Theory of island biogeography

¶ … Island Biogeography & Uneven Distributions of Species

The theory of island biogeography explains the uneven distributions of species population in islands, or why some islands have more diverse numbers of species than other islands. The theory suggests that the number of species an island reflects a balance between the rate at which new species occupy it and older species become extinct. Resources are limited in nature and because the resources of an island are particularly limited, "as the number of resident species increases, the smaller and more prone to extinction their individual populations are likely to become. The rate at which additional species will establish populations will be high when the island is relatively empty, and the rate at which resident populations go extinct will be high when the island is relatively full" (Ehrlich, Dobkin & Wheye 1988). Also, according to the theory of metapopulations it is more likely for a species to survive if it is spread out into large areas, to reduce the likelihood the species will be decimated by a change in geological fortunes ("A Short Introduction to Metapopulation Models and GIS," RAMAS: Ecological and Environmental Software, 2008).

The theory of island biogeography is helpful in explaining why there is more biodiversity in larger land areas. This is reflected in a long-term study of a bird community in an oak wood in Surrey, England with thirty-two breeding species and a turnover of three additions and three extinctions annually vs. As projected average of five in a similar population located an isolated ocean island (Ehrlich, Dobkin & Wheye 1988).