Edge effects on the pollination of tropical cloud forest plants

102 Pages·1993·3.8 MB·English

by  Murcia, Carolina

EDGEEFFECTSONTHEPOLLINATIONOFTROPICAL
CLOUDFORESTPLANTS
By
CAROLINAMURCIA
OAFDTIHSESEmR^ITVAETRISOINTPYROEFSEFNLTOERDIDTAOITNHpElGRSAXDUFATUELSfCKHO^O^T
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1993
1
ACKNOWLEDGMENTS
Iwouldliketothankthemembersofmydoctoralcommittee,Drs.
PeterFeinsinger,FrankG.Nordlie,DouglasJ.Levey,RichardA.Kiltie,
FrancisE.PutzandKentH.Redford,fortheiradviceduringallphasesof
theproject.IwouldHketothankespeciallyPeterFeinsingerforhissupport
andencouragementthroughallmygraduatestudentyears.Iwouldalso
liketoextendmyappreciationtothefollowingpersons:NataliaArangofor
herassistanceandcompanionshipduringthefieldworkphase;Ronald
EdwardsforgraciouslywalkingmethroughthenuancesofIBM
computingfortheCorrespondenceAnalysis,G.Kattan,R.Edwardsand
Dr.CarmineLancianiforcommentingonportionsofearUerdraftsofthis
dissertation;Mr.LuisFelipeCarvajal,Mr.EduardoCalderonandMr.
AntonioGonzalezCaicedoforpermissiontoworkontheirproperties;Mr.
LuisMiguelConstantinoforidentifyingsomebutterflies;Mr.German
Parrafortheidentificationofbees;Mr.StingerGualaandDr.WalterJudd
fortheirhelpindeterminatingtheplantmaterial.Manyoftheideas
presentedherebenefittedgreatlyfromdiscussionswithfellowstudentsin
theDepartmentofZoology,toallofthemIthank.
FinancialsupportforthisprojectwasprovidedbytheDepartmentof
Zoology,UniversityofFlorida,theUnderbillFoundation,andthe
FundacionparalaPromoci6ndelaInvestigacidnylaTecnologia,Bancode
laRepublica,Bogot^i,Colombia.
i
Finallyandmostimportantly,Iwouldliketoacknowledgethesupport
andencouragementofmyhusband,GustavoKattan,whoputupwithmy
upsanddownswithloveandasmile.
l•U•
TABLEOFCONTENTS
page
ACKNOWLEDGEMENTS ii
ABSTRACT vi
CHAPTERS
1 INTRODUCTION 1
2 BACKGROUND 5
LandscapeEcologyandEdges 5
HistoricalPerspectivesonEdges 7
WhyIsExposuretotheEdgeDeletereous
fortheFragments? 10
PhysicalEdgeEffects 10
DirectBiologicalEdgeEffects 12
IndirectBiologicalEdgeEffects 14
EdgesandPlant-AnimalInteractions 15
3 EDGEEFFECTSONTHEPOLLINATIONOFTROPICALCLOUD
FORESTPLANTS
Introduction 18
Methods 23
StudySite 23
SamplingScheme 26
ThePlants 31
StatisticalAnalysesandVariables 34
EffectofSampleSizeonStandardDeviation 36
TemporalVariationofEdgeEffect 36
Experiments 37
EdgeDescription 38
Results 40
Pollination 40
EffectofSampleSizeonStandardDeviation 55
TemporalVariationofEdgeEffect 55
Experiments 58
EdgeDescription 58
iv
Discussion 66
StudyDesign 66
ThePlant-PollinatorInteractionSystem 68
EdgeEffectonPhysicalConditions 71
TimeSinceEdgeCreation 72
Conclusions 74
4 TOWARDSAUNIFIEDTHEORYOFEDGES
Contrast asaDeterminantofEdgeeffects 75
FutureDirections 82
LITERATURECITED 84
BIOGRAPHICALSKETCH 93
V
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
EDGEEFFECTSONTHEPOLLINATIONOFTROPICAL
CLOUDFORESTPLANTS
By
CarolinaMurcia
May1993
Chairperson:Dr.FrankNordlie
MajorDepartment:Zoology
Exposuretoedgeisoneconsequenceofhabitatfragmentationthat
canresultindetrimentaleffectsonthefaunaandfloraoffragmented
habitats.Inthisstudy,edgeisdefinedasasharptransitionbetweennatural
andanthropogenichabitats,suchasbetweenforestandpastures.Iassessed
theeffectofproximitytotheedgeonthepolUnationlevelsof13cloudforest
plantspeciesinColombia.Icollectedthestylesofplantslocatedinthree
zonesofeachofthree forestfi-agments:edge(0-10m),transitionzone(10-50
m),andinterior(50-200m).
