Data & Scripts from: The importance of seawater tolerance and native status in mediating the distribution of inland fishes

Understanding the factors that explain species distribution is one of the main focus of ecology. Although many previous studies have already analysed the importance of different variables for the distribution of freshwater fish species, we statistically compare, for the first time, the importance of environmental and anthropogenic variables in mediating the distribution of primary (i.e. strict freshwater), secondary (i.e. salt-tolerant) and peripheral (i.e. diadromous and estuarine) native and alien fish species, and study the relationship between these factors and fish traits. We provide the first comprehensive distribution modelling exercise of the most common freshwater fish (68 species: 51 native and 17 alien) across the Iberian Peninsula. We computed the variable importance for the ensemble model to estimate the most influential factors and compare them among the fish groups studied. Our results show that geographical and environmental variables (e.g. basin, distance to the sea or mean annual temperature) are more important than anthropogenic factors (e.g. land use or hydrological alteration) in explaining freshwater fish distribution. We found significant differences in predictive accuracy and the importance of variables explaining the distribution of native and alien species but especially among primary, secondary and peripheral fish. River basin was the most important predictor for primary native and many alien species, whereas distance to the sea was the most relevant predictor for secondary and peripheral species. Mean temperature and upstream reservoir capacity had positive effects on the distribution of alien species but were less important for native fishes. The reduction of flow variability by damming and associated environmental degradation in the Iberian Peninsula has mainly favored phytophilic, water-column, warm-water alien fishes introduced from more hydrologically stable habitats such as central European and southeastern North American regions. Overall, our results show marked differences in the factors regulating the distribution of native and alien species but that Darlington’s classification (i.e. primary, secondary, and peripheral divisions) is even more important.