Seed dispersal and post-dispersal seed fate of four tree species in a neotropical cloud forest PDF
Preview Seed dispersal and post-dispersal seed fate of four tree species in a neotropical cloud forest
SEEDDISPERSALANDPOST-DISPERSALSEEDFATEOFFOURTREESPECIES INANEOTROPICALCLOUDFOREST By DANIELG.WENNY ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENTOFTHE REQUIREMENTSFORTHEDEGREEOFDOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1998 Toraygrandfather,DonaldG.Baker, wholedmeonhikesinthewoodsofNewHampshire, andtomykids,MaliaandJack, withwhomIcanbarelykeepup. ACKNOWLEDGMENTS FirstandforemostIthankmyadvisor,DougLevey,forhisadvice, encouragement,patience,andhelpwithallaspectsofthisproject Hisinputwas instrumentalinitssuccess,andIwillalwaysbegratefulforhishelp. Hefoundafew seedseventhoughthesunbitterneludedhim. IfIdiscoveranewspecies,Iwillnameit afterhiminappreciation. Ialsothankmycommittee,KarenBjomdal,ColinChapman, JackPutz,andBuzzHolling(alsoFrankBonaccorsoandPeteFeinsingeratanearlier stage)forhelpdevelopingtheresearchproposal,clarifyingthedirectionofthedissertation, andeditingtheresultingmanuscripts. Ifeelgratefultheypointedmeintherightdirection andletmetakeafewsteps. Othermembersofthefacultywerehelpfulwithadviceon experimentaldesign,statisticalanalysis,seminarpresentations,andgeneralrealitychecks: RichKiltie,DaveSteadman,MikeMiyamoto,FrankNordlie,ColletteSt.Mary,Brian McNab,LarryMcEdward,JohnAnderson,andCraigOsenberg. NatWheelwright, GeorgePowell,CarlosGuindon,NaliniNadkarni,JackLongino,andGregMurrayalso providedencouragementandadvice. Thisresearchwouldnothavebeenpossiblewithoutvaluablefieldassistancefrom VictorPer6z,RicardoGuindon,JasonBennett,andWendyGibbons. Ithankthem sincerelyfortheirhardworkunderlessthanidealconditionsandsometimeswithvague instructions. Manyotherpeoplehelpedwiththeproject,eitherdirectlyorindirectly. The Monteverdecommunityisauniqueandwonderfulplace,andthetwoandahalfyearsI spenttherewereamongthehighlightsofmylife. IespeciallythanktheGuindon, Campbell,andRockwellfamiliesformakingme(andWendy)feelsowelcomethere. SpecialthanksgotoBenito,Carlos,andTomasGuindonforsharingtheirknowledgeof iii thearea,andtoGregMurray,MauricioGarcia,RodrigoSolano,BillHaber,Willow Zuchowski,FrankJoyce,AlanPounds,andAlanandKarenMastersforpatiently answeringmyendlessquestions. Finally,thanksgotoJudyPoeandBrucePackfor rentingustheirbeautifuloctagonalhouseonthecliffedge,andtoLeynRockwellfor emergencyrepairs. Crucialfinancialsupportatthebeginningofthisprojectwasreceivedfromthe OrganizationforTropicalStudies:apilotstudygrant(PewCharitableTrust),anda TropicalFellowship(JesseSmithNoyesFoundation). ThanksgotoLucindaMcDadeand ShaunBennettforfacilitatingOTSsupport. OtherearlyfundingfromSigmaXiGrants-in- AidofResearchandAmericanMuseumofNaturalHistory(FrankM.ChapmanMemorial Fund)isgratefullyacknowledged. Thebulkofthefieldworkwassupportedbya DissertationImprovementGrantfromtheNationalScienceFoundation(DEB93-21553). IndirectfinancialsupportwasalsocontributedbytheGibbonsandWennyfamilies. Iam alsogratefulforlogisticsupportfromtheOrganizationforTropicalStudies,Monteverde Institute(e-mailaccess),andtheTropicalScienceCenter(labspace). Mostofall,Igreatly appreciatethemanyyearsofsupportfromtheUFDepartmentofZoology. Ithankmyextendedfamilyforencouragement,visitstoCostaRicaduringthethree yearsoffieldwork,andfornotaskingtoomanytimeswhatexactlyIwasdoing. Most importantwassupportfrommywife,WendyGibbons,whohelpedwithfieldwork,edited draftsofproposalsandpapers,andwasgenerallynicewhenIneededafriend. Thanksgo toeveryonewhospentadayortwointhefieldinexchangeforatour. Iapologizetomy mother,whohelpedcarryequipment3milestothestudysiteaftermypromiseofaquetzal, whichIwasunabletofindthatdayoronasecondvisitayearlater. Finally,Iwouldliketonotemyappreciationofthezoology,botany,andwildlife graduatestudentswhomademytenureheremoreenjoyable. Ithankthemfordiscussions, editingmanuscripts,statisticaladvice,sufferingthroughpracticeseminars,schemingup sideprojects,andsayingtheylikedtheOzricTentaclestapesImadeforthem:Seth IV Bigelow,ScotDuncan,RonEdwards,SusanMoegenburg,JayO'Sullivan,GregPryor, RafaelSamudio,LennySantesteban,MarkSpritzer,MarkusTellkamp,and... Special thanksgotoSusanMoegenburgforbeingtheideallycheerfulofficemateandtoJason Evertforbeingtheideallyinvisibleofficemate. TABLEOFCONTENTS ACKNOWLEDGMENTS iii ABSTRACT viii CHAPTERS 1 GENERALINTRODUCTION 1 2 SEEDDISPERSAL,SEEDPREDATION,ANDSEEDLING