Geology, climate, and hydrochemistry shape the spatial patterns of multiple diversity facets and functional traits of fishes

Abstract In a large river with significant environmental variations in space (i.e., microhabitat) or over time (i.e., seasonality and/or long‐term trend), discovering the spatial changes in fish diversity, distributions, and functional traits would provide an important foundation for the understanding of ecosystem structure and function. In the Pearl River in China, three datasets as fish distribution, species functional traits, and environmental variables were constructed and sorted to (1) test the relationships between and congruence of taxonomic diversity, functional diversity, and phylogenetic diversity by a randomisation procedure, (2) map the spatial pattern of diversity and the correlation to environmental variables by maximal information coefficient, and (3) determine the fish traits tendency under environmental changes by the fourth‐corner method. The Pearl River possesses the highest fish richness among all the rivers in China, with 438 freshwater fish species including 119 cave species. At basin scale, phylogenetic diversity showed faster change than functional diversity, suggesting a little divergence of functional traits despite high phenotypic or genetic diversity across species, as parallel evolution. However, at a small scale, when only considering cave fishes, the variation rate of species traits was faster than that of species increase, as evolutionary radiation in a variety of microhabitats. For all three aspects of diversity, random permutation tests confirmed that congruence values in each grid cell were significantly different from the random expectations. Besides widely accepted variables such as altitude, precipitation, and slope concerned with fish biogeography, hydrochemical variables showed influential impacts on the morphological and growth traits of fishes in the Pearl River characterised by the dominance of the karst habitat.