Structure of freshwater fish trophic networks across South America
Despite advances in trophic network theory and analytic techniques, macroecological patterns of fish trophic networks have been scarcely explored. Here, several models of community organization in aquatic systems were explored to test the effects of latitude, basin area, altitude and habitat type on the size, connectivity, nestedness and complexity of fish trophic networks and on the diversity of fish dietary groups across freshwater systems of South America. First, a dataset was created gathering scientific publications and theses that offered information about the trophic structure and gut contents of freshwater fish communities, using Google Scholar as the search engine. Then, the species richness of dietary groups was calculated for each fish community and gradients were explored through redundancy analyses. Additionally, trophic networks were built and analyzed through null models and GLMs. The results evidenced networks had higher numbers of nodes and links at low latitudes and large basin areas. Furthermore, most networks were significantly nested and connected. However, differences in network structure were observed among aquatic habitats. Networks from floodplains showed large sizes but low connectance and nestedness, while networks from headwaters were highly connected and nested, but were smaller. All these patterns seem to be related to latitudinal and elevation gradients, the hierarchical organization of hydrographic drainages and species-area relationships.