Aim: Barriers continue to be built globally despite their well-known negative effects on freshwater ecosystems. Fish habitats are disturbed by barriers and the connectivity in the stream network reduced. We implemented and assessed the use of barrier data, including their size and magnitude, in distribution predictions for 20 species of freshwater fish to understand the impacts on freshwater fish distributions. Location: Central Germany. Methods: Obstruction metrics were calculated from barrier data in three different spatial contexts relevant to fish migration and dispersal: upstream, downstream and along 10km of stream network. The metrics were included in a species distribution model and compared to a model without them, to reveal how barriers influence the distribution patterns of fish species. We assess impacts of barriers by estimating species’ specific range gains and losses due to barrier inclusion in the model. Results: Barriers were important for the predictions of many fish species with the metric upstream barriers being the most relevant barrier predictor across the fish community. With the inclusion of barriers, most species saw a reduction in their predicted range and habitat suitability decreased, particularly species with small ranges or considered as threatened. Main conclusions: Predictions from this SDM application point out how and where barriers influence fish distributions in the studied catchment. Our results indicate a reduction in suitable habitat due to barriers and suggest a higher extirpation risk. This species-specific and spatially-explicit information is highly valuable for target-oriented river restoration measures, biodiversity conservation efforts and catchment management in general.
Scale effects on the performance of niche-based models of freshwater fish distributions