PolUnationlevels,measuredasthemediannumberofpollentubesthat
reachedthebaseofthestyles,werenotconsistentlyaffectedintheir
pollinationbytheproximitytotheedge.Intra-individualcoefficientof
variation,i.e.vEiriationinpollinationlevelsamongflowersinindidividuals
wasalsonotaffectedbytheproximitytotheedge.Fewplantspecies were
significantlyaffectedbytheedge,andthosethatwereaffecteddifferedinthe
directionoftheedgeeffects.Tomeasuretheedgeeffectonthepotentialfor
vi
limitationofseedsetanditspenetrationonsuccessivelevelsoftheplant-
pollinatorinteraction,Imeasuredtheproportionofflowersineachindividual
withanimiberofpollentubeseqvialtoorlargerthanhalfthenumberof
ovules.Inoneoftwocaseswheretherewasanedgeeffectonpollination
levels,thepotentialforseedsetwasalsoaffected.Edgeeffects,whenpresent,
wereinconsistentbetweenfloweringseasons.
Fieldexperimentswithtwointroducedplantspeciesshowedno
differencesinpollinationlevelsbetweentheplantsplacedattheedgeandin
theforestinterior.
Thereareseveral possibleexplanationsfortheseresults.First,above-
groimdenvironmentalconditionsdonotdifferbetweentheedgeandthe
interior,thusmakingitimlikelythatthepolHnatorsareaffectedbytheedge.
m
Second,below-groimdconditionsareaffectedonlyforthefirst10 intothe
forest,andthisaffectsthedensitiesofthefocalplantsinonlyoneofthe
fragments.Finally,plant-pollinatorinteractionscanberobusttosome
pertiu'bationsbecausegenerally,theseinteractionshavelittlespecies-
specificity.
vii
CHAPTERONE
INTRODUCTION
Whenanatiiralecosystemismodifiedbyhumanstheresultisoftena
mosaicofisolatedremnantsofnativevegetationinterspersedwithlarge
areasofmodifiedhabitat.Thisprocessofhabitatfi-agmentationhas
deleteriousconsequencesformostofthenativebiota.Firstandmost
obviouslythetotsdareaoftheoriginalvegetationisreduced.Thisreduction
inareaoftenresultsinspeciesextinction.Becausetheprocessofextinctionin
fragmentsisanalogoustothatoccurringonislands,thetheoryofisland
biogeographyprovidedtheinitialconceptualfi*ameworkforstudyingthis
processinterrestrialecosystems(Diamond1975,SimberlofiFandGotelli1984,
SimberloffandAbele1976,Terborgh1976,Wilcox1980),butsee(Margules,
etal.1982).
Inadditiontoareductionintotalarea,fragmentationcanhave£in
impactontheorganismsthatremaininthefragmentthroughwhathasbeen
termed"edgeeflfects"(Lovejoy,etal.1986,Saiinders,etal.1991,Soul61986,
Wilcove,etal.1986).Edgeeffectsresultfromtheinteractionbetweentwo
adjacenthabitats.Infi*agmentedhabitats,edgeeffectsareexacerbatedasa
consequenceofbidimensionalgeometry.Withthereductioninfragmentarea,
thearea/perimeterratiodecreases.Asaresult,alargerproportionofthe
habitatisleindisexposedtotheedge,orlineofcontactwiththeotherhabitat.
Theintensityofedgeeffectsisstrongestintheimmediatevicinityofthe
edge,anddeclinesawayfi-omtheedge(Blanchard1992,GatesandGysel
1978,HesterandHobbs1992,Kapos1989,Ranney,etal.1981,Wales1972,
2
Williams-Linera1990a,Williams-Linera1990b).Inadditiontodistancefrom
theedge,severalfactorsseemtomitigatethestrengthoftheeffect:edgeage
(Blanchard1992,Williams-Linera1990b),aspect(Gysel1951,Ranneyetal.
