When food access is challenging: evidence of wood mice ability to balance energy budget under predation risk and physiological stress reactions

摘要

Prey species must balance the energetic cost of locomotion, foraging effort, and predation risk. In our work, we assessed how the wood mice (Apodemus sylvaticus) balance these costs by manipulating food access difficulty and predation risk. Live trapping was conducted in Madrid (Spain) where 80 Sherman traps were set in four different plots. To assess how wood mice manage their energy budget, all traps were first subjected to a control period followed by four treatments of 3-day duration in which food access was experimentally manipulated (free access, straw balls, straw balls wrapped in metal wire, opened plastic bottles, closed bottles). Predation risk was simulated by exposing half of the traps to fox feces. To quantify food intake, we weighed the remnants of food left by each captured mouse. Furthermore, we collected mouse fecal samples from traps to evaluate the physiological stress response by quantifying fecal corticosterone metabolites (FCM). Results showed that despite mice generally avoiding traps treated with fox feces, predation risk did not modulate food intake or FCM levels. By contrast, the experimental manipulation of food access determined the amount eaten and increased FCM levels, probably owing to the different degrees of difficulty and the energy required to obtain the food. Moreover, recaptured individuals ate more, indicating that experience critically determines mice ability to reduce the costs of accessing food. By analyzing the joint variation between mice intake and FCM levels depending on food restriction treatments, we found that mice were able to modulate their energetic expenditure depending on food access difficulty probably in order to achieve a positive marginal value of energy.