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Lecture1Thenaturallaboratoryparadigm

Wallace1902,IslandLife

CHAPTER1Thenaturallaboratoryparadigm

...itisnottoomuchtosaythatwhenwehavemasteredthedifficultiespresentedbythepeculiaritiesofislandlife,weshallfinditcomparativelyeasytodealwiththemorecomplexandlessclearlydefinedproblemsofcontinentaldistribution...

(Wallace1902,IslandLife,p.242)

Thenaturallaboratoryparadigm

Islands,

beingdiscrete,internallyquantifiable,numerous,andvariedentities,provideuswithasuiteofnaturallaboratories,fromwhichthediscerningnaturalscientistcanmakeaselectionthatsimplifiesthecomplexityofthenaturalworld,enablingtheoriesofgeneralimportancetobedevelopedandtested.

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TextBook

I.IslandsasNaturalLaboratories

II.IslandEcology

III.IslandEvolution

IV.IslandsandConservation

TextBook

I.IslandsasNaturalLaboratories

Setsouttodetailthepropertiesofthesenaturallaboratories,withoutwhichwecanmakelittlesenseofthebiogeographicaldataderivedfromthem.

TextBook

II.IslandEcology

Isconcernedwithpatternandprocessonecologicaltimescales,andisfocusedonpropertiessuchasthenumberandcompositionofspeciesonislandsandhowtheyvarybetweenislandsandthroughtime.

TextBookIII.IslandEvolution

Focusonevolutionarypatternandprocess,atalllevelsfromtheinstantaneouslossofheterozygosityassociatedwiththecolonizingeventonanisland,throughtothemuchdeepertemporalframeworkassociatedwiththegreatradiationsofislandlineages onremoteoceanicarchipelagoslikeHawaii.

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TextBookIV.IslandsandConservation

Incorporates togethertwocontrastingliteratures,concernedrespectivelywiththethreatstobiodiversityderivedfromtheincreasedinsularization ofcontinentalecosystems,andthethreatsarisingfromthelossofinsularization ofremoteislands.

Chapter2Islandenvironments

Theorigins,environments,andgeologicalhistoriesoftheplatformsonwhichtheactiontakesplace.

Therearemanyformsof‘islands’tobefoundintheliterature,fromindividualthistleplants(islandsofsortsforthearthropodsthatvisitthem)inanabandonedfield,throughtoremotevolcanicarchipelagos liketheGalápagosandHawaiianislands.

Herbaceous plant of the daisy family

Figure1.1Therearemanydifferenttypesofislandsinadditiontothosefoundintheworld’soceans.Thisfigureillustratesjustafewofthese(basedonanoriginalinWilsonandBossert 1971).

Examplep.3lowerrightparagraph

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Chapter3Thebiogeographyofislandlife:biodiversityhotspotsincontext

Concentratesonthebiogeographicalaffinitiesandpeculiaritiesofislandbiotas—anecessarystepbeforetheprocessesofevolutiononislandsaretackled.

Thechapterthusbeginsintheterritoryofhistoricalbiogeographersconcernedwithtracingthelargestscalesfromthespace–timeplotandwithworkingouthowparticulargroupsandlineagescametobedistributedastheyare.

Thisterritoryhasbeenfoughtoverbytheopposingschoolsofdispersalist andvicariance biogeography.

Figure1.2Aschemeofdifferenttime–spacescalesofecologicalprocessesandcriteriathatdefinecorrespondingscalesofinsularity.(1)individual scale;(2)population scale1:dynamics;(3)population scale2:differentiation;(4)evolutionary scale.(RedrawnfromHaila 1990,Fig.1.)

