Effect of rodents on acorn dispersal and survival of the Liaodong oak.docx
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Effect of rodents on acorn dispersal and survival of the Liaodong oak.docx
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EffectofrodentsonacorndispersalandsurvivaloftheLiaodongoak
EffectofrodentsonacorndispersalandsurvivaloftheLiaodongoak(QuercusliaotungensisKoidz.)
Hong-JunLiandZhi-BinZhang
InstituteofZoology,ChineseAcademyofSciences,Beijing100080,PRChina
Received6November2001;
revised26March2002;
accepted13May2002. ;
Availableonline8August2002.
Abstract
Weusedanewmethodoflabelingseedswithsmallpiecesofcodedtin-tagstoinvestigatetheeffectofrodentontheseedfateofLiaodongoak(Quercusliaotungensis)inamountainousarea(40°00′N,115°30′E)ofBeijing,China.Inthefallof1999and2000,atotalof1994and660acornswerereleasedandthenseedlosswaschecked.Bothsidesofthe50 mwidetransectwereextensivelycheckedtolocatethetaggedseedsortheirfragments.TheresultsindicatedthatApodemusspeciosus,RattusconfucianusandA.agrariuswerepotentialLiaodongoakacornpredators.Nearlyallacornswereconsumedbysmallrodentswithin10daysafteracornplacement,demonstratingthatseedpredationwasveryheavyandthatrodentpredationcontributestothepoorseedregenerationoftheoak.Thedispersaldistancesofmostseedswerewithin20 m.Thedispersaldistanceoftheburiedseedswasthelongestanditwasinfavorofseedsurvivalandseedlingrecruitment.Rodentspreferredtoeattaggedseedsunderdenseshrub.Thisismostlyrelatedtopredationriskindifferentmicro-environments.Rodentstendedtoburythetaggedseedsunderdenseshrub.Thisburialplaceofrodentdoesnotfavortheseedlingrecruitmentoftheoak.Therodentspreferredtomoveseedstothehorizontalanddowndirectionsofaslopeandthistendencywouldsaveenergyforrodents.Theseedingregenerationrateoftaggedacornswereverylowin2years.RodentpredationisthecausativefactoroflowregenerationofLiaodongoakinthestudyregion.
AuthorKeywords:
Liaodongoak(Quercusliaotungensis);Rodent;Seeddispersal;Seedsurvival;Regeneration
ArticleOutline
1.Introduction
2.Methods
2.1.Studysite
2.2.Keyrodentspeciesaffectingseedsdisappearance
2.3.Seed-marking-releasingexperiment
2.4.Statistics
3.Results
3.1.Keyrodentspeciesaffectingthedisappearanceofoakacorns
3.2.Thefateofacornsinsitu
3.3.Thefateofacornsdispersed
3.4.Dispersaldistance
3.5.Micro-environmentofthedispersedacornsortheirpreservedfragments
3.6.Dispersalslope-directions
3.7.Cachesize
3.8.Seedsurvival
4.Discussion
4.1.Speciesaffectingacorndisappearanceandrecruitment
4.2.Seedpredation
4.3.Dispersal
4.4.Survivalofthetaggedseeds
Acknowledgements
References
1.Introduction
Thepropagulesofplantsareexposedtohighriskofattackbynaturalpredatorssuchasinsects,vertebratesandfungi(Janzen,1970).Seedmortalityduetopredationbyanimalsmayaffectplantfitness,populationstructureanddynamics,communitystructureandmaintenanceofspeciesdiversity(Janzen;Grubb;Clark;Schupp;SchuppandWillson).Inforestecosystems,rodentsarerecognizedasanimportantfactoraffectingacornfate(ShawandShaw;KanazawaandNishikata,1976;Kikuzawa,1988;Herrera,1995).Inmostsituations,alargeproportionofdispersedacornsbyrodentsareconsumed,henceveryfewacornsareabletobecomeseedlings(Sork;MiyakiandHerrera).However,rodentscanalsodispersesomeacornsandburyafewofthem.Seeddispersalisrecognizedaskeyphaseaffectingplantregeneration,speciessurvivalanddistribution(HoweandSmallwood,1982).Seeddispersalaffectsfitnessofparentandoffspringplantsthroughitseffectsonseeddensity,thedispersaldistancefromtheparenttree,andthehabitatwhereseedsarrive.Differencesindispersalmayinfluenceearlyseedandseedlingsurvivalbyaffectingincidenceofpredationorattackbypathogens,thehabitattowhichseedsaredispersed,aswellasthetypesofplantswithwhichthedevelopingplantwillcompete(Schupp;Schupp;JordanoandWillson).
Althoughseeddispersalbyanimalsisoneofthemostimportantmechanismsintheecologyandevolutionofmutualisticsystems(Bronstein,1994),westillhaveverylimitedknowledgeaboutseeddispersalsystems.Oneofthereasonswhyresearchprogressisslowisthedifficultyintrackingthefateofalltheseedsthataredispersed(Sork,1984).Adisadvantageofpresenttechniquesisthattaggedseedsarenotdistinguishablefromeachother.ZhangandWang(2001a)developedanewmethodoflabelingseedswithsmallpiecesoftin-tags.Thetin-taggedseedsarecodedandthenidentifiedeasilyfromeachother.Thismethodmakesitpossibletodeterminethedistributionofindividualseedsdispersedbyanimalsandtheultimatefatesofthoseseeds.
