Predation

Predation is the interaction in which one species, the predator, captures, kills, and feeds upon another species, the prey -- represented as (+, −), since the predator clearly benefits while the prey is harmed (indeed, the individual prey usually dies). A lion killing and eating a deer, an owl catching a mouse, and a frog snapping up an insect are all everyday examples of predation.

Predation plays several important ecological roles within a community, beyond simply transferring energy from one trophic level to the next. First, predators help keep prey populations in check, preventing any single prey species from growing so large that it exhausts its own food supply or crowds out other species. Second, by controlling the abundance of the prey species they most efficiently exploit, predators can indirectly maintain overall species diversity within a community -- if a predator's preferred prey happens to be the species that would otherwise competitively dominate and exclude other, weaker competing species, then removing the predator can allow that one dominant prey species to take over, sharply reducing diversity. Predators that have this outsized, diversity-preserving effect on their community relative to their own abundance are called keystone species; a well-documented example is the starfish Pisaster, whose removal from a rocky intertidal community allowed its main prey, mussels, to multiply unchecked and competitively crowd out most of the other species that had previously coexisted there.

Because predation exerts such strong selective pressure, both predators and prey have evolved a rich set of adaptations over evolutionary time -- predators evolve traits that make them more efficient hunters, and prey species evolve traits that make them harder to catch, in a continual evolutionary "arms race" between the two.

Adaptations that improve a predator's hunting efficiency include sharp claws and teeth or beaks specialised for seizing and tearing prey, keen sensory systems (excellent eyesight, hearing, or smell) for detecting prey at a distance, speed and stealth for pursuit or ambush, camouflage that lets an ambush predator remain undetected until the prey is within striking range, and, in some species, venom or toxins used to subdue prey quickly and safely. …