEEPIGENETICCASESOFGENESILENCINGWILLNOTBEREmECTEDINSEQUENCEDATA THE ASSESSMENT OF GENE EXPRESSION IS KEY TO THE UNDERSTANDING OF GENE FUNCTION ANDITSIMPORTANCEINSPECIESADAPTATIONANDINVASIVENESS-OLECULAREVOLUTION ISTSAREBECOMINGMOREAWAREOFTHENECESSITYTOAPPROACHADAPTIVEPROCESSESAT BOTHGENEANDGENOMELEVELS

3%,%#4)/. $%6%,/0-%.4!,2%30/.3% !.$).6!3)/.3 'ENETICCHANGEANDSUBSEQUENTALTERATIONSINDEVELOPMENTALRESPONSEHAVEBEEN MINIMALLY ADDRESSED IN INVASIVE PLANT SPECIES 3IMILARLY ALTHOUGH THE EVALUA TIONOFDEVELOPMENTALQUANTITATIVETRAITSHASBEENCONSIDEREDTHEORETICALLY THERE IS LITTLE EMPIRICAL EVIDENCE FOR OR AGAINST THEIR IMPORTANCE IN PLANT INVASIONS 4HEGENETICANDECOLOGICALINTERACTIONSTHATRESULTFROMCHANGESINDEVELOPMENTAL GENES OR FROM GENES OF MAJOR EFFECT COULD HAVE PROFOUNDLY COMPLEX REPERCUS SIONS&OREXAMPLE THERELEASEFROMENEMIESMAYALLOWFORDECREASEDALLOCATION TOPROTECTIVEMECHANISMSANDACONCOMITANTINCREASEINlTNESSTHATRESULTSFROM


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).42/$5#4)/. %COLOGICALTHEORYSUGGESTSTHATINTERSPECIlCINTERACTIONSARISINGBETWEENANALIEN SPECIES AND NATIVE SPECIES HOLD THE KEY TO INVASION SUCCESS BY AN ALIEN SPECIES 4HEWELL KNOWNHYPOTHESISTHATANALIENSPECIESTHATHASFEWNATURALENEMIESIS MORE LIKELY TO BE A SUCCESSFUL INVADER EG "LOSSEY AND .ÚTZOLD -ITCHELL AND0OWER IMPLIESTHEIMPORTANCEOFATROPHICINTERACTION4HEHYPOTHESIS THAT A COMMUNITY WITH HIGHER SPECIES RICHNESS IS MORE RESISTANT TO A BIOLOGICAL INVASION3TACHOWICZETAL +ENNEDYETAL ISSTRONGLYBASEDONTHE COMPETITIONTHEORY4ILMAN &URTHER THEWAYTHROUGHWHICHABIOLOGICAL -7#ADOTTE ETAL (EDS) #ONCEPTUALECOLOGYANDINVASIONBIOLOGY 225n ¥3PRINGER0RINTEDINTHE.ETHERLANDS

-+ONDOH

INVASION AFFECTS THE LOCAL COMMUNITY IS AN ALIEN NATIVE INTERSPECIlC INTERACTION SUCHASRESOURCECOMPETITION TROPHICINTERACTIONANDALLELOPATHY4HEIMPORTANT ROLE OF INTERSPECIlC INTERACTIONS IN A BIOLOGICAL INVASION SUGGESTS THE DETAILED EVALUATIONOFTHEINTERSPECIlCINTERACTIONSBETWEENALIENANDNATIVESPECIESASAN INTERESTINGAPPROACHTOTHEBIOLOGICALINVASIONISSUES 4HERE ARE TWO DIFFERENT BUT NOT MUTUALLY EXCLUSIVE VIEWS OF WHAT CHARAC TERIZES AN ALIEN NATIVE INTERACTION THE hSPECIES IDENTITYv AND hCONTACT EXPERI ENCEvVIEWS4HESPECIES IDENTITYVIEWFOCUSESONTHEIDENTITYOFTHEFOCALSPECIES EG "AKER 2OY +OLARAND,ODGE 4HEALIENANDNATIVESPECIES ARECHARACTERIZEDBYlXEDSETSOFSPECIES SPECIlCTRAITSSUCHASCOMPETITIVEABILITY (ERBOLD AND -OYLE 0ETREN AND #ASE (OLWAY "YERS WHICH INmUENCE THEIR INTERACTION AND THUS THE INVASION SUCCESS AND ITS IMPACT ONTHELOCALCOMMUNITYEG 7ILLIAMS )NTHISVIEWANINTERSPECIlCINTER ACTION THAT ARISES BETWEEN AN ALIEN AND NATIVE SPECIES IS EXPLAINED MAINLY BY THEIRINHERENTSPECIES SPECIlCTRAITSANDSOAREITSPOPULATION LEVELCONSEQUENCES -ACKETAL 4HECONTACT EXPERIENCEVIEW3AKAIETAL FOCUSESONTHELACKOFhCONTACT EXPERIENCEvBETWEENALIENANDNATIVESPECIESASTHEMAJORFACTORCHARACTERIZING THEIRINTERACTION.ATIVESPECIESTHATCOEXISTINTHELOCALHABITATHAVETHEEXPERI ENCEOFENCOUNTERSORINTERACTIONSWITHEACHOTHEROVERVARYINGTIMESCALES WHICH PROVIDESTHEOPPORTUNITYFORLOCALSPECIESTOADAPTTOEACHOTHEREG ,AWLORAND -AYNARD3MITH )NCONTRAST ANALIENSPECIESANDANATIVESPECIES DUETO TEMPORALORSPATIALSEPARATION SHAREARELATIVELYSHORTHISTORYANDARELESSLIKELY TO ADAPT TO EACH OTHER 4HE LACKOF ADAPTATION SHOULDHAVEMAJORIMPACTON THEALIEN NATIVE INTERSPECIlCINTERACTION EG 7ARE $ILL -ARURRAN #ROYAND(UGHES (UGHESETAL -ALONEYAND-CLEAN #ALLAWAYAND!SCHEHOUG 2EHAGEETAL ANDTHERESULTANTCOMMUNITY STRUCTURE'RIFlNETAL 2ICCIARDIETAL 2ICCIARDIAND!TKINSON (OWEVER ONLYAFEWSTUDIESHAVECOMPREHENSIVELYCONSIDEREDTHECONTACTEXPERI ENCEEFFECTINTHECONTEXTOFBIOLOGICALINVASIONISSUESBUTSEE3AKAIETAL .OW WENEEDASTRONGCONCEPTUALBASISFORTHEISSUEOFHOWCONTACTEXPERIENCE INmUENCESABIOLOGICALINVASIONFORGUIDINGFURTHERRESEARCH )N THIS CHAPTER ) PRESENT A THEORETICAL FRAMEWORK FOR APPLYING THE CONTACT EXPERIENCEVIEWTOALIEN NATIVETROPHICINTERACTIONS)CHOSETHISPARTICULARINTER ACTION AS IT IS KNOWN TO PLAY THE ESSENTIAL ROLE IN SHAPING COMMUNITY STRUCTURE EG (AIRSTONEETAL &RETWELL 0OWER )TDRIVESDIVERSEPREY PREDATOR POPULATION DYNAMICS INmUENCES POPULATION DENSITY AND DISTRIBUTION (AIRSTONE ET AL GENERATES TWO MAJOR INTERSPECIlC INDIRECT INTERACTIONS [RESOURCE COMPETITION 4ILMAN AND APPARENT COMPETITION (OLT "ONSALL AND (ASSELL BUT SEE #HANETON AND "ONSALL ] THAT LIMIT THE NUMBER OF COEXISTING SPECIES AND FORMS A MAJOR COMPONENT OF THE NATURAL SELECTION PRESSURE %NDLER &URTHER THE MACROSCOPIC FOOD WEB TOPOLOGY CANBEANESSENTIALDETERMINANTOFPOPULATIONSTABILITY0IMM ANDECOSYS TEMFUNCTION4HÏBAULTAND,OREAU

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-+ONDOH

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COMBINATION PREY FROM ! AND PREDATOR FROM " OR VICE VERSA CAN DIFFER FROM THEORIGINALINTERACTIONWITHIN(ABITAT!OR"

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!CCORDING TO BIOLOGICAL INVASION THEORY AN ALIEN PREY SPECIES CAN HAVE MORE ADVANTAGESTHANANATIVEPREYSPECIESINTHELOCALHABITATBECAUSETHEALIENSPE CIES IS LESS LIKELY TO HAVE NATURAL ENEMIES IN THE NEW HABITAT EG %LTON "LOSSEYAND.ÚTZOLD -ACKETAL +EANEAND#RAWLEY -ITCHELL AND0OWER 4ORCHINETAL 4HISISKNOWNASENEMYRELEASEHYPOTHESIS 4HISHYPOTHESISSUGGESTSTHATTHELACKOFANATIVECONSUMERSCONTACTEXPERIENCE WITHTHEALIENPREYSPECIESLOWERSTHESTRENGTHOFTHETROPHICINTERACTIONBETWEEN THEM&ROMTHECONTACTEXPERIENCEPOINTOFVIEW THEREARETHREEPOTENTIALREASONS FORTHISHYPOTHETICALPATTERN&IRST ANATIVECONSUMERDOESNOTRECOGNIZETHEALIEN SPECIESASPOTENTIALPREY3ECOND THENATIVECONSUMERDOESNOThKNOWvHOWTO HANDLE THE NOVEL PREY SPECIES 4HIRD EVEN IF THE ALIEN PREY SPECIES IS NOT NOVEL ITMIGHTBEHAVEINANOVELWAYDUETOAHABITAT SPECIlCEVOLUTIONARYPROCESS (OWEVER ) SUGGEST THAT THE ENEMY RELEASE HYPOTHESIS ONLY CONSIDERS A PART OF THE TOTAL PICTURE OF ALIEN NATIVE TROPHIC INTERACTIONS &IRST THE HYPOTHESIS OVERLOOKS THE PREYS ANTI PREDATORY BEHAVIOR !S THE LACK OF CONTACT EXPERIENCE MAY LOWER THE ALIENS DEFENCE EFlCIENCY AGAINST THE NATIVE PREDATOR 2EHAGE ET AL THEN THEIR INTERACTION STRENGTH CAN BE STRONGER 4AKING THIS EFFECT INTO ACCOUNT THE LACK OF CONTACT EXPERIENCE HAS TWO OPPOSITE CONSEQUENCES LOW PREDATION EFlCIENCY WHICH DECREASES THE INTERACTION STRENGTH AND LOW DEFENCE EFlCIENCY WHICH INCREASES THE STRENGTH 3ECOND THE ENEMY RELEASE HYPOTHESIS OVERLOOKS ALIENS PREY )F THE LACK OF CONTACT EXPERIENCE AFFECTS THE ALIENSVULNERABILITYTONATIVENATURALENEMIES THISSHOULDBEALSOAPPLICABLETO THE INTERACTION OF THE FOCAL ALIEN AS A PREDATOR AND A POTENTIAL PREY IN THE LOCAL HABITAT )N THIS INTERACTION THE BEHAVIORS INmUENCED BY THE CONTACT EXPERIENCE ARETHEALIENSFORAGINGBEHAVIORANDTHENATIVESDEFENCEBEHAVIOR )NSUMMARY FOURDIFFERENTBEHAVIORSMUSTBECONSIDEREDTOEVALUATETHEEFFECT OF THE LACK OF CONTACT EXPERIENCE ON INTERACTION STRENGTH AND INVASION SUCCESS THEALIENSFORAGINGBEHAVIORANDANTI PREDATORYBEHAVIORANDTHENATIVESFORAG INGBEHAVIORONTHEALIENANDANTI PREDATORYBEHAVIORAGAINSTTHEALIEN&IG 4HECOMPLEXINTERACTIONBETWEENTHEFOURINTER RELATEDBEHAVIORSMAKESCONSIS TENTPREDICTIONMOREDIFlCULTTHANPREVIOUSLYTHOUGHT!SSUMETHAT3PECIES!IS INTRODUCEDTOALOCALHABITATINWHICHITINTERACTSWITHANATIVENATURALENEMY 3PECIES% ANDANATIVEPREY 3PECIES2ANDASSUMETHATTHESTRENGTHOFATROPHIC INTERACTIONISDETERMINEDBYTHEBALANCEBETWEENTHEPREYSANTI PREDATORYDEFENCE AND THE PREDATORS FORAGING BEHAVIOR 7HETHER THE LACK OF CONTACT EXPERIENCE

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&IG &OURBEHAVIORSAFFECTINGTHETROPHICINTERACTIONSBETWEENANALIENSPECIESANDA NATIVESPECIES)FPREDATORAVOIDANCEISMOREDEPENDENTONCONTACTEXPERIENCETHANISPREY CONSUMPTION AN ALIEN SPECIES WILL HAVE A STRONGER INTERACTION WITH THE NATIVE SPECIES )FPREYCONSUMPTIONISMOREDEPENDENTONCONTACTEXPERIENCETHANISPREDATORAVOIDANCE AN ALIEN SPECIES WILL HAVE A WEAKER INTERACTION WITH THE NATIVE SPECIES )F THERE IS NO CONSISTENTTREND THEINTERACTIONSTRENGTHWILLBECHARACTERIZEDBYAHIGHERVARIANCE

BENElTS THE ALIEN SPECIES DEPENDS ON THE LEVEL OF EACH SPECIES CONTINGENT PRE ADAPTATION !GRAWAL AND +OTANEN 2ICCIARDI AND !TKINSON TO AN INTERACTING SPECIES 4HE ALIEN SPECIES WOULD BE AT AN ADVANTAGE IF ITS PRE ADAPTIVEDEFENCELEVELTO3PECIES%WEREHIGHER THEPRE ADAPTIVEDEFENCELEVELOF 3PECIES2TO3PECIES!WERELOWER THEPRE ADAPTIVEFORAGINGLEVELOF3PECIES%TO 3PECIES!WERELOWER ORTHEPRE ADAPTIVEFORAGINGLEVELOF3PECIES!TO3PECIES2 WEREHIGHER )F THERE IS A CONSISTENT PATTERN IN WHICH BEHAVIOR FORAGING OR ANTIPRE DATORY DEFENCE OR TROPHIC ROLE ISMOREDEPENDENTONCONTACTEXPERIENCE THEN ITISPOSSIBLETOMAKEACONSISTENTPREDICTIONONHOWTHECONTACTEXPERIENCEAFFECTS THE INTERACTION STRENGTH &OR EXAMPLE IF PREDATOR RELIES MORE ON THE EXPERIENCE THANPREYDOES ATROPHICINTERACTIONINTHEABSENCEOFCONTACTEXPERIENCEWILLBE WEAKERTHANANINITSPRESENCE)FTHEPREYISMOREDEPENDENTONTHEEXPERIENCE A TROPHIC INTERACTION BETWEEN NOVEL SPECIES WOULD BE STRONGER THAN THE NORMAL ONE)FTHEREISNOCONSISTENTPATTERNINWHICHONETROPHICROLEISMOREDEPENDENT ON CONTACT EXPERIENCE THE DISRUPTION OF THE PREDATION DEFENCE BALANCE SHOULD LEAD TO MORE VARIABLE TROPHIC INTERACTION STRENGTH 7HICH IS THE REAL PATTERN IN NATURE )T WOULD BE INTERESTING TO EXAMINE HOW THE FREQUENCY DISTRIBUTION OF THE INTERACTION STRENGTH OF ALIEN NATIVE INTERACTIONS DIFFERS FROM THAT OF NATIVE NATIVEINTERACTIONS )TISWELLRECOGNIZEDTHATCOMPETITIVEABILITYISAFFECTEDBYTHEINTERACTINGEFFECTS OF RESOURCE AVAILABILITY BOTTOM UP EFFECT AND VULNERABILITY TO NATURAL ENEMIES


TOP DOWN EFFECT EG 0OWER ,EIBOLD 4HEORY SUGGESTS THAT THE COEXISTENCE OF SPECIES SHARING A SIMILAR RESOURCE AND NATURAL ENEMY REQUIRES A TRADE OFFBETWEENRESOURCECOMPETITIONANDNATURAL ENEMYAVOIDANCE,UBCHENCO ,EIBOLD )FTHESTRENGTHOFANALIEN NATIVETROPHICINTERACTIONISCHAR ACTERIZEDBYAHIGHVARIANCE ITMIGHTLEADTOTHEPREDICTIONTHATTHECOMPETITIVE SUPERIORITYOFANALIENSPECIESSHOULDBEABNORMALLYHIGHORLOW)FTHETROPHICLINK TOTHECONSUMPTIONOFTHEALIENSPECIESISWEAKANDTHELINKFROMTHEALIENSPECIES ISSTRONG THEALIENWILLHAVEAHIGHPOPULATIONDENSITY)FTHETROPHICLINKTOTHE CONSUMPTION OF THE ALIEN SPECIES IS STRONG AND THE LINK FROM THE ALIEN SPECIES IS WEAK THE ALIEN WILL HAVE A LOW POPULATION DENSITY 4HIS IMPLIES THAT ALTHOUGH THERE ARE MANY ALIEN SPECIES THAT CANNOT BECOME ESTABLISHED WHEN AN ALIEN SPECIESSUCCEEDSINBECOMINGESTABLISHED ITTENDSTOBEVERYABUNDANT !LIEN NATIVEMISMATCHINGINADAPTIVESPEEDAND hBOOM AND BUSTvPATTERNOFALIENPOPULATIONS

!LTHOUGHTHELACKOFCONTACTEXPERIENCEMAY AS)HAVEARGUEDINTHELASTSECTION LOWERTHEFORAGINGEFlCIENCYORDEFENCEEFlCIENCYATTHEINITIALSTAGEOFINVASION THEEFlCIENCYISLIKELYTOBEGRADUALLYIMPROVEDASANALIENSPECIESANDRESIDENTSPE CIESLEARNOREVOLVETOADAPTEACHOTHER#ARROLLAND$INGLE -ARONAND6ILA 4HEPREVIOUSSTUDIESTHATCONSIDERTHECOADAPTIVEPROCESSHAVESTRESSEDTHE DISADVANTAGEOFANALIENSPECIESBYSUGGESTINGTHATANALIENSPECIESISOFTENCHARAC TERIZEDBYALOWPOPULATIONDENSITYANDLOWGENETICDIVERSITY WHICHLOWERSEVOLU TIONSPEED4SUTSUIETAL 4HISISWHYMULTIPLEINTRODUCTIONS WHICHINCREASE GENETICDIVERSITY ENHANCEALIENSINVASIONSUCCESS+OLBEETAL (OWEVER THEDISADVANTAGEOFALIENSPECIESCANBECOMPENSATED!NEXAMPLE ISALIENSBEHAVIORALPLASTICITY'RAY 3OLAND,EFEBVRE ANALYZEDTHE RELATIONSHIP BETWEEN BRAIN SIZE IN BIRDS AND INVASION SUCCESS IN .EW :EALAND THEYFOUNDTHATSPECIESWITHLARGERBRAINSHADAHIGHERPROBABILITYOFINTRODUCTION SUCCESSTHANDIDSPECIESWITHSMALLERBRAINS4HISPATTERNISEXPLAINEDBYTHEEFFECT OF BRAIN SIZE ON THE BIRDS INTERACTION WITH RESOURCES A BIRD WITH A LARGER BRAIN IS BETTER AT DISCOVERING NEW FOODS IN THE NEW HABITAT 3OL AND ,EFEBVRE 4HISVIEWPROVIDESASPECIESIDENTITYEXPLANATIONFORINVASIONSUCCESS IE ASPE CIESWITHHIGHPLASTICITYISASUCCESSFULINVADER (ERE FROM THE VIEWPOINT OF CONTACT EXPERIENCE ) SHOW ANOTHER FACTOR THAT MAYOVERCOMETHEALIENSDISADVANTAGE#ONSIDERTHATASMALLNUMBEROF3PECIES ! IS INTRODUCED TO A COMMUNITY WHERE A POTENTIAL PREDATOR 3PECIES % EXISTS &IGS !FTER ITS INTRODUCTION THE ALIEN 3PECIES ! WOULD LEARN OR EVOLVE TO LOWERTHEPREDATIONPRESSUREBY3PECIES% WHILE3PECIES%WOULDADAPTTOINCREASE THE PREDATION PRESSURE ON 3PECIES ! .OTE THAT IN THIS CO ADAPTATION PROCESS THE ADAPTIVE SPEEDS WOULD DIFFER DUE TO DIFFERENCES IN THE CONTACT OPPORTUNITIES BETWEENALIENANDNATIVESPECIES7HENANALIENSPECIESISINTRODUCED ITSABUN DANCESHOULDBEMUCHLOWERTHATTHATOFNATIVESPECIES4HISIMPLIESTHATTHEALIEN PREY HAS MORE OPPORTUNITY TO GAIN EXPERIENCE IN HANDLING THE NATIVE PREDATOR

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&IG !LIEN NATIVEMISMATCHINGINEVOLUTIONARYSPEEDLEADSTOBOOM AND BUSTPATTERN OF ALIEN POPULATIONS %ACH COLUMNISFORANALIENPREDATORANDITSPREYLEFTCOLUMN AND ANALIENPREYANDITSPREDATORRIGHTCOLUMN INTHEPRESENCEOFPREY PREDATORCOEVOLUTION %ACHPANELSHOWSPOPULATIONDYNAMICSTOP#.#! 2.2! ADAPTIVELEVELMIDDLETHE FRACTIONOFADAPTEDINDIVIDUALS #!#.#! FORTHEPREDATORAND2!2.2! FORTHEPREY ANDPER CAPITAPREDATIONRATEBOTTOMANN#.2.ANA#!2.AAN#.2!AAA#!2! ;#. #! 2.2! = )NTHETOPANDMIDDLEPANELSTHETHICKLINESANDTHINLINESAREFORPREDATOR ANDPREY RESPECTIVELY#ONSIDERPOPULATIONSOFANALIENSPECIESANDNATIVESPECIES EACHOF WHICHCONSISTSOFMANYNON ADAPTEDINDIVIDUALSWITHLOWDEFENCEABILITYORLOWFORAGING ABILITY ANDAFEWADAPTEDINDIVIDUALSWITHHIGHDEFENCEABILITYORHIGHFORAGINGABILITY 4HE POPULATION DYNAMICS IS DESCRIBEDBYD #. D TRC +Cn#.n#! #.EANN#.2. EAAN#.2!nMC#.D#!DTRC+Cn#.n#! #!EAAA#.2.EAAN#.2!nMC#!D2. DTRR+Rn2.n2! 2.nANN#.2.nANA#!2.nMR2.D2!DTRR+Rn2.n2! 2!nAAN#. 2!nAAA#!2!nMR2! WHERE#. #! 2.AND2!AREPOPULATIONABUNDANCESOFNON ADAPTED PREDATOR ADAPTED PREDATOR NON ADAPTED PREY AND ADAPTED PREY RESPECTIVELY RI IS THE INTRINSICGROWTHRATE +IISCARRYINGCAPACITYSUPPORTEDBYRESOURCESTHATARENOTEXPLICITLY REPRESENTEDBYTHEEQUATIONS MIISTHEMORTALITYRATEOFTHEPREYIR ANDPREDATORC E ISTHEASSIMILATIONEFlCIENCY4HEPER CAPITAPREDATIONRATESHOLDTHATANAANNAAAAAN IMPLYINGTHATTHEPREDATIONRATEOFTHENON ADAPTEDPREDATORONTHENON ADAPTEDPREYIS SAMEWITHTHATOFTHEADAPTEDPREDATORONTHEADAPTEDPREY0ARAMETERSANNANDAAAARESET TOAVALUEWITHWHICHANALIENSPECIESCANNOTPERSIST4HISSETTINGCONlRMSTHATATEMPORAL INCREASE OF AN ALIEN SPECIES IS DUE TO THE ALIEN NATIVE MISMATCH IN EVOLUTIONARY SPEED 4HEINITIALCONDITIONISTHAT#. #! 2. 2! FORPREDATORSINVASIONAND FORPREYSINVASION0ARAMETERS THATAREUSEDARERC RN +C +N MC MN ANN ANA AAN AAA E FORPREDATORSINVASIONAND FORPREYSINVASION


&IG !LIEN NATIVE MISMATCHING IN SPEED OF ADAPTIVE BEHAVIORAL PLASTICITY LEADS TO BOOM AND BUSTPATTERNOFALIENPOPULATIONS%ACHCOLUMNISFORANALIENPREDATORSPECIES ANDITSPREDATORPREYLEFTCOLUMN ANDANALIENPREYSPECIESANDITSPREDATORRIGHTCOLUMN INTHEPRESENCEOFTHELEARNINGPROCESS%ACHPANELSHOWSPOPULATIONDYNAMICSTOP# 2 ADAPTIVE LEVEL MIDDLE !# FOR THE PREDATOR !2 FOR THE PREY AND INTERACTION STRENGTH BOTTOM !# n A !2 )N THE TOP AND MIDDLE PANELS THE THICK LINES AND THIN LINES ARE FOR PREDATORANDPREY RESPECTIVELY!SCALEFORPREYPOPULATIONLEVELISINDICATEDONTHERIGHTOF EACHPANEL#ONSIDERPOPULATIONSOFAPREYSPECIESANDAPREDATORSPECIES WHOSEPOPULATION DYNAMICSISDESCRIBEDBYD#DTRC+Cn# #EnMC#ANDD2DTRR+Rn2 2 n & # 2 n MR 2 WHERE # AND 2 ARE POPULATION ABUNDANCES OF THE PREDATOR AND PREY RESPECTIVELY RIISTHEINTRINSICGROWTHRATE +IISCARRYINGCAPACITYSUPPORTEDBYRESOURCES THAT ARE NOT EXPLICITLY REPRESENTED BY THE EQUATIONS MI IS THE MORTALITY RATE OF THE PREY I R AND PREDATOR C E IS THE ASSIMILATION EFlCIENCY 4HE PER CAPITA PREDATION RATE & IS A TEMPORAL VARIABLE AND DETERMINED BY PREDATORS FORAGING RELATED ADAPTIVE LEVELS !# AND PREYS DEFENCE RELATED ADAPTIVE LEVEL !2 THAT IS & B !# n A !2 4HE ADAPTIVE DYNAMICS IS GIVEN BY D !# D T 'C !#MAX n !# 2 AND D !2 D T 'R !2MAX n !2 !# n A !2 # WHERE 'C AND 'R ARE THE LEARNING RATES !#MAX AND !2MAX ARE THE MAXIMUM LIMITS OF ADAPTIVE LEVELS FOR THE PREDATOR AND PREY RESPECTIVELY ) USED THE PARAMETERS 'C 'R !#MAX !2MAX ;n!#=A ANDINITIALCONDITION !# !2 !# 4HIS ASSUMPTION IMPLIES THAT THE PREDATION RATE OF THE NAIVE PREY WHOSE !2 AND NAIVE PREDATOR !# !# IS SAME WITH THAT OF THE MAXIMALLY ADAPTED PREDATOR !# !#MAX ON THE MAXIMALLY ADAPTED PREY !2 ; n !#=A 0ARAMETER !# IS SET TO A VALUE WITH WHICH AN ALIEN SPECIES CANNOT PERSIST TO CONlRM THAT A TEMPORAL INCREASE OF AN ALIEN SPECIES IS DUE TO THE ALIEN NATIVE MISMATCH IN ADAPTIVE SPEED 4HEINITIALCONDITIONISTHAT# 2 !# FORPREDATORSINVASIONAND FORPREYSINVASION0ARAMETERSTHATAREUSEDARERC RN +C +N MC MN A B E FORPREDATORSINVASIONAND FORPREYSINVASION

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THANVICEVERSA4HEREFORE THEADAPTATIONPROCESSISALIEN BIASED ANDTHETROPHIC INTERACTION BETWEEN A NATIVE PREDATOR AND AN ALIEN PREY IS LIKELY TO BE KEPT LOW AFTERTHEINTRODUCTION&IGS 4HESAMEISTRUEFORTHEINTERACTIONBETWEENTHE ALIENSPECIES3PECIES! ASAPREDATORANDTHENATIVEPREY3PECIES2 &IGS "ECAUSETHEOPPORTUNITYFORTHEALIENPREDATORTOGAINEXPERIENCEWITHTHENATIVE PREY IS GREATER THAN FOR THE OPPOSITE SITUATION AN IMBALANCE CAN EXIST BETWEEN THEALIENSPREDATIONEFlCIENCYANDTHENATIVESDEFENCEEFlCIENCY4HEREFORE THE TROPHICINTERACTIONBETWEENTHEALIENPREDATORANDNATIVEPREYWOULDTENDTOBE RELATIVELYHIGHINTHETRANSIENTDYNAMICS 4HIS ALIEN NATIVE MISMATCH IN ADAPTIVE SPEED SUGGESTS THAT THE ALIEN SPECIES HAS AN ADVANTAGE IN NOT BEING EXPERIENCED BY INTERACTING SPECIES 4HIS MAKES ANALIENSPECIESLESSVULNERABLETONATURALENEMIESANDLOWERSTHEPREYSDEFENCE LEVELAGAINSTTHEALIENSPECIES ALLOWINGTHEALIENSPECIESTOINCREASEITSPOPULATION QUICKLYAFTERINTRODUCTION4HISADVANTAGEWILLLASTUNTILTHEALIENSPECIESBECOMES ABUNDANT ATWHICHPOINTITBECOMESEASIERFORTHENATIVESPECIESTOHAVECONTACT EXPERIENCE WITH THE ALIEN SPECIES !FTER THE ALIEN SPECIES BECOMES ABUNDANT THE NATIVE SPECIES WILL CATCH UP WITH THE ALIEN SPECIES DEFENCE AND PREDATION BEHAVIORAGAINSTTHEALIENSPECIESWILLDEVELOP ANDTHEALIENSPECIESWILLBECON TROLLEDMOREEFlCIENTLY4HISSUCCESSFULLYGENERATESTHEhBOOM AND BUSTvPATTERN OFALIENPOPULATIONSTHATISOFTENOBSERVEDINNATURE&IGS 7ILLIAMSONAND &ITTER $ISRUPTIONOFSWITCHINGBEHAVIORANDCOMMUNITYINSTABILITY

!NORGANISMCANCHANGETHESPECIESORTROPHICSPECIES TOINTERACTINRESPONSE TO A CHANGE IN THE RELATIVE ABUNDANCE OF POTENTIAL INTERACTING SPECIES !BRAMS "OLKERETAL 4HISISCALLEDhSWITCHINGBEHAVIORv-URDOCH 4HEREARETWOTROPHICINTERACTION RELATEDSWITCHINGBEHAVIORS FORAGING-URDOCH AND DEFENCE &RYXELL AND ,UNDBERG SWITCHES ! FORAGING SWITCH REFERSTOACHOICEOFDIETWITHHIGHERQUALITYORQUANTITYFROMASETOFNUTRITIONALLY SUBSTITUTABLE POTENTIAL DIETS A FORAGING SWITCH OR FORAGING SHIFT 3TEPHENS AND +REBS )TISASIMPLESTRATEGYTOMAXIMIZETHEENERGETICORMATERIALGAINPER UNITEFFORTWHENDIFFERENTSTRATEGIESAREREQUIREDTOlNDORCAPTUREDIFFERENTDIETS THE USE OF A LESS PROlTABLE RESOURCE LOWERS THE GAIN PER UNIT EFFORT 4HERE ARE A NUMBER OF EXAMPLES IN WHICH ORGANISMS SWITCH TO MORE VALUABLE OR ABUNDANT DIETS AS THE RELATIVE ABUNDANCE OR QUALITY OF THE POTENTIAL DIETS CHANGE SEE 3TEPHENS AND +REBS 4HE OTHER SWITCHING BEHAVIOR IS A DEFENCE SWITCH #ONSIDER A PREY SPECIES WITH MULTIPLE PREDATORS AND ASSUME THAT THE AVOIDANCE OF DIFFERENT PREDATORS REQUIRES DIFFERENT STRATEGIES WITH TRADE OFFS BETWEEN THEM 4HISMIGHTOCCURWHENPREDATORSATTACKINDIFFERENTMANNERSORTHETOTALPREDA TORAVOIDANCEEFFORTISLIMITED3OLUK3IHETAL )NSUCHACASE APREY MUST ALLOCATE ITS DEFENCE EFFORT AMONG THE POTENTIAL PREDATORS WITH MORE EFFORT BEINGALLOCATEDTOTHEMORERISKYPREDATOR,IMA


&IG &ROM THE VIEWPOINT OF CONTACT EXPERIENCE A BIOLOGICAL INVASION IS DIVIDED INTO FOURPHASESTHE) PRE ADAPTATION )) ADAPTIVE MISMATCHING ))) NATIVE ADAPTATION AND )6 POST ADAPTATIONPHASES&IRST JUSTAFTERTHEINTRODUCTION THEALIENANDNATIVESPECIES ARENOTEXPERIENCEDWITHEACHOTHER ANDTHEIRTROPHICINTERACTION WHICHDEPENDSONTHE PRE ADAPTATIONLEVELOFEITHERSPECIES ISUNLIKELYTOHAVEACONSISTENTPATTERNIE 0HASE) PRE ADAPTATIONPHASE 3ECOND THEALIENSPECIESSTARTSTOGAINEXPERIENCEWITHTHENATIVE SPECIESHOWEVER THENATIVESPECIESCANNOTGAINEXPERIENCEWITHTHEALIENSPECIESBECAUSE THE ABUNDANCE OF THE ALIEN SPECIES IS LOW 4HIS ALIEN BIASED ADAPTIVE PROCESS PROVIDES THE ALIEN SPECIES WITH A MINORITY ADVANTAGE RESULTING IN THE RAPID GROWTH OF THE ALIEN SPECIESIE 0HASE))ADAPTIVE MISMATCHINGPHASE 4HIRD AFTERTHEALIENSPECIESBECOMES ABUNDANT THENATIVESPECIESBEGINSTOGAINEXPERIENCEWITHTHEALIENSPECIESIE 0HASE )))NATIVEADAPTATIONPHASE $URINGTHISTHIRDPHASE THELOCALCOMMUNITYCANEFlCIENTLY SUPPRESSANALIENSPECIES)NTHELASTPHASE THEALIENANDNATIVESPECIESAREWELLADAPTEDTO EACHOTHER0HASE6)POST ADAPTATIONPHASE ANDTHEPOPULATIONOFTHEALIENSPECIESWILL BECOMECOMPARABLETOTHATOFTHENATIVESPECIES4HESOLIDANDDOTTEDLINESREPRESENTTHE SUPERIORITYOFANALIENSPECIESTOANATIVESPECIESANDTHEPOPULATIONABUNDANCEOFTHEALIEN SPECIES RESPECTIVELY;3UPERIORITY=MEANSNOSUPERIORITY;POPULATIONLEVEL=MEANS COMPARABLEABUNDANCEOFTHEALIENSPECIESTOTHATOFNATIVESPECIES

4HEORY SUGGESTS THAT A FORAGING SWITCH ENHANCES SPECIES COEXISTENCE EG 4ANSKY 'LEESON AND 7ILSON #ONSIDER A SIMPLE TROPHIC SYS TEM CONSISTING OF TWO PREY SPECIES AND ONE PREDATOR SPECIES )N THE ABSENCE OF A FORAGING SWITCH THE TWO PREY SPECIES MIGHT NOT COEXIST BECAUSE THE SPECIES WITHLOWVULNERABILITYTOPREDATIONTENDSTOOUT COMPETETHEOTHERTHROUGHTHE NEGATIVE INDIRECTEFFECTMEDIATEDBYTHESHAREDPREDATORAPPARENTCOMPETITION (OLT "YCONTRAST INTHEPRESENCEOFAFORAGINGSWITCH THETWOPREYSPECIES CANCOEXISTBECAUSETHESPECIESTHATISLESSABUNDANTTENDSTOBEATTACKEDLESSOFTEN BY THE SWITCHING PREDATOR /NE PREY SPECIES CAN PROVIDE ANOTHER PREY SPECIES WITH AN OPPORTUNITY TO AVOID THE PREDATOR 4HE SAME IS TRUE FOR MORE COMPLEX SYSTEMS+ONDOH

-+ONDOH

!DEFENCESWITCHALSOENHANCESSPECIESCOEXISTENCE,IMA-ATSUDAETAL )NASIMPLESYSTEMCONSISTINGOFTWOPREDATORSPECIESANDONEPREY SPECIES THETWOPREDATORSPECIESTENDNOTTOCOEXISTBECAUSERESOURCECOMPETITION LEADSTOTHEEXTINCTIONOFTHEINFERIORPREDATORSPECIES4ILMAN )NTHEPRES ENCEOFANADAPTIVEDEFENCESWITCH HOWEVER ACOMPLETELYDIFFERENTPICTUREARISES !NADAPTIVEPREYISMORELIKELYTOBEDEFENSIVEAGAINSTTHEMOREABUNDANTPREDA TORSPECIES CREATINGAMECHANISMOFMINORITYADVANTAGE4HEREFORE THESWITCH INGPREYCANENHANCETHEPREDATORSCOEXISTENCE-ATSUDA ETAL SHOWED THATANADAPTIVEDEFENCEPREVENTSTHEEXTINCTIONOFTHEPREDATORSPECIESINATWO TROPHIC LEVEL SYSTEM WITH HIGHER SPECIES RICHNESS SUGGESTING THAT THE DEFENCE SWITCHCANENHANCESPECIESCOEXISTENCEINACOMPLEXFOODWEB4HISISALSOTRUEIN ANEVENMORECOMPLEXFOODWEB+ONDOH UNPUBLISHEDMANUSCRIPT )N GENERAL ADAPTIVE SWITCHING BEHAVIOR REQUIRES THE ABILITY TO DISCRIMINATE MULTIPLEPREYORPREDATORSPECIESANDKNOWLEDGEOFTHERELATIVEQUANTITYORQUAL ITYOFTHEPOTENTIALLYINTERACTINGSPECIES3TEPHENSAND+REBS #ONSIDERONE PREDATORANDMULTIPLEPREYSPECIES FOREXAMPLE4HEFORAGERISUNLIKELYTOBEABLE TOCHOOSETHEMOREABUNDANTORMORENUTRITIOUSPREYSPECIESIFTHISPREYSPECIES IS NOT DIFFERENTIATED FROM OTHER PREY SPECIES 3IMILARLY IN THE ABSENCE OF SPE CIESRECOGNITIONABILITY APREYSPECIESISUNLIKELYTOMAKEACORRECTSWITCHINITS DEFENCEBEHAVIORAGAINSTPREDATORS 4HE FACT THAT TROPHIC INTERACTION RELATED SWITCHING BEHAVIOR WHICH REQUIRES CORRECT RECOGNITION OF THE INTERACTING SPECIES TENDS TO ENHANCE SPECIES COEX ISTENCE SUGGESTS ANOTHER IMPORTANT ROLE OF CONTACT EXPERIENCE IN MAINTAINING BIODIVERSITY!NALIEN NATIVEINTERACTION INWHICHSPECIESRECOGNITIONISLESSLIKELY TOOCCUR MIGHTAFFECTBIODIVERSITYMAINTENANCEINACOMPLETELYDIFFERENTWAYFROM THATOFANATIVE NATIVEINTERACTION-ORESPECIlCALLY ANALIEN NATIVEINTERACTION MIGHT BE MORE LIKELY TO LOWER THE PROBABILITY OF SPECIES COEXISTENCE THAN WOULD ANATIVE NATIVEINTERACTION 4HIS INTERPRETATION IS BASED ON A MODEL ANALYSIS BY +ONDOH 5SING A DYNAMIC MATHEMATICAL MODEL OF A FOOD WEB &IG +ONDOH REVEALED ANIMPORTANTROLEOFTHEFORAGINGSWITCHINBIODIVERSITYMAINTENANCE#ONSIDERA FOODWEBOF.SPECIES EACHOFWHICHISCONNECTEDBYADIRECTEDTROPHICLINKWITH PROBABILITY#CONNECTANCE )NTHISMODEL #DETERMINESTHENUMBEROFPOTENTIAL PREYSPECIESTHATACONSUMERCANUSEIE ;. =#ONAVERAGE !CONSUMERSPE CIESISCAPABLEOFCHOOSINGTHEMOREABUNDANTPREYSPECIESFROMTHEPOTENTIALDIET WITHPROBABILITY&"YCONTRAST AFRACTION & OFPREDATORSDOESNOTDISCRIMINATE BETWEEN PREY SPECIES AND USES EVERY POTENTIAL PREY +ONDOH ANALYZED THE INTERACTIVE EFFECT OF THE PREDATORS CAPABILITY OF AN ADAPTIVE FORAGING SWITCH AND THE FOOD WEB COMPLEXITY ON COMMUNITY PERSISTENCE 4HE ANALYSIS SHOWED THATANADAPTIVEFORAGINGSWITCHPOTENTIALLYINVERTSTHECOMPLEXITY STABILITYRELA TIONSHIPOFAFOODWEB)NTHEABSENCEOFADAPTIVESWITCHINGBEHAVIOR INCREASING FOOD WEB COMPLEXITY LOWERS COMMUNITY PERSISTENCE WHILE IN THE PRESENCE OF ADAPTIVE SWITCHING A COMMUNITY IS MORE LIKELY TO BE PERSISTENT WHEN THE FOOD WEBSTRUCTUREISMORECOMPLEX+ONDOH &URTHER THERELATIONSHIPBECOMES


&IG 0OPULATIONPERSISTENCECHANGINGWITHCHANGINGFRACTIONOFADAPTIVEFORAGERSFOR VARYINGFOOD WEBCOMPLEXITY#n .n #ONSIDERAFOODWEBWITH.SPECIES ANDCONNECTIONPROBABILITY#0OPULATIONDYNAMICSOF3PECIESIISGIVENBY Æ8I"RInSI8I -EIKFKIAKI8K n -FKIAKI8K " KDSPISPREY KDSPISPREDATOR WHERE RI IS THE INTRINSIC GROWTH RATE SI THE SELF REGULATION STRENGTH EIJ THE CONVERSION EFlCIENCYFIJTHEFORAGINGEFlCIENCYOFPREDATORIONPREYJAIJTHEFORAGINGEFFORTOFPREDATOR IALLOCATEDTOPREYJ4HEFORAGINGEFFORTOFADAPTIVEFORAGERCHANGESTOINCREASETHEENERGY GAINPERUNITEFFORT ÆIJ'AIJ"EIJFIJ8J n -EIKFKIAKI8K " KDSPISPREY 3EE+ONDOH FORMOREDETAIL)USEDTHEFOLLOWINGPARAMETERSTOCREATETHISlGURE 8I AIJ RI SI EIJ FIJ ' RAN; = THE NUMBER OF POTENTIAL PREY SPECIES RAN; = RAN; = 2ANDOM MODEL IS USED AS A FOOD WEB TOPOLOGY 0OPULATIONPERSISTENCEISDElNEDBYLN;THEPROBABILITYTHATNOSPECIESGOEXTINCT=.

