Global patterns and predictors of primary freshwater crab richness across taxa and realms

Freshwater ecosystems are among the most important in the world and provide essential functions and services to humans. In this study, we examine the roles of environmental and historical factors in explaining contemporary patterns of species richness. We investigated spatial patterns of species richness of freshwater crabs by compiling geographic distribution maps for 1271 species. We employed six environmental variables slightly correlated and non-collinear to test environmental hypotheses. At a global scale, we identified three regions characterized by particularly high species richness: in northern South America (Neotropical biogeographic realm), in the Western Ghats and Sri Lanka (Oriental), and southwestern China (Oriental). The best-fitting model that explained global richness variation included environmental hypotheses: T emperature - S peciation , R esource Availability , H abitat H eterogeneity and A nthropic Impact . We also observed a historical influence on the pattern of richness, with distinct sets of environmental predictors of richness across taxa and biogeographic realms. Our models suggest that freshwater crab richness is associated with by varying processes occurring within specific environmental and historical scenarios. In general, we documented a concentration of freshwater crab richness in areas heavily impacted by human activities. These findings hold implications for the conservation of this taxonomic group.