theory of island biogeography: a standalone construct

Robert MacArthur and Edward O. Wilson introduced the theory in their 1963 paper An equilibrium theory of insular zoogeography and developed it fully in their 1967 book The Theory of Island Biogeography. It predicts that the number of species living on an island settles at a dynamic balance point where the rate at which new species arrive (immigration) equals the rate at which resident species die out (extinction), so the species count can stay roughly constant even as the particular species present keep turning over. The balance point is set mainly by two features of the island: its area, because larger islands sustain larger populations that go extinct less often, and its distance from a mainland source, because more remote islands are harder to reach and so receive fewer immigrants. Simberloff and Wilson's 1969 experiments, in which small mangrove islands were cleared of insects and then recolonised, gave the first controlled evidence that species number returns to such an equilibrium. The theory is distinctive as the framework that treats an island's biodiversity as a rate-driven equilibrium rather than a fixed list, and its reach extends beyond true islands to any isolated habitat patch, which is why it underpins reserve design and the study of habitat fragmentation.[1][2][3]

Unit

Predicted equilibrium species richness (number of species) on an island or isolated habitat patch, as a function of area and isolation

Recovery means

Not applicable

Measured by

Assessed by comparing observed species counts across islands of differing area and distance (species-area and species-isolation relationships) and by defaunation-recolonisation experiments that track the return to equilibrium