-+ONDOH

CLOSER TO NEGATIVE AS THE FRACTION OF ADAPTIVE FORAGERS DECREASES OR THE SPEED OF THEADAPTIVESWITCHDECREASES+ONDOH !POSSIBLEINTERPRETATIONOF+ONDOHSRESULT ISTHATACOMMUNITYWITH A GREATER FRACTION OF ALIEN SPECIES IS MORE LIKELY TO LOSE A SPECIES ESPECIALLY IN A MORECOMPLEXFOODWEB&IG "ECAUSEANALIENSPECIESISLESSLIKELYTODISCRIMI NATEBETWEENNOVELNATIVESPECIES ITMIGHTNOTBEABLETOSWITCHDIETSCORRECTLY IMPLYING THAT A CORRECT FORAGING SWITCH IS LESS LIKELY TO OCCUR AS THE FRACTION OF ALIENSPECIESINCREASESINTHEFOCALFOODWEB&URTHER IFANATIVEPREDATORCONFUSES ANALIENSPECIESWITHANATIVEPREY THEPREDATORMIGHTFAILTOEVALUATETHERELA TIVEABUNDANCEORQUALITYOFTHENATIVESPECIES4HUS THEINTRODUCTIONOFANALIEN SPECIESINTERRUPTSSWITCHINGBEHAVIORANDCANTHREATENLOCALBIODIVERSITYBYLOW ERINGTHEPOPULATIONSTABILITY )NTHISSCENARIO THEEFFECTOFANALIENSPECIESISANALOGOUSTOTHECONFUSIONOF THEBODYSSIGNALINGSYSTEMCAUSEDBYENDOCRINEDISRUPTORS#OLBORNETAL %NDOCRINE DISRUPTORS OCCUPY A HORMONE RECEPTOR AND ARE MISTAKENLY RECOG NIZEDASTHECORRECTHORMONE RESULTINGINABODYDISORDER#OLBORNETAL 4HE OCCUPATION INTERFERES WITH THE PROPER HORMONE SIGNAL AND PRODUCES AN EXCESSIVE OR INSUFlCIENT CELLULAR RESPONSE #OLBORN ET AL )F BIODIVERSITY IS MAINTAINED BY ADAPTIVE SWITCHING BEHAVIOR AS +ONDOH SUGGESTS AN ALIENSPECIESTHATCONFUSESSPECIESRECOGNITIONMIGHTBEREGARDEDASANENDOCRINE DISRUPTORATTHECOMMUNITYLEVEL

35--!29 4HISCHAPTERPRESENTSAHYPOTHESISOFTHEWAYINWHICHTHELACKOFCONTACTEXPERI ENCEINmUENCESTHETROPHICINTERACTIONBETWEENALIENANDNATIVESPECIES!LACKOF CONTACTEXPERIENCECANLEADTOAFAILUREOFTROPHICROLERECOGNITION PREYHANDLING ORPREDATORAVOIDANCE WHICHCANRESULTINATROPHICINTERACTIONWITHABNORMALLY HIGHORLOWSTRENGTHANDDESTABILIZEDPREY PREDATORINTERACTIONS!MISMATCHIN THE ADAPTATION SPEED BETWEEN ALIEN AND NATIVE SPECIES CAN PRODUCE A TEMPORAL EXPLOSION IN THE ALIEN SPECIES ABUNDANCE ! FAILURE OF SPECIES DISCRIMINATION IN AN ALIEN NATIVE INTERACTION CAN DISRUPT THE ADAPTIVE RESPONSE TO QUALITATIVE AND QUANTITATIVE CHANGES IN THE PREY OR PREDATOR AND CAN THEREBY THREATEN BIODI VERSITY 4HESE HYPOTHESES IMPLY THAT AN ALIEN NATIVE INTERACTION IS QUALITATIVELY DIFFERENT FROM A NATIVE NATIVE INTERACTION AND CREATE A GENERAL PATTERN OF ALIEN SPECIESINVASIONSANDTHEIREFFECTSONLOCALCOMMUNITIES .EVERTHELESS THESE HYPOTHESES STILL RELY ON A NUMBER OF SIMPLIFYING ASSUMP TIONSCONCERNING THEEFFECTOFEXPERIENCEONATROPHICINTERACTION4HESEASSUMPTIONS TIONS ARE REQUIRED BECAUSE WE KNOW LITTLE ABOUT HOW CONTACT EXPERIENCE AFFECTS SUCHMACROSCOPICPROPERTIESASTROPHICINTERACTIONSTRENGTH TROPHICLINKmEXIBIL ITY ANDPOPULATIONSTABILITY7ENEEDTOEXAMINETHEBEHAVIORALBASISOFATROPHIC INTERACTIONANDTESTTHEPOSSIBILITYTHATANALIEN NATIVEINTERACTIONISQUALITATIVELY DIFFERENT FROM A NATIVE NATIVE INTERACTION )N SO DOING IT IS IMPORTANT TO ISOLATE


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-+ONDOH

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).42/$5#4)/. /NEOFTHEDIFlCULTIESOFCONSERVATIONBIOLOGYISTHEGENERALLACKOFEXPERIMENTAL APPROACHES "ECAUSE IT IS OFTEN UNETHICAL OR SIMPLY BECAUSE THIS NEW DISCIPLINE DEALSWITHSMALLANDORFRAGILEPOPULATIONS EXPERIMENTSONTHOSEPOPULATIONSARE NOT ALWAYS FEASIBLE !S A RESULT THE KNOWLEDGE ON POPULATION DYNAMICS WHEN NOT DEALING WITH LABORATORY POPULATIONS OF CAGED INVERTEBRATES HAS OFTEN COME FROMTHEORETICALSTUDIES WITHNOTABLEEXCEPTIONSSUCHASTHOSEBASEDONOFSOME POPULATIONS ISOLATED ON PARTICULAR ISLANDS EG #LUTTON "ROCK AND #OULSON 'RENFELL ET AL (OWEVER ONE ASPECT THAT IS OFTEN LACKING FROM THEORETICALSTUDIES ASWELLASFROMNATURALISOLATEDPOPULATIONS ISTHEINTERSPECIlC DIMENSIONINTHEABOVECASES ITISRATHEREXCEPTIONALTOTAKEINTOACCOUNTMORE THANTWOINTERACTINGPOPULATIONS9ET ASWEHOPETOSHOWINTHISCHAPTER DIRECT AND INDIRECT hCOMPLEXv INTERSPECIlC RELATIONSHIPS MAY BE THE MAJOR ECOLOGICAL FORCESINSOMECOMMUNITIES4HEYCANTHUSBECRUCIALFORAPPLIEDECOLOGYASWELL -7#ADOTTE ETAL (EDS) #ONCEPTUALECOLOGYANDINVASIONBIOLOGY n ¥3PRINGER0RINTEDINTHE.ETHERLANDS

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AS REPRESENT HEURISTIC TOOLS FOR STUDENTS AND INTELLECTUAL CANDIES FOR FUNCTIONAL ECOLOGISTS (OWEVER THEREISANENORMOUSSETOFECOLOGICALEVENTSTHATCANBEVIEWEDAS NATURAL LARGE SCALEEXPERIMENTSBIOLOGICALINVASIONS3EVERALASPECTSMAKEBIO LOGICALINVASIONSANINTERESTINGTOOLFORTHESTUDYOFINTERSPECIlCINTERACTIONSTHEY AREOFVARIOUSTYPES INVOLVEMANYDIFFERENTORGANISMS ANDHAPPENINCONTRASTED ECOSYSTEMS"IOLOGICALINVASIONSAREOFTENAVERYRICHSOURCEOFINFORMATIONFORTHE UNDERSTANDINGOFECOSYSTEMFUNCTIONING ASTHEYORIGINATEFROMINTRODUCTIONSTHAT AREGENERALLYRELATIVELYWELLDOCUMENTED)NADDITION INMANYCASES THEINVADED ECOSYSTEM IS AN ISLAND WITH ALL THE ADVANTAGES THAT INSULAR ECOSYSTEMS PROVIDE FOR FUNDAMENTAL RESEARCH CLOSED ECOSYSTEMS WITH LIMITED SIZE AND OF RELATIVELY SIMPLEANDNON REDUNDANTTROPHICWEBS)NTHESAMEWAYTHATTHEPHYSIOLOGYOF AN INDIVIDUAL MAY BE BETTER UNDERSTOOD DURING ILLNESS THE DISFUNCTIONING OF AN ECOSYSTEMMAYHELPGAINKNOWLEDGEABOUTITSNORMALFUNCTIONING)NTHISREGARD THECHANGESGENERATEDBYTHESIMPLEMODIlCATIONSTHATARESPECIESINTRODUCTIONS ANDTHEIRCONSECUTIVESPREADPROVIDEMANYDIFFERENTTYPESOFINFORMATION4HUS BIOLOGICAL INTRODUCTIONS REPRESENT SIMPLE EXPERIMENTS OF SPECIES ADDITION INTO A NEWTROPHICWEB3UCHEXPERIMENTSCANBENElTFROMCONTROLSANDREPLICASINTHE CASEOFARCHIPELAGOES 3IMILARLY SPECIES DELETIONS CAN BE STUDIED IN LARGE SCALE EXPERIMENTS THAT AREEVENMOREACCESSIBLETOPOPULATIONORCOMMUNITYBIOLOGISTS ASTHEYCANBE DESIGNEDBYTHEMTHECONTROLORERADICATIONOFTHEALIENSPECIES7ITHTHISNEW TOOLOFSPECIESADDITIONANDDELETIONFROMTHECOMPARATIVELYSIMPLEISLANDECOSYS TEMS ONEMAYGAINMOREKNOWLEDGEOFBASICPROCESSESSUCHASCOLONIZATION DIS PERSION SPATIALSPREAD ASWELLASTHEDYNAMICSOFINTERACTINGPOPULATIONS7EWILL HEREFOCUSONTHISLATTERASPECT RESTRICTINGOURANALYSISONTHREE ANDFOUR SPECIES INTERACTIONS ANDSHAMELESSLYBASINGITONOURPREVIOUSSTUDIES )N THIS CHAPTER WE WILL PRESENT A NUMBER OF MATHEMATICALLY SIMPLE MODELS THAT DEPICT SOME hCOMPLEXv INTERSPECIlC RELATIONSHIPS WITH THE AIM OF SHOWING HOWTHESTUDYOFBIOLOGICALINVASIONSANDTHEIRCONTROLCANBEUSEFULFORTHESTUDY OF FUNDAMENTAL ECOLOGICAL PROCESSES THAT ARE MORE PROBLEMATICAL TO UNDERSTAND INOTHERCONTEXTS(ERE COMPLEXRELATIONSHIPSAREDElNEDASINTERACTIONSWITHIN TROPHICWEBSTHATENCOMPASSMORETHANTWOPOPULATIONSWITHPOSSIBLEINDIRECT PROCESSES AND THAT MAY NOT BE REALLY COMPLEX IN A BIOLOGICAL SENSE BUT THAT AREMOREDEMANDINGTOSTUDYANALYTICALLY7EALSOUSE@CONTROLINASOMEWHAT LENIENTSTYLE4HISTERMCANHAVETWOMEANINGSITCANBEAGENERALTERMOFACTION AGAINSTANALIENSPECIESRANGINGFROMSIMPLEREDUCTIONUPTOERADICATION ANDIT CAN MORE SPECIlCALLY MEAN REDUCTION OF THE POPULATION SIZE DOWN TO ACCEPTABLE LEVELS INECOLOGICALORECONOMICTERMS4HELATTERISCALLED@MITIGATIONOR@REDUC TION AND IS OPPOSED TO @ERADICATION )N THIS #HAPTER WE WILL USE @MITIGATION FOR PARTIAL POPULATION REMOVAL @ERADICATION WHEN REMOVAL IS TOTAL AND @CON TROLASAGENERALTERM7EWILLARTICULATEOURPRESENTATIONINTWOPARTSTHElRST PART DEPICTS SYSTEMS WHERE SPECIES ARE ADDED TO A TROPHIC WEB THE BIOLOGICAL INVASIONS ANDTHESECONDPARTDEPICTSSYSTEMSWHERESPECIESAREREMOVEDCON

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SERVATION PROGRAMS FOCUSING ON THE POSSIBLE ASSOCIATED INDIRECT PROCESSES IN EACHCASE!SECONDARYOBJECTIVEOFTHISCHAPTERISTOCONVINCETHEREADERS BETHEY STUDENTSINBIOLOGYORCONSERVATIONMANAGERS THATMATHEMATICALMODELINGISA POWERFULTOOLTOUNDERSTAND ANDINSOMECASETOPREDICT ECOSYSTEMFUNCTIONING AND REACTIONS 9ET FOR PEDAGOGIC PURPOSES WE WILL PRESENT OUR ANALYSES BASED ONTHEDESCRIPTIONOFSEVERALCONCRETEEXAMPLESWITHLITTLEORNOEMPHASISONTHE TECHNICAL ASPECTS OF THE MATHEMATICAL MODELS 7E PROVIDE REFERENCES FOR MORE DETAILSABOUTTHEMODELSANDTHEIRANALYSIS !LLTHEMODELSPRESENTEDHEREAREDETERMINISTICCOUPLEDDIFFERENTIALEQUATIONS BASEDONCLASSICAL,OTKA 6OLTERRAPREDATIONORCOMPETITIONMODELS%ACHPOPULA TION IS DESCRIBED BY A SIMPLE LOGISTIC EQUATION MODIlED TO TAKE INTO ACCOUNT ITS RELATIONSHIPWITHTHEOTHERPOPULATIONS !LTHOUGHBIOLOGICALLYSIMPLE THEMOD ELSPRESENTEDHERECANSHOWARELATIVELYHIGHMATHEMATICALCOMPLEXITYWHENIT COMES TO FOR EXAMPLE DETERMINING EQUILIBRIUM POINTS #ONlDENT THAT THE SIM PLESTMODELSARETHEMOSTUSEFUL'INZBURGAND*ENSEN WESYSTEMATICALLY REFRAINEDFROMUNDULYADDINGCOMPLEXITYTOOUREQUATIONS WHICHRESULTSINALACK OF PREDICTIVE POWER 4HESE MODELS ARE THEREFORE NOT AIMED AT PROVIDING PRECISE VALUESOFPOPULATIONTRENDSOROFCONTROLMEASURESINTHElELDNEITHERTHENATURE OFTHEMODELS NORTHESTATEOFCURRENTKNOWLEDGEINTHElELDWOULDALLOWUSEFUL QUANTITATIVEPREDICTIONS2ATHER THEAIMOFTHISEXERCISEISTOEMPHASIZETHELINK BETWEENSPECIES THEIMPORTANCEOFINDIRECTINTERACTIONS ANDTHEUNEXPECTEDOUT COMEOFCONTROLACTIONSIFTHEYARENOTTHOROUGHLYTAKENINTOACCOUNT7EBELIEVE THATTHEQUALITATIVEINFORMATIONPROVIDEDBYOURMECHANISTICMODELSISSUITABLETO OFFERTHEINFORMATIONWESEEKINTHISCONTEXT!LSO WHILEPARAMETERISINGMODELS TOREPRODUCElELDRESULTSISAVERYUSEFULWAYOFIDENTIFYINGPLAUSIBLEMECHANISMS OFTROPHICINTERACTIONS ITDOESNOTINITSELFPROVIDEADIRECTTESTOFTHEIMPORTANCE OFTHOSEPLAUSIBLEMECHANISMS4HEINFORMATIONTHEYGENERATESHOULDALWAYSBE COMPLETED BY INFORMATION COMING FROM EMPIRICAL AND EXPERIMENTAL STUDIES )N THIS#HAPTER WEWILLONLYDEALWITHTHEMODELINGPART )NORDERTORENDERTHEREADINGOFTHISCHAPTERLESSTEDIOUS WEWILLDESCRIBEIN DETAILTHEPROCESSLEADINGTOTHEMODELFORTHElRSTEXAMPLEONLY ANDWILLONLYGIVE THEMODELFORTHEOTHEREXAMPLES!LTHOUGHSOMEWILLDIFFERINDETAILS ALLMODELS AREBASEDONSIMILARPRINCIPLES!PARTFROMTHEMORECOMPLETEDESCRIPTIONOFTHE lRSTCASE ALLEXAMPLESWILLBEPRESENTEDINASIMILARWAY TOALLOWEASYCOMPARI SONSBETWEENCASES

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A 4HECASE )NTRODUCED SPECIES ARE NOTORIOUS FOR THEIR DELETERIOUS IMPACT ON INVADED COM MUNITIESANDTHEIRDIRECTEFFECTSONTROPHICSYSTEMS SUCHASDECREASEOFPREYOR COMPETITOR POPULATIONS 7HILE THEY REPRESENT CATASTROPHIC EVENTS IN TERMS OF BIODIVERSITY CONSERVATION THOSE EFFECTS ARE NOT OF MAJOR INTEREST TO THEORETICAL ECOLOGY &OR THIS REASON WE WILL FOCUS ON LESS OBVIOUS EFFECTS STARTING WITH AN EXAMPLECONCERNINGTHEEXTINCTIONOFANENDEMICPARROTCAUSEDBYTHEINTRODUC TIONOFRABBITSTOANINSULARSYSTEM 4HE RABBIT IS ONE OF THE MOST DOCUMENTED INTRODUCED MAMMAL SPECIES OFTEN ASSOCIATED WITH A DRAMATIC IMPACT ON ENDEMIC PLANT SPECIES 4O DATE THIS HER BIVORE HAS BEEN INTRODUCED MOST OF THE TIME PURPOSEFULLY TO MORE THAN ISLANDS &LUX AND &ULLAGAR 2ABBITS HAVE A HIGH ECOLOGICAL ADAPTABILITY ANDASSUCHEASILYSUCCEEDWHENINTRODUCEDINTOECOSYSTEMSWHEREINDIGENOUS GRAZERSARELESSNUMEROUSANDCOMPETITIVE&LUX 4HEVERYRAPIDINCREASE OFTHEIRPOPULATIONSCANLEADTOADRAMATICQUANTITATIVEANDQUALITATIVEIMPOVER ISHMENTOF THEVEGETATION#HAPUISETAL 3ELKIRK ETAL RESULTINGIN DRAMATIC DENUDATION OF THE SOIL 3COTT AND HAVE AN IMPACT ON ANIMAL SPECIESWHICHDEPENDONTHEVEGETATION'ILLHAM %FFECTS OF RABBITS ON INDIGENOUS VERTEBRATE SPECIES CAN ALSO BE MORE COMPLEX 4HESEMAMMALSAREPREYEDUPONBYOTHERINTRODUCEDVERTEBRATES INPARTICULARBY FERALDOMESTICCATS#ATS FOREXAMPLE AREOPPORTUNISTICPREDATORSWHICHSWITCH PREYACCORDINGTORELATIVESPATIALANDORTEMPORALAVAILABILITY&ITZGERALD 7HENRABBITSAREABUNDANT DOMESTICCATSAREKNOWNTOPREYLARGELYUPONTHEM (OWEVER RABBITSCANCONSTITUTEASMALLERPARTOFTHECATDIETWHENBIRDS REPTILES OROTHERMAMMALSARERELATIVELYMOREABUNDANT)NSEVERALSUB !NTARCTICISLANDS RABBITSAREONLYASECONDARYPREYITEMINMONTHSWHENSEABIRDSAREPRESENT BUT APPEARTOENABLECATSTOSUBSISTOVERWINTERWHENSEABIRDSAREABSENT#HAPUIS A B !SIMILAREFFECTISDOCUMENTEDINTHESPATIALDIMENSIONRABBITSOFTEN ENABLECATSTOREACHREMOTECOLONIESORPOPULATIONSOFINDIGENOUSPREYINISLANDS WITH HETEROGENEOUS INDIGENOUS PREY DISTRIBUTION "ROTHERS AND #OPSON )NTHESECASES THEPRESENCEOFRABBITSHASANINDIRECTEFFECTONOTHERPREYSPECIES USEDBYINTRODUCEDCATS 0REDATIONBYCATSINTRODUCEDTO-ACQUARIE)SLANDCAUSEDTHEDECLINEOFBURROW NESTINGPETRELS"ROTHERS ANDTHEEXTINCTIONOFANENDEMICPARAKEETAND ABANDEDRAIL4AYLOR #ATSWEREINTRODUCEDTOTHEISLANDYEARSBEFORE THEINTRODUCTIONOFRABBITS HOWEVERTHECATDRIVENEXTINCTIONOFBIRDSDATESBACK


TOJUSTYEARSFOLLOWINGTHEINTRODUCTIONOFRABBITS4AYLOR 2ABBITSWERE NOTOBSERVEDASHAVINGANYDIRECTEFFECTSONTHELANDBIRDS)NFACT ITISBELIEVED THAT THE RABBIT POPULATION ALLOWED A SIGNIlCANT INCREASE IN THE CAT POPULATION RESULTING IN AN INCREASED PREDATION PRESSURE ON THE LAND BIRD SPECIES 4HIS PRO CESS RELATED TO THE MORE GENERAL hAPPARENT COMPETITIONv EG !BRAMS !BRAMS ET AL (OLT HAS BEEN TERMED HYPERPREDATION #OURCHAMP ETAL3MITHAND1UIN )T IS GENERALLY ASSUMED THAT LIFE HISTORY TRAITS AND BEHAVIOR OF THE INTRODUCED PREYMAKEITRESISTANTTOHIGHLEVELSOFPREDATIONPRESSURE!HIGHERREPRODUCTIVE RATE HIGHDENSITYANDEFlCIENTANTI PREDATORRESPONSESWHICHAREOFTENLACKINGIN THEINDIGENOUSSPECIES EXHIBITEDBYTHEINTRODUCEDPREYCOULDENABLEANINCREASE INTHEPREDATORPOPULATIONWITHOUTALARGEDECREASEINTHEINTRODUCEDPREYPOPU LATION&URTHERMORE THELACKOFSERIOUSCOMPETITORSANDTHERELATIVELYFEWPARA SITESTYPICALLYFOUNDININTRODUCEDPOPULATIONSCANALSOINCREASETHEIRPOTENTIALFOR DRAMATICPOPULATIONGROWTHTHEENEMYRELEASEHYPOTHESIS+EANEAND#RAWLEY 4HESEFEATURESIMPLYTHEABILITYTOSUSTAINHIGHPREDATIONPRESSURE ASCATS ARESUPPOSEDTOREMOVEONLYTHEINDIVIDUALSWITHLOWSURVIVALDISPERSINGYOUNG SICK AND DEAD 3MITH AND 1UIN 4HE RESULTING INCREASED POPULATION OF PREDATORS CANNOT BE SUSTAINED BY THE INDIGENOUS PREY SPECIES WHICH COMPARED WITHTHEINTRODUCEDPREYSPECIES HASINFERIORLESSWELLADAPTED REPRODUCTIVEAND ANTI PREDATOR CHARACTERISTICS 4HE CONJUNCTION OF A LOW ADAPTATION TO PREDATION ANDANARTIlCIALLYHIGHPREDATIONPRESSURECANLEADTOADRAMATICDECREASEINAN INDIGENOUSPREYPOPULATION UPTOTOTALEXTIRPATION B 4HEMODEL 7E WILL THUS PRESENT A SIMPLE MODEL OF HYPERPREDATION TO ILLUSTRATE HOW THE EXTINCTION OF THE BIRD POPULATION ON -ACQUARIE )SLAND CAN BE EXPLAINED BY AN INDIRECTEFFECTOFTHEINTRODUCEDRABBITS&ORHEURISTICPURPOSES WElRSTPRESENTA TWO SPECIESMODEL ANDTHENMODIFYITINTOATHREE SPECIESMODEL7EHOPETHAT THISWILLHELPTHEUNDERSTANDINGOFTHISMODELANDOFTHEOTHERSETSOFEQUATIONS INTHISCHAPTERWHICHAREALLBASEDONTHESAMEPRINCIPLE 7EUSETHEEXAMPLE OF BIRD LOCAL PREY RABBIT INTRODUCED PREY AND CAT INTRODUCED PREDATOR AND WILLREFERTOTHESESPECIESFORTHESAKEOFSIMPLICITY BUTOTHERSPECIESCANPRESENT SIMILARRELATIONSHIPS 4HEBIRD CATMODELCANBEGIVENTHEFOLLOWINGFORM ¨ µ µ © µ µ ª

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FOR THE BIRD AND THE RABBIT PREDATION RATES RESPECTIVELY SO THAT THE PREDATION RATEISSTILLAFUNCTIONOFTHEAVAILABILITYOFTHEPREYBUTVARIESWITHRELATIVEPREY PROPORTIONS4HEADAPTATIONOFTHEINTRODUCEDPREYINTERMSOFANANTI PREDATOR BEHAVIORAL RESPONSE IS GIVEN BY A PREFERENCE OF THE PREDATOR FOR THE INDIGENOUS PREY WHICH IS MORE EASILY DETECTED ANDOR CAUGHT OVER THE INTRODUCED PREY 4HISPREFERENCEISARATIO_ WITHASIMPLEBIOLOGICALMEANINGGIVENEQUALAVAIL ABILITY THEPREDATORWILLPREYUPONTHEINDIGENOUSPREY_TIMESMOREOFTENTHAN ONTHEINTRODUCEDPREY7EASSUMETHAT_* ANDTHATONERABBITANDONEBIRD PREYITEMSAREENERGETICALLYEQUALLYVALUABLETOTHECAT4HEPREDATIONTERMSARE NOWGIVENBY

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.OTETHATSIMILARFORMULATIONSOFTHEMODELCOULDBEUSEDANDTHATTHEAFORE MENTIONEDCHOICESAREARBITRARY)NPARTICULAR WEUSEDAPREDATIONTERMPROPOR TIONAL TO THE NUMBER OF PREY 7E DID SO TO KEEP THE FORMULATION OF THE ORIGINAL PAPER#OURCHAMPETAL BUTALTERNATIVEMODELSCANREPRODUCETHEHYPER PREDATIONPROCESS!LSO LIKEFORTHERESTOFTHEMODELSPRESENTEDINTHISCHAPTER WEDONOTTAKEINTOACCOUNTTHEFURTHERRISKSENCOUNTEREDBYPOPULATIONSWHENAT SMALLSIZESENVIRONMENTALANDDEMOGRAPHICSTOCHASTICITY !LLEEEFFECTSETC -OST OFTHOSEWOULDANYWAYONLYSTRENGTHENOURPOINT4HECLASSICALCOMPARTMENTAL REPRESENTATIONOFTHEMODELISPRESENTEDIN&IG! THECORRESPONDINGSETOFEQUA TIONSISSHOWNIN&IG" ANDASELECTEDREPRESENTATIONOFTHEPOPULATIONTRENDS WITHTIMEISGIVENIN&IG#4HEOTHEREXAMPLESWILLBEILLUSTRATEDWITHlGURES FOLLOWINGTHESAMEFORMAT 4HE STUDY OF THIS SET OF EQUATIONS BOTH ANALYTICALLY AND NUMERICALLY SEE #OURCHAMP ET AL SHOWS THAT THE INDIRECT EFFECT OF THE INTRODUCED PREY MAY BE VERY IMPORTANT )NDEED ACCORDING TO THE VALUES OF THE PARAMETERS THE INCREASE OF THE PREDATOR POPULATION TRIGGERED BY THE PRESENCE OF THE INTRODUCED PREYCANDRIVETHEINDIGENOUSPREYTOVERYLOWNUMBERSANDPOTENTIALLYTOEXTINC TION 4HE EFFECT OF HYPERPREDATION IS THE STRONGEST FOR SPECIES WITH LOW INTRINSIC GROWTHRATEANDLOWENVIRONMENTALCARRYINGCAPACITY4HISMODELALSOILLUSTRATES THATTHEHYPERPREDATIONPROCESSMAYBEDUETOACOMBINATIONOFWELL ADAPTEDLIFE HISTORYTRAITSANDEFlCIENTBEHAVIORALRESPONSEOFPREY BUTTHATTHEhBETTER ADAPTEDv BEHAVIORALRESPONSEMAYHAVEMOREIMPORTANCETHANhBETTER ADAPTEDvLIFEHISTORY TRAITS ATLEASTFORTHECASESCONSIDERED#OURCHAMPETAL 4HUS APREYSPE CIESINTRODUCEDINTOANENVIRONMENTINWHICHAPREDATORHASALSOBEENINTRODUCED ISLIKELYTOALLOWSOHIGHANINCREASEOFTHISPREDATOR THATLOCALPREY LESSADAPTEDTO HIGHLEVELSOFPREDATION COULDSUFFERAPOPULATIONDECLINEANDPOSSIBLYEVENEXTINC TION3UCHAPROCESSHASCONSEQUENCESWHENITCOMESTOMANAGEMENTACTIONS C #ONSERVATIONCONSEQUENCES (ISTORICALLY CONSERVATION PROGRAMS FOR MANY ISLANDS HAVE PROCESSED CASE BY CASE5NTILRECENTLY INTRODUCEDSPECIESWEREALWAYSCONSIDEREDSEPARATELY WITH AT BEST SEPARATE PROGRAMS FOR EACH SPECIES AND TIMINGS DEPENDING MOSTLY ON FUNDINGANDLOGISTICS OR MOREFREQUENTLY ONESINGLEPROGRAMFORTHEVISIBLYMOST

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&IG 2EPRESENTATION OF THE HYPERPREDATION MODEL WITH THE INTRODUCED PREY INDI GENOUS PREY AND INTRODUCED PREDATOR BEING ILLUSTRATED BY RABBITS 2 BIRDS " AND CATS # RESPECTIVELY ! COMPARTMENTAL REPRESENTATION AND ILLUSTRATION OF THE ISLAND FROM WHERETHEEXAMPLEISTAKEN HERE-ACQUARIE)SLAND OFF.EW:EALAND%ACHBOXREPRESENTS A POPULATION AND THE ARROWS REPRESENT mUXES BETWEEN THEM 4HE LARGE CURVED ARROW REPRESENTSANINDIRECTEFFECT%ACHSPECIESISILLUSTRATEDINACOLORTHATISALSOUSEDFORTHE SET OF EQUATIONS " AND FOR THE DRAWINGS THAT REPRESENT THE POPULATION DYNAMICS OF THE INTERACTING SPECIES AFTER INTRODUCTION OF A SPECIES # OR CONTROL OF AN INTRODUCED SPECIES $ )N THIS EXAMPLE FOLLOWING THE CAT INTRODUCTION RED ARROW THE INCREASE OF THE CAT POPULATIONALLOWEDBYTHELARGEPOPULATIONOFRABBITSLEADSTOBIRDEXTINCTION# &OLLOWING CONTROL GREEN ARROW IN $ THE BIRD POPULATION ONLY PARTIALLY RECOVERS IF ONLY THE CAT IS CONTROLLEDTOPPANELOF$ (OWEVER THESAMECATCONTROLLEVELLEADSTOCATERADICATIONAND FULLRECOVERYOFBIRDSIFBOTHTHERABBITSANDTHECATARECONTROLLEDBOTTOMPANELOF$


DEVASTATINGSPECIES!SARESULT WHENACONSERVATIONPROGRAMINVOLVEDANISLAND SUCHASTHEONEWEJUSTMENTIONED WITHAHYPERPREDATIONPROCESSTAKINGPLACE THEKEYROLEOFTHEINTRODUCEDPREYWASNOTSYSTEMATICALLYOBVIOUS0REDATORSARE OFTENPERCEIVEDASHAVINGTHEMOSTIMPORTANTDELETERIOUSEFFECTSONINVADEDECO SYSTEMS AND CONSEQUENTLY CONTROL PROGRAMS WERE MORE OFTEN DIRECTED AT THEM SOMETIMESNEGLECTINGTHEINTRODUCEDPREY9ET WEHAVEJUSTSEENTHATINTHEPRES ENCEOFINTRODUCEDPREDATORS INTRODUCEDPREYCOULDHAVEANINDIRECTIMPACTON INDIGENOUSPREY"ASINGOUREFFORTSONTHEMODELPRESENTEDINTHEPREVIOUSSECTION OFTHISCHAPTER WESTUDIEDTHERELATIVEEFlCIENCYOFCONTROLPROGRAMSAIMINGEITHER ATTHEPREDATORONLY ORATTHEINTRODUCEDPREYANDPREDATORSIMULTANEOUSLY4HE MODEL ON WHICH WE BASED THIS HAS BEEN PUBLISHED IN #OURCHAMP ET AL ANDTHISMODELISONLYSLIGHTLYDIFFERENTFROMTHEASSOCIATEDMODELWITHOUTCONTROL #OURCHAMPET AL 7EWILLNOTREPRODUCETHEMODELHERE ASTHEINTEREST LIESNOTINTHEDETAILSOFTHEEQUATIONS4HEONLYIMPORTANTPOINTISTHEADDITIONOF ACONTROLEFFORTONEITHERTHEALIENPREYORTHEALIENPREDATORORBOTH 4HISCONTROL ISADDEDTOTHECORRESPONDINGEQUATIONBYASIMPLELINEARTERM7EEMPHASIZETHE FACTTHAT INTHEMODEL THEINTRODUCEDPREYRABBIT STILLHASNODIRECTEFFECTONTHE LOCALPREYBIRD 3OMEPOSSIBLEPOPULATIONTRENDSOFTHESYSTEMINPRESENCEOFCONTROLARESHOWN IN &IG $ 4HE STUDY OF THIS MODEL SHOWS THAT CONTROL OF RABBITS CAN FACILITATE THE ERADICATION OF CATS )NDEED WHEN NO CONTROL IS UNDERTAKEN THE CAT POPULA TIONSTAYSLARGE MAINLYBECAUSEOFTHEPRESENCEOFRABBITS ANDCANELIMINATETHE BIRDSINTHELONGTERM7HENCATSONLYARECONTROLLED THEPRESENCEOFRABBITSCAN PRECLUDECATERADICATION ANDTHEBIRDPOPULATIONRECOVERYISONLYPARTIAL)NCON TRAST FORTHESAMECATCONTROLEFFORT ERADICATIONOFRABBITSALLOWSERADICATIONOF CATSANDTOTALRECOVERYOFBIRDS!CTUALLY IFTHECONTROLOFINTRODUCEDPREYISNOT SUFlCIENT THEINDIGENOUSPREYWILLBEDESTROYED EVENIFTHEPREDATORPOPULATION ISBEINGCONTROLLED /BVIOUSLY WE ARGUE HERE THAT EVEN IN ABSENCE OF VISIBLE DIRECT EFFECT INTRO DUCEDPREYSHOULDBECONTROLLEDWHENAPREDATORHASBEENINTRODUCED INORDER TO PREVENT AN ARTIlCIAL PREDATOR POPULATION INCREASE )N ADDITION REMOVING AN INTRODUCEDPREDATORPOPULATIONWITHOUTCONTROLLINGTHEINTRODUCEDPREYMAYBE DIFlCULTTOACHIEVESINCETHEYCONSTITUTEACONSTANTSOURCEOFFOODTOTHEPREDATOR !LSO IT WOULD NOT BE AN APPROPRIATE SOLUTION BECAUSE REMOVING THE PREDA TIONPRESSUREWOULDINCREASETHEDIFlCULTIESOFLATERCOPINGWITHINTRODUCEDPREY WHICH ARE OFTEN CHARACTERIZED BY HIGH REPRODUCTIVE RATES /N THE OTHER HAND CONTROLLING ONLY THE INTRODUCED PREY IS UNSATISFACTORY IN THE LONG TERM BECAUSE PREDATORSCOULDREPORTHIGHPREDATIONPRESSUREONTHEINDIGENOUSPREY#OMBINED CONTROLOFBOTHSPECIESSEEMSHERETOBETHEBESTRESTORATIONSTRATEGY)NADDITION STARTING BOTH CONTROL PROGRAMS TOGETHER WOULD ALSO RESULT IN ADVANTAGES DUE TO SYNERGETIC EFFECTS COSTS MAY BE REDUCED IF COSTS RELATED TO TRANSPORTATION OR HUNTINGANDTRAPPINGCANBESHAREDBYTHETWOPROGRAMS ANDEFlCIENCYMIGHTBE INCREASEDEG THROUGHTHEADDITIVEEFFECTSOFPRIMARYANDSECONDARYPOISONINGOF PREDATORS&LUX 2AMMELLETAL 2OBERTSONETAL

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4OCONCLUDE ITISWORTHREITERATINGTHATTHEHIGHEREFlCIENCYOFDUALCONTROLIS NOTDUETODIRECTEFFECTSOFRABBITSONBIRDSHABITATDESTRUCTIONANDCOMPETITIONFOR FOODANDSHELTER SINCETHEYARENOTTAKENINTOACCOUNTHERE.ORISTHEPREDICTED SUCCESS OF DUAL CONTROL DUE TO THE PREFERENCE OF THE PREDATOR SINCE THIS PREFER ENCEISSETINFAVOROFTHEINDIGENOUSPREYINTHEMODEL4HISSUCCESSISDUETOTHE ADDRESSINGOFTHEHYPERPREDATIONPROCESS 4HEHYPERPREDATIONPROCESSFOUR SPECIESINTERACTIONS

