the ecological importance wildlife of predators · wildlife facts the ecological importance of...

Wild

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Fact

sThe Ecological Importance of PredatorsPredators have profound effects throughout their ecosystems. Dispersing rich nutrients and seeds from foraging, they influence the structure of ecosystems. And, by controlling the distribution, abundance, and diversity of their prey, they regulate lower species in the food chain, an effect known as trophic cascades. Regrettably, the U.S. Department of Agriculture’s Wildlife Services ignores the positive role that predators play in their surrounding habitat, as demonstrated through their reckless practice of killing large numbers of predators. Wildlife Services has a long history of persecuting predators, considered competitors for game animals such as fish and elk, and viewed as threats to livestock and agriculture. As a result, in many areas, large predators have been eliminated entirely and most of these species now occupy only a fraction of their historical distribution.

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NRDC: The Ecological Importance of Predators (PDF)

Tohelpdemonstratethecriticalrolethatpredatorsplayinprotectingandsustainingtheirsurroundingenvironments,severalpredatorsarehighlightedhere:

WolvesWolvesareoneofthemostcloselystudiedpredatorswhoseecologicaleffectshavebeenwidelydocumented.TheirexterminationandsubsequentreintroductionintoareasliketheRockyMountainshasrevealedtoresearchersthatinareaswherewolvesareabsent,uncheckedpopulationsdecreasetheabundanceofnativeplantspecies,andtheirovergrazingleadstothegeneraldegradationofforestsandriparianhabitat;1thisoverbrowsinghasalsobeenlinkedtoadecreaseinneo-tropicalmigrantsongbirds.2Thereintroductionofwolves,however,restoresthesehabitats,andadditionallyreducescoyotepopulations,therebyboostingpronghornantelopeandothersmallmammalpopulations.3Furthermore,byincreasingtheavailabilityofcarrionthroughouttheyear,wolvesincreasethefoodsourcesforraptorsandotherscavengers.4Throughtheirroleregulating

preyspecies,wolveshaveaprofoundeffectonthesurroundingplant,bird,andmammalcommunitiesthroughoutthegreaterecosystem.

Mountain LionsWhilemountainlionsarelargelysolitarycreatures,withanexpansivehomerange,theirroleastoppredatorshasasignificanteffectontheirecosystem.Muchlikewolves,mountainlionsaffectvegetationbyregulatingungulatespeciesthatbrowseinriparianhabitat.Forexample,thelossofmountainlionsinYosemiteNationalParkhasbeenlinkedwithadecreaseinblackoakrecruitment.5Similarly,inZionNationalPark,theabsenceofmountainlionshasledtoareductionincottonwoodtrees.Thesechangesintheplantcommunitieshaveinturnledtogreaterstreamerosionandadecreaseinthenumberofterrestrialandaquaticspeciesincludingwildflowers,butterflies,reptiles,andamphibians.Inadditiontoaffectingoverallspeciesdiversity,thedensityofnativefishishigherinareaswithmountainlionsthaninthosewithout.6

The Ecological Importance of Predators

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1 Ripple,W.J.andE.J.Larsen.2000.Historicaspenrecruitment,elkandwolvesinnorthernYellowstoneNationalPark,USA.BiologicalConservation95:361-370;Beschta,R.L.2003.Cottonwoods,elkandwolvesintheLamarValleyofYellowstoneNationalPark.EcologicalApplications13:1295-1309.

2 Berger,J.,P.B.Stacey,L.Bellis,M.P.Johnson.2001.Amammalianpredator-preyimbalance:Grizzlybearandwolfextinctionaffectavianneotropicalmigrants.EcologicalApplications11:947-960.

3 Berger,K.M.andM.M.Conner.2008.Recolonizingwolvesandmesopredatorsuppressionofcoyotes:impactsonpronghornpopulationdynamics.EcologicalApplications18:599-612

4 Wilmers,C.C.,R.L.Crabtree,D.W.Smith,K.M.Murphy,W.M.Getz.2003.TrophicFacilitationbyIntroducedTopPredators:GreyWolfSubsidiestoScavengersinYellowstoneNationalPark.JournalofAnimalEcology72:909-916.

5 Ripple,W.J.andR.L.Beschta.2008.Trophiccascadesinvolvingcougar,muledeer,andblackoaksinYosemiteNationalPark.BiologicalConservation141:1249-1246.6 Ripple,W.J.andR.L.Beschta.2006.Linkingacougardecline,trophiccascade,andcatastrophicregimeshiftinZionNationalPark.BiologicalConservation133:397-408.7 Mitchell,B.R.,M.M.Jaegar,R.H.Barrett.2004.Coyotedepredationmanagement:currentmethodsandresearchneeds.WildlifeDamageManagement,InternetCenter

forUSDANationalWildlifeResearchCenter-StaffPublications.http://digitalcommons.unl.edu/icwdmusdanwrc/345.8 Knowlton,F.F.,E.M.Gese,M.M.Jaeger.1999.CoyoteDepredationControl:AnInterfacebetweenBiologyandManagement.JournalofRangeManagement52:398-412.9 Henke,S.E.andF.C.Bryant.1999.EffectsofCoyoteRemovalontheFaunalCommunityinWesternTexas.JournalofWildlifeManagement63:1066-1081;CrooksK.R.,

