Interspecific variations in fish occupancy and abundance are driven by niche characteristics in a monsoon climate river basin

Aim The interspecific relationships between species occupancy and abundance have been broadly studied in terrestrial systems; however, the causes underlying this relationship in freshwater fishes remain poorly addressed. The main aims of this study were (a) to examine the occupancy-abundance relationship in 62 fish species in a monsoon climate river; (b) to determine the relative importance of species niche, functional traits and phylogenetic relatedness in shaping the occupancy-abundance relationship. Location The Chishui River, the Yunnan-Guizhou Plateau and the Szechwan Basin, China. Taxon Freshwater fishes. Methods A linear model was used to test the relationship between distribution and mean abundance across fish species. The outlying mean index analysis was performed to estimate niche breadth and niche position parameters for each fish species. In addition, using principal coordinates analysis, we created four trait vectors describing the similarity of species' traits. Fish phylogeny was obtained from a global molecular phylogenetic tree of actinopterygian fishes. We used a combination of linear models, commonality analyses and boosted regression trees to evaluate the relative effects of the niche metrics, traits and phylogenetic relatedness on occupancy and abundance. Results Fish occupancy was strongly (R-2 = 0.749) and positively correlated with mean abundance in the Chishui River. Niche parameters, especially niche position, were the main determinants of variation in occupancy (e.g. total contribution of niche position and breadth using commonality analyses: 0.587 and 0.318) and abundance (0.323 and 0.151) across species. Furthermore, traits and phylogeny had little to no effect on fish occupancy (0.034 and 0.037) and abundance (0.021 and 0.003). Main conclusions Freshwater fishes in the Chishui River fit the common macroecological pattern of positive relationship between occupancy and abundance. Niche parameters, but not traits and phylogeny, are the primary correlates of riverine fish distribution and abundance.