A 4HECASE 4HECATISAWELL KNOWNPREDATOROFBOTHINSULARBIRDSANDSMALLINTRODUCEDMAM MALS SO THE EXAMPLE ABOVE SHOULD BE RELATIVELY EASY TO SPOT 7HENEVER A LOCAL POPULATIONISTHREATENEDBYANINTRODUCEDPREDATOR ADIETSTUDYOFTHEPREDATORIN QUESTIONSHOULDBECONDUCTEDINORDERTOASSESSTHEIMPORTANCEOFTHEIMPACTON THELOCALPOPULATION BUTALSOPOTENTIALHYPERPREDATIONPROCESSES(OWEVER THERE ARECASESWHERETHISSTRATEGYISNOTOBVIOUS BECAUSETHECAUSEOFAPREYPOPULA TIONDECLINEMAYNOTBESPOTTEDASEASILY!NINTERESTINGILLUSTRATIONOFTHISISTHE SEVEREDECLINEOFTHEINSULARFOXONTHE#HANNEL)SLANDSINTHES 4HE#HANNEL)SLANDSGROUPISMADEUPOFEIGHTSMALLISLANDSOFFTHE#ALIFORNIAN COAST 53! 4HE ISLAND GREY FOX 5ROCYON LITTORALIS IS A SMALL CARNIVORE THAT ARRIVEDONTHElRSTISLAND YEARSAGO4HEFOXNOWINHABITSTHESIXLARGEST ISLANDSANDHASEVOLVEDONEACHOFTHESEINISOLATION RESULTINGINSIXPOPULATIONS REPRESENTING SIX DIFFERENT SUBSPECIES ALL ENDEMIC TO THESE ISLANDS /N THE THREE NORTHERNISLANDS THEINSULARFOXESANDTHEIRMAINCOMPETITOR THEENDEMICSPOT TED SKUNKS 3PILOGALE GRACILIS AMPHIALA WERE THE TWO TERRESTRIAL TOP PREDATORS OF THE#HANNEL)SLANDS)NTHEEARLYS ASTUDYCONDUCTEDONTHEHOMERANGE OFTHEFOXESWITNESSEDACONSIDERABLEDECLINEINTHETHREENORTHERNISLANDPOPU LATIONS 2OEMER 4HIS SEVERE DECLINE HAD NO OBVIOUS CAUSE AT lRST AND MANY CLASSICAL ECOLOGICAL FORCES WERE INVESTIGATED LACK OF SUFlCIENT RESOURCES COMPETITIONWITHTHESPOTTEDSKUNKANDDISEASES0REDATIONWASALSOINVESTIGATED ALTHOUGH THE INSULAR FOX WAS THE TOP TERRESTRIAL PREDATOR OF THESE ECOSYSTEMS 3USPICIONTHATFOXESWEREKILLEDBYGOLDENEAGLESLEDTOANEWEFFORTOFRESEARCHIN THISDIRECTION'OLDENEAGLESHAVEHISTORICALLYBEENSEENVISITINGTHEISLANDS BUT THEY NEVER STAYED LONG ENOUGH TO CONSTITUTE A THREAT TO THE LOCAL PREY ! STUDY COMBINING METABOLIC AND ENERGETIC APPROACHES WITH POPULATION MODELING DEM ONSTRATEDTHATTHELOCALPREYWERETOOFEWTOALLOWAPAIROFDISPERSINGEAGLESTO BREEDONANDCOLONIZETHEISLANDS9ETITBECAMEOBVIOUSTHATEAGLESWEREKILLING FOXESASWELLASSPOTTEDSKUNKS/NONEOFTHESEISLANDS 3ANTA#RUZ lELDWORKERS EVENTUALLYDISCOVEREDAGOLDENEAGLENEST INWHICHFOXREMAINSATTESTEDFORTHE SUSPECTED PREDATION ON THIS SPECIES "UT THE PROBLEM REMAINED (OW WOULD THE EAGLETHREATENFOXSURVIVALTHROUGHPREDATION IFTHEREWASNOTENOUGHLOCALPREY ONTHEISLANDTOALLOWTHECONTINUOUSPRESENCEOFTHEEAGLES4HEDISCOVERYOFTHE NEST PROVIDED THE ANSWER REMAINS OF PIGLETS WERE ALSO FOUND IN THE NEST &ERAL


PIGS3USSCROFA WEREINTRODUCEDONTOTHETHREENORTHERNISLANDSWHERETHEFOXES ARE DECLINING THEY WERE ALSO PRESENT ON TWO OF THE SOUTHERN ISLANDS BUT HAVE ALREADY BEEN OR ARE ALMOST ERADICATED THERE )N ADDITION TO THE DIRECT DAMAGES THATINTRODUCEDPIGSAREKNOWNTOCAUSETOTHEmORAANDFAUNATHEYINVADE(ONE THISALIENSPECIESALSOTHREATENEDSOMELOCALSPECIESTHROUGHANINDIRECT PROCESS "Y PRODUCING PIGLETS ALL YEAR ROUND THEY PROVIDED VISITING EAGLES WITH ENOUGHRESOURCESFORTHEMTOCOLONIZETHEISLANDS%AGLESALSOIRREGULARLYDEPRE DATEDOTHERLOCALPREYSUCHASFOXESORSKUNKS(OWEVER EVENTHISLOWPREDATION RATEONASPECIESTHATISILL ADAPTEDTOAVIANPREDATION BEHAVIORALLYASWELLASAT THE POPULATION LEVEL WAS SUFlCIENT TO DRIVE THE FOX POPULATION TOWARDS EXTINC TION 4HE DECLINE WAS ALL THE MORE DRAMATIC THAT THE BREEDING EAGLE POPULATION RAPIDLYGREWINNUMBERS THEREBYINCREASINGTHEPRESSUREONTHEFOXPOPULATION )N THE MEAN TIME THE NOCTURNAL SKUNKS BENElTED FROM THE ARRIVAL OF THE EAGLE BECAUSETHEYBENElTEDFROMTHERELEASEOFCOMPETITIONPRESSUREFROMTHEDECLIN INGFOXPOPULATIONSWHILEALSOBEINGKILLEDLESSOFTENTHANTHEM4HEHYPOTHESIS WAS THUS THAT THE ARRIVAL OF PIGS HAD ALLOWED VISITING EAGLES TO STAY AND BREED ANDTHEREBYTHEYATTRACTEDASHAREDPREDATORTOINSULARPREY0IGSAREWELLADAPTED TO PREDATION THEY PRODUCE NUMEROUS PIGLETS THAT CAN ESCAPE EAGLE PREDATION ONCE THEY REACH THREE MONTHS OF AGE 4HEREFORE THERE WERE LESS CONSEQUENCES FORTHEPIGPOPULATIONTHANTHELOCALPREYDUETOTHEARRIVALOFTHEEAGLE2OEMER ET AL B 4HEMODEL 4O TEST THIS HYPOTHESIS A MODEL OF THE POPULATION DYNAMICS OF THE INTERACTING SPECIESWASCONSTRUCTEDANDPARAMETERIZEDWITHDATAOBTAINEDFROMTHElELD4HE MODEL WAS BASED ON A SIMPLE COMBINATION OF TWO CLASSICAL ,OTKA 6OLTERRA MOD ELS ONE OF COMPETITION AND ONE OF PREDATION 4HE SKUNK AND THE FOX POPULATION DYNAMICSWEREDESCRIBEDBYACOMPETITIONMODEL THEPIGANDTHEEAGLEPOPULA TIONDYNAMICSWEREDESCRIBEDBYAPREDATIONMODEL ANDAPREDATIONTERMOFTHE EAGLEWASADDEDONBOTHFOXANDSKUNKPOPULATIONS5SINGACORRECTIONTERMFOR PROPORTIONS AND PREFERENCE COEFlCIENTS q AND m RESPECTIVELY AS IN THE PREVIOUS EXAMPLE WEENDUPWITHASYSTEMOFFOUREQUATIONS ONEPREDATORANDITSTHREE PREY TWO OF WHICH ARE COMPETITORS 4HE SYSTEM AND ILLUSTRATIONS OF POPULATION TRENDSARESHOWNIN&IG-OREDETAILSCANBEFOUNDIN2OEMERETAL 3IMPLESIMULATIONSSHOWTHATINABSENCEOFTHEPIGSIFTHESYSTEMISRUNWITHAN INITIALNUMBEROFPIGSSETATZERO ANYINTRODUCTIONOFEAGLES HOWEVERLARGE WILL EVENTUALLY LEAD TO COLONIZATION FAILURE AND FOX POPULATION PERSISTENCE (OWEVER WHENPIGSAREPRESENT ASINGLEPAIROFEAGLESWILLBEABLETOCOLONIZETHEISLANDAND BUILDAPOPULATIONTHATISSOLARGETHATFOXESWILLGOEXTINCTWHILEPIGSWILLREMAIN ATMODERATEDENSITIES )T IS ALSO INTERESTING TO NOTE THAT THE DECLINE IN FOX NUMBERS CONSECUTIVE TO THEHYPERPREDATIONPROCESSTRIGGEREDBYTHEINTRODUCTIONOFPIGS ISCONCOMITANT WITHANINCREASEOFTHEENDEMICSKUNK)NFACT THEARRIVALOFEAGLESREVERSEDTHE

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&IG 2EPRESENTATION OF THE HYPERPREDATION MODEL EXAMPLE WITH FOUR SPECIES FOX & BLUE SKUNK 3 GREEN PIG 0 YELLOW AND EAGLE % RED !S IN &IG ! IS THE COMPARTMENTALREPRESENTATION " ISTHERESULTINGSETOFEQUATIONS # ISTHEILLUSTRATION OFPOPULATIONSTRENDSGIVENBY" FOLLOWINGPIGINTRODUCTIONANDEAGLECOLONIZATION AND $ IS THE POPULATIONS TRENDS FOLLOWING PIG ANDOR EAGLE CONTROL 4HE PARAMETERS ARE THE SAME THAN PREVIOUSLY WITHq AND m BEING THE PREFERENCE PARAMETERS OF THE EAGLE FOR THE FOXANDTHESKUNKOVERTHEPIG RESPECTIVELYSAMEAS_IN&IG 4HECONTROLSTRATEGY$ ISREPRESENTEDINTHREEDIMENSIONS4OHELPVISUALIZETHE$EFFECT THECOLORSDONOTREFER TO SPECIES BUT TO DIFFERENT POPULATION SIZES 4HIS GRAPH SHOWS THAT THE POPULATION SIZE OF FOXESISPROPORTIONALTOEAGLECONTROL BUTINVERSELYPROPORTIONALTOPIGCONTROL!SARESULT IF EAGLES ARE NOT CONTROLLED SIMULTANEOUSLY FOXES WILL DECLINE FOLLOWING PIG CONTROL ONLY )N ABSENCE OF SIGNIlCANT EAGLE MITIGATION HIGH LEVELS OF PIG MITIGATION CAN RESULT IN FOX EXTINCTIONDARKAREA


COMPETITIVE OUTCOME BETWEEN THE TWO TOP TERRESTRIAL PREDATORS SHIFTING FORCES FROM DIRECT COMPETITION IN FAVOR OF THE FOX TO APPARENT COMPETITION IN FAVOR OF THESKUNK4HISSECONDAPPARENTCOMPETITIONPROCESS EMBEDDEDINTHElRSTONE RENDERSANYCONSERVATIONSTRATEGYATTHELEASTCOMPLICATED ASTHEINSULARSPOTTED SKUNKISENDEMICFROMTHENORTHERN#HANNEL)SLANDSANDISCURRENTLYBENElTING FROMTHEFOXDECLINE C #ONSERVATIONCONSEQUENCES &OXES ARE NOW EXTINCT IN THE WILD ON TWO OF THE THREE NORTHERN ISLANDS WITH THE POPULATION ON THE THIRD ISLAND 3ANTA #RUZ ON THE VERGE OF EXTINCTION INDIVIDUALSINTHEWILDATTHEENDOF /URMODELINGEXERCISESUGGESTSTHAT THE EXTINCTION OF TWO POPULATIONS OF THE TOP PREDATOR IN TWO INSULAR ECOSYSTEMS ISLIKELYDUETOANINDIRECTPROCESSAPROCESSWHEREANINTRODUCEDPREYATTRACTED ASHAREDPREDATORANDELIMINATEDANENDEMICPREYTHROUGHAPPARENTCOMPETITION ONLY /BVIOUSLY THESOLUTIONTOTHISPROBLEMLIESWITHTHEPIGS4HEMOSTEVIDENTPLAN OFACTIONWASTOREMOVETHEPIGSFROMTHENORTHERNISLANDS4HISWOULDHAVETHE DOUBLEADVANTAGEOFSTOPPINGTHEIRDIRECTDELETERIOUSEFFECTSONTHELOCALmORAAND FAUNA ASWELLASELIMINATINGTHEPREYBASISFORTHEEAGLES LEADINGTHEMWITHLITTLE MORE CHOICE THAN STARVATION OR EMIGRATION )N FACT SEVERAL CONSERVATION STRATE GIES WERE IMPLEMENTED SIMULTANEOUSLY !MONG THEM EAGLE LIVE TRAPPING WAS QUITESUCCESSFUL WITHLESSTHANTENINDIVIDUALSPROVINGIMPOSSIBLETOTRAPORTHAT KEPTCOMINGBACKFROMTHETRANSLOCATIONAREA(OWEVER ITWASEASYTOSEETHATAS LONGASPIGSREMAINED EAGLESWOULDSTARTBREEDINGONTHEISLANDAGAINANDTHUS STARTANEWPOPULATION4HESOLUTIONTHEREFORESEEMEDTOBETHECOMPLETEREMOVAL OFPIGSFROM3ANTA#RUZ)SLAND9ET THESTUDYOFAMODELBASEDONTHEPREVIOUSONE SHOWEDONCEMORETHATINDIRECTINTERACTIONSMAYLEADTOCOUNTER INTUITIVERESULTS #OURCHAMPETALB !SFORTHEPREVIOUSEXAMPLE THEBASICMODELSHOWN IN&IG"WASCHANGEDSIMPLYBYADDINGALINEARCONTROLTERMTOTHEPIGANDTO THEEAGLEEQUATIONS "Y VARYING THE CONTROL RATE OF PIGS AND EAGLES FROM ZERO NO CONTROL TO ONE ERADICATION WE CAN MIMIC DIFFERENT CONTROL STRATEGIES CONTROL OF PIGS ONLY OF EAGLESONLYOROFBOTHSPECIES WITHDIFFERENTSTRENGTH ANDCOMPARETHEIRRELATIVE EFlCIENCYWITHNORISKTOTHELOCALPOPULATIONS$OINGSOREVEALEDTHATMITIGATION OFPIGSWOULDINFACTLEADTOADECREASEINTHEFOXPOPULATION&IG$ %RADICATION OFPIGS THEINTENDEDCOURSEOFACTIONON3ANTA#RUZ WOULDLEADTOFOXEXTINCTION $UE TO THE LOW FOX POPULATION AND THE LARGE EAGLE POPULATION THE FOXES WOULD BE ENTIRELY DESTROYED BEFORE THE EAGLES DIED OR EMIGRATED )N THEORY THE SOLU TION IS THUS SIMPLE REMOVE BOTH THE EAGLES AND THE PIGS (OWERVER IN PRACTICE THE REMOVAL OF SUCH A LARGE PIG POPULATION IS LOGISTICALLY DIFlCULT )N ADDITION THE REMOVAL OF THE EAGLE WOULD BE IMPOSSIBLE THROUGH LIVE TRAPPING ONLY AND ETHICALLYANDLEGALLYCHALLENGING BECAUSEGOLDENEAGLESAREPROTECTEDSPECIESIN THE53!ANDTHEREFORECANNOTBEKILLED

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4OCONCLUDETHISPART ITMAYBEINTERESTINGTONOTETHATWHENMORESPECIESAND MORE INTERACTIONS ARE TAKEN INTO ACCOUNT NEW PROCESSES MAY BE UNVEILED THAT COULD NOT BE PERCEIVED WITH ONLY TWO SPECIES STUDIES 9ET IF BETTER UNDERSTAND ING A SYSTEM IS UNDOUBTEDLY USEFUL FOR CONSERVATION MANAGERS IT IS NOT ALWAYS SUFlCIENT FOR THEM TO BE ABLE TO KNOW HOW TO ACT )N THE PRESENT CASE A STUDY TAKING ALL SPECIES INTO ACCOUNT REVEALED THAT A SEEMINGLY OBVIOUS LINE OF ACTION PIG REMOVAL WOULD INDEED LIKELY ACHIEVE RESULTS OPPOSITE TO THOSE DESIRED AND POSESADIFlCULTDECISIONTOMAKEREMOVEAPROTECTEDPOPULATIONINORDERTOSAVE AN ENDANGERED SUBSPECIES )F IT IS OBVIOUSLY NOT TRIVIAL TO MAKE CONSERVATION CHOICES EVEN IN THE SIMPLEST SITUATIONS IT CAN SOMETIMES BECOME A CHALLENG ING DILEMMA THEORETICALLY LOGISTICALLY LEGALLY AND MORALLY )N THE PRESENT CASE THE ONLY REMAINING POPULATIONS OF SEVERAL FOX SUBSPECIES WERE THREATENED WITH IMMINENTEXTINCTION(OWEVER THEPROXIMATECAUSEOFTHISTHREATISTHEPRESENCE OFAPROTECTEDBIRD&URTHERMORE THEDECLINEOFTHEFOXBENElTSTHEONLYPOPULA TIONS OF AN ENDEMIC SKUNK !S WE HAVE SEEN WHEN A DIFlCULT CHOICE IS MADE THEOPPOSITEOUTCOMEMAYWELLARISE&URTHERMORE ALLTHISISWITHOUTCONSIDERING SPECIESOUTSIDETHISSIMPLISTICSYSTEM/NECOULDALSOCONSIDERTHEQUESTIONUNDER AWIDERANGLE FOREXAMPLEINCLUDINGTHE3AN#LEMENTELOGGERHEADSHRIKE ,ANIUS LUDOVICIANUSMEARNSI ACRITICALLYENDANGEREDBIRD TOWHICHTHEINSULARFOXISTHE MAINPREDATOR/N3AN#LEMENTE)SLAND THEFOXPOPULATIONHASBEEN IRONICALLY ADVERSELY IMPACTED BY A 53 .AVY PROGRAM TO PROTECT THIS BIRD ATTEMPTING TO THWARTANYPREDATIONOFSHRIKES FOXWEREINITIALLYTRAPPEDANDSHIPPEDOFFISLAND OREUTHANIZEDDURINGTHESHRIKE NESTINGSEASONFOXESREMOVEDIN OF WHICHPERMANENTLY "UTTHISISANOTHERSTORYx !LONG THE SAME LINE OF THIS CONSERVATION RIDDLE THE NEXT PART OF THIS CHAPTER INVESTIGATES THE IMPORTANCE OF DIRECT INTERACTIONS IN CONTROL PROGRAMS WITH THE AIMOFSHOWINGTHATTHEREMOVALOFTHEPRIMARYCAUSEOFAECOSYSTEMDISFUNCTION WILLNOTALWAYSHELPRESTORETHEINITIALCONDITIONS)NSOMECASES NOTTAKINGINTO ACCOUNTINDIRECTINTERACTIONMAYLEADTOEVENFURTHERDAMAGE TOTHEPOINTTHAT ITMAYBEWISERTOADVOCATENOTTOREMOVEPOPULATIONSTHATAREKNOWNTOCAUSE DIRECTNEGATIVEIMPACTSONINVADEDCOMMUNITIES ATLEASTUNTILADEQUATEKNOWL EDGEISGAINEDANDRELEVANTCONTROLSTRATEGIESAREINFERRED #ONTROLOFINVADERSASASPECIESREMOVALEXPERIMENT 2ELEASEFROMINTRODUCEDHERBIVORES

/NECONCEPTTHATISRELATIVELYNEWINTHESTUDYOFINVADINGSPECIES ANDTHATHAS BEEN THE CORE PRINCIPLE OF OUR OWN STUDIES IS THAT EVEN IF A SPECIES IS PROVEN TO BEINmICTINGIMPORTANTDAMAGESTOACOMMUNITYITINVADES THEMEREREMOVALOF THATSPECIESMAYNOTSYSTEMATICALLYBETHESOLUTIONTORESTORINGTHECOMMUNITY !S WE HAVE SHOWN WITH THE #ALIFORNIA #HANNEL )SLANDS EXAMPLE UNCONSIDERED CONTROLMAYEVENLEADTOTHEOPPOSITEOUTCOME THATIS FURTHERDAMAGE INCLUD INGPOSSIBLEEXTINCTIONOFTHESPECIESINTENDEDTOBEPROTECTED4HISFACTHIGHLIGHTS


THENEEDTOHAVEACLEARANDCOMPLETEVIEWOFTHERELATIONSHIPSAMONGSPECIESTHAT ARECONNECTEDDIRECTLYORINDIRECTLYWITHTHEINTRODUCEDSPECIESTHATISSUBJECTTO CONTROL)TNOWADAYSSOUNDSTRIVIALTOSTATETHATALLTHESPECIESTHATINTERACTWITHA POPULATIONFORWHICHREMOVALISPLANNED ARELIKELYTOBEAFFECTEDINDIVERSEWAYS BYANYSUCHACTIONS4HUS THESUCCESSOFANERADICATIONPROGRAMISMEASUREDNOT ONLY BY THE COMPLETE REMOVAL OF THE CONTROLLED SPECIES BUT ALSO BY THE ABSENCE OFFURTHERDYSFUNCTION9ET SUCHERRORSSTILLOCCURREGULARLYDURINGCONSERVATION PROGRAMS SOMETIMES SIMPLY BECAUSE CONSERVATION PROGRAMS HAVE INSUFlCIENT FUNDS TO ALLOW THOROUGH PRE CONTROL STUDIES OF THE INVADED COMMUNITY AS WELL AS LONG TERM POST CONTROL MONITORING 3OMETIMES SIMPLY BECAUSE CONSERVATION ACTIONISURGENTLYNEEDEDANDTHEREISNOTIMEFORSUCHPRE CONTROLSTUDY 4HE IMPORTANCE OF KNOWING THE RELATIONSHIPS BETWEEN INVADING SPECIES AND THOSEINTHEINVADEDCOMMUNITYISWELLILLUSTRATEDBYTHEGOATANDPIGERADICATION ONTHE3ARIGAN)SLAND4HISISLANDISPARTOFTHE#OMMONWEALTHOFTHE.ORTHERN -ARIANA )SLAND IN THE 0ACIlC /CEAN )NTRODUCED PIGS AND GOATS THREATENED THE LOCAL mORA AND FAUNA TRIGGERING A CONSERVATION PROGRAM CONSISTING MAINLY OF GOAT AND PIG ERADICATION +ESSLER !S THE ISLAND IS ISOLATED AND HENCE DIFlCULT TO ACCESS THE PROGRAM DESIGNED INCLUDED ONLY A MINIMAL PRE ERADICA TIONSTUDY4HEPROGRAMWASCONSIDEREDAFULLSUCCESSINTERMSOFREMOVINGTHE INTRODUCEDMAMMALS HOWEVERITFAILEDINITSABILITYTODETECTTHATTHEISLANDHAD ALSOBEENCOLONIZEDBYANINTRODUCEDVINE /PERCULINAVENTRICOSA WHICHAPPEARED TOBEAPREFERENTIALFOODITEMFORTHEGOATS)TISPERHAPSNOTSURPRISINGTHATTHIS VINEWASNOTFOUNDINTHEPRE CONTROLSTUDYASITWASLIKELYTOHAVEBEENATALOW DENSITYDUETOSELECTIVEGRAZINGBYGOATS%VENAVERYTHOROUGHSTUDYMIGHTHAVE FAILED TO SEE IT 9ET IT MAY BE VALUABLE TO POINT OUT THAT WHEN POSSIBLE SIMPLE FENCEDEXCLOSURESTUDIESPRIORTOERADICATIONSCANOFTENHELPLANDMANAGERSSEEIF UNWANTEDRESULTSWILLARISEAFTERANERADICATIONOFHERBIVORES)FSO THENAPPROPRI ATECONTROLOFNON NATIVEPLANTSCANBEPLANNEDALONGWITHTHEHERBIVOREREMOVAL 5NFORTUNATELY THISWASNOTDONEANDTHECONTROLPROGRAM WHICHAIMEDATRELEAS ING PLANT SPECIES FROM GOAT GRAZING HAD A DIFFERENT IMPACT ON THE OVERALL PLANT COMMUNITYTHANTHEONEEXPECTED!STHEPRESSUREOFGRAZINGWASREMOVEDFROM ALL GRAZED PLANTS INTRODUCED PLANTS WERE ABLE TO FULLY EXPRESS THEIR COMPETITIVE SUPERIORITY WITH REGARDS TO NATIVE PLANTS RESULTING IN THE RAPID INVASION OF THE COMMUNITY&IGSHOWSHOW WITHINONLYTWOYEARS THEREMOVALOFANEXOTIC GRAZERLEDTOACOMPLETEINVASIONOFTHEISLANDCOMMUNITYBYANEXOTICPLANTTHAT APPEARSTOHAVEACOMPETITIVESUPERIORITYOVERLOCALPLANTS!SMOSTOFTHE3ARIGAN )SLANDECOSYSTEMISNOWCOVEREDBYVINES ONECANEASILYIMAGINEHOWTHEINDIRECT EFFECT OF HAVING REMOVED GOATS IS NOW DELETERIOUS FOR THE LOCAL PLANTS AS WELL AS ANIMALSTHATDEPENDUPONTHEM 4HEMESOPREDATORRELEASEEFFECT

4HEPROCESSWEHAVESEENWITHTHERELEASEOFANEXOTICPLANTMAINTAINEDATLOW DENSITYBYABROWSERCANBEGENERALIZEDTORELEASESFROMALMOSTANYOTHERTYPEOF

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&IG %VOLUTIONOFTHELANDSCAPEOF3ARIGAN)SLAND FOLLOWINGTHEERADICATIONOFGOATS !S THIS INTRODUCED HERBIVORE NO LONGER HELD IN CHECK THE EXPANSION OF THE INTRODUCED VINE A FAVORED FOOD ITEM THE VINE RAPIDLY INCREASED COVERING MOST OF THE INSULAR PLANT COMMUNITIES WITHIN TWO YEARS 4HIS ILLUSTRATES HOW AN EXOTIC GRAZER AFFECTED THE COMPETITIONRELATIONSHIPSBETWEENLOCALANDINTRODUCEDPLANTS ANDHOWITSREMOVALCAN LEAD TO DRAMATIC AND UNEXPECTED OUTCOME FOR THE COMMUNITIES WHICH PROTECTION WAS AIMEDAT


NATURALENEMY7EWILLILLUSTRATETHISWITHTHENEXTTWOEXAMPLES4HISIS HOW EVER NOTTOBEMISTAKENWITHTHEENEMYRELEASEHYPOTHESIS+EANEAND#RAWLEY WHICHPROPOSESTHATINVADINGSPECIESARESOSUCCESSFULPARTLYBECAUSETHEY ARE RELEASED IN THE INVADED HABITAT FROM THE PRESSURE OF THEIR NATURAL ENEMIES RARELYINTRODUCEDWITHTHEM /N3TEWART)SLAND .EW:EALAND APOPULATIONOFINTRODUCEDCATSWASTHREAT ENING ONE OF THE LAST POPULATIONS OF KAKAPO 3TRIGOPS HABROPTILUS AN ENDEMIC mIGHTLESSPARROT!DIETSTUDYREVEALEDKAKAPOREMAINSINOFCOLLECTED CATSCATS+ARLAND"EST 4HISSEEMINGLYLOWPREDATIONPRESSURECANHAVE A DRAMATIC EFFECT ON INSULAR POPULATIONS WHICH EVOLVED IN THE ABSENCE OF SUCH PREDATORSANDARETHEREFORENOTADAPTEDTOEVENLOWLEVELSOFPREDATION-OREOVER THEKAKAPOPOPULATIONWASALREADYSMALLANDFRAGILE ADDINGTOTHEWEIGHTTHAT INTRODUCEDCATSCOULDHAVEONITSFATE4HISCOULDHAVEBEENSUFlCIENTTOTRIGGER APROGRAMOFCATCONTROLONTHEISLAND (OWEVER RATSKNOWNTOBEIMPORTANTBIRDPREDATORS HADALSOBEENINTRODUCED ON3TEWART)SLAND)NTHESAMEDIETSTUDY+ARLAND"EST RATREMAINSWERE FOUNDINOFTHESECATFAECES4HISSHOWSTHEINDIRECTROLECATSMIGHTPLAYIN PRESERVINGNATIVEFAUNA THROUGHREDUCTIONOFRATPREDATIONPRESSUREONKAKAPO )NFACTITISEASYTOSEETHATINSOMECASESTHEINDIRECTPOSITIVEEFFECTOFCATPREDA TIONONRATSISMOREBENElCIALFORTHELOCALPREYTHANTHEDIRECTNEGATIVEEFFECTSOF CATPREDATIONONTHEPREYTHEMSELVES)NSUCHCASES THEELIMINATIONOFTHEFERAL CAT POPULATION COULD LEAD TO A MORE SEVERE NEGATIVE IMPACT ON THE LOCAL SPECIES THROUGH AN INCREASE IN THE RODENT POPULATION AS A CONSEQUENCE OF THE REMOVAL OFTHEIRPREDATORS4HEATTEMPTEDREDUCTIONOFTHECATPOPULATIONON!MSTERDAM )SLANDHASBEENABANDONEDASITISALLEGEDTOHAVECAUSEDACOMPENSATINGRISEIN THE NUMBER OF RATS AND MICE (OLDGATE AND 7ACE 4HIS PROCESS TERMED hMESOPREDATOR RELEASEv HAS BEEN DESCRIBED IN FRAGMENTED INSULAR ECOSYSTEMS 3OULÏ ET AL AND APPLIES WELL TO MANY INSULAR FOOD WEBS EG 3CHOENER AND3PILLER #ONVERSELY THE ERADICATION OF RODENTS lRST WHICH HAS NOW PROVEN FEASIBLE EVEN ON RELATIVELY LARGE ISLANDS MIGHT INDUCE CATS TO SWITCH PREY RESULTING IN ABRUTALINCREASEINPREDATIONPRESSUREONTHETHREATENEDINDIGENOUSSPECIES AS EXPERIENCED FOR STOATS AND RATS IN .EW :EALAND -URPHY AND "RADlELD 4HISISASIMILARPROCESSTOTHEONEDESCRIBEDABOVEFORTHEPIGCONTROLINPRESENCE OFEAGLESON3ANTA#RUZ)SLAND!STHEOPTIMALCONTROLSTRATEGYISNEITHERSIMPLE TOlND NORINTUITIVE ITISCONVENIENTTOSTUDYITTHROUGHTHEANALYSISOFAMATH EMATICAL MODEL WHICH MIMICS THE DYNAMICS OF THE THREE SPECIES IN THIS SYSTEM 4HEMAINRESULTSOFSUCHASTUDY#OURCHAMPETAL A AREREPRODUCEDBELOW TOILLUSTRATEHOWTHECONTROLOFANINVADINGSPECIESCANPROVIDEANIDEALOPPORTU NITYTOPROGRESSINTHEUNDERSTANDINGOFTHENUMEROUSANDOFTENCOMPLEXINTERAC TIONSAMONGPOPULATIONS &OR THE SAKE OF CLARITY WE WILL NOT PRESENT THE MODEL EQUATION IN ANY DETAIL 3UFlCE TO SAY THAT THE SYSTEM IS DESCRIBED BY A SET OF THREE COUPLED EQUATIONS ONE PREY PARROT ITS PREDATOR THE RAT IN THIS CASE A MESOPREDATOR AND ONE

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SUPERPREDATORCAT WHICHEATSBOTHTHEPREYANDTHEMESOPREDATOR4HEMODEL ANDTHERESULTINGPOPULATIONTRENDSAREREPRESENTEDIN&IG 4HESTUDYOFTHEABOVESYSTEMLEADSTOTHEQUITEOBVIOUSCONCLUSIONTHATBOTH PREDATORS SHOULD BE ERADICATED AT THE SAME TIME (OWEVER NOT ONLY IS SUCH A STRATEGY CHALLENGING FROM A LOGISTICAL POINT OF VIEW BUT IN ADDITION IT MAY NOT ALWAYS BE THE BEST SOLUTION ESPECIALLY IF THE SYSTEM INCLUDES MORE INTRODUCED PREDATORS )NDEED THE PREY MESOPREDATOR SUPERPREDATOR SYSTEM THAT WE HAVE JUST DESCRIBED CAN BE FURTHER COMPLICATED 4HERE ARE CASES WHERE THE PRESENCE OF A THIRD PREDATOR CAN RENDER THE ERADICATION OF THE MESOPREDATOR PROBLEMATIC IF IT ALSO ACTS AS A PREDATOR TO THIS THIRD PREDATOR AND THUS AT THE SAME TIME AS A MESOPREDATOR AND A SUPERPREDATOR "EING AWARE OF THE POTENTIAL DANGERS OF REMOVINGASUPERPREDATORWHENAMESOPREDATORISPRESENT THEMANAGERSOFTHE CONSERVATION PROGRAM OF "IRD )SLAND 3EYCHELLES DECIDED RIGHTLY TO SIMULTANE OUSLYREMOVEINTRODUCEDCATSANDRATSINORDERTOPROTECTTHELOCALBIRDCOLONIES 4HEY HAD HOWEVER OVERLOOKED THE PRESENCE OF THE INTRODUCED CRAZY ANT !NOPLOLEPIS LONGIPES WHICH WERE PRESENT IN VERY LOW NUMBERS ON THE ISLAND &EARE 4HE LARVAE OF THESE ANTS SEEM TO HAVE BEEN AN IMPORTANT PREY ITEMOFTHEINTRODUCEDRODENTS SUCHTHATTHERATERADICATIONLEDTOADEMOGRAPHIC EXPLOSIONOFTHEANTS4HISRESULTEDINTHEANTSCOVERINGALARGEPARTOFTHEISLAND WITHAHEAVYIMPACTONLANDCRABSANDBIRDCOLONIES)NFACT THISPROBLEMOFCHAIN REACTIONFOLLOWINGTHEREMOVALOFANINTRODUCEDSPECIES ALSOCALLEDSURPRISEEFFECT OR3YSIPHUSEFFECT-ACKAND,ONSDALE CANBEGENERALIZEDTOOTHERNATURAL ENEMIESSUCHASHERBIVORESORCOMPETITORS 4HECOMPETITORRELEASEEFFECT

4HE CONTROL OF AN INVADER HAS THE POTENTIAL TO RELEASE ANY SPECIES INTERACTING WITH THE CONTROLLED INVADERS FROM ITS PRESSURE BE IT EXPLOITATION OR INTERFER ENCE 4HEREFORE ONE CAN IMAGINE VERY SIMILAR PROCESSES WITH A BROWSER OR A COMPETITOR,ETUSCONSIDER ASAlNALEXAMPLE AhCOMPETITORRELEASEEFFECTv,ET USSETTHESCENEANISLAND INVADEDBY SAY ARATSPECIES4HEISLANDISNORTHOF .EW #ALEDONIA IN THE %NTRECASTEAUX 2EEF ,ET US CALL IT 3URPRISE )SLAND WHICH SUITSVERYWELLASTUDYONSURPRISEEFFECTS!THOROUGHSTUDYOFTHEINVADEDECO SYSTEM COMPLETED TO CHARACTERIZE THE IMPACT OF INTRODUCED RATS ON THAT ISLAND REVEALEDTHEPRESENCEOFASMALLISOLATEDPOPULATIONOFINTRODUCEDDOMESTICMICE 4HEPOPULATIONSEEMSSMALLANDRESTRICTED SOTHATTHEIRIMPACTONTHEECOSYSTEM ISLIKELYTOBENEGLIGIBLE)NFACT INSIMILARSITUATIONS THEYHAVEBEENINTHEPAST NEGLECTED PARTLY BECAUSE MOUSE POPULATIONS ARE DIFlCULT TO ERADICATE PARTLY BECAUSESUCHSMALLPOPULATIONSWERENOTVIEWEDASATHREAT ANDPARTLYBECAUSE THE CONSERVATION PROGRAM CONCERNED ANOTHER SPECIES AND FUNDS AND PROTOCOLS WERENOTAVAILABLETODEALWITHMICE!SANEXAMPLE THERATANDRABBITCONTROLOF 3AINT0AUL)SLAND INTHE!NTARCTICOCEAN HASBEENVERYSUCCESSFULINERADICATING THESE TWO INTRODUCED MAMMALS IT WAS EVEN AT THE TIME THE GREATEST AREA EVER CLEANEDUPFROMINTRODUCEDRABBITS BUTTHEPROGRAMDIDNOTFOCUSONTHESMALL


&IG 2EPRESENTATION OF THE MESOPREDATOR RELEASE PROCESS WITH THE INTRODUCED SUPERPREDATORBEINGTHECAT# RED THEINTRODUCEDMESOPREDATORBEINGTHERAT2 YELLOW AND THE INDIGENOUS PREY BEING THE BIRD " BLUE !S IN &IG ! IS THE COMPARTMENTAL REPRESENTATION THEEXAMPLECOMINGFROM3TEWART)SLAND OFFTHE.EW:EALANDMAINLAND " IS THE RESULTING SET OF EQUATIONS AND THE TWO FOLLOWING PANELS ARE TYPICAL POPULATION TRENDS FOLLOWING INTRODUCTIONS OF THE SUPERPREDATOR # TOP AND OF THE MESOPREDATOR # BOTTOM OR CONTROL OF THE SUPERPREDATOR ONLY $ TOP AND OF BOTH THE SUPERPREDATOR ANDTHEMESOPREDATOR $ BOTTOM 0ANEL# SHOWSTHATINSOMECASES ASUPERPREDATOR INTRODUCTION WILL DECREASE THE PREDATION PRESSURE ON LOCAL PREY VIA ITS PREDATION ON THE MESOPREDATOR TOP WHILE A MESOPREDATOR INTRODUCTION WILL ALLOW AN INCREASE OF THE SUPERPREDATORPROCESSSIMILARTOTHEHYPERPREDATION LEADINGTOAFURTHERDECREASEOFTHE PREY VIAACOMBINATIONOFINCREASEDPREDATIONOFTHEINCREASEDSUPERPREDATORPOPULATION AND ADDITIONAL PREDATION FROM THE NEWLY INTRODUCED MESOPREDATOR BOTTOM 0ANEL $ SHOWS THAT CONTROL OF BOTH INTRODUCED PREDATOR NEEDS TO BE DONE TO PROTECT THE PREY BOTTOM AS THE CONTROL OF ONLY THE SUPERPREDATOR CAN TRIGGER A MESOPREDATOR RELEASE WHICHEVENTUALLYLEADSTOTHELOCALPREYEXTINCTIONTOP

