BIOLOGICAL diversity, population size and body size are interde-pendent1–8, but there is little consensus on the nature or causes of these relations. Here we analyse the most thoroughly sampled ecological community to date, a grassland insect community sample containing 89,596 individuals of 1,167 species. Each taxonomic order had a distinct body size at which both species richness and number of individuals were highest, but these peak sizes varied more than 100-fold among five major orders.
