Distribuzione, dieta e selezione dell'habitat di martora e faina sulle Alpi Occidentali italiane

Pine martens (Martes martes) and stone martens (Martes foina) are the most similar carnivores in Europe, taking into account genetics, morphology and feeding habits; notwithstanding, their distribution ranges largely overlap throughout Europe. In sympatry, niche partitioning has been reported to depend on different habitat preferences and activity patterns, but very little is still known about their relationships, mainly because of their elusiveness and low densities. As a result, currently there is no available information about their feeding habits and habitat selection in the Italian Western Alps, and very little is known even about their relative distributions. Therefore, the first aim of this study was to investigate the presence and distribution of pine and stone martens in the Alpine region included in the provinces of Turin and Cuneo. The second aim was to examine the composition of their diets, as to assess food niche overlap. Lastly, the third aim was to uncover the major environmental factors affecting their distribution using a Species Distribution Model. Between February and December 2019, marten-like scats were searched for in 30 randomly selected 100 km2 squares along linear transects (mean length ± SE = 7.0 ± 2.0 km). A portion (ca. 30%) of each scat was preserved in 96% ethanol and by freezing until DNA extraction, while the rest was retained for dietary analysis; the UTM coordinates of each sample were filed and projected onto a GIS. Mitochondrial DNA was isolated from “fresh” scats and the specific identification was accomplished by a PCR-RFLP method based on the amplification of the D-loop region using primers specific for Martes and Mustela and the successive digestion of the PCR products with the restriction enzymes HaeIII and RsaI, whose restriction patterns allow to easily discriminate between the species. The feeding habits of pine and stone martens were analyzed in terms of both frequency of occurrence and volume, as to assess dietary breadths and food niche overlap. Finally, Maxent was applied to identify the environmental variables that affect the distribution of the two species and may determine their spatial niche divergence. By surveying a total of ca. 203.1 km of transects, 168 marten-like scats were collected, of which 117 were selected for DNA extraction. The rate of success of DNA amplification was 61.5% (n = 72) and restriction digestion patterns allowed to identify 37 pine martens and 32 stone martens. 27 squares (90.0%) were found positive for at least one marten species and the species resulted to coexist in 9 squares (30.0%). Dietary breadths were similar (B = 6.6 for pine martens and B = 5.4 for stone martens) and food niche overlap resulted to be relatively high (α = 0.7); notwithstanding, pine martens significantly ate more mammals and stone martens ate more fruit. Pine martens selected mainly coniferous forests, at intermediates altitudes, generally wetter if compared with stone martens, which conversely selected mainly broad-leaved-forests, generally drier and warmer. Lastly, their coexistence was favoured by mixed forests and by the absence of open habitats. Therefore, despite the small sample size, results showed that pine and stone martens are widely distributed and often coexist; however, a slight spatial niche partitioning and a slighter resource partitioning resulted, suggesting that probably some other form of niche partitioning is required.