Species turnover in Amazonian frogs: Low predictability and large differences among forests

The factors explaining species turnover at different spatial scales have been intensively studied, but most work in Amazonia has focused on plants. Less attention has been paid to animals, for which it is not as obvious which environmental variables should be considered when studying differences in species composition among sites. Our aim is to understand the determinants of anuran turnover in Amazonian terra-firme forests and how the perception of these may change among regions and across spatial scales. We sampled frogs in 56 plots along ponds and streams distributed over three terra-firme forest areas in Eastern Amazonia. Using multiple regressions on distance matrices, we partitioned the variation in species turnover into components explained by variation in environmental and spatial distances. This was done in parallel for each area separately, and for all areas together in order to assess how consistent the results are between scales and across areas at the same scale. Each community seemed to respond to a set of factors specific to that area, and the identity of the variables that emerged as significant was different among areas and scales. Both geographical distances and environmental differences had larger explanatory power at the regional scale (R2=42.1%) than at the local scale (R2=3.5-36.2%, depending on the area). The large differences among results obtained in different areas caution against making broad generalizations about species turnover patterns from one community to others, as real differences may exist among areas.