Variation in predation risk and vole feeding behaviour: a field test of the risk allocation hypothesis

Abstract

Many prey animals experience temporal variation in the risk of predation and therefore face the problem of allocating their time between antipredator efforts and other activities like feeding and breeding. We investigated time allocation of prey animals that balanced predation risk and feeding opportunities. The predation risk allocation hypothesis predicts that animals should forage more in low- than in high-risk situations and that this difference should increase with an increasing attack ratio (i.e. difference between low- and high-risk situations) and proportion of time spent at high risk. To test these predictions we conducted a field test using bank voles ( Clethrionomys glareolus) as a prey and the least weasel ( Mustela nivalis nivalis) as a predator. The temporal pattern and intensity of predation risk were manipulated in large outdoor enclosures and the foraging effort and patch use of voles were measured by recording giving-up densities. We did not observe any variation in feeding effort due to changes in the level of risk or the proportion of time spent under high-risk conditions. The only significant effect was found when the attack ratio was altered: the foraging effort of voles was higher in the treatment with a low attack ratio than in the treatment with a high attack ratio. Thus the results did not support the predation risk allocation hypothesis and we question the applicability of the hypothesis to our study system. We argue that the deviation between the observed pattern of feeding behaviour of bank voles and that predicted by the predation risk allocation hypothesis was mostly due to the inability of voles to accurately assess the changes in the level of risk. However, we also emphasise the difficulties of testing hypotheses under outdoor conditions and with mammals capable of flexible behavioural patterns.

Behavioural responses of Anopheles gambiae sensu stricto M and S molecular form larvae to an aquatic predator in Burkina Faso

“…gambiae modify their behaviour to a significant extent in the presence of a natural predator, the backswimmer A. jaczewskii , by becoming less active and positioning themselves at the wall of the container, which appears to be the safest location under our experimental settings. Activity reduction in response to increased predation risk has been shown for a number of species, including mosquitoes [36], crayfish [49], tadpole [50] and voles [51], and might, therefore, represent a general mechanism for predator vigilance. In mosquitoes, reduced movement appeared to reduce both encounter rates with and conspicuousness to Notonecta [52,53].…”

The effect of prior experience on a prey’s current perceived risk

“…Additionally, if the pattern of high-and low-risk periods experienced by prey is consistent, the pattern and ratio of high to low risk should inXuence the strength of their antipredator behavior [i.e., the risk allocation hypothesis (RAH), Lima and BednekoV (1999)]. Although empirical studies have produced mixed support for the RAH (e.g., Sih and McCarthy 2002;Sundell et al 2004;Foam et al 2005), the data suggest that the longerterm temporal pattern of predation risk can inXuence prey behavior.…”

Molecular organization of vomeronasal chemoreception

“…4g,h). Moreover TrpC2 −/− animals exhibited abnormal ingestive behavior of the predator bedding suggesting that VNO inputs also inhibits foraging 24,25 (Supplementary fig. 7).…”