Localextinctionandcolonisationinnativeandexoticfish inrelationtochangesinlanduse
Dorothe´eKoppA,JordiFiguerolaB,ArthurCompinA,Fre´de´ricSantoulA
andRe´gisCe´re´ghinoA,C
AEcoLab,LaboratoireEcologie FonctionnelleetEnvironnement,UMR5245,Universite´de
Toulouse, 118routedeNarbonne,31062ToulouseCedex9,France.
BEstacionBiologicadeDon˜ana,AvenuenidadeMariaLuisas/n,PabellondelPeru,
41013Sevilla,Spain.
CCorrespondingauthor.Email:
Abstract. Distributionpatternsofmanynativeandexoticfishspeciesarewelldocumented,yetlittleisknownaboutthe temporaldynamicsofnativeandexoticdiversityinrelationtochangesinlanduse.Wehypothesisedthatcolonisationrates wouldbehigherforexoticfishspeciesandthatextinctionrateswouldbehigherfornativespeciesinlargestreamsystems. Wealsopredictedthatcold-water specieswouldbemoreimpactedthanthermallytolerantspecies.Totestthese hypotheses,weusedgeneralisedlinearmixedmodelstocomparechangesinnativeandexoticfishspeciesrichnessover
10yearsinaFrenchdrainagebasinsubjectedtolandscapealterations.Exoticfishweremoresusceptibletolocalextinction thanthenativeones.Extinctionwasgreateramongcold-tolerantspeciesandathigherelevations.Colonisationbyexotic specieswashigheratlowerelevations.Althoughadecadeofexpandingurbanisation affectedfishcolonisation, agriculturallandsexperiencedhigherextinctionrates.Inthecontextofglobalchangesinlanduseandpopulation pressure,ourstudysuggeststhatthetemporaldynamicsoffishdiversityaredrivenbylandscapealterationsaswellasby thethermaltoleranceofspecies.
Additionalkeywords:agriculture,freshwaterfishes,introductions,thermalpreferences,urbanisation.
Introduction
Worldwide, manycountrieshaveestablishednational Biodiversity ActionPlans(BAPs,e.g.USA,Australia,New Zealand,Tanzania).Thesepolicychangeswereimplementedin responsetoagrowingconcernthatdevelopmentoverprevious decadeswashavingasignificant impactuponbiodiversity, despiteconsiderable benefitstothecitizensofnations.Under thisframework, assessingtheeffectsoflandscapealterations (e.g.urbanisation,agriculture)oncommunitydynamicsisnowa priorityforbiologicalconservation(McKinney2002).Muchof thecurrentresearchhasreporteddeclinesinthediversityof targetorganisms(e.g.variousinvertebrates, fish,mammalsor plants)inrelationtolandscapealterations,fromlocaltoglobal scales.Apartfromtheirdirecteffectsupondiversity and ecologicalprocesses,changesinlanduseorhabitatdestruction canalso promotebiologicalinvasionsby exoticspecies.These biologicalinvasionsconstituteasignificant component of globalenvironmentalchangesandmayaffecthumanhealthand wealth,ecosystem functions andnativebiologicaldiversity (Vitouseketal.1996).Freshwatersareparticularlysubjectedto habitatdegradation,hydrologicalterations,pollutionandthe spreadofinvasivespecies(Dudgeonet al.2006).Forexample,
recentestimatesindicatethat25%oftheworld’sfreshwaterfish arethreatenedwithextinction(Vie´etal.2009).
Many species present a metapopulation structure, with colonisation/extinctionoccurringatlocalscales(Case1991).
Theequilibriumbetweenbothprocessesdetermines trendsin population ranges.However,researchhasfocussedoncharac- terisingcolonisationandwavesofestablishment(e.g.Leprieur etal.2008;Gozlanetal.2010)andlittleisknownaboutthe
temporalstabilityofbothexoticandnativepopulations in invadedareas(Strayeretal.2006).Inthiscontextofspecies lossandbiologicalinvasions,theresponseoflocalcommunities
toenvironmentalchanges canbeperceivedintermsofcoloni- sation bysomesetsofspecies andextinctionofotherspecies overtime.Localcolonisationisdefinedasaspeciesbeing
detectedinalocationfromwhichitwaspreviously absent, whereaslocalextinctionisdefinedastheabsenceofaspeciesin alocationwhereitwaspreviouslypresent(Nicholsetal.1998). Assumingthat exotic species coloniseecosystemsas agri-
culturalorurbanlandcoverincreases(Pooletal.2010),one maypredictthatexoticandnativespecies differintheir colonisation/extinction responses to environmental changes
(Koppetal.2009).
