Risk preferences depend on environmental richness in rats performing a patch-foraging task

Abstract

Risk, or variance over outcomes, features prominently in many decisions, but the factors that determine when and how risk modulates decision making remain unclear. We tested how risk affected rats strategies for exploiting a diminishing food source as the overall richness of the environment was manipulated. Long-Evans rats earned food by sequentially visiting two foraging patches with different reward schedules--a low-variance standard option and a high-variance risky option--that provided the same average rate of reward. When rats switched between options, they encountered either a long or short delay during which no food was available to simulate the cost of travelling between patches. When the travel delay was short rats allocated more time to the low-variance standard reward schedule than the high-variance risky option. When the travel time was long rats spent the same amount of time in risky and standard patches. Consistent with previous work, rats "overharvested" patches, remaining for longer than the optimal patch residence duration. Overharvesting was prevalent in both risky and standard patches, and the magnitude of overharvesting increased with successive visits to the same patch, suggesting that overharvesting was not driven by uncertainty about the reward statistics of patches.