Taxonomic and functional diversity in a subtropical stream: A longitudinal pattern analysis

Identifying the spatial patterns of fish diversity in streams is basic for the conservation and management of stream fishes. The “upstream–downstream” patterns in the taxonomic α‐diversity of stream fishes have been widely surveyed. However, the longitudinal patterns in the functional diversity and β‐diversity of stream fishes have been given less attention. In this study, we surveyed fishes along an upstream–downstream gradient in a headwater stream of the Qiantang River, China, and examined the longitudinal variations in fish diversity. Our aims were to assess whether the longitudinal patterns in fish diversity were consistent between the taxonomic and functional metrics and between the α‐ and β‐aspects of diversity. We found that both species richness and functional richness of fishes showed a hump‐shaped relationship with the distance from headwaters, while both taxonomic and functional β‐diversities presented the U‐shaped distributions along the river continuum. Functional diversity related more to the distance from headwaters than taxonomic diversity. Despite their similar relationship with the distance from headwaters, taxonomic and functional β‐diversities were dominated by species turnover and function nestedness components, respectively. Our results suggest that, along the river continuum in a subtropical stream, the α‐ and β‐aspects of fish diversity present different longitudinal variations. Although the taxonomic and functional diversity shows similar relationships with distance from headwaters, their spatial variations are driven by different ecological processes.