Biogeographic regionalization of snakes in the Atlantic Forest hotspot: interpolating the faunal dissimilarity

Aim: Snake faunal dissimilarity within tropical forests is not well characterized, nor are the factors underlying these patterns. Our aim was to disentangle the ecological and historical factors driving biogeographical subregions (BSR) for snakes.
Location Brazilian Atlantic Forest (BAF).
Methods: We compiled 274 snake inventories to build a species-by-site matrix and used unconstrained ordination and clustering techniques to identify the number of snake BSR. We applied an interpolation method to map axes of compositional variation over the whole extent of the BAF, and then classified the compositional dissimilarity according to the number of snake BSR identified a priori. We used multinomial logistic regression models and deviance partitioning techniques to investigate the influence of contemporary climatic stability, productivity, topographic complexity, and historical climate shifts in explaining the BSR.
Results: We identified 198 snake species organized into six BSR, three of them located along the BAF coast and the other three predominantly inland BSR. Climatic stability made the largest contribution to explaining the variability in snake BSR, followed by productivity and historical variation in climate. Topography was important only if historical variation in climate was excluded from the analysis.
Main conclusions: The highest rates of snake endemism within BAF were in the coastal BSR, as compared to the inland BSR that are mostly composed of open habitat specialists. Our findings suggest that the topographic complexity of the BAF acts on snake distributions not as a physical barrier, but rather as a climatic barrier, providing historical climate refuges for species living along altitudinal gradients. Overall, the predominance of climatic stability and historic variation in climate in explaining snake BSR reinforces the importance of thermoregulatory constraints in shaping the distribution of tropical ectotherm species.