ABSTRACT
The theory of island biogeography combines geographical influences on species diversity with species change, and stresses the dynamism of insular communities. Frank W. Preston (1962), and Robert H. MacArthur and Edward O. Wilson (1963, 1967) proposed it independently. Preston stressed the idea that island species exist in some kind of equilibrium. MacArthur and Wilson explicitly set down an equilibrium model. Their central idea was that an equilibrium number of species (animals or plants) on an island is the outcome of a balance between immigration of new species not already on the island (from the nearest area of mainland) and extinction of species on the island. In other words, it reflects the interplay of species inputs (from colonization) and species outputs (from extinctions). The equilibrium is dynamic, the consequence of a constant turnover of species. In its simplest form, the MacArthur-Wilson hypothesis makes two key assumptions about what happens to immigration and extinction rates as the number of species living on the island mounts:
1 The rate of species immigration drops (Figure 22a). This happens because, on the average, the more rapidly dispersing species would become established first, causing an initial rapid drop in the overall immigration rate, while the later arrival of slow colonizers would drop the overall rate to an ever-diminishing degree.
