The Daily Energy Budget Rule

In its original formulation, the Optimal Foraging Theory encompasses several concepts such as the Daily Energy Budget Rule.

The Daily Energy Budget (DEB) rule is an attempt to explain the decisions of foragers on a daily basis, based on the foraging currency such as the net gain of energy gain.

The DEB make use of a daily survival threshold, which corresponds to the energetic costs for the most basic needs of a forager. Such threshold will typically include the basal metabolism, the energetic cost of searching for preys and the energetic cost of pursuit, capture, and eating those preys.

Consequently, if the mean net rate of energy gain of a foraging strategy is enough to reach that threshold necessary to survive to the next day, we say that the DEB is positive.

On the opposite, if the mean net rate of energy gain is not enough to reach the daily survival threshold, then we say that the DEB is negative, and might be a pressure for the forager to adopt a different, potentially more risky foraging strategy to assure survival.

For this reason, the DEB is a powerful tool to evaluate risk sensitivity and if a forager would rather adopt a risk-prone of a risk-averse behavior.

The most famous application of the DEB, and observed in nature, is that between two foraging strategies that both yield enough energetic gain to reach the survival threshold (thus the DEB being positive in both cases) but with different variability, the forager will always choose the least variable option, and therefore the lowest risk. For example, between a constant feeding option and a variable feeding option that could provide either much less or much more calories, a forager will take the constant feeding option if the budget is positive.