Identifying climatic niche shifts using coarse-grained occurrence data: a test with non-native freshwater fish

Aim We tested whether coarse-grained occurrence data can be used to detect climatic niche shifts between native and non-native ranges for a set of widely introduced freshwater fishes. Location World-wide. Methods We used a global database of freshwater fish occurrences at the river basin scale to identify native and non-native ranges for 18 of the most widely introduced fish species. We also examined climatic conditions within each river basin using fine-grained climate data. We combined this information to test whether climatic niche shifts have occurred between native and non-native ranges. We defined climatic niche shifts as instances where the ranges of a climatic variable within native and non-native basins exhibit zero overlap. Results We detected at least one climatic niche shift for each of the 18 studied species. However, we did not detect common patterns in the thermal preference or biogeographic origin of the non-native fish, hence suggesting a species-specific response. Main conclusions Coarse-grained occurrence data can be used to detect climatic niche shifts. They also enable the identification of the species experiencing niche shifts, although the mechanisms responsible for these shifts (e.g. local adaptation, dispersal limitation or physiological constraints) have yet to be determined. Furthermore, the coarse-grained approach, which highlights regions where climatic niche shifts have occurred, can be used to select specific river basins for more detailed, fine-grained studies.