DOI: 10.5061/dryad.gv24p
title: Data from: Abundance inequality in freshwater communities has an ecological origin

description: 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.
description: Diatom
 dataThe file “Diatom data”
 contains 3 Excel spreadsheets, i.e. “Raw data,” “Community data,” and
 “Species data.” The Raw data spreadsheet shows the population density,
 measured in cells/cm^2, and the population density rank for all species
 (BioDataTaxonName) across 3213 diatom samples, listed by their sample
 identification. The diatom samples were collected from 1580 distinct
 stream localities, listed by their station identification. The Community
 data spreadsheet contains relevant information for the diatom samples,
 including latitude, longitude, date of collection, species richness,
 evenness, total density (cells/cm^2), statistics of the Poisson lognormal
 fit to the sample species abundance distribution (parameters mu and sigma,
 gof (goodness of fit), and p (proportion of species revealed by the
 sample)), statistics of the square root fit to the sample rank-abundance
 distribution (intercept a0, slope a, and their standard errors and 95%
 confidence intervals), ln Tolerant:Sensitive ratio, and density and
 richness of the three diatom guilds (low profile, motile, and high
 profile). Environmental data were available for a subset of 2949 samples.
 The Species data spreadsheet lists the 1777 diatom species
 (BioDataTaxonName) encountered in this study with guild designation
 whenever possible and occurrence across 1582 stream
 localities.Fish
 dataThe file “Fish data”
 contains 3 Excel spreadsheets, i.e. “Raw data,” “Community data,” and
 “Species data.” The Raw data spreadsheet shows the abundance, measured as
 number of individuals, and the abundance rank for all species
 (BioDataTaxonName) across 761 fish samples, listed by their sample
 identification. The fish samples were collected from 399 distinct stream
 localities, listed by their station identification. The Community data
 spreadsheet contains relevant information for the fish samples, including
 latitude, longitude, date of collection, species richness, evenness, total
 abundance (number of individuals), statistics of the Poisson lognormal fit
 to the sample species abundance distribution (parameters mu and sigma, gof
 (goodness of fit), and p (proportion of species revealed by the sample)),
 statistics of the square root fit to the sample rank-abundance
 distribution (intercept a0, slope a, and their standard errors and 95%
 confidence intervals), ln Tolerant:Intolerant ratio, and abundance and
 richness of the three fish tolerance groups (tolerant, intolerant, and
 moderate). Environmental data were available for a subset of 732 samples.
 The Species data spreadsheet lists the 460 fish species (BioDataTaxonName)
 encountered in this study with tolerance group designation whenever known
 and occurrence across 1005 stream localities.