Vicariance vs.Dispersalist HypothesesIslandstudieshavebeencaughtupinthisdebatebecausetheyseeminglyprovidesuchremarkableevidenceforthepowersoflong-distancedispersal,whereasrejectionofthisinterpretationrequiresalternative(vicariance)hypothesesfortheaffinitiesofislandspecies,invokingplatemovementsand/orlostlandbridges,toaccountforthebreakingupofformerlycontiguousranges.Someofthepostulatedland-bridgeconnectionsnowappearhighlyimprobable;neverthelessthechangingdegreesofisolationofislandsovertimeremainsofcentralimportancetounderstandingthebiogeographyofparticularislands.Aswillbeseen,thevicariance anddispersalist hypotheseshavebeenputintotoostarkanopposition;bothprocesseshavepatentlyhadtheirparttoplay.

Biodiversity ‘hotspots’&‘threatspots’

Remoteislandbiotasdifferfromthoseofcontinentsinanumberofways,beinggenerallyspeciespoor anddisharmonic (peculiarintaxonomiccomposition),yetrichinspeciesfoundnowhereelse,i.e.endemic tothoseislands.

Islands,particularlylargeandremoteislands,contributedisproportionatelytoglobalbiodiversity,i.e.theyarebiodiversity‘hotspots’

Newdiscoveriesunderlinetheacceleratedrateofattritionofislandbiotasthroughhumanaction,whichqualifiesmanyislandstodayas‘threatspots’aswellascentres ofendemism.

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IslandBiogeographicalTheories

Table1.1Someprominentislandbiogeographicaltheoriesandthegeographicalconfigurationsofislandsforwhichtheyholdgreatestrelevance.

Chapter4Speciesnumbersgames:themacroecology ofislandbiotas

Ananalysisofthemacroecology ofislands,focusedonwhatwelight-heartedly termSpeciesnumbersgames.Undoubtedly,themostinfluentialcontributiontothisliteraturehasbeenRobertH.MacArthurandEdwardO.Wilson’s(1967)Thetheoryofislandbiogeography.

Thespecies–areaeffect—thatplotsofspeciesnumberversusareahaveacharacteristicform,differingbetweenmainlandandislandbiotas

MacArthur& Wilson’sequilibriumtheory

Whetheronislandsorcontinents,theformoftherelationshipbetweenareaandspeciesnumberisoffundamentalbiogeographicalimportance.

WewillshowthatMacArthurandWilson’sequilibriumtheoryhasactuallyprovedremarkablydifficulttotest,andthatwhileitsheuristicinfluenceremainsstrong,itspredictivevalueappearslimited.Inlargemeasurethismaybebecauseofinsufficientattentiontothescaleofthestudysystem.

Chapter5CommunityassemblyanddynamicsItemergesthatislandbiotastypicallyarenotmerelya‘random’sampleofmainlandpools.Thereisgenerallysomedegreeofstructure inthedata.

JaredDiamond(1975a)formulatedasetof‘assemblyrules’basedlargelyondistributionaldata(birdsonislandsoffthecoastofNewGuinea).Heinvokedastrongroleforinterspecificcompetitioninstructuringecologicalassemblagesonislands,buthealsorecognizedaroleforlong-termecological(andevolutionary–ecological)processes.

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Assemblyrules

Thisapproachbecameembroiledinheatedcontroversy,focusedbothonourabilitytomeasurepatternandonthecausalinterpretationofthepatternsdetected.

Oneimportantformofstructureisnestedness,thetermgiventothesituationwhereuponrankingasetofislandspecieslistsbyspeciesrichness,eachspeciessetisfoundtorepresentapropersubsetofthenextlargerspeciesset.

Again,themeasurementofnestedness anditscausalinterpretationturnouttobelessthanstraightforward,butitappearsclearthatasignificanttendencytonestedness iscommonwithinisland (andhabitatisland)archipelagos.

Chapter6Scaleandislandecologicaltheory:towardsanewsynthesisTherehasbeenanincreasingrealizationthatecologicalphenomenahavecharacteristicspatial andtemporalsignatures,whichtendtobeLinked.

Placingislandecologicalstudiesintoascaleframework,helpsusreconcileapparentlycontradictoryhypothesesasactuallybeingrelevanttodifferentspatio-temporaldomains.

