Data from: Estimates of niche position and breadth vary across spatial scales for native and alien inland fishes

Estimates of species’ niche position and breadth is considered fundamental to understanding their ecological and evolutionary responses to natural and anthropogenic environmental change. Methodological challenges arise from the fact that macroecological inference is substantially affected by the selection of a certain geographical extent. This is particularly relevant for understanding alien species introduction success and associated species’ niche characteristics which can be estimated either from their invaded region, their native region, or both. However, surprisingly little is known regarding how the estimation of species niche breadth and position is affected by the geographical extent of investigation, especially for alien species. Here we estimate and compare climatic niche metrics of native and alien Iberian inland fishes using the outlying mean index (OMI) at three different geographical extents spanning from regional to global. Furthermore, we investigate how the introduction date of alien species affects niche characterisation. Our results show that niche metrics differed depending on the geographical extent of the investigation, as well as with respect to species nativity (native vs. alien). Differences in climatic niche position between native and alien species observed at a global scale vanished at a regional scale. The niche breadth of widely distributed alien species was highly underestimated when only considering the invaded region, and further mediated by species’ introduction date into the invaded area. In conclusion, estimating niches of freshwater species, especially of alien invaders should carefully consider the geographical extent of the investigation. We suggest that analyses that jointly consider regional and global scales will improve the estimation of niche characteristics of widely distributed organisms, particularly regarding the climatic niche, and the assessment of the invasive potential of species.