Functional diversity of fish in the Yuan-Red River: Role of species turnover and trait shifts

Understanding how environmental change and species introductions shape functional diversity is essential for conserving freshwater biodiversity. This study examines these drivers in the upper Yuan-Red River Basin over three decades (1990-2020). Using morphological traits from fish specimens, we applied generalized least squares models, hypervolume analysis, and variation partitioning to assess trait variation, functional space reorganization, and contributions of native versus non-native species. Functional space overlap between periods was only 20.6% for natives, while non-natives expanded rapidly, increasing overlap with natives from minimal to 40% by the 2020s. Locomotion traits associated with precipitation and non-native richness; feeding and habitat traits with dams, non-native richness, and water quality. Diversity indices remained stable and climatically driven, despite underlying trait restructuring. Conservation should prioritize maintaining natural flow regimes.