Chapter7Arrivalandchange

Westartwiththefoundingeventonanislandandworkinturnthroughtheecologicalandevolutionaryresponsesthatfollowfromthenewcolonistencounteringthenovelbioticandabioticconditionsoftheisland.A seriesoftraits,syndromes,andpropertiesemergeascharacteristicofislands,includinglossofdispersalpowers,lossofflowerattractiveness,thedevelopmentofwoodiness,characteristicshiftsinbodysizesofvertebrates,andrathergeneralistpollinationmutualisms.

Chapter8Speciationandtheislandcondition

Theattainmentofspeciation,theemergenceofseparatespeciesfromoneancestor,isofcentralinterestwithinbiology,andsowedevotethischaptertoabriefaccountofthenatureofthespeciesunit,andofthevaryingframeworksforunderstandingtheprocessofspeciation.

Thus,weexaminefirstthegeographicalcontextofspeciation,inwhichislandsconvenientlyprovideuswithastrongdegreeofgeographicalseparationbetweentheoriginalsourcepopulationandtheislandtheatre,butinwhichtheextentofintra-archipelagoandintra-islandisolationisoftenhardertodiscern.Second,weexaminethevariousmechanisticframeworksforunderstandingspeciationevents,and,finally,weconsiderphylogeneticframeworks fordescribingtheoutcomeofevolutionarychange.

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Chapter9EmergentmodelsofislandevolutionWhichprovidedescriptionsandinterpretationsofsomeofthemostspectacularoutcomesofislandevolutionarychange,includingtheclassicexamplesofthetaxoncycleandofadaptiveradiation.

Fromthisworkitisbecomingincreasinglyevidentthattheever-changinggeographicalconfigurationandenvironmentaldynamism ofoceanicarchipelagosarecrucialtounderstandingvariationinpatternsandratesofevolutionarychangeonislands.

Chapter10Islandtheoryandconservation

Whichdebatesthecontributionofislandecologicalthinkingwithinconservationscience.Asweturncontinentsintoapatchworkquiltofhabitats,wecreatesystemsofnewlyinsularized populations.Whataretheeffectsoffragmentationandareareductionwithincontinents?Notjusttheshort-termchanges,butthelong-termchanges?

Theprocessesofecosystemresponsecantakeconsiderableperiods(oftendecades)toplayout,meaningthattoday’sfragmentationisstoringupnumerousextinctionsforthefuture.However,thefactthatresponsesareoftenlaggedmeansthatthereisanopportunityformitigationmeasurestobeputinplay,toreducetheso-called‘extinctiondebt’,providingsocietycaresenoughtoact.

IslandExtinction

Figure1.3Timeseriesofextinctionsofspeciesofmolluscs,birds,andmammalsfromislandsandcontinentssinceaboutAD1600.

Chapter11AnthropogeniclossesandthreatstoislandecosystemsThereismountingevidencethathumansarerepeatoffenderswhenitcomestoextinguishingislandendemics.Whereverwehavecolonizedislands,whetherinthePacific,theCaribbean,theAtlantic,theIndianOcean,ortheMediterranean,wehaveimpactedadverselyonthenativebiota,andoftenontheecosystemservicesonwhichweourselvesrely.

Typically,therehavebeenatleasttwomajorwavesofextinctions,oneassociatedwiththeaboriginalorprehistorichumancolonizations,andthesecondfollowingcontactwithmodernEuropeansocieties.

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Chapter12Islandremedies:theconservationofislandecosystemsWhereas,onthecontinents,theincreasinginsularization ofhabitats isaprimecauseforconcern,theproblemforoceanicislandbiotastodayistheincreasingbreakdownoftheinsularization oftheirs.

Theprimeagentsofdestructionareintroducedexoticspecies(especiallymammalianbrowsersandpredators),habitatloss,predationbyhumans,andthespreadofdisease.

Whatisanislandanyhow?