Data from: Abundance inequality in freshwater communities has an ecological origin

The hollow-shaped species abundance distribution (SAD) and its allied rank-abundance distribution (RAD), revealing that abundance is highly unevenly distributed among species, are among the most studied relationships in ecology. The pervasiveness of this pattern, with analogues in physical and social sciences, has led to uncertainty as to whether its underlying mechanisms in biological communities are statistical, neutral, or ecological. Here, I examined the parameters of a Poisson lognormal fit of the SAD and a square root fit of the RAD in diatom and fish communities across US streams. To explain the variability in the SAD and RAD parameters, I developed a novel framework identifying environmental favorability as the ultimate source and species tolerance and community richness as the proximate factors. Thus, as environmental favorability increased, trait organization shifted from a few tolerant to multiple sensitive forms, resulting in greater richness and diminished abundance disparity between locally common and rare species. The proposed framework further expanded the ideas of the recently proposed hierarchical theory of macroecology by showing that in diatoms the RAD belonged to the same family of relationships as those of population density with body size and distribution.