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MOUSEPOPULATIONTHATWASKNOWNTOOCCURONTHEISLAND-ICOLAND*OUVENTIN 4HE STUDY OF THE 3URPRISE ECOSYSTEM SUGGESTS THAT RESOURCES ARE ABUNDANT ENOUGH FOR THE INTRODUCED MICE TO DEVELOP A LARGER POPULATION THAN THEY HAVE DONE4HISSUGGESTSTHATTHEMOUSEPOPULATIONISRESTRICTEDBYANATURALENEMY ANDITCOMES NATURALLYTOMINDTHATITISTHECOMPETINGRATTHATRESTRICTEDTHEM FROM FURTHER EXPANDING THEIR RANGE !LTHOUGH IT IS QUITE DIFlCULT TO UNAMBIGU OUSLY DEMONSTRATE SUCH COMPETITION RELATIONSHIPS lELD SPECIALISTS SEEM UNANI MOUS IN THE VIEW THAT RATS ARE STRONG COMPETITORS OF MICE TO THE POINT OF OFTEN EXCLUDINGTHEMWHENCOMMONRESOURCESAREFEW)TSEEMSTHENQUITEPREDICTABLE ESPECIALLY AFTER HAVING READ THE PREVIOUS EXAMPLES OF hSURPRISE EFFECTSv IN THIS CHAPTER THATTHEPLANNEDERADICATIONOFTHEINTRODUCEDRATSON3URPRISE)SLANDIS LIKELYTORELEASETHEMICEFROMRATCOMPETITION ANDTHUSTOALLOWTHEMTOINCREASE INNUMBERS3UCHANOUTCOMEISNOTONLYINTUITIVELYLOGICAL ITISALSOVERYEASYTO DEMONSTRATETHROUGHTHEANALYSISOFABASIC,OTKA 6OLTERRACOMPETITIONMODEL TO WHICHACONTROLTERMISADDEDTOONEOFTHECOMPETITORS&ORTHESAKEOFSIMPLIC ITY WE STUDY THIS THREE SPECIES SYSTEM ONE PREY AND TWO COMPETING PREDATORS THROUGH ONLY A TWO COMPETITORS MODEL THE SHARED PREY IS IGNORED HERE WHICH ALSOALLOWSAGENERALIZATIONOFTHESYSTEMTONON PREDATORCOMPETITORS !NALYSIS OF THIS SYSTEM CLEARLY SHOWS THAT THE MITIGATION OF THE HIGHER COM PETITORTHERAT WILLLEADTOANINCREASEOFTHELOWERCOMPETITORASPRESSUREFROM COMPETITIONISLIFTED4HEHIGHERTHEMITIGATION THELARGERTHEMOUSEPOPULATION ! SUDDEN COMPLETE REMOVAL OF THE RAT POPULATION IS LIKELY TO RESULT IN A DEMO GRAPHICEXPLOSIONOFTHEMOUSEPOPULATION4HISWASTHECASEON3AINT0AUL)SLAND FOLLOWINGTHEREMOVALOFRATSIN-ICOLAND*OUVENTIN RELEASEDFROM THEIRCOMPETITORS MICENUMBERSINCREASEDDRAMATICALLY TOSUCHAPOINTTHATFOR ATIMETHEYFAREXCEEDEDTHECARRYINGCAPACITYOFTHEHABITAT/BVIOUSLY MICEARE LESSHARMFULTHANRATS ANDTHUSINSOMECASESTHEENDBENElTOFTHERATREMOVAL IS POSITIVE EVEN IF THE MOUSE POPULATION INCREASES 9ET MOUSE OUTBREAKS CAN BEVERYPROBLEMATIC ASMICEHAVEBEENSHOWNTOBEACTIVEPREDATORSOFINVERTE BRATES REPTILES AND EVEN BIRDS THAT CAN BE TIMES THEIR WEIGHT #AMPOS AND 'RANADEIRO #UTHBERT AND (ILTON &ITZGERALD ET AL ,E 2OUX ETAL .EWMAN 3MITHETAL "UT THIS COMPETITOR RELEASE EFFECT IS IN FACT NEITHER SURPRISING NOR VERY INTER ESTING FOR THE STUDY OF INTERSPECIlC RELATIONSHIPS 4HE OBVIOUS APPROACH TO SUCH SITUATIONSSEEMSSIMPLYTOAPPLYASIMULTANEOUSCONTROLTOBOTHCOMPETITORS!ND ITISALLTHEBETTERTHATWEAREDEALINGWITHCOMPETINGRODENTS ASASIMULTANEOUS CONTROLISEASILYFEASIBLEWITHACOMMONRODENTICIDE FOREXAMPLE%NDOFSTORY OR SOITSEEMS)NFACT JUSTTOMAKESURENOMORESURPRISESAREGOINGTOEMERGEFROM THESYSTEM ITISPOSSIBLETOCOMPLETETHEMODELBYADDINGASIMULTANEOUSCONTROL TERMTOTHEINFERIORCOMPETITORASWELLSEE&IGS!AND" )TSEEMSLOGICALTOLINK THETWOCONTROLRATES FORTHEYWILLOFTENBEATLEASTINTHECASEOFRODENTS CON TROLLEDINTHESAMEPROGRAM&OREXAMPLE ONECANHAVEtRbtM WITHtMBEING THECONTROLRATEOFTHEMICE THELOWERCOMPETITORTHEMOUSE ANDbTHECONTROL


SPECIlCITY!VALUEOF SAY FORbMEANSTHATSUPERIORCOMPETITORSARECONTROLLED TWICEASMUCHASINFERIORCOMPETITORS4HISISVERYLIKELYIF FOREXAMPLE BAITSARE ACCESSIBLEINPRIORITYTOHIGHERCOMPETITORS ORIFTHETRAPPINGDESIGNISAIMEDAT THEHIGHERCOMPETITOR BUTTHEYALSOALLOWTOTRAPTHELOWERCOMPETITOR ALTHOUGH WITHALOWEREFlCIENCYTHEPROGRAMAIMISTOREMOVETHERATS BUTRATTRAPSALSO CANCATCHMICE 3TUDYINGTHISVERYSIMPLESYSTEMREVEALSINFACTASUBTLERANDLESS EXPECTEDCOMPETITORRELEASEEFFECT!SSHOWNIN&IG# THESIMULTANEOUSMITIGA TION OF BOTH COMPETITORS CAN LEAD TO A RELEASE OF THE LOWER COMPETITOR )N SOME CASES THISRELEASECANAMOUNTTOACTUALPOPULATIONEXPLOSIONS)TISPOSSIBLETHAT AIMINGATCONTROLLING SAYANINTRODUCEDRODENT ACONTROLPROGRAMWILLLEADTOA DRAMATICINCREASEOFANOTHERRODENT EVENIFTHATONEISCONTROLLEDTOO -OREOVER &IG $ SHOWS THAT THE COMPETITOR RELEASE IS DIRECTLY PROPORTIONAL TO THE CONTROL RATE 4HIS MEANS THAT THE MORE THE TARGETED SPECIES IS CONTROLLED THEMOREIMPORTANTTHECOMPETITORRELEASEEFFECTWILLBE4HISISNOTSOOBVIOUSTO PREDICT ASITIMPLIESTHATTHEINFERIORCOMPETITORISCONTROLLEDTOO WITHACONTROL EFFORTTHATINCREASESATTHESAMERATEASTHATOFTHESUPERIORCOMPETITOR)NOTHER WORDS THEMORERODENTSARE CONTROLLED THE MOREMICEAPPEAR%VENIF MICEARE ACTUALLY CAUGHT IN TRAPS AND KILLED BY POISON THE MORE WE KILL THEM THE MORE THEIRPOPULATIONWILLINCREASE1UITETHEOPPOSITEOFANEXPECTEDOUTCOME !LTHOUGHTHISPROCESSMAYBELESSINTUITIVEANDTHEREFORELESSOFTENFORESEEN IT ISAPOSTERIORIQUITEEASYTOUNDERSTAND4HISISLIKELYTOOCCURASSOONASTHELOWER COMPETITORBENElTSFROMTHEDIFFERENTIALEFFECTOFTHESIMULTANEOUSCONTROLOFBOTH COMPETITORS WHEN ITS INDIRECT POSITIVE EFFECT THE REMOVAL OF THEIR COMPETITORS EXCEEDSITSDIRECTNEGATIVEEFFECTTHEIROWNREMOVAL /BVIOUSLY SUCHAPROCESSCANBEINTERESTINGIFTHELOWERCOMPETITORISALOCAL SPECIES WHICHSURVIVALWASTHREATENEDBYTHECONTROLLEDPOPULATION)NTHISCASE THE DRAMATIC INCREASE OF ITS POPULATION FOLLOWING COMPETITION RELEASE IS NOTH ING LESS THAN THE PROGRAM OBJECTIVES 4HIS CAN BE CONSIDERED IN CASES WHERE AN INTRODUCED SPECIES IS TO BE REMOVED BECAUSE IT THREATENS A LOCAL POPULATION THROUGH COMPETITION BUT WHERE CONTROL PROGRAMS WERE NOT IMPLEMENTED FOR FEAROFDAMAGETONON TARGETSPECIES)NTHOSECASES ANYUNINTENDEDNON TARGET DEATHSHOULDBEMORETHANBALANCEDBYTHEDEATHOFTHEINTRODUCEDCOMPETITORS 4HEREISNOHAPPYENDING HOWEVER IFTHELOWERCOMPETITORAPPEARSTOBEANOTHER INTRODUCED SPECIES WHICH INCREASE CAN INmICT FURTHER DAMAGES TO THE INVADED ECOSYSTEM ESPECIALLY IF THAT INCREASE IS DRAMATIC !GAIN IN MANY CONSERVATION SITUATIONS MANAGERS HAVE TO MAKE TRADE OFF CHOICES AND IT MAY APPEAR THAT A COMPETITOR RELEASE BE EVENTUALLY LESS DETRIMENTAL THAN ALLOWING THE PRESENCE OF THE INTRODUCED PREDATOR 9ET DRAMATIC INCREASES OF ALIEN SPECIES ARE OFTEN VERY HARMFULTOECOSYSTEMS ANDTHISEVENTUALLYSHOULDALWAYSBEASSESSED 4HERE IS MUCH MORE THAT COULD BE SAID ABOUT SUCH A SYSTEM EVEN AS SIMPLE ASITIS ANDABOUTTHECASESTUDIESINWHICHTHEOVERLOOKINGOFANENEMYRELEASE LEDTOSURPRISEEFFECTSTHATEVENTUALLYCAUSEDFURTHERDAMAGESTOINVADEDECOSYS TEMS(OWEVER BEINGTHATTHEAIMOFTHISCHAPTERISTOCONVINCETHEREADERTHAT BIOLOGICALINVASIONSANDTHEIRCONTROLCANPROVIDEANEXCELLENTMODELSYSTEMFOR

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&IG )LLUSTRATIONOFTHECOMPETITORRELEASEEFFECT0ANEL! SHOWSTHECOMPARTMENTAL REPRESENTATIONOFTHEEXAMPLETAKENFROM3URPRISE)SLAND OFF.EW#ALEDONIA WHERETWO RODENTSARECOMPETITORSRATS2 RED BEINGASUPERIORCOMPETITOROVERTHEMICE- YELLOW 4HEEQUATIONSETINTHEPRESENCEOFSIMULTANEOUSCONTROLISGIVENINPANEL" (ERE BOTH # AND$ REPRESENTPOPULATIONTRENDSFOLLOWINGCONTROL0ANEL# SHOWSTHEPOPULATION TRENDSOFTHETWOCOMPETITORSASAFUNCTIONOFTIME FORTWODIFFERENTCOMBINATIONSOFCONTROL EFFORT AND CONTROL SPECIlCITY SEE TEXT )N BOTH CASES THE RODENT CONTROL CAN LEAD TO THE DEMOGRAPHICEXPLOSIONOFONEOFTHERODENTPOPULATIONS0ANEL$ SHOWSTHEPOPULATION TRENDSOFTHELOWERCOMPETITOR ASAFUNCTIONOFTHECONTROLEFFORTANDTHECONTROLEFlCIENCY !SIN&IG$ THECOLORSAREGIVENHERETOFACILITATETHE$EFFECT4HISPANELSHOWSTHATIF THECOMPETITIONISSTRONG THEDEMOGRAPHICEXPLOSIONOFTHELOWERCOMPETITORISPROPORTIONAL TO ITS CONTROL !S THE COMPETITION PRESSURE FROM THE SUPERIOR COMPETITOR IS LIFTED BY THE CONTROL THE RESULTING GAIN IN POPULATION GROWTH IS COMPENSATING THE LOSSES OCCURRED BY THECONTROL RESULTINGINALARGERPOPULATIONTHANINABSENCEOFCONTROL


THE STUDY OF INTERSPECIlC RELATIONSHIPS WE WILL ONLY CLOSE THIS EXAMPLE BY AN OBVIOUS IFOVERLOOKED STATEMENT)NSOMECASES THEDIRECTNEGATIVEIMPACTOFA SPECIES CAN HIDE AN INDIRECT POSITIVE EFFECT ON THE SAME COMMUNITY SOMETIMES ONTHEVERYSAMESPECIES)NACLASSICALSYSTEMWHERESPECIESADDITIONORREMOVAL ISNOTTHERULE SUCHINTERACTIONSCANREMAINHIDDEN)NTHECASEOFINVADEDCOM MUNITIESANDOFASSOCIATEDCONSERVATIONPROGRAMS SPECIESREMOVALCANHIGHLIGHT THESE UNDETECTED RELATIONSHIPS 3UCH HIGHLIGHT IS HOWEVER DONE IN THE FORM OF FURTHERDAMAGEINTHESYSTEM WITHARISKOFBIODIVERSITYLOSS ANDSHOULDTHERE FOREBEANTICIPATED)FINDIRECTPOSITIVEEFFECTSAREGREATERTHANTHEDIRECTNEGATIVE EFFECTS ONE MUST BE EXTREMELY CAUTIOUS IN ANY RESTORATION ACTION INTENDED TO PROTECTTHEAFFECTEDSPECIES

#/.#,53)/. "IOLOGICAL INVASIONS ARE PRIMARILY CONSIDERED FOR THEIR HARMFUL EFFECTS ON BIO DIVERSITY IN INVADED ECOSYSTEMS ESPECIALLY ON ISLANDS 4HIS IS FAR FROM SURPRIS ING AS ISLANDS ARE PLACES OF MAJOR BIOLOGICAL DIVERSITY AND ARE OFTEN INCLUDED IN ECOLOGICAL HOTSPOTS -YERS ET AL 2EID AND OF HIGH PROBABILITY OF EXOTICSPECIESINTRODUCTION&OREXAMPLE MAMMALINTRODUCTIONSHAVEBEEN DOCUMENTEDONISLANDS%BENHARD WHILE'ARGOMINYETALRECORDEDMORE THAN EXOTIC SPECIES OF mOWERING PLANTS IN THE WILD IN .EW #ALEDONIA ALONE 'ARGOMINY ET AL 4HESE lGURES HAVE UNDOUBTEDLY INCREASED NOWADAYS 4HENUMBEROFSPECIESTHATWENTEXTINCTASARESULTOFTHESEINVASIONSISIMPOSING TOO#ONSEQUENTLY THENUMBEROFCONTROLPROGRAMSHASBEENONTHERISETHISLAST DECADE ANDHEREAGAINTHEREAREAGREATNUMBEROFDOCUMENTEDEXAMPLES WITH FOR EXAMPLE OVER ERADICATION PROGRAMS JUST FOR EXOTIC MAMMALS IN .EW :EALAND#26EITCH PERSCOMM 7EHAVESOFARINSISTEDMUCHONCAUTIONANDPLANNINGINANYMITIGATIONERADI CATIONEFFORTINMANAGEMENTPROGRAMS7EFEELITISNEVERTHELESSESSENTIALTOSTART OURCONCLUSIONBYREWORDINGTHEOBVIOUSTHEBESTRESPONSETOBIOLOGICALINVASION ISALMOSTALWAYSMITIGATE ANDWHENPOSSIBLEERADICATE THEALIENPOPULATION)N MANY CASES A HESITANCY TO PROCEED WITH THIS HAS CAUSED MORE DAMAGE TO BIODI VERSITY THAN HAVE THE UNEXPECTED RESULTS OF POORLY PLANNED OR SIMPLY UNLUCKY ERADICATIONS (OWEVER THEAIMOFTHISCHAPTERWASTOTAKEADIFFERENTPOINTOFVIEWREGARD INGBIOLOGICALINVASIONS ANDTOSHOWTHATSUCHEVENTS HOWEVERNOTSYSTEMATIC CAN BE VIEWED AS OPPORTUNITIES TO INCREASE FUNDAMENTAL KNOWLEDGE IN ECOLOGY !DDITIONSANDDELETIONSOFSPECIESINTROPHICWEBSTHATARECOMPARATIVELYMUCH SIMPLER THAN USUAL SHOULD GREATLY ENHANCE OUR ABILITY TO DISCERN INTRINSIC DYNAMICAL PROCESSES AS WELL AS DIRECT AND INDIRECT INTERACTIONS BETWEEN SPECIES ANDHEREWEVIEWPOPULATIONDYNAMICSASGOODMARKERSOFSUCHMECHANISMS 4HISAPPROACHALSOHASTHEDUALADVANTAGEOFADDRESSINGMECHANISMSONAREAL SCALE SOMETHING IMPOSSIBLE IN LABORATORY BASED STUDIES AND OF ENCOMPASSING

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ALL THE CHARMING CONSTRAINTS OF BIOLOGICAL REALITY SOMETHING MISSING IN PURELY THEORETICALECOLOGY )TIS OFCOURSE NOTOURPURPOSETOMINIMIZETHECONTRIBUTIONOFTHEORYINTHIS REGARD $ESPITE THEIR INDUBITABLE ADVANTAGE IN THIS DOMAIN lELD BASED STUDIES THAT USE INVASIONS AS AN EXPERIMENT HAVE MUCH TO GAIN FROM A SYNERGY WITH CONCOMITANTLABORATORYANDTHEORETICALAPPROACHES7EEVENURGECONSERVATION BIOLOGISTS AND BIODIVERSITY MANAGERS TO USE THEORETICAL BASED RESULTS TO FOUND THEIRCONSERVATIONPROGRAMDESIGN ANDTOLOOKINTOHISTORICALCASESINORDERNOT TOENDLESSLYREPEATMISTAKESOFTHEPAST!NIDEAASSOCIATEDTOTHISISTHENEEDFOR CONSERVATIONISTS AS WELL AS BIODIVERSITY MANAGERS TO KNOW WHEN TO STOP A PRO GRAMANDRETHINKTHESTRATEGY#OURCHAMPETALA 4OKNOWWHENWEARE STARTINGTOPLAYTHEWITCHSSORCERERANDWHENTOSTOPISANESSENTIAL YETDIFlCULT FACULTY(ISTORYHASSHOWNUSTHATOFTENMOREHARMISGENERATEDWHENTRIALAND ERRORPROCESSESAREUSEDINDISCRIMINATELY/NEGOODEXAMPLEOFTHISISGIVENBYTHE ATTEMPTEDMITIGATIONOFRATSINSUGARCANElELDSIN*AMAICA4HERE CANEGROWERS INTRODUCEDANTS&ORMICAOMNIVORA WHICHDIDNOTREDUCERATNUMBERSBUTSOON BECAME A PROBLEM THEMSELVES 4O REMOVE RATS AND ANTS TOGETHER IT WAS THEN DECIDEDTOINTRODUCETOADS"UFOMARINUS "UTTOADSSTILLDIDNOTCONTROLRATS AND BECAME A PEST THEMSELVES &INALLY SMALL )NDIAN MONGOOSES WERE INTRODUCED TO CONTROLRATSANDTOADS-ONGOOSESFAILEDTOCONTROLEITHER ANDBEGANPREYINGON NATIVEBIRDS POSINGNEWTHREATSTOWILDLIFE3ILVERSTEINAND3ILVERSTEIN 7ERECOGNIZETHATTHEREHASBEENMUCHTOGAINFROMTHESEKINDSOFHISTORICAL MISTAKES AND THAT THESE HARD WON LESSONS MIGHT EVEN TURN OUT TO BE GLOBALLY BENElCIAL FOR THE BIODIVERSITY IN THE LONG RUN (OWEVER WE BELIEVE THE TRIAL AND ERROR APPROACH TIME HAS NOW PASSED AND BIODIVERSITY MANAGERS SHOULD PERSEVERE IN THE CURRENT TREND OF BASING RESTORATION STRATEGIES ON SOUND SCIEN TIlCGROUNDS4HISCANONLYBEDONEINDEVELOPINGSPECIlCSTUDIESONPOPULATIONS INTERACTINGININVADEDCOMMUNITIESASWELLASTHOSETHATUSESUCHINVASIONSASA DIDACTICTOOLTOUNDERSTANDBASICPROCESSESINPOPULATIONECOLOGY

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"ROTHERS . 0 "REEDING DISTRIBUTION AND STATUS OF BURROW NESTING PETRELS AT -ACQUARIE)SLAND!USTRIALIAN7ILDLIFE2ESEARCH "ROTHERS .0AND#OPSON '2-ACQUARIE)SLANDmORAANDFAUNAMANAGEMENT INTERPRETING PROGRESS AND PREDICTIONS FOR THE FUTURE 0APERS AND 0ROCEEDINGS OF THE 2OYAL3OCIETYOF4ASMANIA #AMPOS ! 2 AND 'RANADEIRO * 0 "REEDING BIOLOGY OF THE 7HITE FACED 3TORM PETRELON3ELVAGEM'RANDE)SLAND .ORTH EAST!TLANTIC7ATERBIRDS #HAPUIS * ,A!LIENMAMMALSINTHE&RENCH3UBANTARCTIC)SLANDS)N0ROGRESSIN CONSERVATIONOFTHE3UBANTARCTIC)SLANDSED02$INGWALL 6OL PP )5#. 4HE7ORLD#ONSERVATION5NION #ONSERVATIONOFTHE3OUTHERN0OLAR2EGION #HAPUIS * , B 2ESTORATION OF TWO ISLANDS IN THE +ERGUELEN !RCHIPELAGO BY ERADICATION OF THE RABBIT /RYCTOLAGUS CUNICULUS )N 0ROGRESS IN CONSERVATION OF THE 3UBANTARCTIC )SLANDS ED 0 2 $INGWALL 6OL PP )5#. 4HE 7ORLD #ONSERVATION5NION #ONSERVATIONOFTHE3OUTHERN0OLAR2EGION #HAPUIS * , "OUSSÒS 0AND"ARNAUD '!LIENMAMMALS IMPACTANDMANAGE MENTINTHE&RENCHSUB ! NTARCTICISLANDS"IOLOGICAL#ONSERVATION #LUTTON "ROCK 4(AND#OULSON 4#OMPARATIVEUNGULATEDYNAMICSTHEDEVILISIN THEDETAIL0HILOSOPHICAL4RANSACTIONSOFTHE2OYAL3OCIETYOF,ONDON3ERIES" "IOLOGICAL 3CIENCES #OURCHAMP & #HAPUIS *,AND0ASCAL -A-AMMALINVADERSONISLANDSIMPACT CONTROLANDCONTROLIMPACT"IOLOGICAL2EVIEWS #OURCHAMP & ,ANGLAIS - AND 3UGIHARA ' #ONTROL OF RABBITS TO PROTECT ISLAND BIRDSFROMCATPREDATION"IOLOGICAL#ONSERVATION #OURCHAMP & ,ANGLAIS -AND3UGIHARA '2ABBITSKILLINGBIRDSMODELLINGTHE HYPERPREDATIONPROCESS*OURNALOF!NIMAL%COLOGY #OURCHAMP & 7OODROFFE 2AND2OEMER 'B2EMOVINGPROTECTEDPOPULATIONSTO SAVEENDANGEREDSPECIES3CIENCE #UTHBERT 2 AND (ILTON ' )NTRODUCED HOUSE MICE -US MUSCULUS A SIGNIlCANT PREDATOR OF THREATENED AND ENDEMIC BIRDS ON 'OUGH )SLAND 3OUTH !TLANTIC /CEAN "IOLOGICAL#ONSERVATION %BENHARD 4 )NTRODUCED BIRDS AND MAMMALS AND THEIR ECOLOGICAL EFFECTS 3WEDISH 7ILDLIFE2ESEARCH &EARE # !NTS TAKE OVER FROM RATS ON "IRD )SLAND 3EYCHELLES "IRD #ONSERVATION )NTERNATIONAL &ITZGERALD "-$IETOFDOMESTICCATSANDTHEIRIMPACTONPREYPOPULATIONS)N4HE DOMESTICCAT THEBIOLOGYOFITSBEHAVIOUREDS$#4URNER0"ATESON PP #AMBRIDGE5NIVERSITY0RESS #AMBRIDGE &ITZGERALD "- $ANIEL -* &ITZGERALD !% +ARL "* -EADS -*AND.OTMAN 02 &ACTORS EFFECTING THE NUMBERS OF HOUSE MICE -US MUSCULUS IN HARD BEECH .OTHOFAGUSTRUNCATA FOREST*OURNALOFTHE2OYAL3OCIETYOF.EW:EALAND &LUX *%#2ELATIVEEFFECTOFCATSMYXOMATOSISTRADITIONALCONTROLORCOMPETITORSIN REMOVINGRABBITSFROMISLANDS.EW:EALAND*OURNALOF:OOLOGY &LUX *%#AND&ULLAGAR 0*7ORLDDISTRIBUTIONOFTHERABBIT/RYCTOLAGUSCUNICULUS ONISLANDS-AMMAL2EVIEW

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'ARGOMINY / "OUCHET 0 0ASCAL - *AFFRE 4AND4OURNEUR *##ONSEQUENCES FOR BIODIVERSITY OF PLANT AND ANIMAL SPECIES INTRODUCTIONS IN .EW #ALEDONIA 2EVUE $ %COLOGIE ,A4ERRE%T,A6IE 'ILLHAM - % 3OME INTERACTIONS OF PLANTS RABBITS AND SEABIRDS ON 3OUTH !FRICAN ISLANDS*OURNALOF%COLOGY 'INZBURG ,2AND*ENSEN #8*2ULESOFTHUMBFORJUDGINGECOLOGICALTHEORIES 4RENDSIN%COLOGY%VOLUTION 'RENFELL " 4 7ILSON + &INKENSTADT " & #OULSON 4 . -URRAY 3 !LBON 3 $ 0EMBERTON *- #LUTTON "ROCK 4(AND#RAWLEY -*.OISEANDDETERMINISM INSYNCHRONIZEDSHEEPDYNAMICS.ATURE (OLDGATE -7AND7ACE .-4HEINmUENCEOFMANONTHEmORASANDFAUNASOF 3OUTHERN)SLANDS0OLAR2ECORD (OLT 2$0REDATION APPARENTCOMPETITION ANDTHESTRUCTUREOFPREYCOMMUNITIES 4HEORETICAL0OPULATION"IOLOGY (ONE *3PATIALAND4EMPORAL!SPECTSOF6ERTEBRATE0EST$AMAGEWITH%MPHASISON &ERAL0IGS*OURNALOF!PPLIED%COLOGY +ARL "*AND"EST (!&ERALCATSON3TEWART)SLANDTHEIRFOODSANDTHEIREFFECTS ONKAKAPO.EW:EALAND*OURNALOF:OOLOGY +EANE 2 - AND #RAWLEY - * %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS4RENDSIN%COLOGY%VOLUTION +ESSLER ##%RADICATIONOFFERALGOATSANDPIGSFROM3ARIGAN)SLAND #OMMONWEALTH OF THE .ORTHERN -ARIANA )SLANDS METHODS AND RESULTS )N %RADICATION OF ISLANDS )NVASIVES PRACTICAL ACTIONS AND RESULTS ACHIEVED ED - #LOUT PP 5NIVERSITY OF !UCKLAND .EW :EALAND ,E2OUX 6 #HAPUIS *, &RENOT 9AND6ERNON 0$IETOFTHEHOUSEMOUSE-US MUSCULUS ON'UILLOU)SLAND +ERGUELENARCHIPELAGO 3UBANTARCTIC0OLAR"IOLOGY -ACK 2 . AND ,ONSDALE 7 - %RADICATING INVASIVE PLANTS HARD WON LESSONS FORISLANDS)N4URNINGTHE4IDETHE%RADICATIONOF)NVASIVE3PECIESEDS#26EITCH - #LOUT )NVASIVE 3PECIES 3PECIALTY 'ROUP OF THE 7ORLD #ONSERVATION 5NION )5#. !UCKLAND .EW :EALAND -ICOL 4AND*OUVENTIN 0%RADICATIONOFRATSANDRABBITSFROM3AINT 0AUL)SLAND &RENCH 3OUTHERN 4ERRITORIES )N 4URNING THE TIDE THE ERADICATION OF INVASIVE SPECIES EDS # 2 6EITCH - . #LOUT PP )5#. 33# )NVASIVE 3PECIES 3PECIALIST 'ROUP)5#. 'LAND 3WITZERLANDAND#AMBRIDGE 5+ -URPHY %AND"RADlELD 0#HANGEINDIETOFSTOATSFOLLOWINGPOISONINGOFRATSINA .EW :EALANDFOREST.EW:EALAND*OURNALOF%COLOGY -YERS . -ITTERMEIER 2! -ITTERMEIER #' DA&ONSECA '!"AND+ENT * "IODIVERSITYHOTSPOTSFORCONSERVATIONPRIORITIES.ATURE .EWMAN $'%FFECTSOFA-OUSE -USMUSCULUS %RADICATION0ROGRAMAND(ABITAT #HANGEON,IZARD0OPULATIONSOF-ANA)SLAND .EW :EALAND WITH3PECIAL2EFERENCETO -CGREGOR3KINK #YCLODINAMACGREGORI.EW:EALAND*OURNALOF:OOLOGY 2AMMELL # ' (OOGENBOOM * * , #OTTER - 7ILLIAMS * - AND "ELL * "RODIFACOUMRESIDUESINTARGETANDNON TARGETANIMALSFOLLOWINGRABBITPOISONINGTRIALS .EW:EALAND*OURNALOF%XPERIMENTAL!GRICULTURE


2EID 76"IODIVERSITYHOTSPOTS4RENDSIN%COLOGY%VOLUTION 2OBERTSON ( ! (AY * 2 3AUL % + AND -C#ORMACK ' 6 2ECOVERY OF THE +AKERORI AN %NDANGERED &OREST "IRD OF THE #OOK )SLANDS #ONSERVATION "IOLOGY 2OEMER '7 $ONLAN #*AND#OURCHAMP &'OLDENEAGLES FERALPIGS ANDINSU LAR CARNIVORES (OW EXOTIC SPECIES TURN NATIVE PREDATORS INTO PREY 0ROCEEDINGS OF THE .ATIONAL!CADEMYOF3CIENCESOFTHE5NITED3TATESOF!MERICA 3CHOENER 4 7 AND 3PILLER $ ! )NDIRECT EFFECTS IN AN EXPERIMENTALLY STAGED INVASIONBYAMAJORPREDATOR!MERICAN.ATURALIST 3COTT **2ABBITDISTRIBUTIONHISTORYANDRELATEDLANDDISTURBANCE-ACQUARIE)SLAND !USTRALIA0APERSAND0ROCEEDINGSOFTHE2OYAL3OCIETYOF4ASMANIA 3ELKIRK 0- #OSTIN !" 3EPPELT 2$AND3COTT **2ABBITS VEGETATIONANDERO SIONON-ACQUARIE)SLAND0ROCEEDINGSOFTHE,INNEAN3OCIETY.37 3ILVERSTEIN ! AND 3ILVERSTEIN 6 !NIMAL INVADERS 4HE STORY OF IMPORTED WILDLIFE !THENUM .EW9ORK 3MITH ! 0 AND 1UIN $ ' 0ATTERNS AND CAUSES OF EXTINCTION AND DECLINE IN !USTRALIANCONILURINERODENTS"IOLOGICAL#ONSERVATION 3MITH 62 !VENANT .,AND#HOWN 3,4HEDIETANDIMPACTOFHOUSEMICEON ASUB !NTARCTICISLAND0OLAR"IOLOGY 3OULÏ - % "OLGER $ 4 !LBERTS ! # 7RIGHT * 3ORICE - AND (ILL 3 2ECONSTRUCTED DYNAMICS OF RAPID EXTINCTIONS OF CHAPARRAL REQUIRING BIRDS IN URBAN HABITATISLANDS#ONSERVATION"IOLOGY 4AYLOR 2 ( (OW THE -ACQUARIE ISLAND PARAKEET BECAME EXTINCT .EW :EALAND *OURNALOF%COLOGY

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#/--5.)49,%6%,-!34).'!.$).6!3)/. )NTHISSECTION WEINTRODUCEASIMPLECASESTUDYOFPLANT CONSUMERSYSTEM AND BRIEmY DISCUSS THAT WHEN SEED PREDATORS ARE GENERALISTS MASTING AT COMMUNITY LEVELISNECESSARYTOREDUCETHEIMPACTOFTHEPREDATOR2OWAN 3ORBUSAUCUPARIA, ISADECIDUOUSTREE WHICHISCOMMONINMUCHOF%UROPE4UTINETAL 4HE mESHYBERRIESPRODUCEDBYROWANTREESSUFFERFROMATTACKBYTHEAPPLEFRUITMOTH !RGYRESTHIACONJUGELLA THATISAPRIMARYPRE DISPERSALSEEDPREDATORWHOSELARVAE RELYHEAVILYONROWANBERRIES3PERENSAB+OBROETAL3ATAKE ETAL 4HESPATIOTEMPORALDATAOBTAINEDFROMACENSUSINSOUTHERN.ORWAY SHOWTHATBERRYPRODUCTIONINROWANISVARIABLEACROSSYEARSMEAN#6 AND IS SPATIALLY SYNCHRONIZED l BOOTSTRAPPED CONlDENCE INTERVAL 4HE DEGREE OF SPATIAL SYNCHRONY IN ROWAN POPULATION IS LOWER THAN THELEVELOFSYNCHRONYLEADINGTOSEEDPREDATOREXTINCTIONIE l&IG AND HENCETHEAPPLEFRUITMOTHSUCCESSFULLYINVADEANDISPERSISTENTINTHISSYSTEM (OWEVER RELATIVELY HIGH DEGREE OF SPATIAL SYNCHRONY IN ROWAN MASTING EFl CIENTLYREDUCESSEEDLOSSESTOTHEAPPLEFRUITMOTHANDSUPPRESSESTHEPOPULATION GROWTHRATEOFSEEDPREDATORSATALOWLEVELASILLUSTRATEDIN&IG4HEPROPORTION OF SEEDS PREDATED WAS NEGATIVELY CORRELATED WITH THE TOTAL NUMBER OF SEEDS EVI DENCINGASATIATEDFUNCTIONALRESPONSEOFTHESEEDPREDATORSBYMASTING)NADDI TION A NEGATIVE RELATIONSHIP WAS OBSERVED BETWEEN THE SEED PREDATION AND THE RATIOOFBERRYPRODUCTIONINSUCCESSIVEYEARS4HISMEANSTHATSEEDCROPSFOLLOW INGPOORSEEDCROPSTENDEDTOESCAPEPREDATIONS TESTIFYINGTOASATIATIONTHROUGH NUMERICALRESPONSEOFTHEPREDATORS3ATAKEETAL 4HEPREDATORSATIATION HYPOTHESIS FURTHER PREDICTS THAT THE MORE VARIABLE POPULATIONS SHOULD ATTAIN HIGHER OVERALL SEED SURVIVAL *ANZEN 7ALLER 3ILVERTOWN 4O ASSESS THIS THE TOTAL PROPORTION OF SEEDS LOST TO PREDATION WAS EXAMINED AS A FUNCTION OF TEMPORAL VARIABILITY IN SEED PRODUCTION MEASURED BY THE #6 4HE RESULTANT LOGISTIC REGRESSION REVEALED A SIGNIlCANTLY NEGATIVE RELATIONSHIP BETWEENTHEPROPORTIONOFBERRIESPREDATEDAND#6THESLOPEnP


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INDICATING THAT LARGER INTER ANNUAL VARIATION IN BERRY PRODUCTION RESULTED IN SMALLERLOSSESTOPREDATION4HESERESULTSSHOWTHATROWANMASTINGHASANADAP TIVEFOUNDATION WHICHREDUCESEEDLOSSESTOANDPREVENTARAPIDEXPANSIONINA PLANTPOPULATION 4HE PERSISTENCE OF THE MOTH IN THE ROWAN MOTH SYSTEM IS IN PART BECAUSE OF THEFACTTHATTHEAPPLEFRUITMOTHISNOTASTRICTSPECIALISTTHEPRIMARYANDPRE FERREDHOSTOFTHEAPPLEFRUITMOTHISROWAN BUTWHENTOOFEWROWANBERRIESARE AVAILABLE FOR EGG LAYING MANY FEMALE MOTHS SWITCH THE HOST TO APPLE !HLBERG )FTHEREAREGENERALISTSEEDPREDATORSINAPLANTCOMMUNITY VARIABLEAND SYNCHRONIZED SEED PRODUCTION ONLY WITHIN A SINGLE SPECIES MAY NOT ENOUGH TO PREVENTINVASIONOFTHESEEDPREDATORANDEVENMASTINGSPECIESSHOWINGASIGNIl CANTSYNCHRONYINSEEDPRODUCTIONMAYSUFFERHEAVYSEEDPREDATION3ILVERTOWN


&IG 0LOTOFPROPORTIONOFSEEDPREDATIONINROWANASAFUNCTIONOF! SEEDCROPSIZE AND" THERATIOOFSEEDCROPSIZEINYEARTANDTHATINYEARTnLAG ,OGTRANSFORMED VARIABLES ARE USED FOR CALCULATION ,INES REPRESENTS THE LOGISTIC REGRESSION MODEL WHICH HAVE INTERCEPTS AND SLOPES OF ! 3% P n 3% P AND " n 3% P n 3% P # 2ELATIONSHIP BETWEEN THE COEFlCIENT OF VARIATION #6 OF ANNUAL SEED PRODUCTION ANDTHETOTALPROPORTIONOFSEEDPREDATION%ACHPOINTREPRESENTSTHERESULTCALCULATEDAT ONE STUDY SITE ,OGISTIC REGRESSION ANALYSIS GAVE THE REGRESSION LINE AS INTERCEPT OF n 3% P ANDSLOPEOFn3% P


STATEDTHATSYNCHRONOUSSEEDPRODUCTIONBETWEENPOPULATIONOFDIFFERENT SPECIESSHARINGTHESAMESEEDPREDATORSREDUCESTHEGROWTHRATEOFTHEPREDATOR POPULATION BY PREDATOR SATIATION 3PATIAL SYNCHRONY IN SEED PRODUCTION AMONG SPECIESHASBEENREPORTEDINANIMAL POLLINATEDSPECIESINARELATIVELYCLOSEDCOM MUNITY IN THE RAIN FOREST -OMOSE ET AL )NOUE AND(AMID3AKAI ET AL AND IN WIND POLLINATED SPECIES IN OPEN HABITATS SUCHASTEMPERATE FOREST AND SAVANNA +OENIG AND +NOPS 3CHAUBER ET AL 3HIBATA ET AL 3UCHA SYNCHRONIZEDANDEPISODIC REPRODUCTION IN A COMMUNITY PROVIDESANINTERESTINGINSIGHT INTO THEEVOLUTIONARY PROCESS HOWPLANT COMMUNITIESENHANCERESISTANCEAGAINSTGENERALISTSEEDPREDATORS

