Elevational patterns of fish functional and phylogenetic community structure in a monsoon climate river basin

Abstract Aim Understanding the patterns and drivers of biodiversity across space and time is commonly based on species diversity, which may ignore species' functional role and evolutionary history and result in an incomplete understanding of community assembly. It is suggested that integrating species, functional, and phylogenetic diversity could provide a more holistic assessment of community assembly in natural ecosystems. This study aimed to explore the elevational patterns and environmental drivers of multiple facets of fish diversity and community structure in a subtropical river during the wet and dry seasons. Location The Chishui River basin, China. Methods We investigated the responses of fish species richness, functional richness, and phylogenetic diversity to elevation in different seasons. Moreover, we compared functional dispersion and mean pairwise distance with those obtained from null models to infer assembly mechanisms shaping community structure. Additionally, we examined the environmental drivers (e.g. water chemistry, temperature, and river size) of fish diversity and community structure. Results Fish species richness, functional richness, and phylogenetic diversity showed a negative relationship with elevation in the Chishui River basin. Fish communities tended to be on average functionally random but phylogenetically clustered. Furthermore, phylogenetic structure exhibited a decreasing pattern along the elevational gradient. Despite no significant seasonal changes for fish diversity (except for phylogenetic diversity), fish communities became more phylogenetically overdispersed and clustered at low and high elevations in the dry season. Additionally, the responses of fish diversity and community structure to environmental variables were not synchronous. Conclusions At the basin scale, environmental filtering was prevalent in shaping fish phylogenetic structure, whereas stochasticity was likely more important for functional structure. Moreover, the ecological mechanisms shaping individual fish communities switched from limiting similarity to environmental filtering as elevation increased, and the underlying forces at two ends of the elevational gradient became more prominent in the dry season.