Habitat suitability modelling of four terrestrial slug species in the Iberian Peninsula (Arionidae: Geomalacus species)

Abstract

Ecological niche modelling (ENM) determines habitat suitability of species by relating records of occurrence to environmental variables. Here, we investigated habitat suitability of four terrestrial slugs of the genus Geomalacus from the Iberian Peninsula using ENM. The potential distribution of these species was estimated using maximum entropy modelling. For this we used published presence records, together with observations from our fieldwork, and 10 layers of environmental variables in a crossvalidation design using 'minimum predicted area' as a measure of success. For each species, the models predicted distributions with high accuracy, while restricting predictions to minimum areas. Precipitation, and to a lesser extent temperature, were the most important variables to predict the distributions of the four species. We then compared the predicted distributions with the currently known distributions. For G. anguiformis and G. maculosus the predicted distributions included the known distributions, but also nearby mountain areas where these species have not previously been found. For G. malagensis and G. oliveirae the models predicted much wider distributions. Subsequent dedicated fieldwork could not confirm the presence of G. oliveirae in the newly predicted areas. Conversely, G. malagensis was found at five new and distant localities, including areas in Portugal where the species has not previously been recorded.