Spatialpatterns ofnativeandexoticspeciesrichnesshave been extensively studied along gradients of disturbance (e.g.Koppetal.2009).However, littleisknownaboutthe temporaldynamicsofnativeandnon-nativediversityinrelation tochanging landscapes.Althoughhabitatdegradation,climate changeorbiologicalinvasionscancauseimmediateextinctions, thereisoftenaconsiderablelagbetweenenvironmentalchanges andthesubsequentextinctions(Oldenetal.2010).Moststudies of thedistributionsof exoticspecieshavebeenbasedon short- termsurveysandhave,thus,yieldedsnapshots thatlacka temporalcontext(Strayer etal.2006).Inlightofrecenturban andagriculturaldevelopment,short-termassessmentsarelikely tobeinadequatetodescribecolonisation/extinctionpatternsand therolesthatexoticspeciesplayovertimeintheareasthey invade.Usinglong-termdataonspeciesoccurrenceorcompar- ingpastvspresenthabitatcharacteristicsmaybeusedtoaddress theseaims(Oldenetal.2010).
Inthisstudy,wefocussedontheAdour-Garonnestream system(France).Thedrainagebasinofthissystemissubjected
tourbanisationandextensiveagriculture.Riverfisharethemost
frequentlyintroducedfreshwater organismsworldwide (Leprieuretal.2008);therefore, theyarerelevantmodel organismstostudythecontributionofnativeandexoticspecies tobiodiversity patternsinaspatialandtemporalcontext.Our specificaimwastoassess theextentofchanges innativeand exoticfishspeciesrichnessoverthepastdecade.Assumingthat increasinganthropogenicimpactenhancesthechancesofsuc- cessfulinvasion byexoticfishesandthatexoticandnative speciesdifferintheirresponsestoenvironmental changes (watertemperature,urbanisation,agriculture),wehypothesised highercolonisationratesforexoticspeciesandhigherextinction ratesfornativeones.Inthecontext ofglobalwarming,wealso predictedthatcold-water specieswouldbemoreproneto extinctionthanthermallytolerantspecies.Totestthesehypoth- eses,weanalysedthepatternsofcolonisationandextinctionby nativeandexoticfishat100sitesfrom1994–97to2004–07,in relationtochanges inlanduse,thelocationofsiteswithinthe streamsystemandthethermalpreferencesofspecies(fromcold towarmwaters).
Materialsandmethods
Studyareaanddatacollection
TheAdour-Garonnestreamsystem(south-westernFrance)hasa
116000km2 drainagebasin.Weselected100samplingsites rangingfrom6to1800mabovesealevel(a.s.l.,seeFig.S1,
availableasSupplementaryMaterialtothispaper),representing
riversfromhighmountain,plainandcoastalareas.Samples werecollectedbyelectrofishing duringlow-flowperiods.To avoidpseudo-absencedata,eachsitewassampledthreetimes between1994and1997andthenthreetimesbetween2004and
2007. The sampling reaches (,100m long) were similar betweentheperiods.Aspecieswiththreeabsencesduringa givenperiodwasconsideredasabsent.Thebiologicalvariables assignedtoeachsitewerethecolonisationbynewfishspeciesor theextinctionofspecies from oneperiod totheother.Asfish temperaturepreferences haveastronginfluenceuponspecies’ potentialrangewithintherivercontinuum(Buissonetal.2008), fishweredividedintowarm-,cool-andcold-watertypeswith
regardtotheirpreferredthermalconditions(Magnusonetal.
1979).Wethenincludedthethermaltolerances offish:cold-, cool-orwarm-tolerant(accordingtoKottelatandFreyhof2007) asexplanatoryvariablesintheanalysis.
For each site, a geographic information system (GIS, MapinfoProfessional7.8,Troy,NY)wasusedtodelineatea
geographicalbufferzonerepresentinga1000-mradiuscentred
onthesite.Thissizefallswithin thatofthe‘reach buffer’ defined byAllan(2004)asabufferof100toseveral hundred metresinwidthoneachbankandsomehundredsofmetrestoa kilometreinlength).Inpractice, thewidthofthebufferzoneis oftenadaptedtothelandscape characteristicsofthestudied areasandrangesfrom30to100moneachsideoftheriver (discussedbyCompinandCe´re´ghino 2007).Sampling sites werethencharacterisedusingelevationabovesealevel(m)and threeland-cover variablesintended toaccountforanthropo- genicpressure.Thethreeland-covervariables,describedforthe twoperiods1994–97and2004–07,werepercentageareawithin abufferzonecoveredbyforest(areasoccupied byforestand woodlandswith nativeor exoticconiferousor deciduoustrees; scrubandherbaceousvegetationassociations), urbanareas (industrial, commercialandtransportunits;artificialandnon- agriculturalvegetatedareas) and agriculturalareas (arable lands,permanent cropsandpasture).Digitalland-cover information wasobtainedfromtheCORINEland-cover data- baseforEurope(EuropeanEnvironment Agency, eea.europa.eu/,accessed June2010).Thisdatabasewasgener- atedfromorthorectifiedsatelliteimagesand providesthematic GISmaplayersincludingupto44land-cover classeswitha mappingscale of1:100000.Thesefourvariableswerechosen because theycharacterisethelocationofsamplingsiteswithin thestreamsystemandwithintheregionallandscapemosaicand theyareeasytodescribeusingaGIS.