1981),orientation(Kapos1989,PalikandMiuphy1990,Ranneyetal.1981,
Wales1972),andalsothetypeofvegetationonbothsidesoftheedge(Chasko
andGates1982).
Attentiontoedgeeffectshasfocusedmainlyonthefragmentationof
\. forestsandtheirreplacementwithsimpleagriculturalorpastoral
ecosystems.Thegeneralpatternofchangesforforest-fieldedgesthatcanbe
extractedfromtheUteratureindicatesthatforestedgestendtohavehigher
solarincidencethantheinteriorofthefragments(Blanchard1992,Kapos
1989,CostingandKramer1946).Consequently,airtemperaturesnearthe
edgeareusuallyhigherandmorevariable(Kapos1989,Williams-Linera
1990a),andsoilstendtobedryer(Kapos1989,CostingandKramer1946)
theinintheforestinterior.Withhigherlightavailability,plantgrowthis
enhanced.Thereforeedgestendtohavehigherfoliardensities(Blanchard
1992,Malcolm1991),andhigherplantdensities(Chen,etal.1992,Palikand
Murphy1990,Ranneyetal.1981,Sork1983,Wales1972,Williams-Linera
1990a),inspiteofhighertreemortalitycausedbyexposvireandwindthrow
(Chenetal.1992,Lovejoyetal.1986).Thisabundanceincoverandplant
densityattractsherbivorousinsects(Blanchard1992),andnestingbirds
(ChaskoandGates1982),whichinturnattractnestpredators(Gatesand
Gysel1978),andbroodparasites(BrittinghamandTemple1983).Although
organismsfromoutsidethefragmentsmaybeattractedtotheedge
(BrittinghamandTemple1983,ChaskoandGates1982,Hester£uidHobbs
1992,LauranceandYensen1991),thechangeinthephysicalenvironment
associatedwithedgesmayalsocausesomeplantsandanimalstoavoidthe
edges(Chenetal.1992,Malcolm1991,Ranneyetal.1981).Thus,changes
associatedwithedgesC£inhaveeffectsatmanylevels.Attheindividuallevel
edgescanaffectthereproductivepotentialofplants(Blanchard1992)and
animals(Angelstam1986,BrittinghamandTemple1983,ChaskoandGates
1982,Gibbs1991,Wilcoveetal.1986);atthepopulationlevel,edgescan
affectthepresenceofspeciesneartheedge(Blanchard1992,Lovejoyetal.
1986,Quintela1986,Ranneyetal.1981);andatthecommunitylevel
changesintheinteractionamongspeciescanbeaffectedaswell.Littleis
knownontheeffectsofedgeatthecommunitylevelbecause,withthe
exceptionofaviannestpredationandbroodparasitism,edgeeffectson
processesthatinvolvespeciesinteractionshaverarelybeenstudied.Of
particularinterestareplant-animalinteractions(suchaspolUnation,
frugivory,herbivory,orseeddispersal),duetotheirimportanceinthe
dynamicsofmanyforests.
Plant-animalinteractionscanbeverysensitivetodisturbancebecauseof
thedualeffectonboththeplantsandtheanimals,andbecauseofthespecies-
specificnatureofmanyoftheseinteractions(Kevan1975,McClsuiahan
1986).Inthiscommunity-levelstudy,Iaddresshowinteractionsamong
plantsandtheirpollinatorsareaffectedbytheirproximitytoaforest-pastiu"e
edge.Becauseresearchersperceiveanddefinetheconceptsofedgeandtheir
effectsdifferently,Ibegin(chapter2)byreviewingtheevolutionofthe
concepts,andtheircurrentdefinitions.Iconfinethisreviewtoedgesbetween
forestsandfield/pastures,becausetheseedgesarethemostrelevanttothe
conservationofforestfragments.Ialsodrawgeneralpatternsonedgeeffects
atalllevelsoforganization(individuals,populationsorcommunities),and
divideedgeeffectsintothreeclasses:effectsonthephysicalenvironment,
directbiologicaleffects,andindirectbiologicaleffects.Thiscontextallowsme