Spatial patterns and the macroecology of South American viperid snakes

The macroecological relationship between geographic range size and body size has been described recently as an envelope region defined in bivariate space and limited by ecological and physical constraints. These constraints can be explained by selective processes acting at different levels and theories for an optimal body size. However, since data are obtained for different species in a large taxonomic group, at continental scales, it is possible that these variables may be strongly affected by spatial and phylogenetic autocorrelations. In this paper, we analyzed data on geographic range size (GRS) and body size (BS) for 36 species of Viperid snakes from South America, searching for spatial trends that could affect the shape of the macroecological constraint space. Data were analyzed using spatial autocorrelation and trend surface analyses, detecting a significant spatial pattern for GRS, fitted by a quadratic trend (R2 = 0.665; P < 0.001). After removing this effect, the relationship between trend residuals for GRS and BS still forms a constraint space, in such a way that results for South American Viperid snakes support both the shape of constraint space previously observed in other taxonomic groups and the ecological and evolutionary processes developed to explain it.