Constraints and demands interact to affect prey dietary reaction to predation

Abstract Prey alter their foraging when threatened by predators. Two mutually inclusive hypotheses explain this response. The first entails that defence behaviours to minimise exposure to predators prevent prey from achieving their preferred diet, while the second postulates that prey deliberately change their diet to fulfil new stress‐induced nutritional demands. We combined field observations and laboratory experiments to determine which hypothesis dictates snail dietary responses to risk of beetle predation. Snails exposed to predation‐risk reduced activity, increased climbing, increased respiration, ate distinctively to achieve a certain nutrient target, and preferred eating on the cage floor at the costs of nutritional imbalance and elevated risk. When only carbohydrates‐rich food was on the floor, stressed snails reduced activity and foraged less, but when only protein‐rich food was on the floor snails increased activity and consumed more carbohydrates than their no‐risk conspecifics. This outcome suggests that nutrient accessibility may determine which hypothesis governs the prey dietary reaction to predation risk. Read the free Plain Language Summary for this article on the Journal blog.