DISTRIBUTION AND ECOLOGY OF LOWLAND PINE MARTEN (MARTES MARTES L. 1758)

The pine marten (Martes martes) has been long considered a prototypical forest-specialist, but recent studies carried out in western Europe have pointed out that the species is more generalist in terms of habitat preferences than previously reported. In the western plain of the River Po residual woods mainly consist of small patches or riparian woods merged in intensively cultivated areas; nonetheless in this apparently unsuitable area the number of roadkill pine martens has increased exponentially since the beginning of the century. The expansion of the pine marten in agricultural lowlands provided an invaluable opportunity for investigating its ecological requirements and the environmental factors that shape this species’ range. To assess the actual level of pine marten penetration in lowland areas of north-western Italy, a non-invasive, faecal mDNA-based genetic method was applied at landscape scale, demonstrating that the pine marten has colonised the overall study area north of the River Po, which probably is acting as a barrier. Pine marten distribution suggests that expansion has mainly followed a north-to-south direction, following the course of major rivers as natural corridors of expansion. The unexpected high frequency of haplotypes of the central-northern European phylogroup supported the hypothesis of Alpine or trans-Alpine populations as sources of pine marten expansion. Based on presence-absence data, Species Distribution Models were applied to identify the main factors driving the colonisation by the pine marten of the western River Po plain and predict its potential south- and eastwards expansion. The distribution of residual wood patches and availability of suitable riparian corridors played a major role in shaping the potential expansion area of the pine marten in agricultural lowlands. This was high only for the western part of the River Po plain and, secondarily, for the pine wood patches bordering the Adriatic coast. The hypothesis that lowland woods may represent marginal habitats for the pine marten was not supported by the data collected about both its density and macronutrient balance. In the valley of the River Ticino, microsatellite analysis of faecal DNA allowed to point out one of the highest densities ever recorded in continental Europe. The high genetic relatedness of identified individuals suggested that the agricultural matrix may act as a barrier to the dispersal of juveniles. Genotyping allowed also to test for the effectiveness of a camera-trapping-based method (Random Encounter Model) for assessing pine marten density. The REM underestimated population size by ca. 40%. Dietary macronutrient ratios of pine marten differed from the target, as assessed by the meta-analysis of available diet data for Europe, to an almost negligible extent, confirming that plasticity in feeding behaviour plays a major role in pine marten expansion in agricultural areas. Genetic surveys confirmed that pine marten expansion is coinciding with a reduction in stone marten range or abundance. When syntopic, stone marten exclusion from woodland by the pine marten is a common output, although the mechanisms underlying the higher competitive ability of the latter are still unclear. By camera-trapping, we tested the hypothesis that spatial and temporal segregation may favour the coexistence of the pine marten with the other mesocarnivores to a wider extent than that of the stone marten. Results from two study areas suggested that pine marten higher competitive ability with respect to the stone marten could be the indirect consequence of its greater plasticity in activity patterns. As different guild compositions result into different interspecific relations among coexisting species, our findings need to be further tested across different communities and study areas.