Soulé,M.E.1999.Mesopredatorreleaseandavifaunalextinctionsinafragmentedsystem.Nature400:563–566.10Roemer,G.W.,M.E.GompperandB.VanValkenburgh.2009.Theecologicalroleofthemammalianmesocarnivore.BioScience59:165-173.11GittlemanJ.L.andM.E.Gompper.2005.Plightofpredators:Theimportanceofcarnivoresforunderstandingpatternsofbiodiversityandextinctionrisk.Pages370–388in

Barbosa,CastellanosI,eds.EcologyofPredator-PreyInteractions.Oxford(UnitedKingdom):OxfordUniversityPress.12Crait,J.R.andM.Ben-David.2007.EffectsofriverotteractivityonterrestrialplantsintrophicallyalteredYellowstoneLake.Ecology88:1040–1052.13Messick,J.P.1987.NorthAmericanbadger.In:M.Novak,J.A.Baker,M.E.ObbardandB.Mallock(eds).WildFurbearerManagementandConservationinNorthAmerica.

OntarioTrappersAssociationandMinistryofNaturalResources,Toronto,Ontario.Pp.586-597.14Eldridge,D.J.andW.G.Whitford.2009.Badger(Taxidea taxus)disturbancesincreasesoilheterogeneityinadegradedshrub-steppeecosystem.JournalofArid

Environments.73:66-73;Eldridge,D.J.2009.Badger(Taxidea taxus)moundsaffectsoilhydrologicalpropertiesinadegradedshrub-steppe.TheAmericanMidlandNaturalist161:350-358.

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CoyotesCoyotesareoftenvilifiedfortheirimpactonlivestockandmanyeffortshavebeenmadetocontroltheirnumbers.Extensiveresearchhasshown,however,thatindiscriminantkillingofcoyotesthroughtheuseofaerialgunning,traps,snares,andM-44sdoeslittle,ifanything,toreducecoyotepopulationsortheirpredationrates.Mostcoyotepredationiscausedbyalphapairsthatarelesslikelytobetargetedbyindiscriminatelethalcontrolmeasures.7Furthermore,exploitedcoyotepopulationshavebeenshowntohaveincreasedjuvenilereproductionandlargerlitters,whichsuggestthatcontrolmeasuresmayactuallyincreasecoyotepopulations.8Incaseswherecoyotenumbershavebeensuccessfullyreduced,othermesopredatorssuchasfoxes,badgersandraccoons,whichcoyotesoftencompetewithandsometimespreyon,haveincreasedsignificantly,therebyalteringthesurroundingecosystem.‘Mesopredatorrelease,’asthisphenomenoniscalled,hasbeenshowntodecreaseoverallspeciesdiversityanddensityofsmallerpreysuchasbirdandrodentpopulations.9Becausebirdsandrodentsareofteneitherseeddispersersorseedpredators,fluctuationsintheirabundancecanhaveacorrespondingeffectonthesurroundingplantcommunity.10Coyotes,therefore,playanimportantroleinmaintainingthebalanceofspeciesdiversitywithintheirecosystems.

River OttersAlthoughnottraditionallythoughtofastoppredators,riverotterspreyonawidevarietyofanimalsincludingfish,crayfish,frogs,insects,

andbirds.Theirpresence,therefore,regulatesthepopulationofthesespecieslowerinthefoodchain.11Additionally,ottersplayanimportantroleindistributingaquaticnutrientsinterrestrialecosystems.Forexample,thepresenceofotter‘latrines’hasbeenshowntoincreasethenitrogencontentandgrowthrateofsomeplantspecies.12Bycontributingtoprimaryproduction,riverottersincreasetheprevalenceandgrowthoftheplantcommunityinthesurroundingriparianhabitat.

BadgersBadgersarefossorialcarnivoresmeaningthattheypreyonanimalsthatmostlyliveundergroundsuchasgroundsquirrels,marmotsandprairiedogs,insects,lizards,andbirds.Badgersalsoliveprimarilyunderground,creatingextensiveburrowsystemsthatareusedasshelterbyotherwildlife.Whenforaging,badgersusetheirstrongsenseofsmelltolocatepreyandthenpenetratethesoilintargetedareas.13Thisdiggingprovidesaerationandnutrientmixing,andhelpsmaintainmoisturetothesoil,allofwhichaidinrecruitingnativeplantspecies.14

Preserving the Balance of EcosystemsPredatorsplayakeyroleinmaintainingthenaturalbalanceofecosystems.Giventhedelicateandinterdependentnatureofthefoodchain,andthelawsoftrophiccascadesandseeddistribution,predatorscannotbeeliminatedwithoutriskingthelargerecosystem.Killingoffpredatorsdisruptsthenaturalbalanceofwildlifeandtheirenvironment.Science-based,non-lethalapproachestopredatorcontrolshouldbeemphasized.