#/.#,53)/. 4HIS CHAPTER FOCUSES ON THE SPATIALLY EXTENDED DYNAMICS OF MASTING PLANTS AND THEIRSEEDPREDATORS0LANTSWITHINAFORESTMAYPRODUCESEEDSANNUALLYORINTER MITTENTLYINTIMEANDSYNCHRONOUSLYORASYNCHRONOUSLYACROSSSPACE4HISRANGE OFDYNAMICALBEHAVIORISCAPTUREDBYTHEPOLLENCOUPLEDTREEMODELEQNS )SAGI3ATAKEAND)WASA A B 4HEEFFECTOFMASTSEEDING ONDYNAMICSANDINVASIBILITYOFSPECIALISTCONSUMERSWASEXPLOREDBYEXAMINING THEPOPULATIONDYNAMICSOFSEEDPREDATORSINABOTTOM UPFASHIONEQNS 7HEN PLANTS PRODUCE SEEDS INTERMITTENTLY PERSISTENCE AND INVASION OF THE PREDATORISMOSTCRITICALLYDEPENDENTONTHEDEGREEOFSYNCHRONYOFSEEDSET4HE PREDATORPOPULATIONCANONLYPERSISTTHROUGHDISPERSALTOADJACENTHOSTPLANTSIN A FOREST SHOWING WEAK SYNCHRONY BECAUSE THERE IS THEN SOME FRACTION OF ASYN CHRONOUSLY REPRODUCING PLANTS WITHIN THE DISPERSAL RANGE OF THE PREDATORS )N CONTRAST EXTINCTIONOFSEEDPREDATORSISLIKELYWHENINTERMITTENTREPRODUCTIONIS HIGHLY SYNCHRONIZED AMONG DIFFERENT PLANTS &IG 3PATIAL SYNCHRONY IN SEED PRODUCTION WITH INTERMITTENCE CREATES NEGATIVE TIME LAG AUTO CORRELATION AND CROSS CORRELATIONINSEEDING WHICHMOSTEFFECTIVELYREDUCEINVASIBILITYOFTHESEED PREDATORSEQN 4HISMEANSTHAThCLASSICvMASTSEEDING EXHIBITINGSEEDSETTHAT IS NEGATIVELY CORRELATED IN TIME BUT POSITIVELY CORRELATED ACROSS SPACE IS A GOOD STRATEGY TO REDUCE SEED LOSS TO SEED PREDATORS )N ADDITION ANALYSIS OF INVASION CRITERIONSUGGESTTHATSPATIALSYNCHRONYATLOCALSPATIALSCALESMAYFURTHERREDUCE LOSSESBYPREVENTINGINVASIONOFSEEDPREDATORS&IG 4HESPATIALSCALEATWHICHSYNCHRONYINSEEDPRODUCTIONREDUCESSEEDLOSSESTO SEED PREDATORS DEPENDS ON THE MOBILITY OF THE PREDATORS +ELLY AND 3ORK )NSECT PREDATORS CONSIDERED IN THIS CHAPTER MAY DISPERSE OVER RELATIVELY SHORT DISTANCES "IRDS OR MAMMALS IN CONTRAST MAY BE HIGHLY MOBILE #URRAN AND ,EIGHTON )N ORDER TO SATIATE SUCH PREDATORS SO AS TO REDUCE SEED LOSSES LARGERSPATIALSCALESOFREPRODUCTIVESYNCHRONYMUSTBEMAINTAINED4HEANALYSIS OFAPPROXIMATEINVASIONCRITERIAGIVENINEQUATIONSANDAPPLIESALSOTOHIGHLY MOBILESPECIALISTCONSUMERSBECAUSETHEFORMULATIONSCANBEWRITTENFORARBITRARY NEIGHBORHOODSIZESNOTRESTRICTEDTONEARESTNEIGHBORDISPERSAL


4HE COMMUNITY CONSEQUENCES OF MASTING ARE ONLY KNOWN FOR SELECTED CASE STUDIES-ICEANDSQUIRRELS FORINSTANCE EXPERIENCEENHANCEDSURVIVALANDRAPID POPULATIONGROWTHINYEARSOFOAKMAST3UCHPOPULATIONMAYCONVERSELYCRASH TOLOWLEVELSINYEARSOFLITTLEACORNBECAUSEOFASHORTAGEOFFOODRESOURCES7OLFF -C3HEA -ASTING HAS ALSO BEEN SHOWN TO HAVE CASCADING EFFECTS THROUGH FOOD WEBS AND ECOLOGICAL COMMUNITIES IN SYSTEMS RANGING FROM OUT BREAKSOFGYPSYMOTHINOAKFORESTSTOHUMANRISKOF,YMEEXPOSURE/STFELDETAL /STFELDAND+EESING 3UCHSTUDIESONTHETROPHICCASCADESFOLLOWING VARIABLEMASTINGMAYPROVIDEKEYINSIGHTSINTOINVASIONASACOMMUNITYPROCESS 3HEAAND#HESSON )NTHISCHAPTER WEFOCUSONTHEDYNAMICSOFASINGLESEEDPREDATORSPECIESON ASINGLEMASTINGRESOURCE)NTHEFUTUREITWILLBEOFINTERESTTOCONSIDERINVASIBIL ITY TO ADDITIONAL SEED PREDATORS AND POSSIBLY EXOTIC SPECIES 7HEN EXOTIC SEED PREDATORSAREINTRODUCEDINTOAPLANTPOPULATIONTHATSHOWMASTING APOTENTIAL STRATEGYTHEPREDATORMAYEMPLOYTOCOPEWITHVARIABLERESOURCEAVAILABILITYMAY BE AN EXTENDED DIAPAUSE +ELLY ET AL AND -C+ONE ET AL DEMON STRATEDTHATPLANTPOPULATIONSSUFFERINGSEEDPREDATIONBYTHEPREDATORSWHOHAVE EXTENDEDDIAPAUSEMAYNEEDTOSHOWEXTREMELYHIGHLEVELSOFMASTSEEDING4HIS DEMONSTRATIONHASBEENRECENTLYSUPPORTEDBYATHEORETICALSTUDYOF3ATAKEAND "JRNSTAD4HEREFORE HOWPRE EXISTINGMASTINGMIGHTMITIGATETHEIMPACT OF INVADING PREDATORS IS DEPENDENT ON THE LEVEL BOTH OF PRE EXISTING MASTING OF PLANTPOPULATIONANDTHEEXTENDEDDIAPAUSEOFINVADER7HENTHERESIDENTSEED PREDATOR PERSISTS ON A MASTING RESOURCE THE COMPETITIVE INTENSITY BETWEEN THE RESIDENT AND INVADING SPECIES WILL mUCTUATE DUE TO SPATIOTEMPORAL VARIABILITY IN RESOURCE AVAILABILITY )NVASION SUCCESS OF AN EXOTIC SPECIES MAY BE ENHANCED WHENTHERESIDENTPOPULATIONISSATIATEDTHROUGHLARGESEEDCROPSBECAUSEUNCON SUMEDRESOURCESMAYRESULTINACOMPETITIVERELEASE4HISINCREASEININVASIBILITY MAYOCCURTHROUGHTEMPORALCOMPETITIVERELEASE ORSPATIALLYTHROUGHTHEFORMA TION OF COMPETITION FREE SPATIAL CLUSTERS )NVASIBILITY OF EXOTIC SEED PREDATORS IS DETERMINED BY THE INTERWINED INTERACTION BETWEEN TEMPORAL PROCESS AND SPATIAL PATTERNILLUSTRATINGTHECOMPLEXCOMMUNITYCONSEQUENCESOFMASTING

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WHICH COULD CONTRIBUTE TO THE HIGH INVASION RESISTANCE OF HYPER DIVERSE ECO SYSTEMS LIKE TROPICAL RAIN FORESTS &INE 3ECOND BECAUSE DENSITIES OF THE INTRODUCED HOST WILL USUALLY BE LOW IMMEDIATELY FOLLOWING INTRODUCTION PATHO GENSINVOLVEDINBIOTICRESISTANCEWOULDNOTBETHOSEFORWHICHTRANSMISSIONOR HOSTSWITCHINGWASSTRONGLYDENSITY DEPENDENT4HIRD THEPATHOGENMUSTEXACT A HIGH lTNESS COST ON THE HOST #OMBINATIONS OF GENERALIZATION AND HIGH VIRU LENCEARENOTUNUSUALINPATHOGENS ESPECIALLYFORSPECIESTHATHAVELONGRESTING STAGES OR SAPROPHYTIC ABILITY EG 0HYTOPHTHORA CINNAMOMI 6ERTICILLIUM DAHLIAE &USARIUM OXYSPORUM %VEN PATHOGENS THAT CAN ATTACK MANY HOSTS HAVE DIF FERENTIAL IMPACTS ON DIFFERENT HOST SPECIES )F A PATHOGEN HAS A GREATER NEGATIVE EFFECTONTHECOMPETITIVEABILITYOFTHENON NATIVEHOSTSTHANONTHENATIVEHOSTS THENITWILLCONTRIBUTETOTHECOMPETITIVEEXCLUSIONOFTHENON NATIVE+EANEAND #RAWLEY 3INCEEVENFAIRLYSPECIALIZEDPATHOGENSOFTENINFECTMANYMEMBERSOFTHESAME GENUS OR FAMILY IT IS LIKELY THAT THE NUMBER OF PATHOGENS COMPETENT TO INFECT A NOVEL HOST DEPENDS ON WHETHER IT IS PHYLOGENETICALLY RELATED TO NATIVE SPECIES ALREADYINTHECOMMUNITY4HEREFORE BIOTICRESISTANCESHOULDFAVORINVASIONBY SPECIES WITH NO CLOSE RELATIVES $ESPITE THIS CLEAR PREDICTION AND THE ACCEPTED PRACTICE OF USING PHYLOGENETIC RELATIONSHIPS IN QUARANTINE AND TRADE POLICY TO TARGET RELATIVES OF WEEDY PLANTS OR IDENTIFY POTENTIAL CARRIER HOSTS SURPRISINGLY FEW STUDIES OF INVASION EVEN MENTION THE PHYLOGENETIC STRUCTURE OF THE INVADED COMMUNITIES)NONERAREATTEMPT -ACK FOUNDTHATFOROUTOFREGIONAL mORAS NATURALIZEDSPECIESWEREMORECOMMONINGENERAWITHNONATIVECONGENERS THAN THOSE WITH NATIVE CONGENERS CONSISTENT WITH THE IDEA OF BIOTIC RESISTANCE (OWEVER THISSTUDYWASNOTABLETOCONTROLFORTHEEFFECTOFOPPORTUNITYWHETHER PLANTSWITHOUTNATIVECONGENERSHAVEAHIGHERPROBABILITYOFSUCCESSFULINVASION GIVENTHEIRPROBABILITYOFINTRODUCTION 5SINGADIFFERENTAPPROACH $UNCANAND 7ILLIAMS COMPILEDALISTOFALLPLANTSPECIESTHATHAVEEVERBEENINTRODUCED FOR CULTIVATION IN .EW :EALAND 4HEY FOUND THAT INTRODUCED SPECIES IN GENERA THATALREADYHADRESIDENTNATIVESWEREMORELIKELY NOTLESSLIKELY TOSUCCESSFULLY NATURALIZE 4HEY SUGGEST THAT SPECIES WITH NATIVE CONGENERS MAY SHARE CHARAC TERISTICS THAT MAKE THEM MORE lT IN THE INTRODUCED RANGE AND THIS FACTOR OVER WHELMSTHEPOTENTIALEFFECTOFLOCALNATURALENEMIES 4HERE IS A STRIKING NEED FOR MORE STUDIES TO DETERMINE WHETHER AND WHEN BIOTIC RESISTANCE BY NATIVE PATHOGENS OCCURS "ECAUSE THERE IS LITTLE INFORMATION ON WHERE AND WHEN UNINTENTIONAL SPECIES INTRODUCTIONS FAIL ASSIGNING MECHA NISMS TO THESE FAILURES HAS BEEN NEARLY IMPOSSIBLE (ORTICULTURE FORESTRY AND AGRICULTURE EACH PROVIDE EXAMPLES OF ENDEMIC PATHOGENS THAT HAVE DECIMATED INTRODUCEDPLANTSPECIESSOTHATGROWINGTHESESPECIESISNOLONGERECONOMICALLY VIABLE -ACK #OUTINHOETAL 7INGlELDETAL (OWEVER EXTRA P OLATINGFROMAGRICULTURALORSILVICULTURALEXAMPLES T O INVASIVEINTRODUCEDSPECIES REQUIRESCAUTION SINCETHEREGENERATIONOFHOSTSISCONTROLLED PREVENTINGTHEHOST POPULATION FROM EVOLVING RESISTANCE OR TOLERANCE TO THE PATHOGEN !DDITIONALLY SIMPLIlEDSYSTEMSINAGRICULTUREANDFORESTRYMAYSIMPLYLACKMODERATINGEFFECTS


OF GREATER BIOTIC COMPLEXITY IN LESS MANAGED SYSTEMS EG HYPERPARASITES OF THEPATHOGENS %SCAPEFROMNATURALENEMIES

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SYMPATRIC SUITES OF NATIVE AND NON NATIVE CLOVERS !LTHOUGH FUNGAL EXCLUSION EXPERIMENTSINTHISSYSTEMREVEALEDSIGNIlCANTIMPACTSOFPATHOGENS THEREWAS NODIFFERENCEINTHERESPONSEOFNATIVEANDNON NATIVESPECIES &INALLY OTHER STUDIES HAVE TAKEN THE APPROACH OF COMPARING DISEASE ON A SINGLE HOST SPECIES IN ITS NATIVE AND INVADED RANGES 7OLFE SURVEYED FOR THE ANTHER SMUT FUNGUS -ICROBOTRYUM VIOLACEUM IN NATIVE POPULATIONS AND INTRODUCEDPOPULATIONSOF3ILENELATIFOLIUM(EFOUNDSIGNIlCANTLYMOREPOPU LATIONS INFECTED AND AT MUCH HIGHER INFECTION FREQUENCIES IN THE NATIVE RANGE THANINTHEINTRODUCEDRANGE-ITCHELLAND0OWER USEDPUBLISHEDRECORDS OF PATHOGEN ASSOCIATIONS WITH PLANT HOSTS IN THEIR NATIVE AND INTRODUCED RANGES0LANTSWEREINFECTEDBYFEWERPATHOGENSPECIESINTHEIRNATURALIZED RANGE 4HERE WAS ALSO AN INDICATION THAT SPECIES LEAVING BEHIND PROPORTIONALLY MORENATURALENEMIESWEREMORELIKELYTOBECATEGORIZEDASNOXIOUSORINVASIVE SPECIESBYLANDMANAGERSANDPUBLICAGENCIES5SINGANEXPERIMENTALAPPROACH "ECKSTEADAND0ARKER DIRECTLYMEASUREDTHEDEMOGRAPHICEFFECTOFPATHO GENSONANINVADERINTHECONTEXTOFKNOWNINFORMATIONFROMTHESPECIESNATIVE RANGE!MMOPHILAARENARIAINITSNATIVE%UROPEISLIMITEDTOANEARLY SUCCESSIONAL ROLEINSHIFTINGBEACHSANDSBYSOIL BORNEPATHOGENS6ANDER0UTTENETAL !SANINVADERONTHEWESTCOASTOFTHE53! !MMOPHILAREMAINSDOMINANTFOR LONGPERIODSOFTIME(OWEVER ESCAPEFROMNATURALENEMIESDOESNOTEXPLAINTHIS CONTRAST BETWEEN ITS NATIVE AND INVASIVE ECOLOGICAL ROLES "Y REPLICATING EXPERI MENTSDONEINTHENATIVERANGE "ECKSTEADAND0ARKER FOUNDTHENEGATIVE EFFECTOFSOILBORNEPATHOGENSONEARLYGROWTHINTHEINVADEDRANGEWASATLEASTAS LARGEORLARGERTHANTHEIREFFECTINTHENATIVERANGE 4O PREDICT WHETHER AN INTRODUCED PLANT IS LIKELY TO BENElT FROM ESCAPING NATURALENEMIES WENEEDTOUNDERSTANDTHERELATIVEIMPORTANCEOFHOST SPECIALIST VS HOST GENERALIST PATHOGENS AND PESTS IN THE INVADED HABITAT -ARON AND 6ILA +EANE AND #RAWLEY )F SPECIALIST PATHOGENS PREDOMINATE AND HOST SHIFTS ARE RARE NATIVE PLANTS MAY BE SUPPRESSED MORE THAN COMPETING INVASIVE SPECIES/NTHEOTHERHAND IFGENERALISTPATHOGENSDOMINATEINASITEANDDONOT SHOW A PREFERENCE FOR NATIVE HOST SPECIES ONE WOULD NOT EXPECT AN INTRODUCED PLANTTOEXPERIENCERELEASE4HEREFORE THEWIDERANGEOFRESULTSSEENINTHEABOVE EMPIRICALSTUDIESMAYBEINPARTEXPLAINEDBYTHERELATIVEIMPORTANCEOFSPECIAL ISTANDGENERALISTNATURALENEMIES!GREATERUNDERSTANDINGOFTHEPHYLOGENETIC STRUCTURE OF PATHOGEN HOST RANGES COUPLED WITH ANALYSIS OF THE PHYLOGENETIC STRUCTUREOFNATURALPLANTCOMMUNITIES7EBBETAL MAYHELPPREDICTTHE RELATIVE IMPORTANCE OF SPECIALIST VS GENERALIST PATHOGENS IN DIFFERENT KINDS OF PLANT COMMUNITIES &OR INSTANCE IN A HIGH DIVERSITY LOWLAND TROPICAL RAINFOREST TREESPECIES HOSTGENERALISTSDOMINATEDTHEPOLYPOREFUNGAL COMMUNITY ALL OF THE MORE COMMON FUNGAL SPECIES WERE FOUND ON MULTIPLE FAMILIES OF HOST TREES'ILBERTETAL &ERRERAND'ILBERT )NCONTRAST INANEARBYLOW DIVERSITYMANGROVEFORESTWITHONLYTHREETREESPECIESPRESENTEACHFROMADIFFER ENT FAMILY OF ALL POLYPORE FUNGAL COLLECTIONS BELONGED TO JUST THREE FUNGAL SPECIES AND EACH SPECIES WAS HIGHLY SPECIALIZED ON JUST ONE MANGROVE SPECIES


'ILBERT AND 3OUSA 2ESEARCHERS ARE JUST NOW BEGINNING TO ADDRESS THE RANGEOFHOSTSPECIALIZATIONINDIFFERENTPLANTCOMMUNITIES ANDTHEWIDERANGEOF OUTCOMESSUGGESTSTHATMANYMORESTUDIESWILLBENEEDEDBEFOREWECANFORMU LATEPREDICTIVEGENERALIZATIONS

).4%.4)/.!,,9).42/$5#%$0!4(/'%.3&/2")/,/')#!,#/.42/, ! DIRECT APPLICATION OF THE .ATURAL %NEMIES (YPOTHESIS IS DEPLOYING NATURAL ENEMIESFROMTHENATIVERANGEOFANINVASIVEPLANTTOCONTROLTHEINVADERPOPU LATION 3UCH CLASSICAL BIOLOGICAL CONTROL USES PLANTS AND PATHOGENS WITH SHARED EVOLUTIONARYHISTORIESBUTANEWENVIRONMENTALCONTEXT4HEREARESEVERALWAYS INWHICHBIOLOGICALCONTROLINTERACTIONSMAYBEDIFFERENTFROMNATIVEPATHOGENS ATTACKINGINTRODUCEDHOSTS&IRST UNLIKENATIVEPATHOGENS WHICHAREPRESUMABLY ADAPTEDTOTHELOCALCLIMATE THEINTRODUCEDBIOLOGICALCONTROLAGENTEXPERIENCES ANOVELENVIRONMENT WHICHCOULDHAVEALARGEIMPACTONDISEASEDEVELOPMENT #ASESTUDIESOFFAILEDBIOLOGICALCONTROLEFFORTSPROVIDEUSWITHMANYEXAMPLESOF THEIMPORTANCEOFTHEDISEASETRIANGLE-ORINETAL 3ECOND BOTHTHEHOST AND PATHOGEN ARE LIKELY TO BE GENETICALLY DEPAUPERATE (OWEVER THE PATHOGEN WILL HAVE BEEN CHOSEN SPECIlCALLY TO BE VIRULENT ON THE INVASIVE HOST PLACING THEHOSTATARELATIVEDISADVANTAGEFOREVOLUTIONARYRESPONSES4HIRD ONLYFAIRLY HOST SPECIlCPATHOGENSARESELECTEDFORBIOLOGICALCONTROLRELEASES MEANINGTHAT PATHOGENNUMERICALDYNAMICSSHOULDALWAYSBECLOSELYLINKEDTOINDIVIDUALHOST DENSITY)NFACT BIOLOGICALCONTROLRELEASESAREANEXCELLENTOPPORTUNITYTOSTUDY FACTORSINmUENCINGNUMERICALDYNAMICS.OTONLYSHOULDTHEREBEATIGHTCONNEC TIONBETWEENPATHOGENANDHOSTDENSITY BUTINITIALCONDITIONSOFTHEINTERACTION ARE WELL KNOWN 4HAT IS THE HOST POPULATION IS ORIGINALLY FREE OF THAT PATHOGEN ANDISUSUALLYATHIGHDENSITY!SUCCESSFULEPIDEMICPROVIDESANOPPORTUNITYTO QUANTIFYBOTHFREQUENCY DEPENDENCEOFTRANSMISSIONOFTHEPATHOGENANDDENSITY DEPENDENCEASTHEHOSTDENSITYDECLINES 0REDICTING THE SHORT TERM AND LONG TERM SUCCESS OF PARTICULAR BIOLOGICAL CON TROL INTRODUCTIONS IS A MATTER OF OBVIOUS PRACTICAL IMPORTANCE 4O MAKE SUCH PREDICTIONS WENEEDTOUNDERSTANDHOWTHENUMERICALDYNAMICSOFAHOSTPLANT FOLLOWING INTRODUCTION OF ITS BIOCONTROL AGENT DEPEND ON HOST DENSITY DISEASE INCIDENCE GENETICVARIATION ANDEVOLUTIONARYCHANGESINVIRULENCEORRESISTANCE 3URPRISINGLY WHILETHEREARESOMECASESFORWHICHWEHAVEGOODINFORMATIONON THE DYNAMICS OF HOST NUMBERS AFTER RELEASE OF A CONTROL AGENT EG (ASAN AND !YRES -ORRIS FORMANYOTHERRELEASESTHEDETAILSOFCHANGESARENOT WELL DOCUMENTED )N PARTICULAR WE SHOULD ASK I IS CONTROL MORE SUCCESSFUL IN GENETICALLYDEPAUPERATEWEEDSII $OTRANSMISSIONRATEANDDEMOGRAPHICIMPACT OFTHEPATHOGENATTENUATEASTHEHOSTPOPULATIONDECLINESIII $OPATHOGENAND HOSTREACHASTABLEEQUILIBRIUMORARETHEYDEPENDENTONMETAPOPULATIONDYNAM ICS TO PERSIST IN THE LANDSCAPE $ETAILED INFORMATION ON NUMERICAL DYNAMICS IN BIOLOGICALCONTROLSYSTEMSISSCARCE BUTDATAARENEARLYNONEXISTENTFORLONG TERM


GENETIC CHANGES IN THE HOST OR PATHOGEN 4HERE IS GREAT UNTAPPED POTENTIAL FOR BIOLOGICAL CONTROL INTRODUCTIONS TO BE USED TO UNDERSTAND THE FACTORS THAT DRIVE THE ECOLOGICAL END EVOLUTIONARY DYNAMICS OF THE PLANT PATHOGEN INTERACTIONS )N FACT THE ONLY BIOCONTROL STUDY WE FOUND THAT TRACKED CHANGES IN PATHOGEN VIRULENCEORHOSTRESISTANCEFORAPLANT PATHOGENSYSTEMWASFORTHERUST0UCCINIA CHONDRILLINAON#HONDRILLAJUNCEASEECASESTUDYBELOW %VOLUTIONARYECOLOGYOFBIOCONTROLWITHPATHOGENS

4HEEVOLUTIONARYDYNAMICSOFINTERACTIONSBETWEENWEEDSANDPATHOGENBIOCON TROL AGENTS HAVE IMPORTANT IMPLICATIONS FOR THE LONG TERM SUCCESS OF BIOLOGICAL CONTROLPROGRAMS'ENERALLY WENEEDTOKNOW I HASVIRULENCEOFTHEBIOLOGICAL CONTROL PATHOGEN CHANGED OVER TIME AND HAS THIS INCREASED OR DECREASED THE SUCCESSOFCONTROLII (ASTHEHOSTDEVELOPEDRESISTANCEOVERTIMEIII (ASHOST SPECIlCITYCHANGEDOVERTIME2ECENTANALYSISOFEMERGINGDISEASESHASSUGGESTED THATECOLOGICALHOSTSHIFTSIE HAVINGAPREADAPTEDABILITYTOUSEANEWLYENCOUN TEREDHOST MAYPREDOMINATEASCAUSESOFNOVELEPIDEMICS ANDTHATHOSTSHIFTSMAY ONLYRARELYBECAUSEDBYMUTATIONSTHATALLOWCOLONIZATIONOFANEWHOST3CHRAG AND7IENER (OWEVER THEDIFlCULTYOFOBSERVINGSUCHGENETICEVENTSMAY DISTORTOURPERSPECTIVE6AN+LINKENAND%DWARDS SYNTHESIZEDINFORMATION ONHOSTRANGEFROMBIOLOGICALCONTROLPROGRAMSUSINGHERBIVORES4HEYFOUND THATHOSTSHIFTSWEREMOREQUANTITATIVETHANQUALITATIVE THATIS WHILEPREFERENCE AND EFlCIENCY ON NOVEL HOSTS EVOLVED THERE WAS NO EVIDENCE OF EVOLUTIONARY CHANGESINFUNDAMENTALHOST RANGE3UCHANANALYSISSHOULDBEDONEFORPATHO GENSUSEDASBIOLOGICALCONTROLAGENTS7HILEPATHOGENSAREGENERALLYTHOUGHTTO OFFER THE OPPORTUNITY FOR HIGH HOST SPECIlCITY SOME HAVE ARGUED THAT HIGH HOST SPECIlCITY MAY BE CORRELATED WITH EVOLUTIONARY LABILITY "ROOKS AND -C,ENNAN 3ECORD AND +AREIVA "ECAUSE THEY ARE UNABLE TO SIMPLY MOVE FROMANUNACCEPTABLEHOSTTOAMORESUITABLEONEASANANIMALMIGHT SPECIALIST PATHOGENSMAYEXPERIENCEEVENSTRONGERSELECTIONFORHOSTSHIFTSTHANHERBIVORES 2OY +NOWINGTHEFREQUENCYOFEVOLUTIONARYHOSTSHIFTSINPATHOGENSAND UNDERSTANDINGTHECONDITIONSUNDERWHICHTHEYOCCURARECRITICALTOTHEPROCESS OFRISKASSESSMENTINBIOLOGICALCONTROL3ECORDAND+AREIVA 'ENERAL THEORY OF HOST PATHOGEN INTERACTIONS HAS PLAYED A LARGE ROLE IN THE CHOICE OF BIOLOGICAL CONTROL AGENTS IN THE PAST -C&ADYEN &OR EXAMPLE IT HAS LONG BEEN THOUGHT THAT SEXUALLY REPRODUCING WEEDS WOULD BE HARDER TO CONTROL BECAUSE THEIR HIGHER LEVELS OF GENETIC VARIATION INTERFERE WITH PATHOGEN POPULATION GROWTH "URDON ET AL HOWEVER A MORE RECENT ANALYSIS HAS DISPUTED THIS ASSERTION #HABOUDEZ AND 3HEPPARD 3IMILARLY THE BELIEF THATPATHOGENPOPULATIONSARELOCALLYADAPTEDTOTHEIRHOSTGENOTYPESHASHADA LARGEINmUENCEONTHEPROCESSOFSELECTIONOFCONTROLAGENTS WITHGENETICANALYSIS PLAYING AN INCREASING ROLE IN THE CAREFUL MATCHING OF AGENT GENOTYPES WITH THE POPULATIONSOFORIGINFORTHEWEEDEG (OLDENAND-AHLBERG (OWEVER THE EVIDENCE FOR CLOSE LOCAL ADAPTATION OF PATHOGENS TO THEIR HOST POPULATIONS IS


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&IG 4HE RELATIONSHIP BETWEEN RELATIVE PLANT ABUNDANCE IN AN OLD lELD SITE AND SOIL FEEDBACK RESPONSE 3QUARES REPRESENT MEANS Y X X R 0.UMBERSREPRESENTDIFFERENTPLANTSPECIES #AREXGARBERI #AREX AUREA #AREX GRANULARIS $AUCUS CAROTA !GROSTIS GIGANTEA 3OLIDAGO GRAMINIFOLIA 3OLIDAGONEMORALIS !STERSIMPLEX !STERVIMINEUS !STERNOVAEANGLIAE #IRCIUM VULGARE #HENOPODIUM AMBROSIOIDES /ENOTHERA BIENNIS #AREX mAVA *UNCUS DUDLEYI 3OLIDAGO CANADENSIS ,INARIA VULGARIS #ICHORIUM INTYBUS #IRCIUM ARVENSE 3OLIDAGORUGOSA 'EUMALEPPICUM 3ATUREJAVULGARIS 0OTENTILLARECTA #ORONILLAVARIA !SCLEPIASSYRIACA !CHILLEAMILLEFOLIUM !POCYNUMCANNABINUM (YPERICUM PERFORATUM !GROSTIS SCABRA 0HLEUM PRATENSE 0OA COMPRESSA %CHIUM VULGARE #ENTAUREA JACEA 2UDBECKIA SEROTINA 0OA PRATENSIS $ACTYLISGLOMERATA #ERASTIUMVULGATUM 'ALIUMPALUSTRE /ENOTHERAPERENNIS 0RUNELLAVULGARIS 4RIFOLIUMPRATENSE #ONVOLVULUSARVENSIS 3ILENECUCUBALUS %RIGERON STRIGOSUS !SPARAGUS OFlCINALIS (IERACIUM AURANTICUM %RIGERON PHILADELPHICUS 6ERONICA OFlCINALIS 0LANTAGOLANCEOLATA 'ALIUMMOLLUGO (IERACIUM PILOSELLA 6ICIA CRACCA (IERACIUM PRATENSE -EDICAGO LUPULINA 2ANUNCULUS ACRIS 4ARAXACUM OFlCINALE &RAGARIA VIRGINIANA #HRYSANTHEMUM LEUCANTHEMUM 4RAGOPOGON PRATENSIS "ROMUS INERMIS 0ANICUM LANUGINOSUM 2EPRINTEDFROM +LIRONOMOS

0LANTSPECIESTHATWEREFOUNDINLOWABUNDANCEINTHElELDCONSISTENTLYDISPLAYED NEGATIVEFEEDBACKINTERACTIONS WHEREASPLANTSWITHHIGHABUNDANCEEITHERHAD LOWNEGATIVEORPOSITIVEFEEDBACKINTERACTIONS+LIRONOMOS


0LANT INVASIONS PROVIDE AN EXCEPTIONAL OPPORTUNITY FOR UNDERSTANDING HOW PLANTS AFFECT SOILS AND DRIVE FEEDBACK PROCESSES .UMEROUS STUDIES HAVE DOCU MENTEDTHEEFFECTSOFINVASIVESPECIESONTHECOMPOSITIONOFSOILBIOTA"ELNAPAND 0HILLIPS +OURTEV ET AL AND SOIL MICROBIAL FUNCTION +OURTEV ET AL %HRENFELD (OWEVER MUCHLESSISKNOWNABOUTTHEROLEOFFEEDBACKS INTHESUCCESSOFEXOTICPLANTS&EEDBACKSMAYALSOAFFECTEVOLUTIONPOTENTIALLY MOST APPARENT IN THE RAPID EVOLUTIONARY CHANGES THAT CAN ACCOMPANY EXOTIC INVASION2ICEAND%MORY )FPLANT SOILFEEDBACKSDRIVEVARIATIONINlTNESSDIFFERENCESAMONGINDIVIDUALS THEN ULTIMATELY FEEDBACK INTERACTIONS MAY BE UNDER SELECTIVE PRESSURE 6AN DER 0UTTEN6AN"REEMANAND&INZI "ASEDONTHEORYDEVELOPEDBY"EVER ET AL AND +LIRONOMOS WE HYPOTHESIZE THAT POSITIVE FEEDBACKS IN GENERALARELIKELYTOLEADTHEPLANTCOMMUNITYTOSHIFTTOWARDSAMONOCULTUREOF THEINVASIVESPECIES(OWEVER WEPROPOSETHATTHELONGEVITYOFPOSITIVEFEEDBACK INTERACTIONS IN EVOLUTIONARY TIME MAY DEPEND ON WHETHER THE INVASIVE PLANT IS HAVINGITSSTRONGESTEFFECTSONTHEPATHOGENICORTHENUTRIENT CYCLINGCOMPONENTS OF THE SOIL ECOSYSTEM &IG -ICROBES HAVE A SHORT GENERATION TIME AND THUS CANRESPONDTOEVOLUTIONARYPRESSURESQUICKLY4HEREFOREPATHOGENSMAYRESPOND RELATIVELYRAPIDLYTOTHEINVASIONOFNON NATIVEPLANTS4HISMAYULTIMATELYLEAD TO GREATER COEXISTENCE AMONG SPECIES WHERE ALTHOUGH THE INVASIVE MAY STILL BE PRESENT IT WILL NOT BE THE OVER WHELMING COMMUNITY DOMINANT )N CONTRAST FEEDBACKSBETWEENINVASIVEPLANTSANDNUTRIENTCYCLESMAYBEMUCHMORELIKELY TO PERSIST 7HEN THE BIOTIC COMPONENT OF THE SOIL NUTRIENT CYCLES IS INVOLVED IT IS EXPECTED THAT THERE WOULD BE A SHIFT IN THE MICROBIAL COMMUNITY TO POPULA TIONSTHATAREBETTERADAPTEDTOTHENEWNUTRIENTSTATUSOFTHEECOSYSTEM&IG !TLASAND"ARTHA3CHIMELAND"ENNETT )NTHECASEOFALTERATIONSTO ABIOTICCOMPONENTSOFTHESOILECOSYSTEM THEREISNODIRECTSELECTIVEPRESSURETO STIMULATEADAPTATION&IG (EREWEDISCUSSINTERACTIONSBETWEENINVASIVESPECIESANDTHESOILECOSYSTEM PATHOGENICANDNUTRIENT CYCLINGCOMPONENTS THEMECHANISMSFORTHESEINTER ACTIONS AND EVIDENCE THAT THESE INTERACTIONS HAVE VERY DIFFERENT EFFECTS ON THE SURVIVALOFINVASIVEVERSUSNATIVESPECIES

).6!3)6%0,!.43!.$3/),0!4(/'%.3 /NEOFTHELEADINGHYPOTHESESFORTHEREMARKABLESUCCESSOFSOMEEXOTICSPECIES ISTHATTHEYHAVEESCAPEDTHESPECIALISTENEMIESTHATCONTROLTHEMINTHEIRNATIVE RANGES+EANEAND#RAWLEY %MBEDDEDWITHINTHISHYPOTHESISISTHEIDEA THAT IF MICROBIAL PATHOGENS LIMIT THE GROWTH OF INVASIVE PLANTS IN THEIR NATIVE RANGE THERE WILL BE NEGATIVE FEEDBACKS BETWEEN THE SOIL MICROBIAL COMMUNITY ANDTHEPLANTINTHENATIVERANGEDUETOTHEACCUMULATIONOFSPECIES SPECIlCSOIL PATHOGENS+LIRONOMOS-ITCHELLAND0OWER#ALLAWAYETAL )N CONTRAST POSITIVE FEEDBACKS MAY OCCUR IN THE INVADED RANGE WHERE EXOTIC


&IG


SPECIES ARE LARGELY FREE FROM SPECIES SPECIlC SOIL PATHOGENS BUT CAN STILL INTERACT WITH LESS HOST SPECIlC MUTUALISTS SUCH AS MYCORRHIZAL FUNGI AND BACTERIA THAT DRIVENUTRIENTCYCLES )N THIS SECTION lRST WE WILL DESCRIBE THE EVIDENCE THAT INVASIVE SPECIES HAVE ESCAPED PRESSURE FROM SOIL PATHOGENS AND THE POTENTIAL FEEDBACK EFFECTS ON THE lTNESSOFINVASIVESPECIES3ECOND WEWILLDISCUSSTHEIMPLICATIONSOFTHISTYPEOF FEEDBACKFORECOSYSTEMSTABILITY $OINVASIVESPECIESBENEFITFROMESCAPINGSOILPATHOGENS

)N A REVIEW OF SPECIES THAT WERE NATURALIZED IN THE 5NITED 3TATES -ITCHELL AND 0OWER FOUND THAT FEWER FUNGI AND FEWER VIRUS SPECIES INFECTEDTHEPLANTSPECIESINTHEIRINVADEDRANGESCOMPAREDTOTHEIRNATIVERANGES &URTHERMORE THEY REPORTED THAT SPECIES THAT EXPERIENCED GREATER RELEASE FROM MICROBIAL PATHOGENS WERE MORE INVASIVE -ITCHELL AND 0OWER (OWEVER THERELATIONSHIPSWERERELATIVELYWEAK PARTICULARLYFORINVADERSOFNATURALAREAS SOIL PATHOGENS WERE NOT DISTINGUISHED FROM OTHER PATHOGENS AND THE PRESENCE OR ABUNDANCE OF PATHOGENS DOES NOT NECESSARILY CORRELATE WITH THE STRENGTH OF THEIREFFECTS -ORE RECENTLY EXPERIMENTS USING SOILS FROM NATIVE AND INVADED RANGES HAVE SUGGESTEDTHATSOMEINVASIVESPECIESHAVEESCAPEDFROMSOILPATHOGENS)FINVASIVE SPECIES SUFFER FROM THE EFFECTS OF SOIL PATHOGENS IN THEIR NATIVE SOILS THEN STERIL IZATIONOFNATIVESOILSSHOULDRESULTINANINCREASEINTHEGROWTHOFTHEINVASIVE )NCONTRAST ININVADEDSOILS THEINVASIVESHOULDBERELATIVELYFREEFROMPATHOGENS BUT MAY BENElT FROM LESS HOST SPECIlC MUTUALISTIC MICROBES )F SO STERILIZATION OFINVADEDSOILSSHOULDRESULTINANEUTRALTONEGATIVEEFFECTONTHEINVASIVESPE CIES 4HESE INTERACTIONS HAVE BEEN EXPLORED FOR 0RUNUS SEROTINA BLACK CHERRY #ENTAUREAMACULOSASPOTTEDKNAPWEED ANDTWO!CERMAPLE SPECIES 2EINHART ET AL COMPARED THE EFFECTS OF SOIL MICROBES ON THE GROWTH OF 0RUNUS SEROTINA IN BOTH ITS NATIVE AND INVADED RANGES )N ITS NATIVE .ORTH !MERICAN RANGE THE SOIL MICROBIAL COMMUNITY OCCURRING NEAR 0 SEROTINA STRONGLY INHIBITED THE ESTABLISHMENT OF NEIGHBORING CONSPECIlCS AND REDUCED SEEDLINGPERFORMANCEINTHEGREENHOUSE)NCONTRAST INITSNON NATIVE%UROPEAN RANGE 0 SEROTINA READILY ESTABLISHES IN CLOSE PROXIMITY TO CONSPECIlCS AND SOIL MICROBIAL COMMUNITIES ENHANCE THE GROWTH OF SEEDLINGS 0REVIOUS RESEARCH IN THE NATIVE RANGE OF 0 SEROTINA DEMONSTRATED THAT SOIL BORNE 0YTHIUM SPECIES /OMYCOTA INHIBIT THE SURVIVAL GROWTH AND ABUNDANCE OF 0 SEROTINA 0ACKER AND#LAY !LTHOUGHTHEGENUS0YTHIUMISFOUNDAROUNDTHEWORLD GENOTYPESAREOFTENHOST SPECIlC$EACONAND$ONALDSON-ILLSAND"EVER 4HUS IN THE NATIVE RANGE 0 SEROTINA EXPERIENCES NEGATIVE PLANT SOIL FEEDBACKINTERACTIONS LIKELYDUETOTHENEGATIVEEFFECTSOF0YTHIUM)NCONTRAST IN THEINVADEDREGION 0SEROTINAEXPERIENCESPOSITIVEFEEDBACKSDUETOESCAPEFROM ITSMAINNATURALENEMY2EINHARTETAL


