1Spotted (habitat and feeding specialist, old growth obligate)vs Barred Owl (generalist, feeds in agricultural areas, nestsin forests, outcompetes Spotted Owl when old growth isfragmented and surrounded by fields).SF Chronicle letter Nov. 2005: “another owl, not land use,threatens spotted owl.” Refute this argument.2Spotted (habitat and feeding specialist, old growth obligate)vs Barred Owl (generalist, feeds in agricultural areas, nestsin forests, outcompetes Spotted Owl when old growth isfragmented and surrounded by fields).SF Chronicle letter Nov. 2005: “another owl, not landuse,threatens spotted owl.” Refute this argument.3Rio Negro (Alex Flecker)Michael Goulding, TheFishes and the Forest4Unfragmented Fragmented1 ha1 ha10 ha10 ha100 ha fragment100 ha fragment1 ha1 ha10 ha1 ha studyplot, forestedgeForest fragmentation experiment in Brazil1 hectare(ha)study plots,forest interior56Freshly cut edgesYears later7Amazon rainforest conversion…• Minimum critical size of ecosystem projectAmazon, northern Brazil (Lovejoy)– Square reserves of jungle in sea of cleared land• Small 1 ha (100 x 100 m) patches:blowdown, edges topple, interior understoryvegetation shriveled• Cow invasionRecovery dynamics—change in edges..8Unfragmented Fragmented1 ha1 ha10 ha10 ha100 ha fragment100 ha fragment1 ha1 ha10 ha1 ha studyplot, forestedgeForest fragmentation experiment in Brazil1 hectare(ha)study plots,forest interior9Species richness,island biogeography,andbiodiversity reservesDec. 4 200610Taxon or guild2 speciesFood chainStrong interactionsspacetimeenergyMacArthur Wilsontheory of IslandBiogeography: Spacebut no time (assumesequilibrium (Sevaluated when E = I)and no biology. Allspecies have equivalentprobabilities ofdispersal, extinction.11Islands: circumscribed hospitable habitats in a “sea”(background matrix) of less hospitable terrain (e.g.,ocean islands, ponds, mountain tops, plant-heldwaters (phytotelmata), boulders• Attractive for study– Can delimit populations, communities withnatural boundaries– Provide replicates for comparative studies ormanipulation12Before 1963, 1967, the field of island biogeographywas important (e.g. Galapagos for Darwin’s andIndonesia for Wallace’s theories of evolution) but“little touched by quantitative theory”Historical (idiosyncratic) questions like:• How did the marsupials get to Australia?• Why have Hawaiian bees diversified from only one genus?MacArthur and Wilson 1967. The EquilibriumTheory of Island Biogeography. Then came:13How far can we get in predicting diversity patterns on islands ifwe ignore biology and focus on island properties?• Island properties– Distance (from mainland source)– Isolation (difficulty of barrier, stepping stones or lack thereof)– Area of island– Habitat structural complexity– Age, time since creation/disturbance•Species properties–Vagility (dispersal ability)–Competitive ability–Growth rate potential–Vulnerability to pathogens, predators–Trophic position14Island Size: Well known log log species area relations for islands:S = c A z, log S = log C + z (log A)• z : constant between .18 and .35,• c : taxon-specific vagility constant.15New GuineaNearer (to New Guinea) than 500 miles Farther than 500 miles Effect of distance from source on island species richness16LE 53-27aNumber of species on islandEquilibriumnumberImmigrationExtinctionRate of immigration or extinctionImmigration = arrivalof a new speciesExtinction = loss ofa species fromisland biotaMacArthur Wilson Equilibrium Theory ofIsland Biogeography17Predictions• S should attain equilibrium value over time,even with continual turnover of species(“dynamic equilibrium”)• Large islands should have lower rates ofextinction, hence higher Sequil• Near islands should have higher rates of immigration, hence higher SequilSMainland, with P species in poolpsmalllargenearfar18S = equilibrium number of sppEquilibrium species number on island when gain rate = loss rate.S reached when Immigration + Evolution = Extinction – Emigration, or, if Evolution and Emigration small, when Immigration = ExtinctionEffects of island size and distance only factors considered.Predict: S far small < S near small, S far large < S near largeMacArthur-Wilson MacArthur-Wilson ““Equilibrium Theory of IslandEquilibrium Theory of IslandBiogeographyBiogeography””S,S,19Prediction: numberof species increasesmore rapidly witharea on islands thanin expandingsampled area ofNew Guinea landmass—holds forWilson’s ants…20Assumptions:• Islands haveattainedequilibrium• No localevolution !speciationThis graph shows thatbird richness on someislands may not be inequilibrium, but stillrecovering fromhistoricaldisturbances….211883 eruptionKrakatoa !RarataRate Number of speciesMost taxa not in equilibriumafter 100 y.22Landscape mosaics: Shape? Size?Edge:Area? Corridors?23Single Large or SeveralSmall (SLOSS)?Quinn and Harrison vsTerborgh…Use of Island Biogeography for reserve designCumulative areaCumulative speciesS = c A zIf total area is limited, severalsmall reserves should protect morerichness because z < 1.024Corridors?Pros: genetic interchange migration recolonization after disasterCons: more edge spread of disease, aliens may act as “sinks” (b < d)Design of reserves that anticipateglobal warmingnorth south orientation? May bewhy N. Am has more species thanEurope--N-S vs E-W orientation ofmountains (Jim Brown)Shape? Edge:Area25Scott Robinson: thrushes,parasitic cowbirds, and chainsawsEdge effectsSource-sinkdynamics(Krebs 299-300)Southeastis source,Midwest issink
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