The MacArthur-Wilson Island Biogeography Theory proposes that the number of species found on islands is determined by a dynamic equilibrium between immigration and extinction rates. It assumes species have equal chances of dispersing to islands and that there is no interaction between species on islands. The theory models how factors like the distance of an island from the mainland and the island's area influence immigration and extinction rates, and thereby the number of species able to exist on the island long-term.

1. MacArthur-Wilson Island Biogeography Theory
Assume all species have an equal dispersal ability and risk of extinction
Assume no interaction between species on an island
Parameters Scaling Factors
Species pool on mainland P 0 For distance (f)
Area of Island A 0 For area (m)
Distance from mainland D 0
Colonization probability c 0
Extinction probability q 0 Equilibrium Values
Spp.richness
Immigration, Extinction, and species richness Immigration rate
Fract.of pool Spp. Richness Immigration Extinction Extinction rate
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Spp. Richness
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0.4 Extinction
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Graph 1. Immigration rate, Extinction Rate and the Equilibrium Point

3. Scaling Factors
0.01
0.25
quilibrium Values
Fraction of Effect of Distance on immigration
Pool Spp. Richness Imm near Imm medium Imm far
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Graph 2. Immigration Rates vs. Island Distance
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4. 0.3
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Graph 3. Extinction Rates vs. Island Area

5. Effect of area on extinction
Ext small Ext medium Ext large
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Spp. Richness
Imm near
Imm medium
Imm far
Ext medium
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. Island Distance
Spp. Richness
Imm medium
Ext small
Ext medium
Ext large
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6. Ext large
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