How Variance and Risk Affect Foraging Behavior

Abstract

Foraging options in the real world differ in mean return but also in variability around that mean. Selecting a variable option then, leads to some degree of uncertainty in the immediate level of return and hence in risk of falling short of a critical threshold. The Energy Budget Rule (EBR) is a common formulation of these ideas in behavioral ecology. If two foraging options have the same mean return but differ in levels of variation, then an animal on a positive energy budget can expect greater fitness if it selects the least variable option (is risk-averse) and an animal on a negative energy budget can expect greater fitness if it selects the most variable option (is risk-prone). Similar ideas for humans have corresponding development in the economic literature. Experimental manipulations of the perceived energy budgets of small animals have led to considerable empirical evidence supporting risk-sensitivity and the EBR. Additional supporting evidence is found in the empirical construction of utility curves portraying risk-sensitivity, predicted trade-offs between mean and variation, and strength of risk-sensitive responses relative to perception of foraging risk. Although some data may offer challenges to the EBR, a recent and more general version of the model (GBR – Gradual Budget Rule), successfully addresses some of these apparent challenges. Additional consideration of psychophysical mechanisms along with functional (fitness) models will likely improve our understanding of how and why animals respond to variation in foraging outcomes.