Island Biogeography

The MacArthur-Wilson theory (1967) predicts species richness as a dynamic equilibrium between immigration (decreasing with S, as new colonizers must be novel) and extinction (increasing with S, as more species compete for limited resources). Larger islands have lower extinction rates (more habitat, larger populations); closer islands have higher immigration rates. The model predicts: S* ∝ A^z (species-area relationship, z ≈ 0.25–0.35) and that turnover is high even at equilibrium — species composition changes even as richness stays constant. This theory fundamentally shaped conservation biology and the design of nature reserves.