Risk Sensitivity

Environmental science has long since proven that organisms are usually acutely aware of their environment and the evolution over time, including the density of preys and predators.

A tempting concept, although very deterministic, is to assume that foragers make conscious choices in their strategies depending on the appropriate risk, evaluating the potential gains versus the downsides (the risk of being eaten, of not finding the expected resources, etc). Whether it is the result of conscious decisions or survival of the fittest, animals have been observed to alter their behavior caused by suboptimal environmental conditions. It is said in this case that foragers are risk-sensitive.

As demonstrated with the Daily Energy Budget rule, between two foraging strategies with the same mean energy gain a forager will always choose the strategy with the lowest variability (constant feeding), thus the lowest risk. The forager is then considered risk-averse, but this only applies if the lowest risk strategy provides enough energy for daily survival (the budget is positive).

If the budget is negative, meaning the constant feeding strategy is not enough to provide energy for daily survival, then the forager might switch to a riskier but potentially more rewarding strategy. The forager's behavior is then characterized as risk-prone.

There are many reasons why a low-risk strategy might slowly or suddenly not be available any longer. For example, overpopulation or incremental depletion of a foraging patch can lead to starvation. The starvation limit can be defined as a food density so low that the necessary foraging time (searching and consuming) to survive is greater than the available foraging time. Another possibility is an increase of the density of predators in the area, limiting the access to a resource previously safe.

The empirical observations are that foragers deprived of food -in a negative budget - are more likely to travel further and invest more time in search of food, thereby utilizing energy that might otherwise have been allocated to purposes such as growth or reproduction. They rely on food sources with greater variability, and they are less afraid of predators (they have inhibited aversion towards predation).