Marginal value theorem

In behavioural ecology, the marginal value theorem considers optimal forager who is exploiting resources that occur in patches, and who must decide when to quit a patch and move on to the next one. The theorem states that the forager will move to the next patch when his rate of payoff decreases to the long-time averaged rate of payoff.

One common image to have in mind is picking apples from trees in an orchard. When one first arrives at a new tree, the rate of apple picking is large but decreases with time, eventually falling to zero. However, a strategy of picking one or two apples from a tree then moving on to the next (fresh) tree would be nonoptimal because you would spend too much time walking between trees. Similarly, a strategy of exhausting each tree would be inefficient because then one would spend too much time searching for the last few apples on a nearly exhausted tree.

The marginal value theorem is a useful benchmark for many problems in which patchy resources are exploited and a decision must be made as to when to leave a patch and find a new one. Examples might include bees visiting flowers, birds eating berries, or even mobile shop owners (in which case the "resource" being exploited is paying customers).

The MVT has been criticised on the grounds that few foragers are optimal (typical nonoptimalities would include inability to assess exploitation rate and lack of knowledge of distant patch existence. Nevertheless, the MVT is a useful benchmark against which to compare many types of forager behaviour.