Intraguild predation

Intraguild predation, or IGP, is the killing and eating of potential competitors. This interaction represents a combination of predation and competition, because both species rely on the same prey resources and also benefit from preying upon one another. Intraguild predation is common in nature and can be asymmetrical, in which one species feeds upon the other, or symmetrical, in which both species prey upon each other. Because the dominant intraguild predator gains the dual benefits of feeding and eliminating a potential competitor, IGP interactions can have considerable effects on the structure of ecological communities.

Intraguild predation can be classified as asymmetrical or symmetrical. In asymmetrical interactions one species consistently preys upon the other, while in symmetrical interactions both species prey equally upon each other. Intraguild predation can also be age structured, in which case the vulnerability of a species to predation is dependent on age and size, so only juveniles or smaller individuals of one of the predators are fed upon by the other. A wide variety of predatory relationships are possible depending on the symmetry of the interaction and the importance of age structure. IGP interactions can range from predators incidentally eating parasites attached to their prey to direct predation between two apex predators.

Intraguild predation is common in nature and widespread across communities and ecosystems. Intraguild predators must share at least one prey species and usually occupy the same trophic guild, and the degree of IGP depends on factors such as the size, growth, and population density of the predators, as well as the population density and behavior of their shared prey. When creating theoretical models for intraguild predation, the competing species are classified as the "top predator" or the "intermediate predator," (the species more likely to be preyed upon). In theory, intraguild predation is most stable if the top predator benefits strongly from feeding on the intermediate predator, and if the intermediate predator is a better competitor for the shared prey resource.

The ecological effects of intraguild predation include direct effects on the survival and distribution of the competing predators, as well as indirect effects on the abundance and distribution of prey species and other species within the community. Because they are so common, IGP interactions are important in structuring communities. Intraguild predation may actually benefit the shared prey species by lowering overall predation pressure, particularly if the intermediate predator consumes more of the shared prey. Intraguild predation can also dampen the effects of trophic cascades by providing redundancy in predation: if one predator is removed from the ecosystem, the other is still consuming the same prey species. Asymmetrical IGP can be a particularly strong influence on habitat selection. Often, intermediate predators will avoid otherwise optimal habitat because of the presence of the top predator. Behavioral changes in intermediate predator distribution due to increased risk of predation can influence community structure more than direct mortality caused by the top predators.

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