Island Biogeography

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Island Biogeography

• Equilibrium Theory
• Explanation of community structure as a function
  of size and distance from species pool
• Dispersal
• Geographic Isolation
• Extinction
• Makes it applicable to more than true islands

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Island Biogeography

• MacArthur and Wilson used past island studies to
  develop the theory
• Species-area relationships
• Species turnover
• Species Isolation

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Species-Area Relationship and Size
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Rare Species and Extinction
Applies to Distance
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Isolation and Species Area
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Species Isolation
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Species Isolation
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Species Turnover
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Species Turnover
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Species Turnover
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Equilibrium Theory of Island Biogeography
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Criticisms of Island Biogeography

• Interspecific differences and species
  interactions
• Assumed immigration, extinction, and turnover as
  stochastic
• Species richness not composition
• Interdependence of immigration and extinction
• Treated as independent processes
• Does not account for recruitment of new
  individuals already on island

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Criticisms of Island Biogeography

• Biogeographically meaningful measures of
  isolation
• Sometimes difficult to identify source without
  studying systematics
• Composition question
• Biogeographically meaningful measures of island
  size
• Spatial heterogeneity
• Ecological and biogeographical history

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Criticisms of Island Biogeography

• Importance of speciation
• If species are derived on island, then model is
  violated
• Speciation probably only important on large,
  isolated islands in terms of number of species
• Disturbance (ecological and geological time
  scales)
• Would prevent equilibrium

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Tests of Island Biogeography
Estimates of turnover on southern California
Channel Islands
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Krakatau Revisited Colonization Curves
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Krakatau Revisited I/E rates
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Krakatau Revisited I/E rates
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Simberloff and Wilson (1970) Experiment
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Krakatoa Revisited Plant Colonization
Succession had to proceed to allow animal
colonization
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Accounting for Succession/Recruitment

• How does succession alter likelihood that
  immigrants will survive and reproduce?
• F failure rate (species failing to est.
  breeding population
• C I F
• C decreases over time

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Disturbance Events

• How to account for disturbance effects?
• Disturbanes at same temporal scale as island I
  and E might prevent equilibrium
• Shorter time scale (fires, drought..) probably
  only slow process

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Possible Effects of Speciation
Effect of Area
Effect of Distance
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Island Applications of Island Biogeography

• Freshwater Lakes
• North American lakes (Post-Pleistocene) relied on
  connections to other waters, including streams
  and rivers, for colonization
• Not near saturation
• Example Great Lakes large but not many
  species lotic sources depauparate

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Island Applications of Island Biogeography

• African lakes much older high diversity from
  speciation through adaptive radiation
• North American lakes, including Great Lakes, show
  evidence of same but not much time has passed

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Species-Area Relationships
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Species-Area Relationship in Rivers

• Greater diversity in N. Amer. rivers
• N. Amer. rivers generally have N-S flow
• Would allow dispersal in advance of glaciers