Spatial non-stationarity in the distribution of fish species richness of tropical streams

Diversity gradients are observed for various groups of organisms. For fishes in streams, the water-energy, productivity, and temporal heterogeneity hypotheses can explain richness patterns. The relationship between species diversity and the variables that represent these hypotheses is generally linear and stationary, that is, the effect of each of those variables is constant throughout a geographically defined area. But the assumption of spatial stationarity has not yet been tested on a great number of diversity gradients. Therefore, we aimed to quantify the spatial stationarity in the relationships between fish species richness in small stream (653 streams) located throughout Brazil, and the water-energy, productivity, and temporal heterogeneity hypotheses using a geographically weighted regression-GWR. There was a conspicuous absence of spatial stationarity in fish species richness. Furthermore, water-energy dynamics represented a possible metabolic restriction acting on the community structuring of fish species richness in streams. This mechanism separated the fish fauna into two regions: (i) The Amazonian region, characterized by a stable climate and populations that are less resistant to climatic variation; and (ii) The central region, featured by greater ranges of temperature and fish populations that are resistant to climatic variation.