Macronutrient regulation by mesocarnivores in a rodent-poor area

Understanding how predators cope with variation in the availability of key prey species is pivotal for understanding the adaptive significance of their feeding strategies. In the framework of nutritional ecology, we explored the yearly diets and macronutrient (protein, lipids and carbohydrates) ratios of mesocarnivores (Martes spp. and red fox Vulpes vulpes), in a protected area (Mount Fenera Natural Park, NW Italy) where the availability of small mammals was unexpectedly low. Small mammal abundance was assessed by live trapping and hair-tube surveys, while diet analysis was based on faecal samples (117 and 104, respectively) collected along transects. All predators compensated for the low availability of their usual main source of protein by switching to alternative, nutritionally equivalent prey: arboreal rodents for martens and earthworms and wild boars for foxes. The higher-than-average use of these prey species indicated that the recorded diets were the result of the search for complementary nutritional resources. Accordingly, both martens and the red fox regulated their nutrient intakes so as to get close to their respective intake targets, suggesting that the nutritional content of food resources may play a major role in shaping the responses of predators to changes in prey abundance. Such dietary flexibility is likely a key factor enabling them to persist across a wide range of habitats, including those undergoing rapid man-driven modification.