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Data from: Moving beyond Bergmann and Converse Bergmann: Can competition or food resources drive spatial variation in body size?

Garfinkel, Chloe1; McCain, Christy12

Published Sep 28, 2026 on Dryad. https://doi.org/10.5061/dryad.pk0p2nh5p

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Abstract

Hypothesis testing for body size trends along elevational and latitudinal gradients is dominated by Bergmann’s rule predicting larger size in colder environments and Converse Bergmann’s rule predicting smaller size where summers are shorter. Despite the mixed to poor support for Bergmann’s and Converse Bergmann’s rules, alternative hypotheses are virtually untested along environmental gradients. Here we aim to contrast Bergmann’s and Converse Bergmann’s rules with alternative spatial hypotheses for intraspecific body size variation: intensity of competition and quantity of food resources across elevationally distributed sites. We use individuals from 11 species of carrion beetles (Staphylinidae: Silphinae) collected across 30 sites in two mountain ranges (Front Range and San Juan Mountains, Colorado, USA). We measure beetle body size (elytral length, estimated weight), quantify food availability, and estimate interference and exploitative competition from community abundance. Predictions of Bergmann’s rule and competition lacked support. Two of ten species supported Converse Bergmann’s rule. In contrast, within-site body size variation was significantly associated with local food abundance. Where food resources were abundant intraspecific body sizes spanned from very small to very large. Resource-poor sites yielded fewer, but uniform, average-sized individuals. Alternative aspects of life history can outweigh climate in shaping insect body size, thus potentially underlying inconsistent elevational body size patterns across studies.