Optimal foraging theory was first introduced in 1966 by Robert MacArthur and Eric Pianka (published in
The American Naturalist). Their intention in proposing the
hypothesis was to explain the
controls on the width of a
predator's
diet. By width, they meant the variety (or lack thereof) of prey items consumed by a
mobile predator.
The essence of the hypothesis is that a predator must spend energy searching for, capturing and then handling prey items. While searching through the environment, a predator is bound to encounter not only the preferred prey type but also a number of potentially profitable items. Thus, the diet width is determined by the predator's response to the discovery of prey.
Essentially, the question is this: should a predator, which targets a preferred (most profitable) prey item, expand its diet to include the next most profitable item encountered? They formulated this mathematically, as follows: the predator will consume the ith prey item if
Ei/hi >= mean(E)/(mean(s)+mean(h))
where Ei is the energy content of the prey item, h is the time required to handle the item, s is the amount of time required to find the item and Ei/hi is the relative profitability of the item.
From this simple equation a number of predictions have been made and verified empirically, to a lesser or greater degree:
- Predators which handle food quickly should be generalists (because h is small)
- Predators which take a long time to consume food items should be highly selective (because h is large)
- In an unproductive environment, predators should have a greater diet width (because mean(s) is large)