Lecture 1 The natural laboratory paradigm
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10/5/21 1 Lecture 1 The natural laboratory paradigm Wallace 1902, Island Life CHAPTER 1 The natural laboratory paradigm . . . it is not too much to say that when we have mastered the difficulties presented by the peculiarities of island life, we shall find it comparatively easy to deal with the more complex and less clearly defined problems of continental distribution . . . (Wallace 1902, Island Life, p. 242) The natural laboratory paradigm Islands, being discrete, internally quantifiable, numerous, and varied entities, provide us with a suite of natural laboratories, from which the discerning natural scientist can make a selection that simplifies the complexity of the natural world, enabling theories of general importance to be developed and tested.
Transcript of Lecture 1 The natural laboratory paradigm
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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
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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?
