Week7 - Island Biogeography: Patterns in Species Richness...

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Island Biogeography: Patterns in Species Richness Wallace, Darwin, Hooker David Lack (1947, 1976) -- critical study of evolution and ecology of Galápagos finches Ernst Mayr (1942, 1963) -- followed Wallace’s footsteps in the East Indies G. Evelyn Hutchinson (1958,1959, 1967) -- studied lakes Prior to 1960, dominant idea was the static theory of islands: insular community structure was fixed in ecological time Robert MacArthur and E. O. Wilson (1963, 1967) -- equilibrium theory of island biogeography; dynamic equilibrium The major contribution to biogeography was the theoretical aspect of modeling Searched for general patterns in the distributions of diverse kinds of species General themes of equilibrium theory of island biogeography: (1) the tendency for species numbers to increase with area; (2) tendency for species numbers to decrease with isolation; immigration and extinction are relatively frequent -- so numbers don’t necessarily change, but species composition does. Other important contributors to island biogeography: Eugene G. Munroe (1948) -- developed the equilibrium theory before MacArthur and Wilson, but ideas buried in doctoral thesis about Caribbean butterflies and never published Frank Preston (1962) -- One of his contributions was the idea that in any region, only a few species are extremely common, and most are moderately or very rare. He also pointed out that small, isolated islands have fewer species that are more prone to extinction because of their rarity. Island Patterns that were used in MacArthur and Wilson’s theory Species-Area Relationship 7-1
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species numbers tends to increase with increasing area this relationship described mathematically by Arrhenius (1920) as S = cA z where S = species number A = island area c = fitted constant that depends on the taxon and biogeographic region; but most strongly on population density z = fitted parameter that represents the slope when both S and A are plotted on logarithmic scales; changes very little among taxa or within a given taxon in different parts of the world, but is correlated with elevation and proximity to the mainland log (S) = log (c) + z log(A) referred to as the “power model” Species-isolation relationship For a variety of taxa and ecosystems, species richness should decline as a negative exponential (sigmoidal function) of isolation Species Turnover number of species increases until saturation; spp go extinct and are replaced by others Equilibrium Theory of Island Biogeography Three basic characteristics: 1. species-area relationship 2. species-isolation relationship 3. species turnover 7-2
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number of species inhabiting an island represents a dynamic equilibrium between opposing rates of immigration and extinction, which are recurrent. (Fig. 13.7) - simplest model
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Week7 - Island Biogeography: Patterns in Species Richness...

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