Although the seminal paper that gave rise to the well known Bergmann’s rule dates back to 1847, the study of broad-scale body size variation still remains as an attractive field of research for ecologists and biogeographers. Despite much emphasis has been placed in examining the ecogeographic pattern of increasing body size towards colder regions for mammals and birds, the analyses have not been exclusively restricted to endotherms. In this respect, following the long-standing idea that some ectothermic organisms can also exhibit geographical gradients in body size at the interspecific level, a recent study found Bergmann’s size clines for anurans in the Holarctic region and proposed a heat balance hypothesis as an explanation for this pattern. However, this analysis was limited to cold temperate regions, and exploring the patterns in warmer tropical climates may reveal that factors other than energy inputs influence anuran body size variation. We address this using a database for anuran species in the Brazilian Cerrado, a region with a pronounced dry season. We examine the relationship between mean body size in a grid of 1°cells and a set of environmental predictors and test the relative support for four hypotheses using an AIC-based model selection approach. To consider the potential effects of spatial autocorrelation we use eigenvector-based spatial filters.
Results/Conclusions
We found the largest species inhabiting high water deficit areas in the northeast and the smallest in the southwest near the Pantanal. Our results are consistent with the water availability hypothesis which, coupled with previous findings, suggests that the major determinant of interspecific body size variation in anurans switches from energy to water related variables across latitudinal space. We propose that anuran body size gradients reflect effects of reduced surface to volume ratios in larger species to control both heat and water balance.