Dataanalyses
Weanalysedtherelationshipofdifferentecologicalfactorsand thepatternsofcolonisationandextinctionin100differentsites infourdifferentriverbasins.Wefittedageneralised linear mixedmodel(GLMM)tothepresence–absencedatacollected foreachspeciesineachdifferentsitein1994–97and2004–07. Bothbasinandsitewithinabasinwereincludedasrandom factorstocontrolforlocalnon-independence ofthedata.We modelledthenon-independenceofdatacomingfromthesame speciesbyassumingacommonpositivecorrelationbetween datafromthesamespeciescomingfromdifferentlocalitiesand azerocorrelationwiththedataofotherfishspecies (see Blackburn andDuncan2001forasimilarapproach).Wecon- structedtwodifferentmodels:oneforlocalcolonisations and anotherforlocalextinctions. Forthemodeloflocalcolonisa- tions,weconsidered onlythedataofnegativecensusforeach speciesxlocalityin1994–97andusedthepresence/absence datafor2004–07astheresponsevariablemodelling theprob- abilityofobtainingapositivecountin2004–07. Forthe extinctionsmodel,weusedthe dataofpositivecensusforeach speciesxlocalityin 1994–97andagain usedthepresence/ absencedataastheresponsevariable,modellingtheprobability of anegativecensusin2004–07.
AllcalculationsweredonewiththeGLIMMIXprocedurein
SAS9.2.(SASInstitute,Cary,NC,USA)usingabinomial
Table1. Modelsanalysingthepatternsof fishextinctionforcold-tolerantspecies(cold),cool-tolerantspecies(cool), thermally-tolerantspecies(warm) andfornativevs.exotic species
OnlyvariableswithP,0.05areinterpretedasstatisticallysignificant.Estimatescorrespondtoslopevaluesassociatedtoeach factorandareonlyreportedforsignificanteffectsretained inthefinalmodel
Extinction / F-value / d.f. / P-value / Estimate±s.e.Elevation / 6.79 / 1,932 / 0.009 / 0.5448±0.2090
Cold / 4.08 / 1,32 / 0.05 / Non-cold,—0.7309±0.6320;cold,0
Cool / 0.07 / 1,31 / 0.79 / –
Warm / 0.13 / 1,31 / 0.72 / –
Nativevsexotic / 18.51 / 1,32 / 0.0001 / Exotics,1.2880±0.2994;native, 0
Urbanisation / 0.28 / 1,931 / 0.60 / –
Agriculture / 7.53 / 1,932 / 0.006 / 0.0103±0.0037
Changeurbanlandcover / 0.54 / 1,931 / 0.46 / –
Changeagriculturallandcover / 0.14 / 1,931 / 0.70 / –
Table2. Modelsanalysingthepatternsoffishcolonisation(forlegend seeTable1)
OnlyvariableswithP,0.05areinterpretedasstatisticallysignificant.Estimatescorrespondtoslopevaluesassociatedtoeach factorandareonlyreportedforsignificanteffectsretained inthefinalmodel
Colonisation / F-value / d.f. / P-value / Estimate±s.e.Elevation / 76.95 / 1,2692 / ,0.0001 / —1.2457±0.1420
Cold / 10.07 / 1,34 / 0.003 / Non-cold,1.2534±0.3894;cold,0
Cool / 0.78 / 1,33 / 0.38 / –
Warm / 5.02 / 1,34 / 0.02 / Non-warm,0.6912±0.3085;warm,0
Nativevsexotic / 0.67 / 1,33 / 0.42 / –
Urbanisation / 0.69 / 1,2691 / 0.41 / –
Agriculture / 1.03 / 1,2691 / 0.31 / –
Changeurbanlandcover / 21.80 / 1,2692 / ,0.0001 / 0.0796±0.0170
Changeagriculturallandcover / 1.11 / 1,2692 / 0.29 / –
distributed errorandalogitlinkfunction. Wefollowed a backwardsselectionprocedure.Theleastsignificantvariable wasexcludedfromthemodelwhichwasthenrecalculateduntil onlyexplanatoryvariablesincreasingfitwithaP,0.05were retained.Environmentalvariableswerelog-transformedtofita normaldistribution(elevation)orrankedwhennotnormalised byusualtransformations(%urban,%agriculturalarea,changes incoversofbothlanduses).Aslandusewasclassifiedinthree exclusivecategories(i.e.%urban,agriculturalandforestareas), astrongcolinearityexistedbetweenthethreevariables.Forthis reason,onlytwoof thecategories(% urbanand% agricultural areas)wereincludedinfurtheranalyses,butstatisticallysignifi- cantrelationshipsofthe samesignforbothvariablesmustalso beinterpretedasanegativerelationship forthethirdone.The categoryexcludedfromtheanalyseswaschosenat randombut qualitativelyidenticalresultsemergedwhenexcludinganother ofthehabitatchangecategories. Changesinlandcoverwere calculatedasthedifferenceintheproportionofhabitatbetween
2004–07and1994–97.
