Optimal Patch Choice

Scientists have proven that animals have great knowledge of their environment, and can evaluate the food potential in a foraging area. However, the mechanisms that lead a specimen to make a particular choice, like staying or leaving the current foraging patch for another one, is still poorly understood. This problem is even harder in a heterogeneous - "patchy" - environment, where the specific habitats of preys might not overlay each other.

A consequence of the choice of a foraging patch is the slow but immediate depletion of that patch through the consumption of a prey, making that patch less attractive over time. This raises the question of when an animal should switch from the current patch to move to another. This is not an easy problem, as several other factors need to be considered, such as the distance to the next patch and the energy cost of exploiting a new patch. Therefore, the optimal patch choice is part of the concept of risk sensitivity.

The marginal value theorem was created to answer this question in foraging ecology. The marginal value theorem suggests that an animal should move to another patch when the value of the current patch decreases below the average value of the patches from the environment. However, this relies on the assumption that an animal has the ability to evaluate the richness of patches in the environment to efficiently switch patches at the best time.

Figure 1. How the marginal value theorem evaluates the optimal time to spend on a patch. If foragers leave too early, they are missing out on efficient foraging, but they leave too late they waste too much energy to search for preys which have become too depleted, thus for a lower gain.