Understanding patterns of taxonomic diversity, functional diversity, and ecological drivers of fish fauna in the Mekong River

Understanding different facets of biodiversity patterns and their ecological drivers are essential for freshwater conservation. This is especially true for fish fauna in the Mekong River, one of the largest rivers in the world, which faces large-scale hydropower development and climate change. Here, we divided the Mekong River into 37 sub-basins to explore the alpha and beta taxonomic and functional diversity of fish fauna and the explanatory power of environmental and spatial factors on fish diversity. We found that species and functional richness varied significantly along environmental gradients, while functional evenness and divergence were weakly correlated with environmental variables. We also found that the high taxonomic beta diversity was mainly contributed by the turnover component, while that of the functional facet was mainly due to the nestedness component. In addition, environmental filtering played a more important role than spatial factors in structuring both taxonomic and functional facets of fish communities. Finally, we found that environmental filtering was more important in determining taxonomic structure than functional structure, which was opposite to the general understanding that functional traits should be better associated with environmental variation. Our study illustrated that functional diversity and taxonomic diversity are complementary ecological indicators when assessing fish diversity of large rivers