Results
Thirty-seven fishspecieswerefoundintheAdour-Garonne basin,amongwhich16wereexotics(according toKeithand Allardi 2001; forcompletelistseeTableS1,availableasSup- plementaryMaterialtothispaper).Ourmodelsindicatethat elevationandland-usevariablescouldexplainlocalextinction andcolonisationpatternsinriverfishinthisbasin.
Fishextinction
Theextinctionmodelrevealedthatlocalextinctionwas signif- icantly higher among cold-tolerant species (F1,32¼4.08; P¼0.05;Table1),sothattheextinctionratewashigherat higherelevation(F1,932 ¼6.79;P¼0.009).Exoticspecieshada highertendencytolocalextinctioncompared withthenative ones(F1,32¼18.51;P¼0.0001;Table1).Theintensification ofagriculture(upto46%atsome ofthestudiedsites)fostered local extinction of fish species (F1,932 ¼7.53; P¼0.006; Table1).
Fishcolonisation
Thecolonisation modelrevealedthatcolonisation hasbeen greateratlowelevations(F1,2792¼76.95;P,0.0001;Table2). Colonisationappearedtobelowerforbothcold-andthermally- tolerantspecies,eithernativeorexotic(F1,34¼10.07;P¼0.003 andF1,34¼5.02;P¼0.02respectively).Finally,theexpansion ofurbanlandsbetween 1994–97and2004–07(upto17%) positively affected colonisation (F1,2792¼21.8; P,0.0001; Table2).
Discussion
IntheAdour-Garonne streamsystem,fishcolonisationwas higheratlowelevations.Accordingtothe‘bioticresistance hypothesis’,thehigherfishrichnessatdownstreamsites(Kopp etal. 2009)shouldpreventtheestablishmentofnon-native
speciesthroughcompetitiveexclusion(Leprieuretal.2008; Oldenetal.2010).However,becausecolonisationwashigherin theseareas,wecaninferthathigherspeciesrichness didnot limitthecapacityofexoticspeciestoestablish.Instead,the hypothesis of‘bioticacceptance’canbeapplicableinoursys- tem.Thishypothesispredictsthatthefactorsthatsupportgreater nativerichnessinaregion(e.g.abundantresourcesandhabitat heterogeneity) alsopromotetheestablishment ofnon-native species.Therefore,biologicalinteractions mayhaveplayeda negligibleroleintheobservedpatterns,contrarytoenviron- mentalfactors.
Cold-tolerant species,whichexperiencedthegreatest extinctionrates,aretypicallyconfinedtomountainstreamsin
theAdour-Garonnebasin.AccordingtoBalcombeetal.(2011),
thesecold-watertolerantspeciesareparticularlysensitiveto increasedstreamtemperature,especiallywhentheyarelocated attheirtemperaturelimits(Morrongielloetal.2011)because temperaturehasadirectphysiological effectonthesefish.As fisharepoikilotherms, watertemperaturestronglycontrols populationdynamicsthroughmetabolism,growthandfecundity (Lobon-Cerviaetal.1996),thus,formingakeyphysicochemi- calhabitatfilter(Poff1997)thatdetermines species’potential refugesitesalongtherivercontinuum (Murawski 1993). Mountainstreamsmayalsorepresentharshenvironmentswhich arephysicallystressful(higherrivercompetenceanderosive forcesgeneratedthroughthecombination ofslopewithother variablessuchaswaterdepthandcurrentvelocityandsnowmelt floods).Thesenaturalenvironmentalfactors,combinedwith lowconnectivityamongsuitable sitesincoldheadwater streams,mayberesponsibleforlowlevelsofcolonisation at highaltitudesites(GidoandBrown1999).