Quercusliaotungensisisoneofthecommonclimaxtreespeciesinwarmtemperatebroad-leaveddeciduousforestsinnorthernChinaandQ.liaotungensisforestsaretypicalvegetationinthemountainsofBeijing(Chen,1992).Becauseofextensivehumandisturbances,primaryLiaodongoakforestsnolongexistandonlysmallpatchesofsecondaryLiaodongoakforestsorshrubsarescatteredamongshrubsorgrasses(Chen,1997).TheacornofQ.liaotungensisisovoid,0.9–1.8 cmwide,1.4–2.3 cmlongand0.6–3.4 ginmass(WangandMa,2001).Theoaks(Quercussp.)canbegroupedintotwosubgenerawhichareWhiteoak(WO)(Lepidobalanus)andRedoak(RO)(Erythrobalanus).Liaodongoak(Q.liaotungensis)belongstotheWO.SinceLiaodongoakacornsarenutritious,theyareexcellentfoodresourcesforsmallmammalsandbirds,especiallyforsmallrodents(Wangetal.,1999).ThenaturalregenerationofQuercusislackinginthefieldinmanywoodlands(ChoandBoerner,1991).Theregenerationmainlydependsonthesproutandthegrowthofthecoppicesisbad.Inthestudyregion,thenaturalseedingregenerationrateofLiaodongoakislessthan0.1%(Zhang,unpublished).ItisveryhardtoseetheseedlingsofLiaodongoakevenaftertheacornmast-year.PreviousstudiesshowedthatrodentseatanddispersealargepartofQuercusacornsintemperateforests(Shaw;KikuzawaandIida).SoitisnecessarytounderstandeffectofrodentsonacorndispersalandsurvivaloftheLiaodongoakforimprovingitsnaturalregeneration.
ThepurposeofthisstudywastoinvestigatetheeffectofrodentsonthefateofLiaodongoakacorns.Specially,weaddressedthefollowingsubjects:
(1)acornsfateinsitu;
(2)dispersedacornsfate;(3)dispersaldistanceandpatternsofthetaggedseeds;(4)micro-environmentswhereseedsaredispersedorburied;(5)survivalofthetaggedseeds.
2.Methods
2.1.Studysite
TheexperimentwascarriedoutinamountainousareanearLiyuanlingVillage,MentougouDistrict,Beijing,China.Thestudysiteislocatedatalatitudeandlongitudeof40°00′N,115°30′E,about120 kmnorthwestofBeijingCity.ThisareabelongstoDonglingMountainRegion,withawarmtemperatecontinentalmonsoonclimate.Inthestudyarea,theecosystemhasbeengreatlydestroyedduetoextensivecuttingandgoatgrazingforalmostacentury.Oak(Q.Liaotungensis),wildwalnut(Juglansmandshurica),wildapricot(Prunusarmeniaca),VitexnegundoandPrunusdavidianaarecommonshrubs.Undershrublands,Elymusexcelsus,Poaspp.,Elsholtziastauntoniarecommongrasses.Larch(Larixprincipis-rupprechtii)andChinapine(Pinustabulaeformis)havebeenplantedinsmallareasbyalocalforestationfarm.Inthestudyregion,theproductionofLiaodongoakacornwasverylowin1999andnearlynosoundandmatureacornswerefound.Incontrast,theabundanceofacornreacheditsmast-yearin2000.Therodentdensitiesin2yearsdidnotshowobviousdifference(trapsuccess3.125%in1999;2.95%in2000).
2.2.Keyrodentspeciesaffectingseedsdisappearance
On29October2000,woodensnarekill-trapswerebaitedwithfreshandripeLiaodongoakacornstodeterminethesmallrodentsthatwerepotentiallyremovingacorns.Inordertominimizethetrappingeffectontherodentpopulationintheplotwhereacornswerereleased,thetrappingplotwasabout400 mawayfromtheseed-releasingtransectbutinthesameslope.Fourtransectswereselected.Twenty-fivetrapstationswithanintervalof5 mweresetalongeachofthefourtransectsfortwoconsecutivenights.TocomparethefoodpreferenceofdifferentanimalsforLiaodongoakacorns,twotrapsweresetsidebysideateachtrapstationatthesametime.OnetrapbaitedwithaLiaodongoakacorn,andanotherbaitedwithafreshpeanut(aroutinebait).Trapswerecheckedeverydayandthecapturedrodentswererecorded.Werepeatedthisexperimenton5November2000.
2.3.Seed-marking-releasingexperiment
On20–30September1999and2000,intactandfreshLiaodongoakacornswerecollectedforseed-marking-releasingexperiment.Topreventdestructionofthekernelinside,tinyholeswerepiercedwithaneedleinthegapbetweentheseedcoatandthekernelatthewidersideoftheacorns.Small,lighttin-tags,4 cmlongand1 cmwidewereconnectedwithathinsteelwire3 cmlong.Thetagswerecodedbyusingasharpmetal-pen.Thetin-taggedseedsareeasytofindafterbeingdispersedbyrodents.Ifseedsareburiedinthesoilbyrodents,thetin-tagsareleftonthesurfaceoftheground.Priorpreliminarystudiesshowedthemetal-taggedseedswouldberemovedasreadilyasunmarkedseeds.Thustheexperimentaltreatmentyieldsrealisticresultsonthemovementpatternofoakacorns.
Inthestudyarea,a220 mtransectwasselectedforseed-releasingand22plotswerelocated10 mapartalongthistransect.Ametalsignwashungneareachplottoidentifytheplots.Toidentifytherealisticresultsofseedsloss,weselectedtheplotswhereveryfewseedsof
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