Climate change may reduce suitable habitat for freshwater fish in a tropical watershed

Freshwater ecosystems have been increasingly threatened due to the impacts of climate change. Fishes have shifted their geographic distribution in response to these environmental changes. By forecasting biodiversity changes, we may provide knowledge for more effective conservation actions. Here, our aim is to assess the alpha and beta spatio-temporal patterns in the climate change context of freshwater fishes in the Brazilian portion of the Upper Paraguay River Basin (UPRB). We use ecological niche models which correlate fish occurrence with environmental variables such as BIO 2, BIO 5, BIO 7, BIO 12, BIO 13, BIO 14, elevation, and stream order. Then, we predicted species distribution current and future and evaluated both the alpha and beta diversity pattern changes over time. Overall, our modeling had good predictive performance (mean ± SD, AUC 0.8 ± 0.04; TSS 0.5 ± 0.08). The future projections reveal a progressive reduction in the species number over time, with alpha diversity decreasing 85%, together with the reduction forecast between 13 and 74% of gamma diversity until the end of the century. The loss of freshwater fishes can result in an ecosystem imbalance because different ecosystem services play in the aquatic environment. Yet it is expected that turnover contributes to promoting future temporal beta diversity in the UPRB. Our results provide at a spatial large scale the impact of climate change on fish diversity, indicating directions to protect ecosystems and socioeconomic processes dependent on fish diversity.