Atthesametime,theintensificationofagriculture(including pasturelandsinmountainousareas)mayhavefosteredlocal extinctionoffishspecies. Theagriculturallandscape ofsouth- westernFranceandwesternEuropeingeneral,hasradically changedoverthepastdecades(Meeusetal.1990)asaresultof land-use conversion,intensificationofproductionsystems and abandonment oftraditionalpractices.Theprincipalpressures causingbiodiversitylossinthecountrysidearehabitatfragmen- tation,degradation anddestructionduetoland-usechange. Importantsourcesofagriculture-derived pollutionincludethe inflowofnutrients,pesticidesandheavymetalsfromdiffuseand pointsources(Allan2004).Fragmentationimpactstheconnec- tivitybetweensuitablehabitats(Fahrig2003)andultimately affectscommunitydynamics(Denoe¨landFicetola2008).
Expansion ofurbanlandspositivelyaffectedcolonisation. Althoughourmodeldoesnotallowustodistinguish whether expansionofurbanlandsfavoursnativeorexoticfishcolonisa- tion,closescrutinyof thedatasetrevealedthatcolonizerswere mainlyexoticspeciessuch asPseudorasboraparva(topmouth gudgeon)andSilurusglanis(Europeancatfish).Arecentstudy intheUnitedStatesrevealedthatnon-nativespeciesdominate watershedssupportinghigh densitiesofdams, roads and urban andagriculturallandscapes, whereaswatersheds characterised byupstreamlandprotectionsupportfishcommunities witha strongcomplementofnativespecies(Pooletal. 2010).Accord- ingtoLeprieuretal.(2008),the‘humanactivityhypothesis’ (i.e.bydisturbingnaturallandscapesandincreasingthe impor- tationofnon-nativespecies,humanactivitiesfacilitategreater
levelsofestablishment)bestexplainsthepatternsofnon-native fishrichnessinriverbasins. Inourstudyarea,landscapes characterisedby increasingproportionsof urbanlanduse were successfully colonisedbyexoticspecies,thus,supporting the ideathatassociation withhumansincreasethechancesof successfuldispersalandestablishmentinnon-nativespecies.
Inconclusion, thecolonisation andextinctionpatterns highlightedinthisstudyonlypartiallymatchedourapriori
expectations.Overadecade,exoticfishweremoresusceptible tolocalextinctionthanthenativeones.The‘threetens’rule(one imported speciesin10appearsinthewild,onein10ofthese becomeestablishedandonein10ofestablishednon-indigenous
speciesbecomesapest)whichwasinitiallyformulated for exoticplants(Williamson andFitter1996)probablydoesnot applytoexoticfish,becausetheseanimalsareintentionally
introduced byhumansinpotentiallysuitablehabitats.There- fore,itislikelythatextinctioninexoticfish wasnotrelatedto unsuccessfulsettlement,butrathertoexternalfactorssuchas
watertemperatureor flowvariability(Costelloeetal.2010).
Regardlessoftheirbiogeographicstatus(eithernativeor exotic),cold-tolerantfishweremorepronetoextinctionthanthe cool-orthermallytolerantones.Thismaybeduetotherapidity of climatechangeswhicharepredictedtoexceedtheabilityof manyspeciestoadapttonewenvironmental conditions (Morrongielloetal.2011;Oldenetal.2011).Therefore,our resultssupportthehypothesesthat:(i)allfishcommunitiesare susceptible toinvasionregardlessofnativespeciesrichness (MoyleandLight1996; GidoandBrown1999);and(ii)water temperature,oritschanges,isamajordriveroffishextinctionin human-impactedlandscapes.Inlightoffutureclimatescenarios, ourstudyfurthersuggeststhat mountainrangesare theareasat greatestextinctionriskforpoikilotherms andourabilityto detectresponses ofnativeandexoticspeciestolandscape alterationsusingacombination ofsimpleenvironmental vari- ablesexemplifiesacost-effectivetechniqueforassessingareas atgreaterinvasionriskinlargestreamsystems.
Acknowledgements
WewishtothanktheFrenchOfficeNational del’EauetdesMilieux Aquatiques(ONEMA)andmorespecificallyDrN.Poulet,forprovidingus withthefishdata.Threeanonymous reviewersandDrA.Boultonmade usefulcommentsonanearlierversionof thispaper.
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