Macroecological Patterns Of Mexican Freshwater Fishes

In spite of its extraordinary diversity and high levels of endemicity, the Mexican freshwater ichthyofauna has not been studied from a macroecological perspective. We document the patterns in geographical range size, body size, and species richness for Mexican native freshwater fishes, considering hydrological regions as study units. We also explore variables that could explain variation in species richness patterns. The Mexican native freshwater ichthyofauna is comprised of 420 species in 26 families, which are distributed in 34 of the 37 Mexican hydrological regions. Frequency distributions of range and body size are right-skewed or approximately normal under logarithmic transformation indicating that most species are small-bodied and rare in terms of occurrence. Linear regression models demonstrate a declining trend for species’ range and body size towards lower latitudes. With respect to patterns in species richness, multiple regressions show that historical processes (i.e., high speciation rate) are the most important factors shaping diversity distribution patterns, and that variables related to habitat area are contributing to the maintenance of spatial gradients in species richness. Rapoport’s and Bergmann’s rules apply to the Mexican freshwater fish fauna. The biogeographical position of the country and geographic isolation of their drainage basins have induced the spatial variation of species richness.