Experimental Zoogeography of Islands: A Model for Insular Colonization

A distinction is made between immigration rate (in spp./time) for an island, and invasion rate (in propagules/time) for a species and an island. An analogous distinction is drawn between an island extinction rate and a species extinction rate (or intrinsic probability of extinction in a given time interval). It is claimed that the most objective definition for "propagule" is any animal of group capable of population increase under any conceivable circumstances. Immigration and island extinction curves are unique only if plotted against time, not against number of species. A model for non—interactive colonization is discussed, and its equilibrium number of species, ° derived. It is shown that data from the defaunated Florida Keys can be interpreted as arising from non—interactive colonization to an ° near the non—interactive ° (and to a point above a more enduring interactive °), followed by a slow decline in ° (as population sizes and interaction increase) to an enduring ° near that obtaining before defaunation. The effect on this scheme of increasing distance from source area is shown, and a simulation of the non—interactive part of the scheme was performed with corroborates that part of the model. Explicit equations for the "expected" colonization, immigration, and island extinction curves are given for non—interactive colonization, and predictions are given about the general changes in these curves as interaction becomes significant.