RECRUITMENTOFOCOTEAENDRESIANA(LAURACEAE) Introduction 6 StudySite 9 StudySpecies 11 Methods 15 Results 23 Discussion 47 Conclusion 64 3 SEEDDISPERSALOFAHIGH-QUALITYFRUITBYSPECIALIZED FRUGrVORES:HIGH-QUALITYDISPERSAL? Introduction 66 StudySite 70 StudySpecies 71 Methods 73 Results 76 Discussion 87 4TWO-STAGEDISPERSALOFTWOSPECIESOFGUAREA(MELIACEAE) Introduction 93 StudySite 95 StudySpecies 95 Methods 96 Results 99 Discussion 107 VI 5ADVANTAGESOFSEEDDISPERSAL:ARE-EVALUATION OFDIRECTEDDISPERSAL Introduction 110 AdvantagesofDispersal 112 TheDiffuseMutualismParadigm 118 ClassicExamplesofDirectedDispersal 120 OtherExamplesofPossibleDirectedDispersal 124 Conclusion:GoingtheDistance,andBeyond 134 APPENDK OCOTEAENDRESIANASITELOCATIONS 138 REFERENCES 152 BIOGRAPHICALSKETCH 178 vii AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy SEEDDISPERSALANDPOST-DISPERSALSEEDFATEOFFOURTREESPECIES INANEOTROPICALCLOUDFOREST By DanielG.Wenny May,1998 Chairman:DouglasJ.Levey MajorDepartment:Zoology Seeddispersalbyanimalsisthoughttobeimportantintropicalforestsbecause mosttreesintheseforestsproducefleshyorarillatefruitsadaptedforconsumptionbybirds andmammals. Verylittleisknownaboutwhathappenstoseedsafterdispersal,yetpost- dispersalfateisimportantindeterminingpatternsofplantrecruitment, Istudieddispersal patternsandpost-dispersalseedfatesoffourtreespeciesinMonteverde,CostaRica. The fourspeciesstudiedincludedtwospeciesofLauraceae(Ocoteaendresiana and Beilschmiediapendula)andtwoMeliaceae{GuareaglabraandG.kunihiana). Idetermined locationsofdispersedseedsbyfollowingbirdsuntiltheyregurgitatedordefecatedseeds andbysystematicallysearchingthestudysiteforrecentlydispersedseeds. Foreachofthe fourspecies,approximately75%oftheseedsdispersedbybirdsweredepositedwithin25 moftheparenttrees. Ocoteaendresianashowedabimodalpatterninwhichbellbirds (Procniastricarunculata)dispersedmanyseedsundersongperchesandthusproduceda secondpeakinseedraininadditiontothepeaknearparenttrees. Markedseedswereused todetermineifpost-dispersalremovalresultedinseedpredationorsecondarydispersal. RemovalrateswerehighforOcotea(99%removed)andGuarea(85-90%),andlowfor vm Beilschmiedia(17%). SecondarydispersalwasobservedforbothGuareaspeciesbutnot fortheLauraceaespecies. SecondarydispersalofGuarearesultedinaslightincreasein overalldispersaldistance,andashiftinmicrohabitat. ThespatialpatternofseedlingrecruitmentwasbimodalforOcotea,reflectingthe initialpatternofdispersal. Beibchmiediarecruitmentwasnotbimodalandwashighestin thezoneapproximately10mfromtheparentalcrowns. Guarearecruitmentwasnot studiedinthefield,butingrowinghouseexperiments,buriedG.glabraseedsgerminated andestablishedseedlingsatahigherratethanseedsonthesoilsurface,suggestinga benefittosecondarydispersal. Theresultsofthisstudyindicatethatdeterminingdispersal patternandpost-dispersalfateareimportanttoassesstheinfluenceofseeddisperserson patternsofseedlingrecruitment IX CHAPTER GENERALINTROD1UCTION "Withplantsthereisavastdestructionofseeds. Seedlings,also,aredestroyedinvast numbersbyvariousenemies."CharlesDarwin(1859:78). "Plantsarenotcharitablebeings."WilliamJ.Beal(1898:84). Seeddispersalbyanimalsiswidespreadandrecognizedasimportantbyvirtueof thelargenumberofplantspecieswithfruitspresumablyadaptedforanimalconsumption. Intropicalforestsinparticular,70-90%ofthetreesandshrubsarethoughttobedispersed byanimals(Stiles1985,Howe1986,Willsonetal.1989,Jordano1992). Thisseed dispersalinteractionischaracterizedasadiffusemutualismbecausemostplantshave multipledispersalagentsandmostseeddispersinganimalsdisperseseveraltomany differentplantspecies. Thus,fruit-frugivorecoevolutiongenerallyoccursamonggroups ofplantsandgroupsofdispersersratherthanatthespecies-specificlevelseeninmany pollinationsystems(WheelwrightandOrians1982). Theadvantageofthismutualismto animalsisanutritivereward,whereastheadvantagestoplantsareescapefromdensity- dependentmortalityneartheparentplantandarrivalinsuitablesitesforestablishment Arrivalinsuitablelocationscanbeeitherarandomprocess,inwhichwidespread disseminationofseedswouldincreasethechanceofcolonizingagoodsite(colonization hypothesis),oranonrandomprocessinwhichseedsaredirectedtosuitablesitesby attractingcertaindispersalagents(directeddispersalhypothesis). Escapeandcolonization arethoughttobethemainadvantagesofseeddispersalformostplants(Howe1986) althoughfewstudieshaveexaminedthesehypothesesindetail.
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