#ENTAUREA MACULOSA IS ONE OF WESTERN .ORTH !MERICAS WORST INVASIVE WEEDS )N SEVERAL EXPERIMENTS #ALLAWAY ET AL HAVE COMPARED THE EFFECTS OF SOIL MICROBESFROMTHENATIVERANGEIN%UROPETOTHEEFFECTSOFSOILMICROBESCOLLECTED FROMINVASIVEPOPULATIONSINTHENORTHWESTERN5NITED3TATES%UROPEANSOILBIOTA HAD MUCH STRONGER INHIBITORY EFFECTS ON # MACULOSA THAN .ORTH !MERICAN SOIL BIOTA 3TERILIZATION OF %UROPEAN SOILS CAUSED ON AVERAGE A INCREASE IN THETOTALBIOMASSOF#MACULOSA SUGGESTINGARELEASEFROMPATHOGENICMICROBES )N CONTRAST STERILIZING INVADED .ORTH !MERICAN SOILS LED AT MOST TO A SLIGHT INCREASEINTOTALBIOMASSOF&ORMOST.ORTH!MERICANSOILS STERILIZATIONLED TOADECREASEINGROWTHOF SUGGESTINGTHAT#MACULOSAHADBENElTEDFROM MUTUALISTICSOILMICROBES4HESERESULTSSUPPORT-ITCHELLAND0OWERS CON CLUSIONTHATINVASIVESPECIESSHOULDSUFFERMUCHHIGHERFUNGALANDVIRALINFECTION INTHEIRHOMERANGESCOMPAREDTOINVADEDRANGES4HEYALSOSUGGESTTHATINSOME CASES MUTUALISMSMAYBEMOREBENElCIALINNON NATIVERANGESBECAUSETHENEGA TIVEEFFECTOFNATURALENEMIESDONOTATTENUATETHEPOSITIVEEFFECTOFMUTUALISTS -UTUALISTS HAVE ALSO BEEN FOUND TO PLAY AN IMPORTANT ROLE IN THE PLANT SOIL FEEDBACK INTERACTIONS OF TWO !CER SPECIES 2EINHART AND #ALLAWAY )NTHElELD DISTANCESBETWEEN!CERCONSPECIlCSWERE LESSINTHEIRINVADED RANGES THAN IN THEIR NATIVE RANGES )N A GREENHOUSE EXPERIMENT THE EFFECT OF SOIL MICROBIAL COMMUNITIES ALSO DIFFERED BETWEEN NATIVE AND INVADED RANGES 2ELATIVE TO STERILIZED CONTROLS SOIL ASSOCIATED WITH BOTH CONSPECIlCS AND HET EROSPECIlCS FROM THE NATIVE RANGE DECREASED THE TOTAL BIOMASS OF !CER SEEDLINGS BY SUGGESTING INHIBITION BY PATHOGENIC MICROBES )N THE INVADED RANGE SOIL ASSOCIATED WITH CONSPECIlCS DECREASED THE BIOMASS OF !CER SEEDLINGS BY AN EVEN GREATER MAGNITUDE (OWEVER SOIL ASSOCIATED WITH HETEROSPECIlCS IN THE NON NATIVE RANGES INCREASED BIOMASS OF !CER SEEDLINGS BY 4HUS WHILE !CERS ACCUMULATE PATHOGENS IN THEIR INVADED RANGE THE SURROUNDING SOIL IS RELATIVELY FREE FROM INHIBITORY MICROBES POTENTIALLY ENHANCING INVASION BY THESETREES 4HUS THERE IS EVIDENCE THAT NOT ONLY DO INVASIVE SPECIES ESCAPE THE NEGA TIVEEFFECTSOFSOILPATHOGENSINTHEIRINVADEDRANGES BUTTHATPOTENTIALLYDUETO THE EFFECTS OF MUTUALISTS FEEDBACK EFFECTS IN INVADED RANGES ARE OFTEN POSITIVE .EXT WEWILLEXPLORETHEPOTENTIALFORTHESEFEEDBACKEFFECTSTOAFFECTCOMMUNITY STABILITY 7ILLESCAPEFROMNEGATIVEFEEDBACKSFROMSOILPATHOGENSPERSIST

4HEEXPERIMENTSDESCRIBEDABOVEINDICATETHATINVASIVESPECIESARELIKELYTOEXPE RIENCE POSITIVE FEEDBACK IN THEIR INVADED HABITAT BECAUSE THEY ESCAPE SPECIALIST SOILPATHOGENSATHOMEBUTCANUTILIZEGENERALISTMUTUALISTSWHERETHEYINVADE 7HATREMAINSTOBEDETERMINEDISHOWTHISFEEDBACKAFFECTSCOMMUNITYDYNAMICS 0LANTSPARTICIPATINGINSTRONGPOSITIVEFEEDBACKSWITHSOILBIOTAAREMORELIKELYTO BECOMECOMMUNITYDOMINANTSTHANTHOSETHATDONOT4HEMOSTCOMPLETESTUDY OF THESE INTERACTIONS WAS DONE BY +LIRONOMOS WHO EXPLORED FEEDBACK


INTERACTIONSAMONGPLANTSPECIESANDSOILMICROBIALCOMMUNITIESINGRASSLANDSIN EASTERN.ORTH!MERICA)NEXPERIMENTSUSINGONLYTHEMYCORRHIZALFRACTIONOFTHE MICROBIALCOMMUNITY HEFOUNDTHATTHEORIGINOFTHElLTRATEFROMSOILSINWHICH THE SAME SPECIES OR A DIFFERENT SPECIES HAD PREVIOUSLY BEEN GROWN DID NOT ALTER THE RESPONSE EITHER POSITIVE OR NEUTRAL TO MYCORRHIZAL FUNGI )N CONTRAST IN EXPERIMENTS USING ONLY THE PATHOGENICSAPROBIC FRACTIONS THE RARE NATIVE SPECIES EXPERIENCED NEGATIVE FEEDBACKS WHEN THE FRACTIONS WERE FROM SOILS THAT HAD PREVIOUSLY GROWN THE SAME SPECIES (OWEVER THE ORIGIN OF THE PATHOGENIC SAPROBIC FRACTION HAD NO EFFECT ON THE GROWTH OF INVASIVE SPECIES /VERALL RELA TIVELY RARE NATIVE SPECIES CONSISTENTLY EXHIBITED NEGATIVE FEEDBACK INTERACTIONS WITH THE SOIL MICROBIAL COMMUNITY A RELATIVE DECREASE IN GROWTH ON @HOME SOIL IN WHICH CONSPECIlCS HAD PREVIOUSLY BEEN GROWN WHEREAS INVASIVE SPE CIES CONSISTENTLY EXHIBITED POSITIVE FEEDBACK INTERACTIONS WITH THE SOIL COMMU NITY 3IMILARLY !GRAWAL ET AL FOUND THAT INTRODUCED PLANTS WERE SUBJECT TO HALF THE NEGATIVE SOIL FEEDBACK AS CONGENERIC SPECIES (OW LONG IN TERMS OF EVOLUTIONARY TIME SCALES SUCH POSITIVE INTERACTIONS WILL BE MAINTAINED REMAINS ANUNKNOWN 4HE BASIC NATURE OF MICROBES SUGGESTS THAT THEY WILL BE ABLE TO RESPOND RELA TIVELY QUICKLY TO PRESSURES EXERTED BY INVASION BY EXOTIC PLANTS !S DISCUSSED ABOVE SOIL BORNE PATHOGENS CAN BE RELATIVELY HOST SPECIlC .EERGAARD +IRKPATRICKAND"AZZAZ!GARWALAND3INCLAIR-ILLSAND"EVER (OWEVER MANY SOIL BORNE PATHOGENS ARE GENERALISTS $IX AND 7EBSTER &OR EXAMPLE "LANEY AND +OTANEN FOUND THAT SEED GERMINATION OF CONGENERIC PAIRS OF INVASIVE AND NATIVE PLANT SPECIES FROM WESTERN /NTARIO DIS PLAYED A SIMILAR POSITIVE RESPONSE TO THE APPLICATION OF FUNGICIDE SUGGESTING NON SPECIES SPECIlCITY OF FUNGAL SEED PATHOGENS IN THEIR SYSTEM &URTHERMORE MICROBES HAVE A SHORT GENERATION TIME AND THUS CAN RESPOND TO EVOLUTIONARY PRESSURES WITHIN A SHORT TIMEFRAME 4HUS PATHOGENIC MICROBES MAY BE ABLE TO RAPIDLY SWITCH TO A NEW INVASIVE HOST 3CLEROTINIA SCLEROTIORUM A FUNGUS NATIVE TO INTERMOUNTAIN PRAIRIES INVADED BY # MACULOSA HAS BEEN FOUND TO DAMAGE # MACULOSA WHEN APPLIED TO THE RHIZOSPHERES AT HIGH CONCENTRATIONS *ACOBS ET AL 2IDENOUR AND #ALLAWAY !S DESCRIBED ABOVE 2EINHART AND #ALLAWAY FOUNDTHATWHILETHESOILCOMMUNITYASSOCIATEDWITHOTHERTREE SPECIESHADAPOSITIVEEFFECTONTHEGROWTHOFINVASIVE!CERS SOILSASSOCIATEDWITH CONSPECIlCSHADANEGATIVEEFFECT4HISSUGGESTSTHATTHEPATHOGENICSOILMICROBIAL COMMUNITYMAYHAVEBEENABLETOADAPTTOTHISNEWHOST ANDACCUMULATIONOF SOILPATHOGENSEVENTUALLYSUPPRESSESTHEOFFSPRINGOF!CERRECRUITS )NSUMMARY SOMEINVASIVESPECIESAPPEARTOHAVEESCAPEDPRESSUREFROMSOIL PATHOGENSANDTHUSBENElTFROMPOSITIVEFEEDBACKINTERACTIONSWITHTHESOILBIOTA WHERETHEYINVADE!LTHOUGHNOTYETEXPLICITLYADDRESSEDINTHELITERATURE MICRO BIALCOMMUNITIESMAYCHANGEOVERTIMEANDTHUSBREAKDOWNPOSITIVEPLANT SOIL MICROBIALFEEDBACKS)FTHISOCCURS THEABUNDANCEOFTHEINVASIVESPECIESSHOULD DECREASE AND THE COMMUNITY SHOULD MOVE TO A POINT WHERE NEGATIVE FEEDBACK INTERACTIONS RESTRICT THE INVASIVES DOMINANCE 4HIS WAS ORIGINALLY SUGGESTED BY


+LIRONOMOS WHO OBSERVED THAT PLANT SPECIlC PATHOGEN LOADS ARE MAXI MIZEDUNDERHIGHPOPULATIONDENSITIES PARTICULARLYMONOCULTURESSUCHASTHOSE CREATEDBYSOMEINVASIVESPECIES ANDWILLEVENTUALLYRESULTINNEGATIVEFEEDBACK ONABUNDANTPLANTS.EXTWECONSIDERHOWFEEDBACKSDRIVENBYMICROBESINNUTRI ENTCYCLESMIGHTRESPONDDIFFERENTLYOVEREVOLUTIONARYTIMETHANFEEDBACKSDRIVEN BYSOILPATHOGENS

).6!3)6%0,!.43!.$3/),.542)%.4#9#,).' )NGENERAL PLANT SOILFEEDBACKSARETHOUGHTTOBEDETERMINEDBYTHEDIRECTEFFECTS OFPATHOGENSANDMUTUALISTS"EVER-ILLSAND"EVER0ACKERAND#LAY "EVER+LIRONOMOS BUTOTHERCOMPONENTSOFTHESOILECOSYSTEM MAYPARTICIPATEINFEEDBACKS)NPARTICULAR INDIVIDUALPLANTCHARACTERISTICS SUCH ASPHENOLOGY NUTRIENTUPTAKE LITTER FALL TISSUECHEMICALCOMPOSITION ANDASSOCI ATIONWITHSYMBIOTICMICROBES CANHAVESIGNIlCANTEFFECTSONSOILNUTRIENTCYCLES (OBBIE !NGERS AND #ARON "ERENDSE "INKLEY AND 'IARDINA .ORTHRUPETAL3CHLESINGERAND0ILMANIS6AN"REEMEN 7ARDLEETAL#HENAND3TARK%ATONAND&ARRELL WHICHMAY IN TURN ALTERTHEGROWTHANDSURVIVALOFTHESPECIESTHATDRIVETHESEEFFECTS"ECAUSE THEY ARE NOVEL MAY HAVE DIFFERENT BIOCHEMICAL CONSTITUENTS "AIS ET AL 6IVANCOETAL ANDAREOFTENDOMINANTCOMPONENTSOFPLANTCOMMUNITIES INVASIVEPLANTSCANHAVEUNUSUALLYSTRONGEFFECTSONSOILNUTRIENTCYCLES6ITOUSEK 6ITOUSEK ET AL 6ITOUSEK $!NTONIO AND 6ITOUSEK %HRENFELDETAL%HRENFELDAND3COTT%HRENFELD )NTHEPREVIOUSSECTIONWESHOWEDTHATMANYINVASIVESPECIESEXHIBITPOSITIVE FEEDBACKSAFTERESCAPINGSOILPATHOGENS ANDTHENSPECULATEDTHATTHESEFEEDBACKS MAYEVENTUALLYBECOMENEUTRALORNEGATIVEASGENERALISTPATHOGENSSWITCHTOTHE HOSTORSPECIALISTSADAPT)NCONTRASTTOTHISSCENARIOINWHICHINVASIVEDOMINANCE MAYFADE POSITIVEFEEDBACKSBETWEENINVASIVEPLANTSANDSOILNUTRIENTCYCLESMAY LEADTOMUCHLONGERTIMEPERIODSOFINVASIVEDOMINANCE.UTRITIONALCONSTRAINTS MAY LEAD TO SIGNIlCANT SHIFTS IN MICROBIAL COMMUNITIES RESULTING IN LONG TERM CHANGESINNUTRIENTPOOLSANDCYCLINGRATES4HESECHANGESMAYALSOOCCURDUETO THEINTRODUCTIONOFNOVELPLANT MICROBEINTERACTIONS SUCHASSYMBIOTICNITROGEN lXATION 3IMILARLY THE DIRECT EFFECTS OF INVASIVE PLANTS ON SOIL NUTRIENTS MAY BE PARTICULARLYLONG LIVEDBECAUSETHEREISNOMEDIATIONBYANOTHERORGANISMWITH THEPOTENTIALTOEVOLVE )N THIS SECTION WE BRIEmY REVIEW THE MECHANISMS BY WHICH INVASIVE SPE CIES MAY ALTER SOIL NUTRIENT CYCLES AND ILLUSTRATE THE POTENTIAL FOR LONG LIVED POSITIVE FEEDBACK INTERACTIONS BY DESCRIBING THE INTERACTIONS OF "ROMUS TECTORUM CHEATGRASS DOWNYBROME AND-YRICAFAYAlRETREE WITHSOILNUTRIENTCYCLESIN INVADEDCOMMUNITIESINTHEWESTERN5NITED3TATESAND(AWAII


4HEEFFECTSOFINVASIVESPECIESONNUTRIENTCYCLES

4HERE ARE MANY MECHANISMS BY WHICH INVASIVE SPECIES MAY ALTER SOIL NUTRIENT CYCLESSEEREVIEWBY%HRENFELD 4HROUGHCHANGESINLITTERPRODUCTIONAND QUALITY INVASIVEPLANTSMAYINCREASE%HRENFELDETAL-ACKETAL OR DECREASE 3AGGAR ET AL %HRENFELD ET AL %VANS ET AL MICROBI ALLY MEDIATED DECOMPOSITION ANDOR MINERALIZATION RATES &OR EXAMPLE LITTER OF -ICROSTEGIUM VIMINEUM AN EXOTIC # GRASS THAT HAS INVADED %ASTERN DECIDUOUS FORESTS HASAHIGHER#.RATIO DECOMPOSESSLOWER ANDIMMOBILIZESMORE.THAN LITTERFROMUNINVADEDFORESTS%HRENFELDETAL )NVASIVESPECIESMAYALSOALTERTHEINPUTOFNITROGENBYNITROGEN lXINGBACTERIA .EARLY OF THE INVASIVE SPECIES LISTED BY THE 53 $EPARTMENT OF !GRICULTURE AREINTHE&ABACEAEFAMILY%HRENFELD ANDCHANGESINECOSYSTEMNITROGEN AVAILABILITY DUE TO ASSOCIATION OF INVASIVE PLANTS WITH SYMBIOTIC NITROGEN lXING BACTERIAHAVEBEENDOCUMENTEDINSEVERALECOSYSTEMS6ERSFELDANDVAN7ILGREN 6ITOUSEKETAL3TOCKETAL9ELENIKETAL &URTHERMORE CHANGESINLITTERQUALITY FROM N ON NITROGENlXING INVADERSMAY ALTERTHEABUN

DANCE AND ACTIVITY OF NON SYMBIOTIC NITROGEN lXING BACTERIA AS FOUND IN (AWAIIANFORESTSINVADEDBY!FRICANGRASSES,EYAND$!NTONIO )NVASIVE SPECIES MAY AFFECT SOIL NUTRIENT CYCLES THROUGH THE PRODUCTION OF SECONDARY CHEMICALS 2OOTS OF #ENTAUREA MACULOSA EXUDE THE POLYPHENOL ¢ CATECHIN #ATECHIN DISPLAYS STRONG ANTIMICROBIAL PROPERTIES FOR AT LEAST SOME GROUPS OF BACTERIA "AIS ET AL AND APPEARS TO AFFECT AT LEAST SOME ASPECTS OF THE SOIL NITROGEN CYCLE ! 4HORPE UNPUBLISHED DATA &URTHERMORE BYCHELATINGMETAL PHOSPHORUSCOMPLEXES CATECHINMAYINCREASE PHOSPHORUS AVAILABILITY IN PHOSPHORUS LIMITED SOILS 4HORPE ET AL IN PRESS 3TEVENSON AND #OLE !N ALLELOCHEMICAL PRODUCED BY #ENTAUREA DIFFU SA HYDROXYQUINOLINE MAY ALSO ALTER NUTRIENT CYCLING THROUGH ANTIMICRO BIAL 6IVANCO ET AL AND CHELATION 4HE -ERCK )NDEX PROPERTIES 4HE DRY MASS OF LEAVES OF -ELALEUCA SPP PAPERBARK WHICH HAS INVADED LARGE AREASOFTHECOASTALSOUTHEAST5NITED3TATES PARTICULARLYTHE%VERGLADES ISUPTO MONOTERPENES"OONAND*OHNSTONE 4HESECOMPOUNDSINHIBITMICRO BIALCOLONIZATIONANDDECOMPOSITIONOFLEAFLITTERINBOTHTHENATIVEANDINVADED RANGESOF-ELALEUCASPP"OONEAND*OHNSTONE )THASALSOBEENSUGGESTED THATALLELOPATHICCHEMICALSRELEASEDBYSOMEINVASIVESPECIESMAYALTERNITROGEN lXATIONINNEIGHBORINGPLANTS7ARDLE ETAL -ANYOTHERINVASIVE SPECIES PRODUCE CHEMICALS WITH ANTIMICROBIAL ACTIVITY 2ICE %HRENFELD HOWEVER THE ROLE OF THESE CHEMICALS IN THE PLANTS INVASIVE SUCCESS IS GENERALLYUNKNOWN )N SUM THERE IS GOOD EVIDENCE THAT BY INTRODUCING A NOVEL CHARACTERISTIC EG A HIGHER #. RATIO ASSOCIATION WITH NITROGEN lXING BACTERIA OR EXUDATION OF AN ANTI MICROBIAL CHEMICAL INVASIVE SPECIES CAN ALTER SOIL NUTRIENT CYCLES IN INVADED COMMUNITIES !LTHOUGH EXPLICIT STUDIES OF THE RAMIlCATIONS OF SUCH ALTERATION OF NUTRIENT CYCLES ARE RARE THESE EFFECTS MAY ULTIMATELY FEEDBACK TO


THE PLANTS THAT CAUSE THEM AND AFFECT THE ORGANIZATION OF PLANT COMMUNITIES 4WODIFFERENTSPECIES "ROMUSTECTORUMAND -YRICAFAYAPROVIDEEXCELLENTEXAM PLES OF HOW INVASIVE PLANTS MAY AFFECT THE SOIL AND HOW SOIL CHANGES AFFECTTHESURVIVALOFINVASIVEANDNATIVESPECIES4HESESTUDIESALSOILLUSTRATEHOW POSITIVE FEEDBACKS BETWEEN INVASIVE PLANTS AND SOIL NUTRIENT CYCLES MAY PERSIST INANECOSYSTEM 4HEEFFECTSOF"ROMUSTECTORUMONSOILNUTRIENTCYCLES

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7ILLPOSITIVEFEEDBACKSBETWEENINVASIVEPLANTSANDSOILNUTRIENT CYCLESPERSIST

!S DESCRIBED ABOVE SINCE INVASIVE PLANTS OFTEN DIFFER FROM NATIVE SPECIES IN CHARACTERISTICS SUCH AS PHENOLOGY NUTRIENT UPTAKE LITTER FALL TISSUE CHEMICAL COMPOSITION ANDASSOCIATIONWITHSYMBIOTICMICROBES THEYCANHAVESIGNIlCANT EFFECTS ON SOIL NUTRIENT CYCLES 3IMILAR EFFECTS ARE OFTEN SEEN DURING SUCCESSION "ERENDSE 3CHIMEL AND "ENNETT 7E SPECULATE THAT IN CONTRAST TO OURPREDICTIONSFOREVOLUTIONARYCHANGEFORINTERACTIONSBETWEENINVASIVEPLANTS


ANDSOILPATHOGENS POSITIVEFEEDBACKSBETWEENINVASIVEPLANTSANDSOILNUTRIENT CYCLESAREMORELIKELYTORESULTINLONGTERMSHIFTSINCOMMUNITYCOMPOSITIONTHAT RESEMBLE SUCCESSION 4HESE CHANGES MAY PROVIDE EXAMPLES OF INVASIONAL MELT DOWN3IMBERLOFFAND6ON(OLLE 7EKNOWOFNOEXAMPLESWHERE DURINGSUCCESSION CHARACTERISTICSOFTHESOIL ECOSYSTEMREVERTBACKTOTHOSERESEMBLINGTHEINITIALCHARACTERISTICSAFTERDISTUR BANCE 7HAT LITTLE IS KNOWN ABOUT THE BIOTIC COMPONENTS OF THE SOIL ECOSYSTEM DURINGSUCCESSIONINDICATESTHATCHANGEINTHEMICROBIALCOMMUNITYISTOWARDS POPULATIONS THAT ARE BETTER ADAPTED TO THE NEW NUTRIENT CONDITIONS OF THE LATER SUCCESSIONALSTAGES3CHIMELETAL3CHIMELAND"ENNETT 4HESESUC CESSIONAL SHIFTS APPEAR TO BE ECOLOGICAL IN NATURE NOT EVOLUTIONARY AND DRIVEN BYSHIFTSINTHESPECIESCOMPOSITIONOFCOMMUNITIESOVERTIME)NCONTRAST INTHE CASEOFALTERATIONSTOABIOTICCOMPONENTSOFTHESOILECOSYSTEM THEREISNODIRECT SELECTIVE PRESSURE TO STIMULATE ADAPTATION 5LTIMATELY THESE TYPES OF CHANGES REQUIRE THAT THE SOIL AND PLANT COMMUNITIES MAY HAVE TO RESPOND ADAPTIVELY TO NEWNUTRIENTCONDITIONS 7HEN INVADER SOIL ECOSYSTEM FEEDBACKS OCCUR THROUGH EFFECTS ON NUTRIENT CYCLES WESUGGESTTHATLONGTERMEFFECTSWILLBESIMILARTOTHOSETHATOCCURDURING SUCCESSION THE DEVELOPMENT OF A NEW COMMUNITY COMPOSED OF SPECIES THAT ARE BETTERADAPTEDTOTHESPECIlCNUTRIENTCONDITIONSOFTHESOILEG"ERENDSE 4HIS HAS BEEN OBSERVED IN SYSTEMS INVADED BY BOTH NATIVE -ARON AND *EFFERIES AND INVASIVE (UGHES ET AL NITROGEN lXING SPECIES )N #ALIFORNIA -ARON AND #ONNORS FOUND THAT NITROGEN RICH PATCHES THAT WERE LEFT BY DEATHOF,UPINUSARBOREOUSBUSHLUPINE WEREINVADEDBYEXOTICANNUALGRASSES 3IMILARLY ASDESCRIBEDINTHEPRECEDINGSECTION SOILSTHATHAVEBEENENRICHEDBY THEEXOTICNITROGEN lXER-FAYAAREMOREPRONETOINVASIONBYOTHEREXOTICPLANTS INCLUDING 0SIDIUM CATTLEIANUM STRAWBERRY GUAVA (UGHES ET AL )N ADDI TION ALTHOUGH ONLY A FEW NATIVE SPECIES HAVE BEEN FOUND TO hMONOPOLIZEv SITES BY CREATING POSITIVE FEEDBACKS VAN DER 0UTTEN INVASIVE SPECIES MAY BE PARTICULARLYCAPABLEOFTHIS ESPECIALLYIFTHEYINTRODUCEANOVELECOSYSTEMPROCESS TOWHICHNATIVESPECIESARENOTADAPTED&OREXAMPLE ALTHOUGH"TECTORUMlRST BECAMEESTABLISHEDINlRE PRONECOMMUNITIESINTHE'REAT"ASINOVERYEARS AGO-ACK NOOTHERSPECIES EITHERNATIVEORINVASIVE HAVESINCEBEENABLE TOESTABLISHINSUBSTANTIALNUMBERS4HESEEXAMPLESSHOWHOWECOSYSTEMCHANG ESINVOLVINGEXOTICSPECIESCANRESULTINUNPREDICTABLESUCCESSIONALTRAJECTORIES

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4YPICALLY POSITIVE FEEDBACKS ARE THOUGHT TO BE CAUSED BY THE ABSENCE OF SOIL PATHOGENS BUT THE PRESENCE OF SOIL MUTUALISTS IN INVADED SOILS 3UCH PATHOGEN DRIVEN POSITIVE FEEDBACKS MAY RESULT IN LONG TERM INVASIVE DOMINANCE BUT EVOLUTIONARY CHANGES IN NATIVE PATHOGENS MIGHT ULTIMATELY LEAD TO SUPPRESSION OFTHEINVADERANDARETURNTONATIVECOEXISTENCE0OSITIVEFEEDBACKSCANALSOBE CAUSEDBYTHEEFFECTSOFINVASIVEPLANTSONTHESOILBIOTATHATDRIVENUTRIENTCYCLES ORONTHEABIOTICCOMPONENTSOFTHENUTRIENTCYCLESTHEMSELVES7EHYPOTHESIZE THAT POSITIVE FEEDBACKS CAUSED BY THE EFFECTS OF THE INVADER ON THE SOIL BIOTA INVOLVED IN NUTRIENT CYCLES ARE LIKELY TO LEAD TO COMMUNITY SHIFTS RESEMBLING SUCCESSIONANDPERHAPSINVASIONALMELTDOWN$OMINANCEBYINVADERSTHATDRIVE POSITIVE FEEDBACKS THROUGH ABIOTIC COMPONENTS OF NUTRIENT CYCLES MAY PERSIST FOR MUCH LONGER THAN DOMINANCE OCCURRING THROUGH POSITIVE FEEDBACKS INVOLV INGTHEMICROBIALCOMMUNITYDUETOTHELACKOFMEDIATIONBYANORGANISMWITH THE POTENTIAL TO ADAPT (OWEVER UNDERSTANDING POTENTIAL EVOLUTIONARY CHANGES AMONGINVADERSANDSOILECOSYSTEMSWILLHELPUSTOACCURATELYPREDICTTHELONG TERMEFFECTSOFBIOLOGICALINVASIONS

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2ICE + * AND . # %MORY -ANAGING MICROEVOLUTION RESTORATION IN THE FACE OF GLOBALCHANGE&RONTIERSIN%COLOGY 2IDENOUR 7,AND#ALLAWAY2-2OOTHERBIVORES PATHOGENICFUNGIANDCOMPETI TIONBETWEEN#ENTAUREAMACULOSAAND&ESTUCAIDAHOENSIS0LANTAND3OIL 2OBINSON $AND!&ITTER4HEMAGNITUDEANDCONTROLOFCARBONTRANSFERBETWEEN PLANTSLINKEDBYACOMMONMYCORRHIZALNETWORK*OURNALOF%XPERIMENTAL"OTANY 3AGGAR 3 0$-C)NTOSH #"(EDLEYAND(+NICKER#HANGESINSOILMICROBAL BIOMASS METABOLICQUOTIENT ANDORGANICMATTERTURNOVERUNDER(IERACIUM(PILOSELLA , "IOLOGICAL&ERTILITYOF3OILS 3CHIMEL * 0 AND * "ENNETT .ITROGEN MINERALIZATION CHALLENGES OF A CHANGING PARADIGM%COLOGY 3CHIMEL *0 2'#ATESAND22UESS4HEROLEOFBALSAMPOPULARSECONDARYCHEMI CALS IN CONTROLLING SOIL NUTRIENT DYNAMICS THROUGH SUCCESSION IN THE !LASKAN TAIGA "IOGEOCHEMISTRY 3CHLESINGER 7 ( AND ! - 0ILMANIS 0LANT SOIL INTERACTIONS IN DESERTS "IOGEOCHEMISTRY 3IMARD 37 $!0ERRYAND-$*ONES.ETTRANSFEROFCARBONBETWEENECTOMY CORRHIZALTREESPECIESINTHElELD.ATURE 3IMBERLOFF $AND"6ON(OLLE0OSITIVEINTERACTIONSOFNONINDIGENOUSSPECIESINVA SIONALMELTDOWN"IOLOGICALINVASIONS 3TEVENSON &*AND-!#OLE#YCLESOFSOILCARBON NITROGEN PHOSPHORUS SULFUR MICRONUTRIENTS*OHN7ILEYAND3ONS )NC .EW9ORK.9 3TOCK 7$ +47IENANDAND!#"AKER)MPACTSOFINVADING. lXING!CACIA SPECIESONPATTERNSOFNUTRIENTCYCLINGINTWO#APEECOSYSTEMSEVIDENCEFROMSOILINCU BATIONSTUDIESAND .NATURALABUNDANCEVALUES/ECOLOGIA 4HORPE ! 3 6 !RCHER AND 4 ( $ELUCA )N 0RESS 4HE INVASIVE FORB #ENTAUREA MACU LOSA INCREASESPHOSPHORUSAVAILABILITYIN-ONTANAGRASSLANDS*OURNALOF!PPLIED3OIL %COLOGY 5PADHYAYA *+ 24URKINGTONAND$-C)LURIDE4HEBIOLOGYOF#ANADIANWEEDS "ROMUSTECTORUM,#ANADIAN*OURNALOF0LANT3CIENCE 6AN "REEMEN . 3OILS AS BIOTIC CONSTRUCTS FAVOURING NET PRIMARY PRODUCTIVITY 'EODERMA 6AN "REEMEN . AND ! # &INZI 0LANT SOIL INTERACTIONS ECOLOGICAL ASPECTS AND EVOLUTIONARYIMPLICATIONS"IOGEOCHEMISTRY VAN DER (EIJDEN - ' ! * . +LIRONOMOS - 5RSIC 0 -OUTOGLIS 2 3TREITWOLF %NGEL 4"OLLER !7IEMKENAND)23ANDERS-YCORRHIZALFUNGALDIVERSITYDETERMINES PLANTBIODIVERSITY ECOSYSTEMVARIABILITYANDPRODUCTIVITY.ATURE 6AN DER 0UTTEN 7 ( AND " ! - 0ETERS (OW SOIL BORNE PATHOGENS MAY AFFECT PLANTCOMPETITION%COLOGY 6AN DER 0UTTEN 7 ( # 6AN $IJK AND " ! - 0ETERS 0LANT SPECIlC SOIL BORNE DISEASESCONTRIBUTETOSUCCESSIONINFOREDUNEVEGETATION.ATURE 6ANDER0UTTEN 7(0LANT SOILFEEDBACKASASELECTIVEFORCE4RENDSIN%COLOGY AND%VOLUTION


6ERSFELD $ " AND " 3 VAN 7ILGREN )MPACT OF WOODY ALIENS ON ECOSYSTEM PROP ERTIES 0AGES IN ) ! 7 -ACDONALD & * +RUGER AND ! ! &ERRAR EDICTORS 4HE ECOLOGY AND MANAGEMENT OF BIOLOGICAL INVASIONS IN SOUTHERN !FRICA /XFORD 5NIVERSITY0RESS #APE4OWN 3OUTH!FRICA 6ITOUSEK 0 - "IOLOGICAL INVASIONS AND ECOSYSTEM PROPERTIES CAN SPECIES MAKE A DIFFERENCE 0AGES IN ' ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL)NVASIONSOF.ORTH!MERICAAND(AWAII3PRINGER 6ERLAG .EW9ORK .9 6ITOUSEK 0-"IOLOGICALINVASIONSANDECOSYSTEMPROCESSESTOWARDSANINTEGRA TIONOFPOPULATIONBIOLOGYANDECOSYSTEMSTUDIES/IKOS 6ITOUSEK 0-AND,27ALKER"IOLOGICALINVASIONBY-YRICAFAYAIN(AWAIIPLANT DEMOGRAPHY NITROGENlXATION ECOSYSTEMEFFECTS%COLOGICAL-ONOGRAPHS 6ITOUSEK 0 - , 2 7ALKER , $ 7HITEAKER $ -UELLER $OMBOIS AND 0 ! -ATSON "IOLOGICAL INVASION BY -YRICA FAYA ALTERS ECOSYSTEM DEVELOPMENT IN (AWAII 3CIENCE 6IVANCO * - ( 0 "AIS & 2 3TERMITZ ' # 4HELEN AND 2 - #ALLAWAY "IOGEOGRAPHICALVARIATIONINCOMMUNITYRESPONSETOROOTALLELECHEMISTRYNOVELWEAP ONSANDEXOTICINVASION%COLOGY,ETTERS 9ELENIK 3' 7$3TOCKAND$-2ICHARDSON%COSYSTEMLEVELIMPACTSOFINVASIVE !CACIASALIGNAINTHE3OUTH!FRICANFYNBOS2ESTORATION%COLOGY 9PSILANTIS 72ISKOFCHEATGRASSINVASIONAFTERlREINSELECTEDSAGEBRUSHCOMMU NITYTYPES53"UREAUOF,AND-ANAGEMENT 7ARDLE $ ! + 3 .ICHOLSON AND ! 2AHMAN %COLOGICLA EFFECTS OF THE INVASIVE WEED SPECIES 3ENECIO JACOBAEA , RAGWORT IN A .EW :EALAND PASTURE !GRICULTURE %COSYSTEMS AND%NVIRONMENT 7ARDLE $ ! AND + 3 .ICHOLSON 3YNERGISTIC EFFECTS OF GRASSLAND PLANT SPECIES ON SOIL MICROBIAL BIOMASS AND ACTIVITY IMPLICATIONS FOR THE ECOSYSTEM LEVEL EFFECTS OF ENRICHEDPLANTDIVERSITY&UNCTIONAL%COLOGY 7ARDLE $ ! + 3 .ICHOLSON - !HMED AND ! 2AHMAN )NTERFERENCE EFFECTS OF THE INVASIVE PLANT #ARDUUS NUTANS , AGAINST THE NITROGEN lXATION ABILITY OF 4RIFOLIUM REPENS,0LANTAND3OIL 7ARDLE $! -.ILSSON #'ALLETAND/:ACKISSON!NECOSYSTEM LEVELPERSPECTIVE OFALLELOPATHY"IOLOGICAL2EVIEW 7ATKINS .+ !(&ITTER *$'RAVES#ARBONTRANSFERBETWEEN#AND#PLANTS LINKEDBYACOMMONMYCORRHIZALNETWORK QUANTIlEDUSINGSTABLECARBONISOTOPES3OIL "IOLOGYAND"IOCHEMISTRY 7ATKINSON ! 2 4HE ROLE OF THE SOIL COMMUNITY IN PLANT POPULATION DYNAMICS 4RENDSIN%COLOGYAND%VOLUTION 7EST (-)NmUENCEOFARBUSCULARMYCORRHIZALINFECTIONONCOMPETITIONBETWEEN (OLCUSLANATUSAND$ACTYLISGLOMERATA*OURNALOF%COLOGY 7ESTOVER +- !#+ENNEDYAND3%+ELLEY0ATTERNSOFRHIZOSPHEREMICROBIAL COMMUNITYSTRUCTUREASSOCIATEDWITHCO OCCURRINGPLANTSPECIES*OURNALOF%COLOGY

#HAPTERSIXTEEN

)NVASIONBIOLOGYASA COMMUNITYPROCESSMESSAGES FROMMICROBIALMICROCOSMS

0(7ARREN 2,AWAND!*7EATHERBY

).42/$5#4)/. )NVASIONS ARE WIDELY REGARDED AS A SIGNIlCANT CURRENT PROBLEM IN POPULATION ECOSYSTEMANDHABITATMANAGEMENT WITHCONSEQUENCESINCLUDINGGLOBALHOMOG ENIZATIONOFmORASANDFAUNAS EXTIRPATIONOFNATIVESPECIESANDINTERFERENCEWITH ECOSYSTEM FUNCTIONING $RAKE ET AL 7ILLIAMSON -ACK ET AL 0IMENTELETAL 3AKAIETAL 3UCHINVASIONSOCCUR ANDHAVEEFFECTS AT LARGESCALES INREALECOSYSTEMS3OWHYCONSIDERINVESTIGATINGSUCHPHENOMENA INARTIlCIALMICROCOSMSYSTEMSINTHELABORATORY7EBELIEVETHATTHEREARESEV ERALCOMPELLINGREASONSWHYLABORATORYMICROCOSMSYSTEMSHAVEAVALUABLEROLE IN THE STUDY OF BIOLOGICAL INVASIONS THESE CENTRE ON THE ISSUES OF MANIPULATION TIMESCALEANDREPLICATION &IRST APPLIED ECOLOGY SEEKS A PREDICTIVE UNDERSTANDING OF INVASIONS WHAT DETERMINESWHICHSPECIESWILLMAKESUCCESSFULINVADERS!RESOMETYPESOFCOM MUNITIESINVASIONPRONE(OWWILLANINVADERIMPACTONACOMMUNITY4HEREARE VARIOUSTHEORETICALEXPECTATIONS BUTTESTINGTHESEINTHElELDISLARGELYDEPENDENT ONEXTRACTINGSTATISTICALSIGNALSFROMDOCUMENTATIONOFTHE@NATURALEXPERIMENTS THAT REAL INVASIONS PROVIDE /PPORTUNITIES FOR CONTROLLED EXPERIMENTATION ARE -7#ADOTTE ETAL EDS #ONCEPTUALECOLOGYANDINVASIONBIOLOGY n ¥3PRINGER0RINTEDINTHE.ETHERLANDS


LIMITEDAND IT ISNOTORIOUSLYDIFlCULT TODOCUMENT SYSTEMATICALLY INVASION ATTEMPTS THATFAIL3IMBERLOFF THENECESSARY@CONTROLFOREVALUATIONOFTHEDETER MINANTS OF INVASION SUCCESS -ICROCOSMS MESOCOSMS AND RELATED TECHNIQUES SUCHASENCLOSUREEXPERIMENTS PROVIDETHEPOSSIBILITYOFMANIPULATINGPOTENTIAL INmUENCES ON INVASION SUCCESS ALBEIT AT THE EXPENSE OF REALISM IN COMPLEXITY ANDSCALING 3ECOND INVASIONSTAKETIME4HEPOPULATIONDYNAMICSOFANINVADINGSPECIES ITS GEOGRAPHIC SPREAD AND THE ADJUSTMENT OF THE RECEIVING COMMUNITIES ARE ALL TYPICALLY EXPRESSED OVER TENS TO HUNDREDS OF GENERATIONS USUALLY TAKING MANY YEARS (OWEVER DESIRABLE THE EXPLORATION OF SUCH EFFECTS IN INVASIONS CURRENTLY HAPPENINGINTHElELDMAYBEIMPRACTICAL-ICROCOSMSYSTEMSUTILIZINGMICROOR GANISMS ALLOW@LONGTERMEFFECTSANDOUTCOMES INTHERANGEOFTENSTOHUNDREDS OFGENERATIONS TOBEDOCUMENTED$RAKEETAL ,AWLER 4HIRD AS THE WEALTH OF CASE STUDIES IN THE INVASIONS LITERATURE TESTIlES INVA SIONSARERATHERINDIVIDUALISTICEVENTSAPARTICULARINVADER INVADINGAPARTICU LARSYSTEM ORREGION UNDERPARTICULARCIRCUMSTANCES4HISMAKESTHEAPPRAISALOF GENERALPATTERNSANDCAUSESDIFlCULT)NPARTICULAR IFWEAREINTERESTEDINPREDIC TION ORATLEASTPREDICTABILITY THENITBECOMESIMPORTANTTOKNOWTHEPROBABILITY OFAPARTICULAROUTCOMEFORWHATIS AFTERALL APROCESSLIKELYTOBESTRONGLYINmU ENCEDBYSTOCHASTICEVENTS)NEXPERIMENTALSYSTEMS REPLICATIONOFCOMMUNITIES AND INVASION EVENTS MAKES IT POSSIBLE TO ASSESS THE VARIATION IN THE OUTCOME OF INVASIONS ANDTHESOURCEOFTHATVARIATION !BEAKERINTHELABORATORYISFARFROMAlELDEXPERIMENTINANATURALECOSYSTEM 3PATIALANDTEMPORALSCALES THETYPESOFORGANISMSINVOLVEDANDTHESIMPLICITYOF THECOMMUNITIESMEANTHATMICROCOSMSCANNOTSIMPLYBETAKENASANALOGUESOF LARGENATURALECOSYSTEMSTHESAMEISTRUEFOROTHERSORTSOFMICROCOSMANDMESO COSMEXPERIMENTS0ETERSENAND(ASTINGS !MICROBIALMICROCOSMISBETTER THOUGHTOFASASMALLSYSTEMINITSOWNRIGHTANDWITHITSOWNPECULIARITIES RATHER THANASALARGESYSTEMWRITSMALL)NASENSE DECIDINGTHEEXTENTTOWHICHRESULTS FROM MICROCOSMS CAN BE APPLIED TO OTHER TYPES OF SYSTEM IS EQUIVALENT TO DECID INGTHEEXTENTTOWHICHRESULTSFROMANYONETYPEOFCOMMUNITYCANBEAPPLIED TO OTHER DISPARATE SYSTEMS FOR INSTANCE THE EXTENT TO WHICH RESULTS FROM PHYTO PLANKTONCOMMUNITIESCANBEAPPLIEDTOFORESTS-ICROCOSMSOFPROTISTSCERTAINLY TELLUSSOMETHINGABOUTTHEBEHAVIOUROFMICROBIALCOMMUNITIES BUTLEAVEOPEN OPENTHEQUESTIONOFWHETHERSUCHBEHAVIOURGENERALIZESTHELATTERISALSOTRUEFOR EXPERIMENTSONFORESTSANDPHYTOPLANKTON -ICROCOSMS CANNOT OF COURSE REPLACE LARGE SCALE lELD EXPERIMENTS ON SPE CIlCECOYSTEMS/NLYTHROUGHSUCHEXPERIMENTSCANSOMEOFTHECOMPLEXITYAND SPECIlCFEATURESOFTHESYSTEMOFINTERESTBECAPTURED(OWEVER LARGE SCALElELD EXPERIMENTSAREOFTENCONCERNEDWITHTESTINGGENERALPRINCIPLESSUCHASTHEROLES OF SPECIES RICHNESS OR SPECIES TYPE EG 7ARDLE (ECTOR ET AL AND THE EFFECTS OF mUCTUATION OR HETEROGENEITY IN THE ABIOTIC ENVIROMENT EG $AVIS AND 0ELSOR 1UESTIONS ABOUT HOW TO GENERALIZE TO OTHER KINDS OF SYSTEM APPLY AS MUCH IN THESE lELD EXPERIMENTS AS IN MICROCOSMS -ANY IMPORTANT

)NVASIONSINMICROCOSMS

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nDB N 0N . nDB .

