Effect of rodents on acorn dispersal and survival of the Liaodong oak.docx

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