Data from: The biogeographical patterns of species richness and abundance distribution in stream diatoms are driven by climate and water chemistry

In this inter-continental study of stream diatoms, we asked three
important but still unresolved ecological questions: 1) What factors drive
the biogeography of species richness and species abundance distribution
(SAD); 2) Are climate-related hypotheses, which have dominated the
research on the latitudinal and altitudinal diversity gradients, adequate
in explaining spatial biotic variability; and 3) Is the SAD response to
the environment independent of richness? We tested a number of climatic
theories and hypotheses (i.e., the species-energy and the metabolic
theory; and the energy variability and the climatic tolerance hypothesis)
but found no support for any of these concepts as the relationships of
richness with explanatory variables were non-existent, weak or unexpected.
Instead, we demonstrated that diatom richness and SAD evenness generally
increased with temperature seasonality and at mid- to high total
phosphorus concentrations. The spatial patterns of diatom richness and the
SAD—mainly longitudinal in the US, but latitudinal in Finland—were defined
primarily by the covariance of climate and water chemistry with space. The
SAD was not entirely controlled by richness, emphasizing its utility for
ecological research. Thus, we found support for the operation of both
climate and water chemistry mechanisms in structuring diatom communities,
which underscores their complex response to the environment and the
necessity for novel predictive frameworks.