OF REACHING SIZE . N BEFORE IT GOES TO EXTINCTION &OR A SPECIES INTRODUCED INTO A WELL MIXED COMMUNITY CLOSE TO STEADY STATE AND AT AN ABUNDANCE MUCH LOWERTHANTHERESIDENTSPECIES BANDDMAYBETAKENASAPPROXIMATELYCONSTANT DURINGTHEEARLYSTAGESOFPOPULATIONGROWTH BECAUSEMOSTINTERACTIONSAREWITH THERESIDENTSPECIES.CANBESETATAVALUEABOVETHELEVELATWHICHDEMOGRAPHIC STOCHASTICITY IS IMPORTANT TO GIVE AN EXPRESSION FOR THE PROBABILITY THAT A NEW SPECIESBECOMESSUCCESSFULLYESTABLISHED 0N nDB NnnRB N

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&IG 0ROBABILITY0N THATANINTRODUCED ASEXUALSPECIESREACHESASIZEABOVEALEVEL AT WHICH DEMOGRAPHIC STOCHASTICITY IS IMPORTANT STARTING WITH N PROPAGULES AND HAVING CONSTANTPERCAPITABIRTHBANDDEATHDRATESWITHRBnD4HESURFACEISCONSTRUCTEDFROM %QUATION

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0ROPAGULEPRESSUREANDTHEPROBABILITYOFESTABLISHMENT

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-ACK +OLAAND,ODGE 4HERESULTSON"LEPHARISMAABOVEARE ALSO NOT ENCOURAGING IN THIS REGARD BECAUSE SUCCESS WAS CLEARLY CONTINGENT ON PROPERTIES OF THE RESIDENT COMMUNITY .ONETHELESS OUR STUDIES DID SHOW SOME LARGE D IFFERENCES AMONG INTRODUCED SPECIES IN THE INITIAL RATESOFINCREASE,AW )TWASSTRIKINGTHAT THEBACTERIOVORE0ARAMECIUMWASCONSTITUTIVELYA ET AL STRONGINVADER WHATEVERRESIDENTCOMMUNITYITENCOUNTERED4HEREAREEVIDENTLY FEATURESOF0ARAMECIUMTHATPREDISPOSEITTOGROWESPECIALLYWELLINMICROCOSMS EVENWHENITSEEMSLIKELYTOBEINCOMPETITIONFORRESOURCESWITHOTHERSPECIES 2ESIDENTCOMMUNITYANDTHEPROBABILITYOFESTABLISHMENT

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WAS NOT STRONGLY INmUENCED BY COMMUNITY DIVERSITY THOUGH A LATER REANALYSIS ,EVINEAND$!NTONIO FOUNDEVIDENCEFORANEGATIVEEFFECTOFDIVERSITYON SUCCESS(OWEVER EXPERIMENTSOFTHISKINDHAVETHEPROPERTYTHATRICHERCOMMU NITIESCONTAINMOREDIFFERENTSPECIES(USTON ANDARETHEREFOREMORELIKELY TOCONTAINPARTICULARSPECIESTHATDISCOURAGEOR POTENTIALLY PROMOTE INVASION BY PARTICULAR NEW SPECIES MAKING IT DIFlCULT TO ATTRIBUTE INVASION OUTCOMES TO EFFECTS OF DIVERSITY PER SE 7ARDLE (ODGSON ET AL LOOKING AT THE ABILITY OF PARTICULAR STRAINS OF THE BACTERIUM 0SEUDOMONAS mUORESCENS TO INCREASE WHEN RARE IN THE PRESENCE OF OTHER STRAINS FOUND AN EFFECT OF DIVERSITY ON THIS MEASUREOFINVASIBILITY BUTTHATITWASMUCHWEAKENEDBYSTATISTICALREMOVALOF THISSAMPLINGEFFECT .UMERICAL STUDIES OF COMMUNITY MODELS SUGGEST THAT COMMUNITIES BECOME INCREASINGLY RESISTANT TO INVASION AS TIME GOES ON AS A RESULT OF THE TURNOVER OF SPECIES0OSTAND0IMM $RAKEB ,AWAND-ORTON )NCREASING INVASIONRESISTANCECANAPPLY EVENIFTHERESIDENTCOMMUNITYISNOTACCUMULAT INGSPECIES ANDSUGGESTSTHATITSHOULDBERELATIVELYHARDFORNEWSPECIESTOINVADE COMMUNITIESWITHLONGHISTORIESOFASSEMBLY!LSOONEMIGHTEXPECTCOMMUNITIES CONSTRUCTED FROM LARGE SPECIES POOLS TO BE LESS READILY INVADED BECAUSE WITH MORECOMBINATIONSOFSPECIESTESTEDDURINGASSEMBLY AlNERDEGREEOFTUNINGTO INVASION RESISTANTSTATESBECOMES POSSIBLE 4ODATEWEKNOWOFONLYONE MICROCOSM STUDYOFTHEEFFECTOFCOMMUNITYAGEONINVASIBILITY,ONGETALUNPUBLISHEDMS IN THIS CASE OLDER COMMUNITIES WERE MORE RESISTANT TO TWO OUT OF THREE SPECIES INTRODUCED THAN THE YOUNGER COMMUNITIES (OWEVER THE OLDER COMMUNITIES WERECREATEDBYALLOWINGALONGERPERIODOFTIMETOELAPSEFROMAlXEDINITIALSET OFSPECIES SOINVASIONRESISTANCEHEREMAYBEBETTERINTERPRETEDASACONSEQUENCE OFBEINGFURTHERALONGATRANSIENTOFCOMMUNITYDYNAMICSRATHERTHANASACON SEQUENCEOFTURNOVEROFSPECIES %NVIRONMENTALFACTORSANDTHEPROBABILITYOFESTABLISHMENT

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#(!.'%34/#/--5.)4)%3&/,,/7).'%34!",)3(-%.4/&).6!$%23 &OLLOWING SUCCESSFUL ESTABLISHMENT AN INVADING SPECIES TYPICALLY BUILDS UP TO A SUBSTANTIAL POPULATION SIZE TAKING THE COMMUNITY BEYOND THE POINT AT WHICH %QUATIONCANPOSSIBLYBEAGOODAPPROXIMATION)NEFFECT THEINVADINGSPECIES BECOMES ABUNDANT ENOUGH TO CHANGE THE BIRTH AND DEATH RATES OF OTHER SPECIES IN THE COMMUNITY POTENTIALLY CAUSING CHANGE IN THEIR DENSITIES 4HE CHANGING DENSITY OF OTHER SPECIES FEEDS BACK TO THE INVADER POTENTIALLY CAUSING CHANGES INITSOWNBIRTHANDDEATHRATES!TTHISSTAGE THEREISNOALTERNATIVETODEALING WITHTHEFULLDYNAMICSOFTHECOMMUNITYAUGMENTEDBYTHEINVADER ANDALLTHE COMPLEXITIESTHATFOLLOWFROMTHIS $ESPITETHEGREATCOMPLEXITIESOFCOMMUNITYDYNAMICS THEREARESOMEQUALITA TIVEQUESTIONSABOUTTHEINVADERANDTHECOMMUNITYITENTERSTHATCANBEADDRESSED AND AGAIN WE DRAW ON EXAMPLES FROM OUR EXPERIMENTS WITH PROTISTS TO DO THIS $OINVADERSPERSISTINTHELONGTERM

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&IG -ISMATCHINESTABLISHMENTANDLONG TERMPERSISTENCEOFPROTISTSINTRODUCEDINTO MICROCOSMS FROM 7EATHERBY "ARS SHOW THE PERCENTAGE OF MICROCOSMS IN WHICH THE INTRODUCED SPECIES BECAME ESTABLISHED OPEN BARS AND PERSISTED IN THE LONG TERM WEEKS SHADEDBARS $ATAAREGIVENFORALLINDIVIDUALMICROCOSMSACROSSALLRESIDENT COMMUNITIESINTOWHICHTHESPECIESWASINTRODUCED SOVALUESTAKEINTOACCOUNTTHEMIXED OUTCOMES SHOWN IN &IG N IS THE NUMBER OF MICROCOSMS INTO WHICH EACH SPECIES WAS INTRODUCEDUSUALLYREPLICATESOFEACHRESIDENTCOMMUNITY BUTINSOMECASESONLY OR


(OWEVER WECANALSOLOOKATTHEBROADERPICTURE ANDFOCUSONTHERESIDENT INTRO DUCTION COMBINATIONS IN WHICH THE MAJORITY OF REPLICATES HAD THE SAME OUT COMEBOTHINTERMSOFESTABLISHMENTANDCOMPOSITIONOFTHElNALCOMMUNITY 4AKINGJUSTTHESEMORECONSISTENTOUTCOMESATOTALOFTHIRTYlVERESIDENT INTRO DUCTION COMBINATIONS IN THE MAJORITY OF CASES THE INTRODUCED SPECIES EITHER ESTABLISHED AND PERSISTED OR FAILED BOTH TO ESTABLISH AND TO PERSIST 4HERE WERE RELATIVELY FEW CASES IN WHICH SPECIES ESTABLISHED AND THEN FAILED TO PERSIST AND NONE IN WHICH SPECIES FAILED TO ESTABLISH BUT YET PERSISTED 4HISLASTCATEGORYMAYSEEMATRUISM BUTITISNOTSO BECAUSEITWOULDBEPOSSIBLE FORANINVADERTOPERSISTWITHOUTSHOWINGNETPOPULATIONGROWTH THEREFOREFAILING TOMEETTHECRITERIONFORESTABLISHMENT 4HUSTHEMESSAGEFROMTHESEMICROCOSM STUDIESISTHATINITIALESTABLISHMENTOFANINTRODUCEDSPECIESWITHINACOMMUNITY WHICH COULD FEASIBLY BE MEASURED EVEN IN THE lELD IS A FAIR BUT NOT PERFECT PREDICTOROFITSFATEINTHELONGTERM $OTHEINVADERSHAVEANIMPACTONTHERESIDENTS

7EHAVESOFARFOCUSEDONTHEFATEOFTHEINVADER BUTITISOFTENNOTTHEINVADER ASSUCHWHICHISOFPRIMARYCONCERN BUTRATHERTHEIMPACTOFTHEINVADERONTHE COMMUNITIESITINVADES0ARKERETAL 'ENERALIZATIONSABOUTTHESEIMPACTS AREBOUNDTOBEHARDTOMAKE BECAUSEOFTHECOMPLEXNONLINEARCOUPLINGSTHAT CHARACTERIZECOMMUNITYDYNAMICS)TISENTIRELYPOSSIBLEFORTHEIMPACTTOBENEGLI GIBLE ORFOROTHERSPECIESTOBEDRIVENTOEXTINCTION!NINVADERMAYTARGETPARTIC ULARSPECIESEG $UTCH%LMDISEASEINTHE5+7ILLIAMSON ORHAVEEFFECTS THAT RAMIFY WIDELY THROUGH THE COMMUNITY EG WHOLE ECOSYSTEM EFFECTS OF -YRICAFAYAONVOLCANICSITESIN(AWAII6ITOUSEKAND7ALKER THEDEMISE OF KELP BEDS FOLLOWING KILLER WHALE ARRIVAL ON THE 0ACIFIC COAST OF . !MERICA %STESETAL -ICROCOSMCOMMUNITIESAREESPECIALLYAMENABLETOSYSTEM ATICINVESTIGATIONOFIMPACTSOFINVADERSBECAUSEWECANTAKETHEMAPARTINAN ORDERLYREPLICATEDWAY TOSEEWHATEFFECTEACHINVADINGSPECIESEVENTUALLYHASON THESPECIESCOMPOSITIONOFEACHCOMMUNITY ANDHOWTHISRELATESTOTHEINVADERS OWN ABILITY TO PERSIST 6ARIOUS SCENARIOS ARE POSSIBLE THE INVADER PERSISTS ANDTHERESIDENTCOMMUNITYISCHANGED THEINVADERPERSISTSANDTHERESIDENT COMMUNITYISUNCHANGED THEINVADERFAILSTOPERSIST BUTTHERESIDENTCOMMU NITYISCHANGED THEINVADERFAILSANDTHERESIDENTCOMMUNITYISUNCHANGED 3ITUATION ISTHECLASSIC@PROBLEMINVASION ANINVADERTHATBECOMESAPART OFTHECOMMUNITYANDCHANGESIT USUALLYBYGENERATINGONEORMOREEXTINCTIONS IN THE RESIDENTS THE INVASION OF THE COMMUNITY COMPRISING "LEPHARISMA AND #OLPIDIUM BY 0ARAMECIUM &IG A PROVIDES AN EXAMPLE OF THIS FROM OUR MICRO COSM EXPERIMENTS 4HESE ARE ALSO THE BEST DOCUMENTED INVASION CASE STUDIES IN NATURALSYSTEMSEG %LTON $RAKEETAL BECAUSEINVADERSTHAT PERSIST AREMOSTREADILYDOCUMENTEDANDSTUDIED ANDTHEIRIMPACTSAREOFCONCERN )N WEHAVESIMPLEAUGMENTATIONOFTHECOMMUNITYBYANINVADER/FCOURSE THECOLONIZINGSPECIESMAYALTERDENSITIESOFOTHERSPECIES BUTNOTTOASUFlCIENT


EXTENTTOCAUSESPECIESLOSSES)NVASIONOF"LEPHARISMASYSTEMSBY0ARAMECIUMPRO VIDESANEXAMPLEALTHOUGHTHERESIDENTPERSISTED&IGB ITWASABOUTONElFTH ASABUNDANTINTHEINVADEDSYSTEMSASINTHEUNINVADEDCONTROLSATTHEENDOFTHE EXPERIMENT4HEREAREEXAMPLESFROMNATURALSYSTEMSOFINVADERSWHICHAPPEARTO ADDTHEMSELVESTOSYSTEMSBUTCAUSELITTLEIMPACTEG THEFULMAR&ULMARISGLACIA LIS ANARCTICSEABIRD7ILLIAMSONETSEQ 4HEFREQUENCYOFNON IMPACTIVE INVASIONSHOWEVERREMAINSACONTROVERSIALISSUE0ARKERETAL FOREXAMPLE SEE3IMBERLOFF (ERBOLDAND-OYLE 0IMM BECAUSEITCANBEDIF lCULTTOESTABLISHIMPACTSANDTESTFORCAUSALITYIFTHEREARENOSUITABLEUNINVADED SYSTEMSFORCOMPARISON 3CENARIO REQUIRESTHATASPECIESFAILSTOPERSIST BUTHASSUFlCIENTLYSTRONG EFFECTS ON THE RESIDENT COMMUNITY WHILE IT IS PRESENT TO CAUSE CHANGES IN SPE CIES COMPOSITION 3UCH SPECIES CAN BE TERMED @CATALYSTS )N OUR EXPERIMENTS CATALYSTS WERE NOT COMMON BUT TWO SPECIES DID PLAY THIS ROLE IN SOME SITUA TIONSPRINCIPALLY%UPLOTESANDALSO!MOEBAINOCCASIONALREPLICATES&OREXAMPLE %UPLOTESESTABLISHEDITSELFINACOMMUNITYCOMPRISING0ARAMECIUM #OLPIDIUMAND 4ETRAHYMENA CAUSEDTHELATTERTWOSPECIESTOGOEXTINCTINMOSTSYSTEMS ANDTHEN WENTTOEXTINCTIONITSELF&IGC )NTHISEXAMPLE%UPLOTESDIDESTABLISHINCREASE IN POPULATION SIZE AFTER INTRODUCTION BUT THERE WERE ALSO CASES EG %UPLOTES INVADINGTHECOMMUNITYOF 0ARAMECIUMAND 4ETRAHYMENA INWHICH THEINVADER DIDNOTCONSISTENTLYINCREASEABOVEITSINITIALNUMBERS BUTNONETHELESSCAUSEDAN EXTINCTIONOFONEOFTHERESIDENTS4ETRAHYMENA BEFOREITSELFGOINGEXTINCT4HERE ISSOMETHEORETICALEVIDENCEOFSUCHEFFECTSINMODELSOFINVASIONSINTOCOMPETI TIVE SYSTEMS #ASE 3OME EXAMPLES OF SITUATIONS IN NATURAL SYSTEMS SEEM TOSHOWTHISBEHAVIOUREG &LUX BUTTHEAPPARENTRARITYOFSUCHOBSERVA TIONS7ILLIAMSON ISCONSISTENTWITHTHERELATIVERARITYOFTHESEEFFECTSINOUR EXPERIMENTALSYSTEMS &INALLYWEHAVESCENARIO )NTHISCASE THEFAILUREOFTHEINTRODUCEDSPECIES TOPERSIST COUPLEDWITHTHELACKOFCHANGEINTHERESIDENTCOMMUNITYEG &IG D SUGGESTSTHAT EFFECTIVELY THEREISNOTHINGWEWOULDRECOGNIZEASANINVASION ATALL)NTHEMAJORITYOFINTRODUCTIONSWITHTHISOUTCOMETHISWASVERYMUCHTHE CASE WITHTHEINTRODUCEDSPECIESSIMPLYDECLININGTOEXTINCTIONAFTERINTRODUCTION (OWEVERTHEREWEREALSOAFEWCASESINWHICHINTRODUCEDSPECIESSHOWEDSUCCESS FULINITIALESTABLISHMENT WHILENONETHELESSEVENTUALLYGOINGEXTINCTANDLEAVING THE RESIDENT SET UNCHANGED FOR EXAMPLE IN MOST INTRODUCTIONS OF %UPLOTES INTO POPULATIONS OF 4ETRAHYMENA %UPLOTES ACHIEVED POPULATIONS OF SEVERAL THOUSANDS OFINDIVIDUALSBEFOREDISAPPEARING%VIDENTLYANINTRODUCEDSPECIESCANACHIEVEA SIGNIlCANTPRESENCEDURINGSOMEPARTOFANULTIMATELYUNSUCCESSFULINVASION "ECAUSE OUR MICROCOSM EXPERIMENTS CONTAINED ALL POSSIBLE PERMUTATIONS OF RESIDENT COMMUNITY AND INTRODUCED SPECIES WE CAN USE THESE RESULTS TO LOOK AT THE FREQUENCIES OF THESE VARIOUS OUTCOMES AND THE CIRCUMSTANCES UNDER WHICH THEYOCCUR4AKINGJUSTTHETHIRTY SIXRESIDENT INTRODUCTIONTREATMENTSINWHICH THEMAJORITYOFREPLICATESENDEDUPWITHTHESAMESPECIESCOMPOSITIONINTHELONG TERM THERESIDENTCOMMUNITYWASALTEREDINJUSTNINEOFTHESE7ARRENETAL


&IG %XAMPLES OF INITIAL GROWTH OF INTRODUCED PROTISTS AND THE COMMUNITIES THAT PERSISTED IN THE LONG TERM FOR COMBINATIONS OF PERSISTENCE AND NON PERSISTENCE OF THE INVADER AND IMPACT OR LACK OF IMPACT ON THE RESIDENTS 3TRUCTURE AND NOTATION AS FOR&IG

!SONEMIGHTEXPECTEG #ASE CHANGESTOTHE RESIDENT C OMMUNITYBECAME MORELIKELYASTHENUMBEROFRESIDENTSPECIESINCREASED RISINGFROMABOUTIN ONE SPECIESCOMMUNITIESTOINTWO SPECIESCOMMUNITIES TOINTHREE SPECIES COMMUNITIES THOUGH THERE ARE ONLY TWO THREE SPECIES COMBINATIONS 4HE EFFECT OF THE INTRODUCED SPECIES WAS MOST OFTEN NEGATIVE CAUSING EXTINCTION OFRESIDENTSPECIESSIXCASES ALTHOUGHTHEREWERETHREEINSTANCESOFTHEREVERSE EFFECT IE A RESIDENT SPECIES #OLPIDUM IN TWO SYSTEMS AND 0ARAMECIUM INONE FOR WHICH PERSISTENCE SEEMED TO BE ENHANCED BY THE PRESENCE OF THE INVADERS !MOEBA 0ARAMECIUMAND%UPLOTES 0UTTING THESE RESULTS TOGETHER WE CAN BREAK DOWN THE THIRTY SIX RESIDENT INTRODUCTIONTREATMENTSINTOTHOSEINWHICHTHEINTRODUCEDSPECIESPERSISTEDAND THE RESIDENT COMMUNITY WAS CHANGED THE INTRODUCED SPECIES PERSISTED BUT THERESIDENTCOMMUNITYWASNOTCHANGED THEINTRODUCEDSPECIESDIDNOTPER SIST BUTTHERESIDENTCOMMUNITYWASCHANGED ANDTHEINTRODUCEDSPECIESDID NOTPERSISTANDTHERESIDENTSWEREUNCHANGED #LEARLYTHEREISNOSIGNIlCANT ASSOCIATION BETWEEN THE LIKELIHOOD OF ESTABLISHMENT OF INTRODUCED SPECIES AND


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#HAPTERSEVENTEEN

5NDERSTANDINGINVASIONS INPATCHYHABITATSTHROUGH METAPOPULATIONTHEORY +#(ARDING *--C.AMARAAND2$(OLT

).42/$5#4)/. -ANYINVASIVESPECIESEXPERIENCEAWORLDTHATISHETEROGENEOUSANDPATCHY AND EXPERIENCEITATMULTIPLESCALES)NTHISCHAPTERWEWILLSHOWHOWMETAPOPULATION THEORY CAN BE USED TO EXPLORE GENERAL MECHANISMS WHICH DETERMINE THE INITIAL SPREAD AND LONG TERM ESTABLISHMENT OF INVASIVE SPECIES IN NOVEL ENVIRONMENTS -ETAPOPULATION ECOLOGY IS A BRANCH OF ECOLOGY THAT IS FOCUSED ON HOW SPECIES PERSISTINFRAGMENTEDOR@SUBDIVIDEDHABITATS(ANSKI (ANSKIAND'AGGIOTTI !LTHOUGH REAL LANDSCAPES ARE OFTEN HIGHLY COMPLEX WITH ADMIXTURES OF SMOOTH GRADIENTS FRACTAL EDGES AND JUXTAPOSED HABITATS VARYING IN QUALITY FOR MANYSPECIESITISNATURALTOCONSTRUETHEIRWORLDASCONSISTINGOFSETSOFSUITABLE HABITAT PATCHES ARRAYED WITHIN A LARGELY INHOSPITABLE MATRIX SEPARATING THOSE PATCHES3OMESUCHSPECIESINHABITNATURALLYPATCHYHABITATS SUCHASISLANDSOR PONDS &IG 3OME METAPOPULATIONS APPEAR IN ARTIlCIALLY CONSTRUCTED HABITAT NETWORKS SUCHASTHEREMAININGFRAGMENTSOFARAINFORESTSURROUNDEDBYCATTLE PASTURES ORCONCRETEREEFSINMARINESYSTEMS0ATCHNETWORKSCANALSOBEFORMED IN MORE SUBTLE WAYS BUT STILL MAKE FUNCTIONAL METAPOPULATIONS 4HE PATCHY DISTRIBUTION OF A HOST SPECIES FOR A SPECIALIST HERBIVORE PARASITE PARASITOID OR -7#ADOTTE ETAL EDS #ONCEPTUALECOLOGYANDINVASIONBIOLOGY n ¥3PRINGER0RINTEDINTHE.ETHERLANDS

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&IG 0ATCHYWORLD PONDSINTHE.ORTHERN0RAIRIEFARMLAND0HOTO3TEWART 2%ETAL &ROM.ORTHERN0RAIRIE7ILDLIFE2ESEARCH#ENTER

COMMENSAL OR INDEED ANY VITAL AND SPATIALLY DELIMITED RESOURCE CAN LEAD TO METAPOPULATION DYNAMICS FOR THE SPECIALIST "IOLOGICAL NONLINEARITIES CAN TRANS FORM SMOOTH ENVIRONMENTAL GRADIENTS INTO PATCHY DISTRIBUTIONS &OR INSTANCE STRONG !LLEE EFFECTS POSITIVE DENSITY DEPENDENCE AT LOW NUMBERS CAN AMPLIFY PATCHINESSINTHEENVIRONMENT7HENDISPERSALISLIMITED PERMANENTRANGELIMITS CANARISEINPATCHYENVIRONMENTSEVENWITHOUTOVERALLENVIRONMENTALGRADIENTS IN THE LANDSCAPE +EITT ET AL %VEN WITHOUT !LLEE EFFECTS IF THE DENSITY OF SUITABLEPATCHESDECLINESALONGANENVIRONMENTALGRADIENT ASPECIESRANGELIMIT MAYEMERGE WHENTHERE IS NODECLINEINTHE QUALITY OFSUITABLEHABITATPATCHES (OLTAND+EITT ! METAPOPULATION IS DElNED AS A SET OF POPULATIONS CONNECTED BY DISPERSAL $ISPERSAL BECOMES PARTICULARLY VITAL TO UNDERSTANDING REGIONAL POPULATION PER SISTENCEWHENLOCALPOPULATIONSCANBECOMEEXTINCT ANDMUSTBERE ESTABLISHED VIACOLONIZATION#LASSICALMETAPOPULATIONTHEORYTHUSFOCUSESONSYSTEMSWHERE THERE IS A POTENTIAL FOR RECURRENT EXTINCTION )N ALL METAPOPULATIONS LONG TERM SPECIES PERSISTENCE RELIES ON THE BALANCE BETWEEN THE RATE OF EXTINCTION OF LOCAL POPULATIONSANDTHERATEOFNEWCOLONIZATIONSOFEMPTYHABITATPATCHES&IG -ETAPOPULATION THEORY IS WELL SUITED FOR DESCRIBING INVASIONS AND THE ESTAB LISHMENT OF NEW SPECIES INTO PATCHY HABITATS 4HERE ARE THREE BASIC QUESTIONS

)NVASIVESPECIESINMETAPOPULATIONSYSTEMS

&IG "LUESQUARESINDICATEPONDSOCCUPIEDBY0ISIDIUMNITIDUMINTHEYEAROFSAMPLING 7HITESQUAREAREPONDSWHERE0NITIDUMHASGONEEXTINCT3TEWARTAND+ANTRUD &ROM.ORTHERN0RAIRIE7ILDLIFE2ESEARCH#ENTER

ONECANASKABOUTANINVASION&IRST CANANINVASIONOCCURATALL3ECOND GIVEN THAT AN INVASION OCCURS HOW RAPIDLY DOES IT OCCUR &INALLY FOLLOWING INVA SION WHAT IMPACTS DOES THE INVADER HAVE UPON THE PRIOR RESIDENT COMMUNITY -ETAPOPULATIONTHEORYCANBEUSEDTOADDRESSEACHOFTHESEBASICISSUES 7EINTRODUCEASIMPLEMODELSTRUCTURETHATCANBEUSEDTOSUMMARISEANDCLAS SIFYSOMEDIFFERENTTYPESOFMETAPOPULATIONINVASIONSCENARIOS7EEXAMINESOME SPECIALCASES STARTINGWITHACASEINWHICHTHEINVASIVESPECIESDOESNOTCOMPETE WITHANYOTHERECOLOGICALLYSIMILARSPECIES4HEDYNAMICSOFTHEINVASIONINTHIS CASEISTHENGOVERNEDBYTHEBIOLOGYOFTHEINVADERONLY ANDCLASSICSINGLESPECIES METAPOPULATIONTHEORYAPPLIES7ETHENCONSIDERAGENERALMETAPOPULATIONMODEL INWHICHTHEINVADINGSPECIESINTERACTSWITHANATIVESPECIES7EDElNECRITERIAFOR WHENINITIALINVASIONOCCURSANDFORWHENLONG TERMCOEXISTENCEISPOSSIBLE7E ALSOLOOKATSOMEINTERACTIONSTHATARESPECIlCCASESOFTHISGENERALMODELA THE INVADERCOMPLETELYEXCLUDESTHENATIVESPECIES B THEINVADERISDEPENDENTONTHE PRESENCEOFANATIVESPECIES AND C THEREISANINTERMEDIATELEVELOFCOMPETITION 7EALSOTOUCHONHOWSPATIALHETEROGENEITYCANINmUENCEINVASION/UROVERVIEW HIGHLIGHTSSOMEGENERALINSIGHTSABOUTTHEPOPULATIONBIOLOGYOFINVASIONWHICH EMERGEFROMMETAPOPULATIONTHEORY


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&IG 4HE CLASSIC ,EVINS METAPOPULATION MODEL FOR A SINGLE SPECIES ! GIVEN PATCHCANBEINONEOFTWOSTATES EMPTYOROCCUPIEDBYSPECIES 4HERATEOFCHANGEIS GIVENBYTHECOLONIZATIONANDEXTINCTIONRATESANDTHEPROPORTIONXOFOCCUPIEDPATCHES CCORRESPONDSTO+_INEQNSAND

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5THENUMBEROFUNSUITABLEPATCHES HFRACTIONOFTHELANDSCAPETHATISHABITABLEFORTHESTUDYSPECIES 'ENERALIZEDMODEL

%_ SINGLEPATCHEXTINCTIONRATEASAFUNCTIONOFIMMIGRATION #_ SINGLEPATCHCOLONIZATIONRATEASAFUNCTIONOFIMMIGRATION 2ESCUEEFFECTIMMIGRATIONINTOAPATCHLOWERSPATCHEXTINCTIONRISK !NTI RESCUE EFFECT IMMIGRATION INTO A PATCH INCREASES PATCH EXTINCTION RISK !LLEEEFFECTCOLONIZATIONSUCCESSISANON LINEARFUNCTIONOFIMMIGRATION ACCELERATINGWITHINCREASINGIMMIGRATIONRATE !NTI !LLEE EFFECT NON LINEAR COLONIZATION SUCCESS DECELERATING WITH INCREASINGIMMIGRATIONRATE -ODELWITHTWODISTINCTHABITATS

HITHEFRACTIONOFALANDSCAPETHATISCOVEREDBYTYPEIHABITATPATCHES PITHEFRACTIONOFTHELANDSCAPETHATISBOTHOFHABITATTYPEIANDOCCUPIED EIEXTINCTIONRATEOFTYPEIPATCHES CIJCOLONIZATIONONTOEMPTYPATCHESOFTYPEI DUETOMIGRANTSGENERATED BYOCCUPIEDPATCHESOFTYPEJ hIRATEOFINCREASEINPATCHOCCUPANCYOFSPECIESWHENITISRARE ANDONLY PATCHTYPEIISPRESENT


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4WOSPECIESMETAPOPULATIONMODEL

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"IOLOGICALCONCLUSIONSFROM,EVINSMODEL

&AILEDINVASIONSCANARISEEITHERFROMPROCESSESTHATAFFECTEXTINCTION ORFROMTHE DETAILS OF THE PROCESS OF COLONIZATION 4HERE ARE MANY REASONS EXTINCTION RATES MAY BE HIGH IN A NOVEL ENVIRONMENT )F WITHIN EACH PATCH THE INTRINSIC GROWTH RATER OFTHEINVADERISNEGATIVEIE R SOBIRTHSDEATHS THENEXTINCTION IS INEVITABLE UNLESS THERE IS VERY RAPID EVOLUTION SEE 'OMULKIEWICZ AND (OLT 4HIS COULD ARISE BECAUSE OF UNFAVORABLE ABIOTIC CONDITIONS OR BECAUSE SUPERIORCOMPETITORSOREFFECTIVEPREDATORSAREPRESENT"UTEVENIFR IFAPATCH HASAVERYLOWLOCALCARRYINGCAPACITY ITMAYSUFFERHIGHRATESOFEXTINCTIONDUE TODEMOGRAPHICSTOCHASTICITYIFITHASALOWR ITMAYALSONOTBEABLETORECOVER RAPIDLY FROM CATASTROPHES AND SO RANDOMLY WALK TO EXTINCTION %NVIRONMENTS WITHFREQUENTCATASTROPHESARELIKELYTOGENERATEHIGHEXTINCTIONRATESFORINVASIVE SPECIES SOALLELSEBEINGEQUAL ARENOTASLIKELYTOBEINVADED "UTEQUALWEIGHTSHOULDBEGIVENTOCONSTRAINTSONTHECOLONIZATIONPROCESSAS POTENTIALCAUSESOFFAILEDINVASIONS)NTHETERMSOFTHEBASICMODEL IFMISREDUCED SOISTHELIKELIHOODOFINVASION4HEQUANTITYMCOMBINESTWOTHINGSAPERCAPITA RATEOFEMIGRATIONFROMANOCCUPIEDPATCH ANDTHENUMBEROFINDIVIDUALSPRESENT THERE AND AVAILABLE TO EMIGRATE 3PECIES THAT ARE SEDENTARY OR PHILOPATRIC ARE LIKELYTOHAVEALOWM3UCHSPECIESSHOULDTENDTOBEPOORINVADERS&ORSPECIES WITH EQUAL PER CAPITA RATES OF EMIGRATION THOSE SPECIES WITH THE HIGHEST ABUN DANCEWITHINOCCUPIEDPATCHESCANGENERATEAHIGHABUNDANCEOFMIGRANTS AND


SO EXPERIENCE THE HIGHEST COLONIZATION RATE INTO EMPTY PATCHES ,ARGE M SHOULD THUSREmECTBOTHHIGHFECUNDITYANDHIGHSURVIVALOFEMIGRANTSACROSSTHEMATRIX HABITAT SEPARATING HABITABLE PATCHES 4HE PROBABILITY OF SUCCESSFUL COLONIZATION + ALSOVARIESGREATLYAMONGSPECIES&ORINSTANCE AHIGH+CANBEEXPECTEDIN SPECIESWHERETHEMIGRANTSHAVEHIGHFECUNDITY SOTHATONEORAFEWIMMIGRANTS CAN ESTABLISH A SUCCESSFUL POPULATION BY QUICKLY PRODUCING A LARGE NUMBER OF OFFSPRING THEREBY AVOIDING INITIAL DEMOGRAPHIC STOCHASTICITY AND WHEN INDI VIDUALS ARE LONG LIVED "IRTH DEATH PROCESS MODELS EG AS IN -AC!RTHUR AND 7ILSON REVEALTHATINCOMPARINGSPECIESWITHAGIVENINTRINSICGROWTHRATE R THE PROBABILITY OF EXTINCTION IS LOWER FOR SPECIES WITH LOWER ABSOLUTE DEATH RATES#ONVERSELY SPECIESWHICHAREATRISKOFFREQUENTSTOCHASTICMORTALITYEVENTS ARE LIKELY TO HAVE LOW INTRINSIC COLONIZATION PROPENSITY AND SO HAVE A LOW + )MMIGRANTSARELIKELYTOBEUNFAMILIARWITHTHEDETAILSOFLOCALRESOURCES REFUGES AND MORTALITY RISKS AND IF LEARNING NEW CONDITIONS IS SLOW OR UNRELIABLE IMMI GRANTSMAYBEVULNERABLETORAPIDELIMINATIONINNOVELENVIRONMENTS /NE MATHEMATICALLY SLIGHT BUT BIOLOGICALLY SIGNIlCANT GENERALIZATION OF THE ,EVINSMODELSUGGESTEDBY,ANDE AND.EEAND-AY ISTORECOGNIZE THATINALANDSCAPE NOTALLEMPTYPATCHESARESUITABLE)FWEASSUMETHATOUTOF 4PATCHES 5AREUNSUITABLE THENHn54ISTHEFRACTIONOFTHELANDSCAPETHAT ISPOTENTIALLYOCCUPIABLEBYTHESPECIES7ORKINGBACKTHROUGHTHESAMESTEPSAS BEFORE WEENDUPWITHDXDT+_H X EX4HEINVASIONCRITERIONNOWBECOMES +MHE!SNOTEDFORASOMEWHATDIFFERENTVERSIONOFTHEMODELIN(OLTAND+EITT THISSIMPLEFORMULATIONOFINVASIONENCOMPASSESAGREATDEALOFBIOLOGY )N ADDITION TO THE MECHANISMS MENTIONED IN THE PREVIOUS PARAGRAPHS ANOTHER REASONWHYANINVASIONCOULDFAILISTHATINSUFlCIENTSUITABLEHABITATISAVAILABLE %VENIFEACHSUITABLEPATCHCOULDSUSTAINAPOPULATIONONITSOWNOVERAREASON ABLETIMESCALE IFTHEREARETOOFEWOFTHEM COLONIZATIONMAYNOTBEABLETOMATCH EVENALOWRATEOFEXTINCTION(OLTAND+EITT SHOWHOWTHESEIDEASPERMIT ONETOCONSIDERINAUNIlEDFASHIONMANYDIFFERENTHYPOTHESESTHATHAVEBEENPUT FORTHREGARDINGTHEFACTORSCAUSINGDISTRIBUTIONALRANGELIMITS 4HE THEORETICALLY BEST INVADER WOULD HAVE LOW EXTINCTION RISK AND HIGH M 4HE THEORETICAL @BEST IS LIKELY TO BE UNFEASIBLE BECAUSE THERE ARE BIOLOGICAL CONSTRAINTS SUCH AS TRADEOFFS BETWEEN LIFE HISTORY TRAITS EG REPRODUCTION AND LONGEVITY IN ANIMALS AND BETWEEN DEVELOPMENT OF VEGETATIVE PROPAGULES AND SEEDPRODUCTIONINPLANTS $YNAMIC,EVINSTYPEMETAPOPULATION

