The selection of the sampling unit and extension of the study area is crucial for understanding the processes and mechanisms influencing biodiversity distribution patterns. Depending on the chosen scale, patterns of distribution will be influenced by different ecological and biogeographical processes. Here, we considered different sample units and extensions of the study area (water bodies in a municipality, water bodies in an ecoregion, municipalities in an ecoregion, and municipalities in the total area of study) to assess the relative importance of ecological and biogeographical factors in the beta diversity of frogs in Brazilian Atlantic Forest. We partitioned total beta diversity into two additive components, spatial species turnover and nestedness. Our hypotheses were: (H1) small grain and small extent, turnover will be the dominant component due to deterministic variation in species responses to habitat heterogeneity; (H2) small grain and intermediate extent, turnover will be higher than values observed for small extent (H1) and nor habitat structure or dispersal limitation will be associated with turnover among ponds; (H3) intermediate grain and intermediate extent, nestedness will be higher because increasing grain size we aggregate anuran species from different sampling units, and consequently, we homogenize the species composition. Because municipalities are under similar environmental conditions we believe that nestedness will be associated with dispersal limitation; and (H4) intermediate grain and large extent, we predict that beta diversity will be higher among municipalities drawn from different ecoregions than among municipalities drawn from within a single ecoregion, and consequently, turnover will be associated with dispersal limitation.
Results/Conclusions
Overall, we compiled distributional records of 86 anuran species (presence and absence) from 12 published studies in the Atlantic Forest. We found that turnover was the main component of beta diversity independently of spatial scale. Considering the same sample unit and increasing the extent of the study area the turnover values increased. On the other hand, considering the same extension and increasing the sampling unit, the turnover values decreased. At smallest scale, environmental variables and geographic distance alternated in their relative importance associated with beta diversity. In contrast, at largest spatial scales, ecoregions showed higher values of relative importance. Our results suggest that relative importance of the ecological and biogeographical processes in frog beta diversity in Brazilian Atlantic Forest is dependent on spatial scales. Thus, considering multiple spatial scales is possible to found different patterns of distribution and bring new perspectives about the processes structuring community assemblages.