MesopredatorReleaseandPreyAbundance:Replyto
LitvaitisandVillafuerte
FRANCISOPALOMARES,MIGUELDELIBES,PABLOFERRERAS,ANDPILARGAONA
EstactónBiolOgicadeDoftana,CSIC,AvdaMafiaLutsas/n,41013,Sevilla,Spain,
LitvaitisandVillafuerte(this issue)disagree with inter pretationoftheresultsofourstudyinvestigating theef fectoftoppredator presenceonsmallgamepopulations (Palomares eta!.,[19951ConservationBiology9:295-
305).Wefoundthatthepresenceofatoppredator(Ibe
nanlynx)benefitedsmallgamepopulations(rabbits) bc cause thc former limits populations of some othcr smallcr predators(Egyptian mongooses) thatalsoprey uponthegamespecies.Weestimatedpredation ratesin twosituations,withandwithout lynx.Webasedoures timatesonfielddataofpredatordensitiesobtainedinan areawherelynxwere restrictedtocertain habitatsand mongooses as a ruLeused smaller and discontinuous patches ofsimilar vegetation surroundingthose areas uscdbylynx(Palomarcsctal.1996;citedasinpressin ourConservationBiologypaper).
LitvaitisandVillafticrtesupporttheircriticism ofour paper with three mainarguments.First,they contend wc did not providc evidence that lynxcan limitmon goose numbers. Theyare right that we did not prove thatmongooscpopulationsarelimitedbylynxbecause we would have needcd an experimentthat includcd lynxremoval.Such anexperimentisnot possible, be causeoftheprotectedstatusoflynx.However,wepro videdevidence thatLynx limitmongoose numbers,al though notinthcConservationBiology papcr, but in anothcrpapercitedinit(Palomaresetal.1996).Thispa per investigates the spatiaLreLationshipsbetweenLynx and smaller carnivores. The mainresults ofthe paper wcre that 1)lynxavoidthe human-disturbedareaout sidetheNationalPark;2)mongooses avoidthelessdis turbed area inside the NationalPark,wherethere are
lynx;3)mongoosesdonotseem togainanytrophic or
restingbenefit bylivingoutside thcprotectedarea;and
4)lynxkilLmongooscs. Formoredetails,plcasercferto thispaper. LitvaitisandVillafucrtearcrighttostatethat theeffectofintraguildpredation onthedemography of terrestrialvertebrateshasbeenthesubjectofLimitedex
.
perimental evaluation; however, plausible evidence of such effects hasincreased inthelastfewyears(Bailey
1992;Hersteinsson Macdonald1992;Lindströmetal.
1995;RaIlsWhite1995).
LitvaitisandVilLafuertealsobelievethatlandscapedif ferencesespecially the largeamount ofhuman-altered habitatsandotherhumaninfluenccs,providca more parsimoniousexplanationforthedifferencesinlynxand mongoosedensitiesthan doesintraguildpredation/me sopredatorrelease.Weagreethatlynxpresencemaybe limitedinareasusedbyhumans(infactthiswasoneof theexplanationsofferedinPalontaresetal.[1996]toex pLainthepattern)andthatsmallerpredatorsmaybeat anadvantageintheseareasasaresult.Theoreticalmod eLsofcoexistencebetweenspeciesstressthelastpoint
(forexample,NeeMay1992;Palmer1992).However, I.itvaitisandVilLafuerteforgotamajorpoint: theirargu
mentdoes notexpLainwhymongooses didnot usethe patches usedbylynx.Patches usedbylynxwereinside a NationalPark,but those mainlyused bymongooses wereoutside thepark.Bothareaswere contiguousand subjectedtohuman-inducedhabitatchanges.Therefore, thc clearest difference betweenpatches used bylynx and mongooseswere that those used by the former wercbigger andnotsubjecttohigh,directhumandis turbance.Furthermore,mongooses are habitat special istsand inthe studyarea selectedhabitats with dense undergrowthvegetationandhigherdensitiesofwarrens and rabbits (Palontares Delibes 1993). Lynxhabitat aLso hasthesecharacteristics.Hence,becauselynxkill mongooses, the most reasonable argumenttoexpLain whymongooseswcresorareintheareaused bylynx maybcbehavioralavoidanceofthisareabymongooses bccauseoftheriskofintraguildpredationbylynx.
LitvaitisandVillafuerteaLsosupportedtheirargument withOehler’s(1995)studythatapparentlyprovidesevi denccthatgcneralist predators<foxesandraccoons)in creasedasforest-dominated Landscapeswerefragmented byagricuLtureandhumansettlementsinanareaofthe UnitedStates.Inthisstudytoppredatorextinction(gray wolOcould not bethereasonfortheincreaseoffoxes
and raccoons because wolves were extirpated nearly two centuriesago. However, decline or extinction of other potential intraguild predatorsof foxes and rac coonsshouldalso havebeenconsideredbeforespecu latingon thesubject. Forexample,foxes andraccoons couldbekilledbycoyotes(RaIlsWhite 1995).
FinalLy,LitvaitisandVillafuertebelievehigherratesof
predationmayhavebeentheproximate causeofrabbit decline intheareas without lynx,buttheyagainargue thatthiswasaresultoflandscape change andnotlynx absence,which would favormongoosesinthese areas. Thepointofthisargumentisbasicallythesameastheir previous one—differences in predator densities be tween areasarethe ultimate cause oftheobservedre suits.Ofcourseitisthecause. However, theyoverlook that the overall predationrateon rabbits ineach area (lynx absenceand presenceinour case)isthesumof the predation fromlynxandmongooses. Becausemon gooseswereInextremelylowdensitiesintheareasused bylynx,overallpredation ratesintheseareaswerelower than inareas without lynx-Therefore, the question of whymongoosesdidnotusetheareaswithlynxarises.
Weagreewith LitvaitisandViiJafuertethattoppreda tom will become increasingly scarce and that some smallerpredators (butmainlythosethatareboth habitat andfeedinggeneralists) mayshow populationincreases solelyasaconsequenceoflandscape alterations. How ever, theoverallabundanceofother, smallerpredators thatarevictims-ofintraguildpredationbytoppredators willalsooronlyincrease asaconsequenceofrarilica tionofthelatter.Thiswillbeespeciallyobviousinhabi tatsusedbythetop predatorsandthatalsosupportthe highestgame populations.Fortunately, theeffectofin-
traguildpredation ontheenhancementofgamepopula tionsisshownnotonlybyourstudy(e.g.seeSovathet al.1995).Conservationistsandmanagersshould usethis information asasound argument to preserveand im prove populationsofendangeredtop predatorsonstiLl wellconservednaturalareas.
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