4HE,EVINSMODELCLARIlESMANYESSENTIALFEATURESOFMETAPOPULATIONDYNAMICS BUT IT RESTS ON QUITE SIMPLE ASSUMPTIONS ABOUT HOW MIGRATION INmUENCES BOTH COLONIZATIONANDEXTINCTION(ANSKI 4HEBASIC,EVINSFRAMEWORKHASBEEN EXTENDEDTOSEVERALSPECIlCCASESINDIFFERENTSTUDIES INCLUDINGFOREXAMPLEALIN EARRESCUEEFFECT(ANSKI 'OTELLIAND+ELLY ANDASPECIlCNONLINEAR !LLEE EFFECT (ANSKI 4HE ,EVINS MODEL WAS RECENTLY GENERALIZED TO ALLOW


FOR THESE AND OTHER DYNAMIC INmUENCES FROM MIGRATION ON BOTH COLONIZATION AND EXTINCTION RATES COMPARE &IGS AND (ARDING AND -C.AMARA 4HEGENERALITYISOBTAINEDBYEXPRESSINGBOTHCOLONIZATIONANDEXTINCTIONRATESAS FUNCTIONSOFIMMIGRATIONRATE ASWENOWDESCRIBE

&IG !N EXTENSION OF ,EVINS MODEL &IG (ERE THE RATE OF COLONIZATION AND EXTINCTIONARENOTlXEDCONSTANTS BUTCANBEANYFUNCTIONOFIMMIGRATIONRATE_ 4HIS MODELCANTHEREFORECAPTURESEVERALTYPESOFSINGLESPECIESDYNAMICS SUCHAS!LLEEEFFECTS RESCUEEFFECTSANDANTI RESCUEEFFECTS(ARDINGAND-C.AMARA

)T IS USEFUL TO THINK OF METAPOPULATION PROCESSES AT TWO SCALES 4HE SMALLEST SCALEISTHEPATCH4HESUBPOPULATIONINHABITINGAPATCHHASAGIVENRISKOFLOCAL EXTINCTION%_ THATMAYBEINmUENCEDBYTHERATEOFIMMIGRATION_TOTHEPATCH %MPTY PATCHES ARE COLONIZED AT RATE #_ THAT VERY LIKELY DEPENDS ON _ 'IVEN THESE@LOCALRATESOFCHANGETHEOVERALLRATEOFCHANGEINTHEPROPORTIONX.4 OFPATCHESTHATAREOCCUPIEDINTHEWHOLEMETAPOPULATIONIS DX #_ nX n%_ X DT

(ARDING AND -C.AMARA (ERE WE AGAIN ASSUME THAT ALL PATCHES ARE POTENTIALLYOCCUPIABLE 4HE,EVINSMODELISTHENASPECIALCASEOFTHISMODELWITH EXTINCTION FUNCTION %_ E AND COLONIZATION FUNCTION #_ +_ !S DESCRIBED BELOW AVARIETYOFBIOLOGICALPROCESSESCANBEMIMICKEDPHENOMENOLOGICALLYWITH THISEXTENDEDFRAMEWORK $YNAMICEXTINCTIONFUNCTIONS 4HEORIGINAL,EVINSEXTINCTIONFUNCTIONHASACONSTANTVALUE E THATISINDEPEN DENT OF IMMIGRATION RATE )N A METAPOPULATION IT CAN BE IMPORTANT TO ALLOW THE EXTINCTIONRATEOFAPATCHTODEPENDONIMMIGRATIONINTOTHATPATCH)MMIGRANTS CANFOREXAMPLELOWERPATCHEXTINCTIONRISKBYPROVIDINGADEMOGRAPHICCONTRI BUTIONTODECLININGPOPULATIONSORBYINTRODUCINGNEWGOODGENESEG REDUCING INBREEDINGDEPRESSION3ACCERIETAL THISISTHERESCUEEFFECT"ROWNAND +ODRIC "ROWN (ANSKI &OLLOWING A CATASTROPHE IMMIGRANTS CAN


SPEED THE RECOVERY OF THE POPULATION ALLOWING IT TO MORE RAPIDLY REBOUND FROM DANGEROUSLY LOW DENSITIES $EPENDING ON THE UNDERLYING PROCESSES LEADING TO A RESCUEEFFECT THEEXTINCTIONFUNCTIONCANHAVEDIFFERENTSHAPES&IG

&IG )LLUSTRATION OF RESCUE EFFECT FUNCTIONS 4HE RATE OF PER PATCH EXTINCTION CAN SOMETIMES DECREASE AS IMMIGRATION RATE INCREASES 4HREE DIFFERENT TYPES OF RESPONSE TO INCREASEDIMMIGRATIONAREILLUSTRATED

(OWEVER INOTHERCIRCUMSTANCESIMMIGRATIONCANLEADTOINCREASEDEXTINCTION RISKWETERMTHISPATTERNANANTI RESCUEEFFECT4HISCANFOREXAMPLEBEDUETO IMMIGRANTSCARRYINGPARASITESORDISEASES ORBECAUSEIMMIGRANTSCARRYDIFFERENT GENES BREAKINGUPLOCALLYADAPTEDBENElCIALGENECOMBINATIONS2OLÉN !LVAREZ ET AL )N PREDATOR PREY SYSTEMS INCREASING IMMIGRATION CAN SOMETIMES DESTABILIZELOCALINTERACTIONS MAKINGEXCURSIONSTOLOWDENSITIESANDHENCELOCAL EXTINCTIONS MORE LIKELY 3CHÚPS (OLT SEE REVIEW IN (OOPES ET AL 7ITHALLTHESEMECHANISMS INCREASINGIMMIGRATIONRATEOVERSOMERANGE OFVALUESISLIKELYTOBOOSTLOCALEXTINCTIONRATES $YNAMICCOLONIZATIONFUNCTIONS )N,EVINSMODELTHECOLONIZATIONRATEPERPATCHINCREASESLINEARLYWITHTHEIMMI GRATIONRATE ANDHENCEINCREASESLINEARLYWITHTHENUMBEROFOCCUPIEDPATCHES


(OWEVER COLONIZATIONMIGHTTAKEOTHERFORMSASWELL)TISCOMMONFORASPECIES TOHAVEPROBLEMSININITIALESTABLISHMENTINAPATCHWHENTHENUMBEROFIMMI GRANTSISLOW DUETODEMOGRAPHICSKEWSLACKOFADULTSORMALESFOREXAMPLE DIF lCULTYINlNDINGMATES ORINBREEDING4HEPHENOMENAOFDISPROPORTIONATELYLOW COLONIZATIONSUCCESSWHENTHEIMMIGRATIONRATEISLOWISANEXAMPLEOFAN!LLEE EFFECT!LLEE (ANSKI 4HE OPPOSITE WHEN COLONIZATION BY A SINGLE MIGRANT IS MORE SUCCESSFUL WHEN THERE ARE FEW OTHER MIGRANTS IS TERMED AN ANTI !LLEE EFFECT (ARDING AND -C.AMARA )TCANOCCURIFMIGRANTSDONOTSETTLEATRANDOMBUTAVOIDCON SPECIlCS EG TERRITORIALITY SO THAT MIGRANTS ACTIVELY SEEK UNOCCUPIED PATCHES 4HIS LEADS TO A VERY RAPID COLONIZATION INITIALLY BUT AFTER A WHILE MOST PATCHES ARE OCCUPIED AND THE EFFECT SHOULD BECOME LESS IMPORTANT )T IS ALSO CONCEIVABLE THATIFRESOURCESAREEXPLOITEDWHICHHAVELOWRATESOFRENEWAL ANINCREASEINTHE NUMBER OF IMMIGRANTS COULD LEAD TO RAPID OVEREXPLOITATION RESOURCE DEPLETION AND THUS A REDUCED PROBABILITY OF SUCCESSFUL ESTABLISHMENT "OTH THESE MECHA NISMSCANLEADTOANANTI !LLEEEFFECTATTHEMETAPOPULATIONLEVEL )MPACTSBYRESIDENTGENERALISTPREDATORSUPONCOLONIZATIONBYANINVASIVEPREY SPECIESARELIKELYTOSHIFTBETWEENANTI !LLEEEFFECTSAND!LLEEEFFECTS DEPENDINGON THEQUANTITATIVEDETAILSOFTHEPREDATORSFUNCTIONALRESPONSE ANDTHENUMBEROF IMMIGRANTS)FARESIDENTPREDATORHASATYPE)))SIGMOIDAL FUNCTIONALRESPONSE THEN OVER A RANGE OF LOW PREY NUMBERS AN INCREASE IN PREY DENSITY DUE TO AN INCREASING NUMBER OF MIGRANTS LEADS TO AN INCREASE IN THE PER CAPITA MORTALITY RATEINmICTEDONTHEPREYEG BECAUSETHEPREDATORBECOMESINCREASINGLYAWARE OFTHENOVELPREYWITHINCREASINGEXPOSURETOIT ANDSOISMORELIKELYTOCAUSEPREY EXTINCTIONWITHINCREASINGNUMBERSOFCOLONISTS 4HISCANBEVIEWEDASANANTI !LLEE EFFECT WHICH COULD BROADLY DESCRIBE ANY KIND OF NEGATIVE DENSITY DEPEND ENCEOPERATINGATLOWDENSITIESWHICHCANNEGATIVELYAFFECTCOLONIZATIONSUCCESS "UTTYPICALLYATHIGHERPREYDENSITIES MOSTPREDATORSHAVESATURATINGFUNCTIONAL RESPONSES EG DUE TO LIMITED HANDLING TIME OR GUT CAPACITY SO THE PER CAPITA MORTALITYRATEEXPERIENCEDBYPREYDECLINESWITHINCREASINGPREYDENSITY)NTHIS RANGE ANINCREASINGNUMBEROFMIGRANTSMAYENHANCECOLONIZATION BYDILUTING THE IMPACT OF PREDATION 3O WHETHER OR NOT A COLONISING SPECIES EXPERIENCES AN !LLEE ORANANTI !LLEEEFFECT DUETORESIDENTPREDATORSWILLDEPENDUPONBOTHTHE PREDATORSFUNCTIONALRESPONSE ANDTHENUMBEROFMIGRANTS 7HOISAGOODINVADERINTHESINGLESPECIESSYSTEM

4O ANALYSE WHETHER A SPECIES CAN INVADE INTO A PATCHY LANDSCAPE WE SUPPOSE THATTHESPECIESHASBEENINTRODUCEDINASMALLNUMBEROFPATCHES7ECANTHEN ASKWHETHERTHENUMBEROFOCCUPIEDPATCHESTENDSTOGROWORDECLINE)NTERMS OFTHEGENERALIZEDMETAPOPULATIONMODELDESCRIBEDABOVEWEARECONCERNEDWITH WHETHERDXDTWHENXISSMALL4HISDEPENDSONTHEBEHAVIOUROFTHECOLONIZA TIONANDEXTINCTIONFUNCTIONSFORSMALLX ANDHENCESMALL_3UPPOSETHAT


#_ 5+_FORSMALL_

AND %_ 5EFORSMALL_

4HUS FOR SMALL NUMBERS OF OCCUPIED PATCHES THE METAPOPULATION BEHAVES AS DESCRIBEDBY,EVINSMODELWITHPARAMETERS+ANDE ALTHOUGHITMAYBEHAVEVERY DIFFERENTLYWHENTHENUMBEROFOCCUPIEDPATCHESINCREASES7ITHTHISASSUMPTION APPROXIMATION ISSTILLVALID SOTHATTHESPECIESCANINVADEIF+ME

7HENDOESANINVASIVESPECIESGETESTABLISHEDINASINGLESPECIES METAPOPULATION

&IGURE A FILLUSTRATE THEEXTINCTIONRATEWHITESURFACE ANDCOLONIZATIONRATEBLACK @HILLS FORSINGLESPECIESMETAPOPULATIONS)TSHOWSHOWDIFFERENTCOMBINATIONSOF #_ AND%_ INmUENCETHEEQUILIBRIAWHERETHETWOSURFACESMEET $EPENDING ONTHEFUNCTIONS#_ AND%_ THEREMAYEXISTATLEASTONENON TRIVIALEQUILIBRIA INPATCHOCCUPANCYX SUCHTHATTOTALCOLONIZATIONANDEXTINCTIONRATESBAL ANCEWHENAPROPORTIONX OFPATCHESAREOCCUPIED)NSOMECASESTHEREMAYBE MORETHANONESUCHEQUILIBRIUMIE FORAGIVENMTHETWORATESAREEQUALAT TWO ORTHREEDIFFERENTX SEE&IGB C E F (ARDINGAND-C.AMARA 4HEEXACT SHAPES OF #_ AND %_ ARE IMPORTANT ALSO FOR THE EXTINCTION RISK OF THE ENTIRE METAPOPULATION ATLOWPATCHNUMBERS&IG 4HEOCCURRENCEOFMULTIPLEEQUI LIBRIAHASEARLIERBEENSTUDIEDINMORECOMPLEXMETAPOPULATIONMODELS(ANSKI AND 'YLLENBERG 'YLLENBERG ET AL )F AT LEAST ONE EQUILIBRIUM EXISTS THENTHEREISATLEASTONESTABLEEQUILIBRIUM(EREBY@STABLEWEMEANTHATIFXIS INITIALLY CLOSE TO X THEN THE PROPORTION OF OCCUPIED PATCHES WILL TEND TO X OVER TIME)N,EVINSMODELTHEREISAUNIQUEEQUILIBRIUMTHATISSTABLE IF+ME&IG A ANDTHEREISNOEQUILIBRIUMIF+M)E4HUSINTHISPARTICULARMODELASTABLE EQUILIBRIUMEXISTSIFANDONLYIFTHESPECIESCANINVADE &OR OTHER SHAPES OF #_ AND %_ IT IS ALSO TRUE THAT IF A SPECIES CAN INVADE THEN THE PROPORTION OF OCCUPIED PATCHES WILL CERTAINLY INCREASE AND TEND TO A STABLE EQUILIBRIUM )N GENERAL HOWEVER THE CONVERSE NEED NOT HOLD AND THE EXISTENCEOFANEQUILIBRIUMISNOTEQUIVALENTTOTHEABILITYTOINVADE4OSEETHIS SUPPOSE THAT THERE IS AN !LLEE EFFECT 4HUS THE PATCH COLONIZATION FUNCTION #_ ISANACCELERATINGFUNCTIONOF_FORSMALL_,ETTHEPATCHEXTINCTIONFUNCTIONBE AS IN ,EVINS MODEL IE %_ E A CONSTANT 4HEN FOR SUITABLE CHOICE OF E THE TOTALEXTINCTIONRATEEXCEEDSTHETOTALCOLONIZATIONRATEFORSMALLX BUTCOLONIZA TIONEXCEEDSEXTINCTIONIFXISSOMEWHATLARGER&IGE 4HUSTHESPECIESCANNOT INVADEHOWEVER IFTHEPROPORTIONOFPATCHESOCCUPIEDWEREARTIlCIALLYINCREASED SOASTOEXCEEDSOMECRITICALLEVEL THENTHEPROPORTIONWOULDCONTINUETOINCREASE ANDTENDTOASTABLEEQUILIBRIUM


&IG !RANGEOFMETAPOPULATIONSWITHDIFFERENTDYNAMICSOFTHEMODELIN&IG7HITE SURFACESARETOTALEXTINCTIONRISKSANDBLACKHILLSTOTALCOLONIZATIONRATESA!NORDINARY ,EVINS METAPOPULATION B ! RESCUE EFFECT MAKES EXTINCTION RISK DECLINE WITH HIGHER MIGRATIONRATESC!DIFFERENTKINDOFRESCUEEFFECTD!NTIRESCUEEFFECTLEADSTOHIGHER EXTINCTION RISK WITH HIGHER MIGRATION RATES E 4HE COLONIZATION FUNCTION IS BELL SHAPED AN!LLEEEFFECTPREVAILSF!NEXAMPLEWITHBOTHARESCUEAND!LLEEEFFECT

(ETEROGENEOUSLANDSCAPES

(OLT CONSIDEREDAGENERALIZATIONOFTHESTANDARD,EVINSMETAPOPULATION MODEL TO A LANDSCAPE WITH TWO DISTINCT HABITATS ! FRACTION HI OF THE LANDSCAPE IS COMPRISED OF PATCHES OF TYPE I 4HE FRACTION OF HABITAT PATCHES THAT ARE TYPE I AND OCCUPIED BY THE SPECIES IS DENOTED BY PI .ECESSARILY WE HAVE PI ) HI AND HIH))FINTHELATTERCASE THEINEQUALITYHOLDSHIH SOMEPATCHESIN THELANDSCAPEAREUNSUITABLEFOROCCUPANCY 5SINGTHESTANDARD,EVINSNOTATION EI DENOTES EXTINCTION ON OCCUPIED PATCHES OF TYPE I AND CIJ IS COLONIZATION ONTO EMPTYPATCHESOFTYPEI DUETOMIGRANTSGENERATEDBYOCCUPIEDPATCHESOFTYPEJ 4HEEQUATIONFORDYNAMICSOFPISDPDTCPCP HnP nEPASIMILAR EQUATIONDESCRIBESDYNAMICSINTHESECONDHABITATTYPE


4HETOTALOCCUPANCYBYTHESPECIESINTHELANDSCAPEISPPP)FWESUM THEDYNAMICALEQUATIONSFORCHANGEINOCCUPANCY WEGETANEXPRESSIONFORDPDT )NGENERAL THISDOESNOTSIMPLIFYTOAFORMINJUSTP(OWEVER IFALLTHECOLONIZA TIONRATESCIJAREEQUALTOACONSTANT C ANDBOTHPATCHESHAVETHESAMEEXTINCTION RATES THE ORIGINAL ,EVINS MODEL EMERGES )N OTHER WORDS ARBITRARY DISTINCTIONS AMONG HABITATS CAN SIMPLY BE IGNORED (OWEVER IF PATCH TYPE INmUENCES EITHER COLONIZATION OR EXTINCTION LANDSCAPE HETEROGENEITY CAN INmUENCE METAPOPULA TIONDYNAMICSEG PATCHTYPESDIFFERIN+ORM !LL THE FACTORS MENTIONED ABOVE WHICH INmUENCE COLONIZATION AND EXTINCTION RATESCANPOTENTIALLYSHOWVARIATIONAMONGHABITATTYPES&ORINSTANCE ANINDI VIDUALBORNINAHABITATPATCHOFTYPEIBEFOREEMIGRATINGMIGHTBECOMEACCLIMA TIZEDTOTHEABIOTICCONDITIONSINITSNATALSITEEG ASINPHYSIOLOGICALADAPTATION TOTHERMALCONDITIONS ANDSOEITHERPREFERENTIALLYSEEKOUTSIMILARHABITATSWHEN ITDISPERSES ORBEVULNERABLETOHIGHMORTALITYIFITSETTLESINTOADIFFERENTHABITAT LEADINGTOFAILEDCOLONIZATION )FONLYPATCHTYPEIISPRESENT THEINITIALGROWTHRATEOFTHESPECIES WHENRARE IShICIIHInEIASINTHESTANDARD,EVINSMODEL 7ITHBOTHPATCHTYPESPRESENT THEASYMPTOTICGROWTHRATEOFTHEINVADINGSPECIESTURNSOUTTOBEh h h3;hnh CCHH= (OLT -ANIPULATINGTHISEXPRESSIONLEADSTOSEVERALSIMPLECONCLUSIONS&IRST ASPE CIESWHICHISAGENERALISTMAYBEABLETOINVADEANDPERSISTBECAUSEITCANENJOY CROSS HABITAT COLONIZATION WHEREAS OTHERWISE SIMILAR HABITAT SPECIALISTS WOULD GOEXTINCTIE EXPERIENCEFAILEDINVASIONS 3ECOND SOMETIMESUTILIZINGASECOND HABITAT MAY BE CRUCIAL IN PERMITTING A SPECIES TO PERSIST IN A LANDSCAPE EVEN IF THERE IS NO COLONIZATION AMONG PATCHES OF THIS SECOND TYPE CONDITION IN (OLT 4HIS CAN HAPPEN IF ALL COLONIZATION FROM AND OF THE SECOND HABITAT TYPE IS INTO AND FROM HABITATS OF THE lRST HABITAT TYPE EG BECAUSE PATCHES OF THE SECONDHABITATTYPEAREWIDELYSPACED BUTTHESECONDHABITATTYPEHASALOWER EXTINCTIONRATETHANDOESTHEPRIMARYHABITATTYPE4HISCANBEVIEWEDASAKIND OF SPATIALSTORAGEEFFECT)TWOULDBEINTERESTINGINFUTUREWORKTOEXTENDTHISTWO HABITATMODELUSINGTHEGENERALIZEDAPPROACHOF(ARDINGAND-C.AMARA #OLONIZATIONAMONGSOMEHABITATSMAYPERMITRESCUEEFFECTS EVENWHILECOLONI ZATIONAMONGOTHERSRESEMBLESTHEANTI RESCUEPATTERN)NSUCHCASES THEEXPECT ED DYNAMICS OF INVASION WOULD BE QUITE SENSITIVE TO THE RELATIVE PROPORTIONS OF THELANDSCAPEOCCUPIEDBYTHEDISTINCTHABITATTYPES

).4%2!#4)/.37)4(!.!4)6%30%#)%3 !NINVASIVESPECIESCANINTERACTWITHANATIVEMETAPOPULATIONINTHESAMEPATCH NETWORK IN VARIOUS WAYS WITH NET EFFECTS ON THE LIKELIHOOD OF INVASION RANGING FROMPOSITIVETONEGATIVE&ORINSTANCE WHENSPECIESCOMPETEFORTHESAMELIM ITING RESOURCE WITHIN PATCHES COMPETITIVE EXCLUSION IS LIKELY -ETAPOPULATION DYNAMICSCANNONETHELESSPERMITINVASIONBYANINFERIORSPECIES IFITISSUPERIOR


AT COLONIZATION OF EMPTY PATCHES ,EVINS AND #ULVER 4ILMAN 4HISREQUIRESATRADEOFFBETWEENCOMPETITIONANDCOLONIZATION ALLOWINGTHEINFE RIOR COMPETITOR TO EXPLOIT MORE EFFECTIVELY THE EMPTY HABITAT PATCHES LEFT BY THE SUPERIORCOMPETITORWHENITSUFFERSEXTINCTIONS!MARSEKARE -ETAPOPULATIONDYNAMICSCANALSOLEADTOEXCLUSIONTHATWOULDOTHERWISENOT OCCUR (OLT &OR INSTANCE ONE SPECIES CAN DELIMIT A SECOND SPECIES INDI RECTLY BYHOSTINGAPATHOGENTHATISMOREHARMFULTOTHESECONDSPECIES(OLTAND ,AWTON !N EXAMPLE IS THE GRADUAL ERADICATION OF THE NATIVE NOBLE CRAY lSH!STACUSASTACUS IN3WEDENWHICHISBEINGREPLACEDBYTHE.ORTH!MERICAN SIGNALCRAYlSH0ACIFASTACUSLENIUSCULUS MEDIATEDBYASHAREDINFECTIOUSDISEASE 4HEINVASIVESPECIESCARRIESAFUNGUS!PHANOMYCESASTACI TOWHICHITITSELFAPPEARS TO BE IMMUNE WHEREAS THE NATIVE SPECIES IS SEVERELY IMPACTED BY THE PARASITE "ANGYEEKHUN )N A METAPOPULATION SUCH INDIRECT EXCLUSION MAY OCCUR EVENIFTHETWOSPECIESOCCUPYDISTINCTHABITATPATCHESINTHISEXAMPLE IFFUNGAL SPORESDISPERSEWIDELYTHEINVASIVESPECIESCOULDPROVIDEALANDSCAPE RESERVOIR FORTHEPATHOGEN WHICHCANELIMINATETHENATIVESPECIESEVENINPATCHESWHERE THEINVASIVESPECIESITSELFNEVEROCCURS 4HERE CAN ALSO BE FACILITATIVE INTERACTIONS BETWEEN INVASIVE AND RESIDENT SPE CIES)NTHELITERATUREONSUCCESSION THEREAREMANYEXAMPLESOFEARLYCOLONIZERS FACILITATINGINVASIONBYLATERCOLONISTSEG NITROGEN lXERSMAYNEEDTOCOLONIZE PRIORTOOTHERSPECIES #ONNELLAND3LATYER )NTHISCASE ONESPECIESALTERS THEABIOTICENVIRONMENTSOASTOENHANCECOLONIZATIONORREDUCEEXTINCTIONFORA SECONDSPECIES-OREOVER ONESPECIESMAYREQUIREANOTHERSPECIESASARESOURCE )NVASIONS BY SPECIALIST PREDATORS PARASITES OR HERBIVORES WILL ALMOST ALWAYS DEPENDUPONTHEPRESENCEOFTHEIRREQUIREDPREYORHOSTS !FLEXIBLEMODELWHICHALLOWSFORMANYKINDSOFINTERACTIONS

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REGARDLESS OF THE STRENGTH OF COMPETITION (ERE STOCHASTIC EVENTS DOMINATE AND THENUMBEROFINDIVIDUALSRELEASEDISCRITICAL7HENCOMPETITORSPECIESOCCURAT HIGHER INITIAL ABUNDANCE THE PROBABILITY OF ESTABLISHMENT DEPENDS INCREASINGLY ONTHESTRENGTHOFCOMPETITION

&IG 2ESULTS OF THE STOCHASTIC BIRTH DEATH MODEL SHOWING THE PROBABILITY OF ESTABLISHMENTASAFUNCTIONOFTHEINITIALABUNDANCEOFANINTRODUCEDSPECIES. GIVEN ARESIDENTCOMPETITORATFOURDIFFERENTABUNDANCES. THEFOURPANELS ANDWITHTHEPER CAPITA STRENGTH OF INTERSPECIlC COMPETITION TAKING SIX VALUES FROM TO SHOWN AS DIFFERENTLINES

4HESE SIMULATION RESULTS HIGHLIGHT TWO PREDICTIONS &IRST THE ABUNDANCE OF A COMPETITORINADDITIONTO THE PER CAPITA STRENGTHOFCOMPETITION SHOULD BEIMPORTANT


IN DETERMINING THE OUTCOME OF AN INTRODUCTION (ENCE WE WOULD EXPECT TO OBSERVEBOTHMORPHOLOGICALOVERDISPERSIONRESULTINGFROMTHECOMPETITIVEEXCLU SION OF MORPHOLOGICALLY SIMILAR SPECIES AND PRIORITY EFFECTS A HIGHER CHANCE OF FAILUREAMONGLATERINTRODUCTIONSBECAUSEALREADYRESIDENTCOMPETITORSHAVEHAD TIMETOINCREASEINABUNDANCE ININTRODUCEDASSEMBLAGESSTRUCTUREDBYCOMPETI TION 3ECOND THESE FACTORS SHOULD INTERACT SUCH THAT THE INmUENCE OF PER CAPITA STRENGTH OF COMPETITION DEPENDS ON THE RELATIVE ABUNDANCES OF THE INTRODUCED ANDCOMPETITORSPECIES ANDTHEIMPORTANCEOFCOMPETITIONDEPENDSONINTRODUC TION EFFORT &IG 4HUS INTER SPECIlC COMPETITION IS PREDICTED TO BE OF MUCH LESSIMPORTANCEINAFFECTINGESTABLISHMENTWHENASPECIESISINTRODUCEDINSMALL NUMBERSSTOCHASTICPROCESSESDOMINATE ORWHENTHERESIDENTCOMPETITOROCCURS ATLOWABUNDANCE4HEEFFECTSOFCOMPETITIONSHOULDBEMOSTAPPARENTWHENBOTH THEINTRODUCEDANDCOMPETITORSPECIESOCCURATHIGHABUNDANCE

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EACHINDIVIDUALTHELENGTHOFTHECULMENFROMTHEBASEOFTHESKULLTOTHETIPOF THEUPPERMANDIBLE THEWIDTHANDDEPTHOFTHEBEAKATTHEANTERIORMARGINOFTHE NARES THELENGTHOFTHETARSUS THELENGTHOFTHEWINGFROMTHEWRISTTOTHETIPOF THELONGESTPRIMARY ANDTHELENGTHOFTHETAIL &OLLOWING2ICKLEFSAND4RAVIS AND-OULTONAND0IMM WESUM MARISEDMORPHOLOGICALDIFFERENCESAMONGSPECIESUSINGTHElRSTTWOAXESDERIVED FROM A PRINCIPAL COMPONENTS ANALYSIS 0#! BASED ON LOG TRANSFORMED VALUES OF ALL SIX MORPHOLOGICAL CHARACTERS WITH INTRODUCTIONS TO EACH DISTRICT ANALYSED SEPARATELY &IG &OR EACH DISTRICT WE USED THE %UCLIDEAN DISTANCE BETWEEN SPECIES IN THIS MORPHOLOGICAL SPACE TO ESTIMATE HOW MORPHOLOGICALLY SIMILAR SPECIESARETOEACHOTHER ANDUSEDTHISASAMEASUREOFTHESTRENGTHOFINTERSPE CIlCCOMPETITION

&IG 0LOTS OF THE lRST TWO AXES FROM A PRINCIPAL COMPONENTS ANALYSIS SUMMARISING MORPHOLOGICAL DIFFERENCES AMONG THE PASSERINE SPECIES INTRODUCED TO EACH OF FOUR ACCLIMATISATIONDISTRICTSIN.EW:EALANDSEETEXT 3PECIESTHATESTABLISHEDARESHOWNAS OPENCIRCLES SPECIESTHATFAILEDARESHOWNASCLOSEDCIRCLES


0REVIOUSSTUDIESHAVEUSEDMINIMUMSPANNINGTREESCOUPLEDWITHRANDOMISA TION TESTS TO SEARCH FOR OVERDISPERSION AMONG SUCCESSFULLY ESTABLISHED SPECIES IN MORPHOLOGICAL SPACE EG -OULTON AND 0IMM -OULTON AND ,OCKWOOD ,OCKWOOD ET AL ,OCKWOOD AND -OULTON ,OCKWOOD ET AL (ERE WE ADOPT A REGRESSION APPROACH BECAUSE WE WANT TO SIMULTANE OUSLY CONSIDER THE INmUENCE OF SEVERAL VARIABLES ON ESTABLISHMENT PROBABILITY &ORINTRODUCTIONSTOEACHDISTRICT WEUSEDTHELOG TRANSFORMED DISTANCEBETWEEN A SPECIES AND ITS CLOSEST NEIGHBOUR IN MORPHOLOGICAL SPACE AS AN ESTIMATE OF THESTRENGTHOFINTERSPECIlCCOMPETITIONSPECIESWITHANEARESTNEIGHBOURMORE SIMILAR IN MORPHOLOGY ARE ASSUMED TO HAVE FACED STRONGER COMPETITION FOR THE SAME RESOURCES ! SPECIES COULD HAVE AS ITS NEAREST NEIGHBOUR ONLY SPECIES THAT WERE PRESENT IN THE SAME DISTRICT AT THE SAME TIME DETERMINED FROM THE YEAR OF INTRODUCTION TO A DISTRICT AND THE YEAR OF EXTINCTION FOR SPECIES THAT FAILED 4HIS AVOIDS A PROBLEM OFTEN PRESENT IN THE USE OF MINIMUM SPANNING TREES WHEREBYALLSPECIESAREINCLUDEDASPOTENTIALCOMPETITORSEVENIFTHEDISTRIBUTIONS OFSOMESPECIESFAILTOOVERLAPINEITHERSPACEORTIME$UNCANAND"LACKBURN 4HELEVELOFCOMPETITIONTHATINDIVIDUALSOFASPECIESEXPERIENCEWILLBEAFUNC TIONOFTHEIRSIMILARITYTOACOMPETITORANDTHEABUNDANCEOFTHATCOMPETITOR.O SPECIESABUNDANCEESTIMATESAREAVAILABLEFORTHEPERIODDURINGWHICHMOSTINTRO DUCTIONSOCCURREDIN.EW:EALANDTHELATES (OWEVER 4HOMSON OBSERVED THAT INTRODUCED PASSERINES INCREASED RAPIDLY IN ABUNDANCE FOLLOWING ESTABLISHMENT!LTHOUGHLEGISLATIONWASORIGINALLYPASSEDPROTECTINGINTRODUCED BIRDS 4HOMSON STATED THAT hWITHIN TEN OR lFTEEN YEARS OF THE COMING IN OF THEBIRDS THEIRNUMBERSINCREASEDTOSUCHANEXTENT THATTHEPROTECTIONAFFORDEDTHEM HAD TO BE TAKEN AWAY AND RESTRICTIVE LEGISLATION IMPOSEDv $URING THIS PERIOD OF RAPIDPOPULATIONINCREASETHENUMBEROFYEARSELAPSEDSINCEINTRODUCTIONSHOULD PROVIDE A REASONABLE INDEX OF RELATIVE ABUNDANCE AT LEAST FOR THOSE SPECIES THAT SUCCESSFULLY ESTABLISHED 7E THEREFORE USED THE TIME DELAY IN YEARS SEPARATING THE INTRODUCTION OF A TARGET SPECIES AND ITS NEAREST COMPETITOR AS AN ESTIMATE OF THATCOMPETITORSRELATIVEABUNDANCE/URASSUMPTIONISTHATTHELONGERTHETIME DELAY THE LONGER A COMPETITORS POPULATION WILL HAVE HAD TO INCREASE AND THE HIGHERITSABUNDANCEWILLBE -ODELDEVELOPMENTANDANALYSIS

/URSIMULATIONSPREDICTHOWI NUMBEROFRELEASEEVENTSAMEASUREOFINTRODUC TIONEFFORT II LOG TRANSFORMEDDISTANCETOTHENEARESTNEIGHBOURINMORPHOLOGI CALSPACEAMEASUREOFTHEPER CAPITASTRENGTHOFINTERSPECIlCCOMPETITION AND III TIME DELAY BETWEEN INTRODUCTIONS AN ESTIMATE OF THE RELATIVE ABUNDANCE OF THECLOSESTCOMPETITOR SHOULDINTERACTTOGENERATEPATTERNSINESTABLISHMENTSUC CESS&IG 4OSEEHOWWELLTHEDATAlTTHESEPREDICTIONSWECONSIDEREDHOWWELL ASERIESOFCANDIDATELOGISTICREGRESSIONMODELSCOULDEXPLAINVARIATIONINESTAB LISHMENTPROBABILITYFORPASSERINEINTRODUCTIONSTO.EW:EALAND/URAPPROACHIS TOlTASERIESOFCANDIDATEMODELSTOTHEDATA TOIDENTIFYTHEBEST lTTINGMODELAS


ABASISFORINFERENCE ANDTHENTOCOMPARETHERESULTSFROMTHATBEST lTTINGMODEL WITHTHESIMULATIONRESULTS /URRESPONSEVARIABLEISBINARYWHETHERASPECIESINTRODUCEDTOADISTRICTESTAB LISHEDORNOT7ECONSIDEREDCANDIDATELOGISTICREGRESSIONMODELSTHATMIGHT EXPLAIN VARIATION IN ESTABLISHMENT SUCCESS ALL OF WHICH INCLUDED THE NUMBER OF RELEASE EVENTS WHICH WE KNOW IS AN IMPORTANT EXPLANATORY VARIABLE &OURTEEN OF THE MODELS INCLUDED COMBINATIONS OF MORPHOLOGICAL DISTANCE INTRODUCTION DELAY AND POSSIBLE INTERACTIONS BETWEEN THESE VARIABLES THAT CAPTURE THE RANGE OF POSSIBLE OUTCOMES MODELS IN 4ABLE 4HE REMAINING MODELS INCLUDED COMBINATIONS OF MORPHOLOGICAL DISTANCE AND YEAR OF lRST INTRODUCTION 7ECONSIDEREDMODELSCONTAININGTHEVARIABLEYEAROFlRSTINTRODUCTIONBECAUSE SPECIESINTRODUCEDALONGTIMEAFTERTHEIRCLOSESTCOMPETITORIE ALONGINTRODUC TIONDELAY WILLALSOHAVEALATERDATEOFINTRODUCTIONINABSOLUTETERMS)THASBEEN NOTED THAT IN ADDITION TO FACING GREATER COMPETITION LATER INTRODUCTIONS WOULD HAVE FACED ADDITIONAL THREATS INCLUDING A GREATER DIVERSITY AND ABUNDANCE OF INTRODUCEDPREDATORS$UNCANETALINPRESS 7EINCLUDEYEAROFlRSTINTRODUCTION ASASURROGATEFOROTHERFACTORSTHATCOULDHAVEVARIEDTHROUGHTIMEANDAFFECTED ESTABLISHMENTPROBABILITY7EDIDNOTCONSIDERINTERACTIONSBETWEENYEAROFlRST INTRODUCTIONANDOTHERVARIABLESBECAUSEWEHADNOAPRIORIREASONTOTHINKTHEY SHOULDBEIMPORTANT 7E USED THE SMALL SAMPLE VERSION OF !KAIKES )NFORMATION #RITERION !)#C TOIDENTIFYWHICHOFTHECANDIDATEMODELSBESTlTTEDTHEDATA"URNHAMAND !NDERSON 4HE BEST lTTING MODEL HAS THE SMALLEST !)#C VALUE ANDWERANKEDMODELSFROMBESTTOWORSTBASEDONTHEDIFFERENCEBETWEENEACH MODELS!)#CANDTHE!)#COFTHEBEST lTTINGMODEL6IVALUES 7ETHENCALCULATED THE !KAIKE WEIGHTS WI SEE "URNHAM AND !NDERSON WHICH PROVIDE A WEIGHTOFEVIDENCEFOREACHMODELGIVENASANAPPROXIMATEPROBABILITYTHATTHE BEST lTTINGMODELISINFACTTHEBESTOUTOFTHECANDIDATESET)FTHEREISCLEARLYA SINGLE BEST MODEL AS JUDGED BY THE WEIGHT OF EVIDENCE THEN THAT MODEL CAN BE USEDASABASISFORINFERENCE)NOURCASE HOWEVER NOSINGLEMODELPROVIDEDABEST lTTOTHEDATA WITHSEVERALCANDIDATEMODELSPROVIDINGASIMILARLYGOODlT2ATHER THANARBITRARILYSELECTINGONEOFSEVERALWELLlTTINGMODELS WEUSEDINFORMATION CONTAINED IN ALL OF THESE MODELS AS A BASIS FOR ROBUST MULTI MODEL INFERENCE 4O DO THIS WE IDENTIlED ALL CANDIDATE MODELS FOR WHICH THE SUM OF THE !KAIKE WEIGHTSFROMLARGESTTOSMALLESTWAS&ROMTHISSETOFBEST lTTINGMODELS WECALCULATEDMODEL AVERAGEDPARAMETERESTIMATES WEIGHTINGTHEPARAMETERSIN EACHMODELBYTHE!KAIKEWEIGHTFORTHATMODELANDTHENSUMMEDTHEWEIGHTED ESTIMATESACROSSALLMODELS"URNHAMAND!NDERSON 7ETHENBASEDOUR INFERENCEONTHESEMODEL AVERAGEDVALUES 2ESULTS

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