Minimal Community Structure: An Explanation of Species Abundance Patterns

Recent proposals that the canonical lognormal distribution and the resulting species-area constant, z 1/4, are artifacts of the general lognormal curve and regression techniques, are shown to be inadequate. An alternative hypothesis is suggested which accounts for these regularities in terms of a hierarchical community structure represented by a sequentially divided niche space. This hierarchical pattern, which can be considered to be a minimal form of community structure, derives from evolutionary and ecological considerations for generating species diversity, and is shown to account for the observed abundance structures of small ensembles as well as large natural communities. Evidence is presented which implies that niche apportionment between species may involve the random division of more than one resource, and an interesting invariance in the pattern of apportionment is observed for assemblages with three species. The possibility that the canonical lognormal distribution is a conceptual artifact resulting from arbitrary systems of classification is considered and shown to be false. Aside from its intuitive appeal, the model presented should be of interest because it offers explanations of two ubiquitous patterns in nature: the canonical lognormal and the resulting species-area constant.