Prey Switching - Mechanisms

Mechanisms

The reason a consumer may switch from eating one resource, to eating another, is because it may increase an individual's foraging efficiency and therefore its inclusive fitness. It has been argued that frequency-dependent predation is predicted from optimal foraging theory. In particular the contingency model predicts that in some circumstances the most profitable resource should be eaten at the expense of the less profitable resources, and that this decision is based on the absolute density of the most profitable type of resource. However frequency-dependent predation can occur even when the absolute density of the most profitable resource remains constant. These ultimate mechanisms help to demonstrate how prey switching and apostatic selection fit into overarching ecological theory. In addition there are proximate mechanisms which may account for why an individual preferentially feeds on the most abundant type of prey.

The location and timing of when a consumer feeds can account for switching behaviour. In experiments with Guppies the switching behaviour displayed was due to the choice of patch. Likewise the switching behaviour of stoneflies was due to the time they were active. The formation of a search image may also lead to the consumer switching which prey it eats. Real suggests that a mechanism similar to search image may account for the switching behaviour displayed by Bombus pennsylvanicus, however they are reluctant to use the term search image, instead suggesting some kind of perceptual constraint. Prey switching may also occur if the consumer becomes more efficient at capturing the most common type of prey, for example increased practice at capturing the most common prey. This was found to be the case for Anax junius which fed on either mayfly nymphs or tubifex worms. From this Bergelson came up with the rule of thumb that consumers should "continue to pursue only those prey types you have successfully captured in the immediate past."

In general there have been a limited number of studies which have identified mechanisms responsible for prey switching behaviour. However it has been suggested that a consumers choice of location to feed may be the most important mechanism. Conversely, search image is controversial with disagreement over whether it actually occurs in nature, and if it does whether it is important.