River Network Connectivity Reductions Dominate Declines in the Richness of Plateau Fish Species Under Climate Change in the Upper Yangtze River Basin

Anthropogenic climate change and disrupted river network connectivity are major factors affecting freshwater fish richness. However, the distribution patterns of this parameter under the combined influence of climate change and reduced river connectivity resulting from hydroelectric development remain unclear. Here, we projected shifts in the richness of Schizothoracinae fish species, the most dominant and economically significant type of fish on and around the Qinghai-Tibet Plateau. Stacked species distribution modeling and predictions were explored to simulate the range shifts of 20 species in the upper Yangtze River Basin under the impacts of connectivity and climate changes. The results revealed that river connectivity reduction dominated the richness shifts and loss in Schizothoracinae fish species. Higher-quality fish habitats are more susceptible to the impacts of connectivity reduction. Although the connectivity reduction caused by dam construction is associated with a slight increase in fish richness in the source region of the basin, it is primarily responsible for the widespread decrease in fish richness under future climate change scenarios. In the 2050s and 2090s under the two shared economic pathway scenarios, future climate change is predicted to enhance the positive impacts of river connectivity changes on fish habitat in the middle to high latitude regions of upper basins but worsen their negative impacts in other regions. Our study highlights the dominant role of river connectivity in influencing freshwater fish richness in the context of climate change, thereby highlighting the importance of connectivity restoration in global freshwater biodiversity conservation and water resource management.