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)—showing that abundance is unevenly
distributed among species—are some of the most studied patterns in
ecology. To explain the nature of abundance inequality, I developed a
novel framework identifying environmental favorability, which controls the
balance between reproduction and immigration, as the ultimate source and
species stress tolerance as a proximate factor. Thus, under harsh
conditions, only a few tolerant species can reproduce, while some
sensitive species can be present in low numbers due to chance immigration.
This would lead to high abundance inequality between the two groups of
species. Under benign conditions, both groups can reproduce and give rise
to higher abundance equality. To test these ideas, I examined the
variability in 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. Indeed, as environmental favorability increased, more sensitive
forms were able to establish large populations, diminishing the abundance
disparity between locally common and rare species. Finally, it was
demonstrated that in diatoms, the RAD belonged to the same family of
relationships as those of population density with body size and regional
distribution.