Effect of island area on Drosophila population densities.

Species of the Drosophila affinis subgroup show a positive correlation between population density and island area on islands in the vicinity of Deer Isle, Maine. The low density of flies on small islands may be due to inbreeding depression, exposure to salt spray, desiccation, or decimation by violent storms. Mushroom-feeding species of Drosophila show great year to year fluctuations in abundance on these islands, probably due to changes in the level of their resource supply. Population fluctuations and non-linear correlations between island area and population size may have complicating effects on the probability of extinction of species on different sized islands.