Effect of biotic dependencies in species distribution models: The future distribution of Thymallus thymallus under consideration of Allogamus auricollis

Climate change will impact the riverine environment of aquatic organisms. However, most studies focus solely on environmental characteristics to evaluate future distribution shifts. Here, we analyse current and future distribution of the freshwater fish species Thymallus thymallus in relation to the caddisfly Allogamus auricollis. Current and future distributions of the two species were evaluated by a consensus model approach integrating seven different distribution model techniques and testing the effect of considering biotic dependence. Predictions for future distributions were calculated on the basis of the most recent representative concentration pathways (RCPs) of the IPCC for the period of the 2050s. Habitat loss and gain, distribution congruence and altitudinal shift between the two species were quantified on the basis of a full river network. The model considering biotic dependence identified the caddisfly as important variable for the distributions of European grayling, mitigating the drastic effects of climate change. Habitat loss of the grayling was attenuated by considering the distribution of the caddisfly in the distribution modelling. Strong temperature increases as well as run-off decreases led to largest habitat loss of both species (up to 70%). Our combined approach highlighted that the consideration of biotic dependencies in climate change studies improves the understanding for potential future changes of distribution patterns.