The causes of biodiversity patterns are controversial and elusive due to complex environmental variation, covarying changes in communities, and lack of baseline and null theories to differentiate straightforward causes from more complex mechanisms. To address these limitations, we developed general diversity theory integrating metabolic principles with niche-based community assembly. We evaluated this theory by investigating patterns in the diversity and distribution of soil bacteria taxa across four orders of magnitude variation in spatial scale on an Antarctic mountainside in low complexity, highly oligotrophic soils. Our theory predicts that lower temperatures should reduce taxon niche widths along environmental gradients due to decreasing growth rates, and the changing niche widths should lead to contrasting α- and β-diversity patterns. In accord with the predictions, α-diversity, niche widths and occupancies decreased while β-diversity increased with increasing elevation and decreasing temperature. The theory also successfully predicts a hump-shaped relationship between α-diversity and pH and a negative relationship between α-diversity and salinity. Thus, a few simple principles explained systematic microbial diversity variation along multiple gradients. Such general theory can be used to disentangle baseline effects from more complex effects of temperature and other variables on biodiversity patterns in a variety of ecosystems and organisms.

Center for Theoretical Study Charles University Prague Czech Republic Department of Ecology Faculty of Science Charles University Prague Czech Republic Department of Biological Sciences Virginia Technological Institute Blacksburg VA USA

Department of Biological Sciences Virginia Technological Institute Blacksburg VA USA

Department of Biology University of New Mexico Albuquerque NM USA

Department of Civil and Environmental Engineering Colorado State University Fort Collins CO USA

Department of Ecology Faculty of Science Charles University Prague Czech Republic

School of Earth and Space Exploration Arizona State University Tempe AZ USA School of Life Sciences Arizona State University Tempe AZ USA

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