The effect of Serra do Mar mountain range on the distribution patterns of the ichthyofauna from the Atlantic Forest coastal basins.
Several factors promote differences in distribution patterns and species composition of a given site. Phenomena occurring in geological time, such as sea level changes, may result in population isolation, decreasing the gene flow, resulting in speciation and diversification events, as well as extinction processes. Similarly, environmental factors have a major influence on freshwater fish communities. The Atlantic Forest is a biome recognized for the high rates of endemism in its coastal ichthyofauna due to historical and/or environmental processes. In recent years, efforts have been made to increase knowledge about the freshwater ichthyofauna of the Atlantic Forest, which increased the numbers of species descripted and contributed to the organization of a more complete inventory for this biome. We build the most extensive database for freshwater fish from the Atlantic Forest, gathering and organizing dispersed knowledge about species presence and distribution, most of which are locally scaled, resulting in information for 496 species. Despite the efforts of many scientists, no work has been done so far to evaluate the factors that influence the beta diversity caused of these organisms in the coastal basins of the Atlantic Forest. Thus, the proposal of this work was to map and identify the processes that are related to the ichthyofauna distribution patterns in the coastal basins of the Atlantic Forest. A cluster analysis was applied aiming to observe patterns of the ichthyofauna similarity between clustered basins. From these groups we proposed and analyzed four models constituted by potentially influential variables which were ranked by importance order, according to the main processes that explain the diversity patterns observed for this ichthyofauna. Still, from the results achieved, a new potential driver of beta diversity emerged - the presence of a mountain range close and parallel to the coast, the Serra do Mar. Together, the model containing environmental variables and the model formed by geological variables with the presence/absence of this mountain range explained more than 30% of the ichthyofauna similarity in 60 coastal watersheds of the Atlantic Forest. Among the proposed models, the orographic effect caused by the presence of Serra do Mar, is the factor that best explains the pattern of distribution of the ichthyofauna of the Atlantic Forest coastal basins in the proposed scale.