Optimal Foraging Theory - The Functional Classes of Predators

The Functional Classes of Predators

Optimal foraging theory uses predators as the object of analysis. There are four functional classes of predators:

• True predators attack large numbers of their prey throughout their life. They kill their prey immediately, or shortly after the attack. They may eat all or only part of their prey. True predators include tigers, lions, plankton-eating whales, seed-eating birds, ants and humans.
• Grazers attack large numbers of their prey throughout their lifetime and eat only a portion of their prey. They harm the prey, but rarely kill it. Grazers include locusts, leeches and mosquitoes.
• Parasites, like grazers, eat only a part of their prey (host) but rarely the entire organism, and spend all or large portions of their life cycle living in/on a single host. This much more intimate relationship is typical of tapeworms, liver flukes and plant parasites such as the potato blight.
• Parasitoids are mainly typical of wasps (order Hymenoptera), and some flies (order Diptera). Eggs are laid inside the larvae of other arthropods which hatch and consume the host from the inside, killing it. This intimate predator-host relationship is typical of about 10% of all insects. Many viruses that attack single-celled organisms (such as bacteriophage) are also parasitoids, in that they reproduce inside a single host that is inevitably killed by the association.