Coexistence of sparrows: a test of community theory.

A study of the coexistence of sparrows in grassland and woodland habitats of the Research Ranch in southeastern Arizona supports the predictability of current community theory. For each of the habitats studied, the production of seeds and the abundance of seed-eating, winter-resident sparrows were measured. The theory correctly predicts the number of species supported in each of the habitats. In both cases for which the prediction is that only one species could be supported, the theory correctly predicts which species should be present.