Predictingdiversityversuscommunitycompositionofaqu

PredictingdiversityversuscommunitycompositionofaquaticplantsattheriverscaleKristinaMakkaya,1,FrancesR.Picka,*,LynnGillespiebaOttawa-CarletonInstituteofBiology,UniversityofOttawa,30MarieCurie,OttawaK1N6N5,CanadabResearchDivision,CanadianMuseumofNature,P.O.Box3443,StationD,OttawaK1P6P4,CanadaReceived4October2006;receivedinrevisedform21December2007;accepted29December2007Availableonline6January2008AbstractWetestedtherelativeimportanceofphysicalversuschemicalfactorsinexplainingaquaticplantspeciesdiversityandcommunitycompositionwithinatemperatelowlandriver.Atotalof38macrophytespecieswereidentifiedat33sitesalongthe104kmlengthoftheRideauRiver,aNationalHeritageRiverofCanada.Speciesrichnessrangedfrom0to15speciespersite,andShannondiversityfrom0to2.98.MacrophytespeciesrichnessandShannondiversityweresignificantlyrelatedtothephysicalcharacteristicsofsites.ForShannondiversity,77%oftheincreasewasexplainedbyanincreaseinsedimentorganiccontentandadecreaseinwatervelocity.Forspeciesrichness,70%oftheincreasewasexplainedbythelatterfactorsinadditiontoanincreaseinthelittoralzone(0–2mdepthcontour)widthandplanktonicchlorophyllconcentrations.RiverwaterchemistrydidnotexplainanyobservedvariationineitherShannondiversityorspeciesrichnessinthismoderatelyenrichedsystem.Incontrasttospeciesrichness,thephysicalandchemicalvariablesmeasuredfailedtoexplainvariationincommunitycomposition.Clusteranalysisdidnotrevealanygroupingofspeciesintodistinctcommunities.Canonicalcorrelationanalysisshowedthatenvironmentalvariableshadminimaleffectonthedistributionofmostspecies,withonlyfloating-leavedspeciesrespondingtowatervelocity.Weconcludethatphysicalfactorscanpredictspeciesdiversityatthewithinriverscalebutnotthespeciescompositionatagivensite,underlyingtheneedtopreservethegeomorphologicaldiversityofriverstomaintainplantdiversity.#2008ElsevierB.V.Allrightsreserved.Keywords:Aquaticplantcommunity;Shannondiversity;Speciesrichness;Lowlandriver;Stochasticprocess1.IntroductionEcologistshavelongbeeninterestedinwhatcontrolsplantdiversity.Anumberoftheorieshavebeenputforwardtoexplainwhatcontrolsthediversitybothataglobalandlocalscale.Onalocalscale,Huston(1979)proposedatwo-dimensional‘‘dynamicequilibrium’’modelthatpredictsspeciesrichnesswillbehighestatanintermediatepointontheproductivity–stressgradientandatintermediatelevelsofdisturbance.Thismodelpostulatesthatextremestressanddisturbanceeliminateallbutthemosttolerantspecies,whereasminimalstressandhighproductivityresultsinspeciesbeingeliminatedthroughcompetitiveexclusion.Theeffectsofdisturbanceoffsettheeffectsofproductivity.Whilethismodelwasdevelopedbasedonterrestrialsystems,itmayalsoapplytoaquaticsystemsaswell(Murphy,2002).Aquaticplant(macrophyte)speciesrichnesshasbeenfoundtoberelatedtofactorscorrelatedwithproductivityandstresssuchaslightattenuation(Willbyetal.,2001),standingcrop(Dodsonetal.,2000),nutrientconcentrationsandtrophicstatus(Rørslett,1991;Jeppesenetal.,2000)aswellaswithdisturbanceregimesaffectingbiomassremovalsuchaswatervelocity(Nilsson,1987),boattraffic(Willbyetal.,2001),waterlevelfluctuations(Rørslett,1991),andfloodfrequency(Barrat-SegretainandAmoros,1996;RiisandBiggs,2003),althoughtheserelationshipsarenotconsistentlyunimodalinshape.Speciesrichnesshasalsobeenfoundtoincreasewithhabitatareaacrosslakes(e.g.Dodsonetal.,2000;DahlgrenandEhrle´n,2005).Plantcommunitycompositionhasalsolongbeenofinteresttoecologists:ecosystemsandbiomesaredescribedintermsofdominantplantcommunities.Mostcommunitycompositionmodelshavebeendevelopedforanimalspecies(e.g.Diamond,1975)andlaterextendedtoterrestrialandwetlandplants.There(2008)338–346*Correspondingauthor.Tel.:[phone]x6364;fax:[phone].E-mailaddress:[e-mail](F.R.Pick).1Presentaddress:EnvironmentCanada,351JosephBlvd.,Gatineau,QuebecK1A0H3,Canada.0304-3770/$–seefrontmatter#2008ElsevierB.V.Allrightsreserved.doi:10.1016/j.aquabot.2007.12.011areagrowingnumberofstudiespertainingtoaquaticplantsinlakes,althoughaconsensushasyettoemergeonwhichvariablesaremostimportantinaffectingcomposition.Somestudiesonlakesshowedtrophicstateandnutrientconcentrationtohaveastrongeffectonspeciescomposition(Srivastaetal.,1995;VestergaardandSand-Jensen,2000)whileothersshowednorelationship(Pip,1979;JacksonandCharles,1988).AsimilardebatesurroundspH(Pip,1979;JacksonandCharles,1988;Srivastaetal.,1995).Otherinfluencesincludeconductivity(ToivonenandHuttunen,1995)andalkalinity(Srivastaetal.,1995;VestergaardandSand-Jensen,2000).Instreamsandrivers,communitycompositionwasaffectedbyalkalinity(Riisetal.,2000),conductivity,andnutrientconcentrations(Murphyetal.,2003)asinlakes,butotherfactorsincludethedownstreamdistancefromsourceandspatialconnectivity(DemarsandHarper,2005),streamsize(Riisetal.,2000),velocity(RiisandBiggs,2003),calciumandmagnesiumionconcentrations(Alietal.,1995;Murphyetal.,2003),substratecharacteristics(FrenchandChambers,1996),andfloodfrequency(Barrat-SegretainandAmoros,1996;RiisandBiggs,2003).Mostecologicalstudiesofaq