Randomness, Area, and Species Richness

Thorough censuses have been made of breeding birds on islands in Pymatuning Lake, a reservoir at the Pennsylvania—Ohio border. Analysis of the censuses yields the conclusion that for these islands the variation of the number of resident avian species with island size is that which one would expect if the birds were distributed randomly, with the probability of a breeding pair residing on an island proportional to the area of the island and independent of the presence of other pairs. This type of random placement of individuals can yield species—area relations which differ from those commonly employed for analysis of biogeographic data.