Feeding habits and overlap among red fox (Vulpes vulpes) and stone marten (Martes foina) in two Mediterranean mountain habitats

The feeding habits of two carnivorous opportunists, red fox (Vulpes vulpes) and stone marten (Martes foina), have been compared in two Mediterranean mountain habitats (mesic and xeric), located in the Sierra Nevada National Park (SE Spain), between April 1997 and March 1998. The analysis of scats revealed a very important interspecific trophic niche overlap in the mesic habitat. In the xeric habitat the differences were significant and the overlap moderate. Seasonal variations existed in the degree of overlap, which reached its highest Level in winter in the mesic habitat and in spring in the xeric habitat. The results indicated that the availability of food in each habitat was important in determining the divergence of the diets. Thus, in the mesic habitat, competition could be possible, although it was not important enough to cause a habitat segregation. Martens seemed to be more adaptive than foxes, probably due to their smaller size and arboreal life, allowing them to exploit fruit which is not as profitable for the fox. Foxes based their diet on small mammals, carrion and cultivated fruit in both habitats. Rabbits were also seasonally important in the xeric habitat. The trophic niche breadth of foxes was higher in the mesic habitat. The inter-habitat comparison showed significant differences in the diet of martens. In the xeric habitat, martens centred their diet on small mammals and fruit of Juniperus phoenicea, Morus ulmifolius and Amelanchier ovalis, while in the mesic habitat their diet was very similar to that of foxes. The trophic niche breadth was higher in the xeric habitat than in the mesic. The habitat conditions particulary influenced the overlap of the diets and these variations were fundamentally caused by the different availability of small fruit.