Global diversity and body size

Most species within any specific group of organisms lie in an optimal, intermediate size range, where there are more chances of the appearance of dominating species. However, the species-abundance relationship observed in insects may be unamenable for extrapolation to other group of organisms. In the microbial world, many species may be found in a small natural sample but the global number of such species may be modest. The extrapolation of these results to the bacterial world may support the abundance of these small-bodied taxa among the diverse species on the Earth.