ABSTRACT
Ecogeographic rules, describing general trends in the variation of biological traits along environmental gradients, are receiving increasing attention in the scientific literature. Among them, Bergmann’s rule is the best-known ecogeographical rule in biology and is gaining prominence given its relevance to better understand body size reductions suggested as a third universal biological response to global warming. Compared to birds and mammals, for which the rule was originally conceived, amphibians and other ectotherms also display geographic patterns of body size variation in response to climatic gradients. These findings have challenged the original adaptive physiological mechanism and have spurred the search for alternative explanations. This chapter reviews the available evidence on the existence of interspecific patterns of body size, from regional to global scales, together with those hypotheses that have received the most empirical support to date. Available data show the emergence of large-scale geographical gradients which, as with other macroecological rules, do not manifest themselves as a universal Bergmannian pattern in which body sizes clearly increase along a latitudinal axis. Environmental signals are generally discernible and tend to show a trade-off between thermoregulation and hydroregulation mediated by surface area to volume ratios. Future studies should complement non-manipulative macroecological evidence with novel 3D imaging methods or biophysical modelling approaches to better characterize the physiological foundations of phenotype-climate relationships in amphibians.
