Island Nations and Geographic Isolation

Islands have long fascinated biologists precisely because their geographic isolation acts as a natural experiment in evolution and ecology. In 1967, ecologists Robert MacArthur and Edward O. Wilson published The Theory of Island Biogeography, proposing that the number of species an island supports at any given time reflects a dynamic equilibrium between two opposing rates: the rate at which new species arrive from the mainland, which falls off with increasing distance from that source, and the rate at which resident species go locally extinct, which rises as island area decreases and available habitat and population sizes shrink accordingly. This elegantly simple model, expressed mathematically as a balance point where immigration and extinction curves intersect, explained a pattern biologists had already observed empirically, that larger islands closer to a mainland tend to host more species than smaller, more remote ones, and the theory went on to influence fields well beyond island biology itself, including the design of nature reserves, which conservation biologists increasingly treat as habitat "islands" surrounded by a human-altered landscape.