Mean population size increases with diversity

A long-standing debate in ecology has been the effect of diversity on the temporal stability of biological systems.

Ecological theory predicts that the stability of populations should decline as community diversity increases, in part, because population size is assumed to decline with community richness.

In the February issue of Ecology Letters, Valone and Hoffman, using an 11-year dataset, have shown that the temporal stability of 17 species of annual plants in natural communities increases with diversity.

Population size also tends to increase with diversity, likely due to variation in local productivity.

Because community diversity, population size and the temporal stability of populations covaried positively, abiotic factors such as productivity may govern population stability to such an extent as to override potential effects of diversity.