Explaining the anuran beta diversity by pond-living tadpoles: the role of dispersal limitation and environmental gradients through multiple scales

Aim: Determining drivers of beta diversity is a hugely complex task, as it involves processes acting synergistically across multiple scales. We employed a large-scale standardized protocol to tease apart the environmental and spatial processes driving beta diversity patterns of pond-living tadpoles across multiple scales. Location: Ponds distributed across 5000,000 km2 in five Brazilian biomes (Amazon, Atlantic Forest, Caatinga, Cerrado and Pantanal). Methods: We sampled tadpoles in three to eight locations in each biome and eight to 61 ponds per location. We used partial distance-based redundancy analyses with variation partitioning to assess the relative influence of environmental and spatial variables on beta diversity, which was estimated using the Raup–Crick index. We applied the same statistical protocol to the analyses conducted at the three spatial scales (metacommunity, regional and subcontinental), consistently maintaining the same grain while increasing the geographic extent. Results: Spatially structured environmental variation was the most important driver of anuran beta diversity. At the regional scale, the spatial component was as important as spatially structured environmental variation, and the environmental component was the most important at the metacommunity scale. Narrow-ranged and widespread species responded equally to environmental variables, but spatially structured environmental variation was more important to widespread species and pure spatial component was more important to narrow-ranged species. Main Conclusions: Our results demonstrate that spatial scale plays a role in understanding the dispersal- and niche-based processes that generate beta diversity patterns. Increasing the geographical extent increases the impact of spatial processes and the influence of environmental factors on anuran beta diversity through spatially structured environmental variation. Even under different environmental conditions, narrow-ranged and widespread species respond in a consistent manner to environmental and spatial dynamics, showing consistent responses to niche- and dispersal processes. This evidence can offer important guidelines for their conservation even for large-scale management that includes multiple biomes.