Most studies focused on species coexistence have been directed at the differential use of habitat and food resources; nonetheless, the differential use of the diel cycle may enhance the coexistence of same-sized species. We investigated the activity patterns of mesocarnivores (red fox (Vulpes vulpes), European badger (Meles meles), pine marten (Martes martes), stone marten (M. foina)) in NW Italy via camera-trapping. We hypothesized that the smallest species would tend to avoid competition by selecting time periods when larger species were less active. Foxes, badgers, and stone martens were mainly nocturnal. In lowland areas overlap between coexisting species was generally low, while in Mediterranean habitats all activity patterns tended to be unimodal and overlap was generally high. The pine marten showed a cathemeral pattern. We suggest that the lower ability of the stone marten to avoid interference competition at community-level may play a major role in determining its widespread exclusion from forested areas by the pine marten.

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A species’ potential distribution can be modelled adequately only if no factor other than habitat availability affects its occurrences. Space use by stone marten Martes foina is likely to be affected by interspecific competition with the strictly related pine marten Martes martes, the latter being able to outcompete the first species in forested habitats. Hence, to point out the environmental factors which determine the distribution and density of the stone marten, a relatively understudied mesocarnivore, we applied two non-invasive survey methods, camera-trapping and faecal-DNA based genetic analysis, in an Alpine area where the pine marten was deemed to be absent (Val Grande National Park N Italy). Camera trapping was conducted from October 2014 to November 2015, using up to 27 cameras. Marten scats were searched for between July and November 2015 and, to assess density, in spring 2017. Species identification was accomplished by a PCR-RFLP method, while 17 autosomal microsatellites were used for individual identification. The stone marten occurred in all available habitats (83% of trapping sites and 73.2% of scats); nonetheless, habitat suitability, as assessed using MaxEnt, depended on four major land cover variables—rocky grasslands, rocks and debris, beech forests and chestnut forests—, martens selecting forests and avoiding open rocky areas. Sixteen individuals were identified, of which 14 related to each other, possibly forming six different groups. Using capwire estimators, density was assessed as 0.95 (0.7–1.3) ind/km2. In the study area, the widespread stone marten selected forested areas, attaining density values like those reported for the pine marten in northern Europe and suggesting that patterns of habitat selection may depend on the relative abundance of the two competing martens.

The macronutrient requirements of the strictly related pine marten (Martes martes) and stone marten (Martes foina) are almost identical, but, at range scale, in areas of putative sympatry (overlapping European ranges) the stone marten tends to be more frugivorous, which makes the contribution of carbohydrate energy to be higher than the target. In contrast, the macronutrient intake of the pine marten would be unaffected by the occurrence of the stone marten, supporting the putative dominance of the first in interspecific interactions. Most available studies examined marten diets separately, highlighting the need for further studies in areas of actual co-occurrence. With this aim, we compared the two martens' diets in the Italian Alps both in sympatric and allopatric conditions, as assessed by the genetic identification of scats. Although fruit and rodents formed the bulk of both species' diets, as predicted the stone marten consumed twice as many fruit species as the pine marten and ate fruit more often in areas of sympatry, thus consuming less protein and more carbohydrates respect to its intake target. This competition-driven, nutritionally imbalanced diet may affect the fitness of stone marten populations and play an important and still underreported role in regulating the relative abundance of marten communities.