On the Relative Abundance of Species

Abstract

A distinction is made between opportunistic and equilibrium species. There is little ecological interest in the relative abundance of opportunistic species, but such species frequently should have a lognormal distribution of abundances. Relative abundances of equilibrium species are of considerable ecological interest and frequently can be deduced from the assumption that an increase in 1 species population results in a roughly equal decrease in the populations of other species. To make the formulae well-defined, it is necessary to assume that by his choice of area the census-taker has achieved a certain sort of randomness. Birds appear to be equilibrium species, while diatoms, colonizing plants and most terrestrial arthropods appear to be opportunistic.