Spatial distribution of the pine marten (Martes martes) and stone marten (Martes foina) in the Italian Alps

The pine marten (Martes martes) and stone marten (Martes foina) are considered similar carnivores in terms of morphology, habitat requirements, diet and distribution. Despite their range overlap widely throughout Europe, few studies have analysed their spatial distribution in sympatry. With the aim of investigating the environmental factors which may enhance their coexistence, we focused on the Italian sector of the Alpine biogeographical region, an area offering homogeneous environmental conditions and resources. Recent, presence-only data were collected through a collaboration network and ad hoc surveys for faecal DNA, yielding a total of 1658 and 329 records for stone marten and pine marten, respectively. Species distribution models (SDM) were run using MaxEnt with sampling bias correction. Three detailed models were fitted, each considering different landscape descriptors (land use, topography and climate) and, finally, an overall model was developed for each species. The pine marten selected forested areas, particularly coniferous forests, at intermediate altitude, while lower-altitude belts, partially including cultivated and urban areas, were more suitable for the stone marten. Both martens avoided open areas. Moreover, the thermophilic stone marten preferred warmer and drier areas than the pine marten. About 50% of the Alpine area was filed as suitable for each species, with 34.6% of cells resulting suitable for both martens. Differential use of space, probably associated with segregation along with other dimensions of their niches (e.g. the temporal niche), lowers resource competition and enhances the coexistence of these strictly-related species.