Spatial Factors Outweigh Environmental Variables in Explaining Fish Beta Diversity Within A Massive Anthropogenically Homogenized Water-Transfer Canal.

Inter-basin water transfer projects serve as critical artificial corridors that optimize the allocation of water resources. Understanding their influence on aquatic community assembly is a frontier issue. This study focused on the Middle Route of the South-to-North Water Diversion Project, the world's largest water transfer project. By integrating eDNA technology with functional trait analysis, we systematically investigated the spatial patterns of fish taxonomic and functional beta diversity in this highly homogenized artificial habitat. In the present study, 39 fish taxa were identified, with significant spatial variations in community structure. A distinct functional trait succession gradient emerged with increasing latitude, characterized by a trend towards smaller-bodied communities and feeding shifts towards piscivores and invertivores. Both taxonomic and functional beta diversity were primarily driven by turnover components and exhibited significant positive spatial correlations. However, functional beta diversity lagged significantly behind taxonomic beta diversity numerically. This synchronous but non-isometric pattern indicates functional convergence induced by the artificial habitat, suggesting potential risks of functional redundancy loss under intense human intervention. Variance partitioning showed spatial factors outweighed environmental factors in shaping beta diversity. This suggests that in physically unobstructed and homogenized artificial ecosystems, dispersal limitation driven by geographic distance and unique hydraulic conditions outweighs environmental filtering as the primary deterministic process shaping diversity patterns. Furthermore, the inclusion of food resource variables increased the explanatory power of the model, suggesting that spatial variation in resource availability may contribute to fish community structure. The findings indicate that management of artificial water diversion systems should transcend conventional water quality monitoring. Strengthening biosecurity surveillance and implementing functional compensatory measures at critical habitat nodes will be essential to offset the "ecological distance" imposed by dispersal limitation. This approach ensures the long-term functional stability of ecosystems and safeguards water supply security within massive anthropogenically homogenized water diversion projects.