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Apex predators (also alpha predators, superpredators, or top-level predators) are predators that, as adults, are not normally preyed upon in the wild in significant parts of their range by creatures not of their own species.

Apex predator species are often at the end of long food chains, where they have a crucial role in maintaining the health of ecosystems. The term "apex predator" has been defined in terms of trophic levels. Trophic levels are "a group of organisms that occupy the same position in a food chain" ^[1]. There are generally four trophic levels in the food chain, "occupied by producers at the bottom and in turn by primary, secondary, and tertiary consumers" ^[2]. One study of marine food webs defined apex predators as greater than trophic level four^[3]; an apex predator, then, is at the top of their food chain. On land, where biological diversity is generally far less than oceanic environments, the third trophic level (eg. lions^[4], tigers^[5], and African wild dogs ^[6]that prey upon large herbivores that in turn eat vegetation) can be the final trophic level and the local top predator. In many land biomes, humans and dogs ^[7] effectively share the role due to their co-operation; in most seas, the orca^[8] has such a role.

Apex predators include a wide variety of animals, all at least part-time predators such as grizzly bears ^[9], wolves^[10], and (as mature adults), snapping turtles ^[11], as well as such obligate carnivores as the great white shark^[12], the giant otter^[13] great horned owl^[14] and the Komodo dragon ^[15]. Size is an obvious advantage in having no larger animals that might prey upon them as adults, as with a sperm whale [1] or the Baikal seal of the distinct ecosystem of Lake Baikal^[16] (even if most seal species are prey items for sharks, killer whales, bears, and lions in much of the world) -- -- but even a relatively small one might exempt itself from predation from larger creatures in a predator-rich environment with the same weapon that it uses to subdue prey. Jaguars, cougars, otters, raptor birds, egrets, caimans, anacondas, piranhas, dogs, and humans that ordinarily prey upon fish have obvious cause to avoid an electric eel.^[17] [2] Social organization allows driver ants and army ants^[18] to prey upon animals far larger than themselves while driving off even humans until the swarm passes. ^[19]. Inaccessibility of its home makes such a hit-and-fly predator as a bald eagle^[20] an apex predator.

Apex predators clearly affect prey species' population dynamics. Research has shown, for instance, that where two competing species are in an ecologically unstable relationship, apex predators tend to create stability if they prey upon both^[21].

Effects on wider ecosystem characteristics, such as plant ecology, have been debated, but there is evidence of a significant impact by apex predators: introduced arctic foxes, for example, have been shown to turn subarctic islands from grassland into tundra through predation on seabirds.^[22] Feral cats^[23] and dogs ^[24]have ravaged native Australian wildlife. Such wide-ranging effects on lower levels of an ecosystem are termed trophic cascades. The American alligator, invulnerable as adults to all creatures other than armed humans and larger members of its species, often proves essential to preserving the ecosystems in which it lives ^[25].

The removal of top-level predators—often through human agency—can radically cause (or disrupt) trophic cascades.^[26][27] One extreme example occurs when the crown-of-thorns starfish whose reef-destroying predation goes out of control when its primary predator, the triton, is depleted through overfishing. ^[28]

• List of Apex Predators