An integrated assessment of β-diversity towards setting priorities for molluscan conservation in a large subtropical...

Understanding the ecological drivers of community variation (β-diversity) and identifying conservation priorities are essential for efficient conservation strategies. However, such studies remain scarce in lotic ecosystems, particularly considering mollusks, a taxonomic group that is among the most threatened in freshwater systems worldwide. Here, we investigated the underlying drivers of taxonomic, functional, and phylogenetic β-diversity and their components (turnover and nestedness) of molluscan communities in the Guijiang River Basin, a major subtropical biodiversity zone. Additionally, we calculated multple facets of ecological uniqueness to determine the conservation sites that could help protect the vast majority of molluscan community variation. We found that: (1) turnover primarily drove taxonomic β-diversity, whereas nestedness dominated functional and phylogenetic β-diversity; (2) environmental filtering and dispersal limitation jointly influenced taxonomic and phylogenetic β-diversity, whereas environmental filtering strongly shaped functional β-diversity; (3) multiple facets of ecological uniqueness were primarily associated with local environmental variables; (4) protecting 25-50 % of sites preserves about 70 % of the area's ecological uniqueness. We emphasize that conservation planning should prioritize the maintenance of environmental heterogeneity to sustain aquatic biodiversity, with particular attention to near-pristine tributaries that support highly unique species assemblages. In summary, this study provides new insights into freshwater molluscan community structure and offers a baseline for informing targeted river conservation strategies.