Unraveling Spatial Patterns and Drivers of Fish Ecological Uniqueness in Subtropical Streams

β-diversity is effective for measuring the degree of compositional variation among communities and can be decomposed into local (LCBD) and species (SCBD) contributions to β-diversity. Previous studies on β-diversity have mostly been limited to the taxonomic level; relatively few studies have been conducted on functional diversity and its two components based on species functional traits, which have seriously hindered the potential application of β-diversity in conservation biology. In addition, increasing anthropogenic disturbance has led to uncertainties in the β-diversity of fish communities in stream ecosystems. In this study, we explored the relationships between multidimensional β-diversity of fish communities and regional landscape factors, local environmental factors, community metrics, and species functional traits to reveal the main drivers of β-diversity in headwater streams of the Xin'an River, China. LCBD and SCBD values were calculated based on species abundance and functional traits, that is, local and species contribution to taxonomic (TLCBD and TSCBD, respectively) and functional (FLCBD and FSCBD, respectively) β-diversity. The results showed that LCBD and SCBD values were affected by biological and environmental factors. Among biological drivers, TLCBD values were positively related to species abundance. FLCBD values were positively related to species abundance, functional originality, specialization, and dispersion, that is, sampling sites with greater ecological uniqueness at the taxonomic level also had greater ecological uniqueness at the functional level. Among environmental drivers, TLCBD and FLCBD values were negatively related to water temperature, substrate coarseness, and agricultural and urban land use, that is, anthropogenic land use and local environmental changes reduce the ecological uniqueness of fish communities in the studied streams. For SCBD, both TSCBD and FSCBD values were affected by species abundance, occupancy, and niche position. We suggest that consideration of SCBD as part of a conservation approach needs to be coupled with species abundance and occupancy, which will help to prioritize areas for conservation and restoration in the study region.