Julián G. Mangas

Spatial distribution models in a frugivorous carnivore, the stone marten (Martes foina): is the fleshy-fruit availability a useful predictor?

Fleshy-fruit availability is rarely used as a predictor in stone marten ( Martes foina ) habitat models, despite its frugivorous carnivore diet. Data on stone marten occurrence, habitat structure and fl eshy-fruit species abundance was collected along 2 km long survey routes within 2 x 2 km sample plots (n = 30). Two different spatial scales were considered: 1) the entire survey route; and 2) 200 m segments within each 2 km survey route. Data analyses included Poisson General Linear Models (GLM) and Generalized Linear Mixed Models (GLMM) for the fi rst and second approaches, respectively. Strawberry tree ( Arbutus unedo ) availability was signifi cantly and positively correlated to stone marten occurrence at both spatial scales, particularly for the large-scale model. At the larger scale, a lower correlation to the traditional habitat structure variables was observed. Tree cover was the most important variable in the small-scale model, but strawberry tree availability was also an important predictor. Stone marten abundance was low in areas of high tree cover and absence of strawberry trees; emphasising the prominent role of strawberry trees per se in the abundance of stone martens. Our results indicated that including fi ne, fi eld-derived estimates of key food resources for species can increase the utility of habitat models.

The presence of a “competitor pit effect” compromises wild rabbit (Orcytolagus cuniculus) conservation

Wild rabbit (Oryctolagus cuniculus) populations have suffered a dramatic reduction over the last 30 years in Spain. Rabbit decline has been recurrently associated with several epizootics and habitat changes. The role of interspecific competition has been usually neglected. This study analyzes the effects of habitat suitability and wild boar (Sus scrofa) occurrence, a hypothetical predator and competitor species, on a small and isolated population of rabbits. To test this effect we used a GLM with the abundance of rabbits as response variable and wild boar occurrence as predictor. To avoid habitat confounding effects we included vegetation structure variables and elevation summarized in PCA factors. Rabbits showed a very restricted and aggregated distribution and a very low abundance across the study area. In contrast, wild boar was present in all sampled plots but one and showed moderatehigh abundance. The three best models included both wild boar occurrence and principal component factor 2. Rabbits were located in opened Mediterranean areas where trees were small and scarce, rock cover was low and wild boar occurrence was also low. Nowadays wild boar populations are not directly controlled in private lands and its hunting is forbidden in National Parks in Spain. Waiting for further research to evaluate the threshold of rabbit densities below which competitors and/or predators may prevent the recovery of rabbit populations, control of wild boars may be useful as a short-term strategy to recover small rabbit populations whenever it is linked to habitat improvements.