Habitat occupancy by semi-aquatic reptiles on an aridity gradient in the western Mediterranean.
The influence of aquatic and riparian habitats on the composition of the local herpetofauna has not been studied extensively. We used redundancy analysis and multivariate ordination methods to evaluate the occurrence of semi-aquatic reptiles in south-eastern France, the Iberian Peninsula, and Morocco where the climate transitions from humid temperate to subtropical desert. All the semi-aquatic reptile species present in this region were studied, including two native turtles (Emys orbicularis and Mauremys leprosa), three native snakes (Natrix astreptophora, N. helvetica, and N. maura), and one introduced turtle (Trachemys scripta). We hypothesized that these species will vary in their responses to differences in the composition of riparian habitats (vegetative community and relative proportion of trees, shrubs, grasses, water and bare ground surface) along the aridity gradient in the region. We found that the habitat niche marginality and niche breadth varied widely across species and climatic regions, although most of the species display a greater habitat niche breadth in the transitional semi-arid belt. Mauremys leprosa and N. maura were the more generalist species, occupying a wide range of freshwater habitats, including streams associated with impoverished vegetation communities, characteristic of the arid southern Mediterranean region.