Body size distributions at community, regional or taxonomic scales do not predict the direction of trait-driven diversification in snakes in the United States

Aim We determine whether trait-driven diversification yields similar body size distributions for snakes in local, regional and phylogenetic assemblages. Location United States, North America. Methods Using total length and mass, we examine body size frequency distributions (BSFD) across 79 sites and respective biomes to determine if these areas represent random subsamples from the source pools of taxon body sizes. Using QuaSSE, we determine if the most probable model of trait-driven diversification in the three most common groups of snakes in North America, the ratsnakes, pitvipers and watersnakes, is similar to the predicted regional BSFD. Results BSFD of snakes at the community, biome, regional and clade scales show symmetric distributions of body size. These patterns may simply be generated from random statistical subsampling. Speciation rates are not highest at or near the modal body size and simulations show that linear trait-driven models can still yield highly symmetric distributions of body size. Main conclusions In this study region, processes such as competition due to size do not alter BSFD from one scale to the other. It is likely that rates of speciation are not highest at the mode in snakes and trait-driven diversification is not likely to account for a regional pool of body sizes from which local communities are drawn, although persistence of modal body sizes through time could yield regional BSFD.