Apex predators
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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 and are not obliged to enter places in which they might be preyed upon. As top killers they often shape the ecology through their predation and rarely have cause for fear of being killed as prey in large parts of their range and alter the behavior of prey species.

Danger to humans is not enough to make an animal an apex predator. While elephants and hippopotamuses often prove more dangerous to humans than bears, hyenas, crocodilians, giant snakes, or the big cats, they are herbivores, and not predators. Even so deadly a creature as a Sydney funnel-web spider, a rattlesnake, sea snake, cone shell, or a Portuguese Man o' War, or a box jellyfish that can kill a human with a venomous bite or stings are themselves prey for creatures immune to their venom.

But even so efficient a predator as a bottlenose dolphin must adapt its behavior to the presence of killers more formidable than itself. An animal that must alter its behavior to avoid being preyed upon is not an apex predator. The giant panda is not an apex predator even if exempt from predation due to its size and its bear-like defenses because it is so slightly predatory that it has no effect upon any prey species. Emperor penguins are not apex predators because they must enter environments in which they can be preyed upon. Emperor penguins, as the largest dwellers inland on ice sheets, are exempt from predation, but their environment lacks food so they must hunt food in seas in which predatory leopard seals lurk.

Classification

Apex predator species are often at the end of long food chains, where they have a crucial role in maintaining the health of ecosystems. They are the absolute top of the food chain. 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; even a polar bear, the largest land predator, has cause to avoid a traditional Inuit hunter and his sled dogs.^[8] In most seas, the orca^[9] has such a role.

Apex predators include a wide variety of animals, all at least part-time predators such as grizzly bears,^[10], wolves^[11] Tasmanian Devil,^[12] and (as mature adults) snapping turtles,^[13] as well as such obligate carnivores as the great white shark,^[14] tiger shark^[15] the giant otter,^[16] great horned owl,^[17] and the Komodo dragon.^[18] Size is an obvious advantage in having no larger animals that might prey upon them as adults within their usual environment, as with a sperm whale,^[19] whale shark,^[20] snow leopard^[21] that dwells in the Himalayas, or the Baikal seal of the distinct ecosystem of Lake Baikal^[22] (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.^[23] [1] Social organization allows driver ants and army ants^[24] to prey upon animals far larger than themselves while driving off even humans until the swarm passes. ^[25]. Inaccessibility of its home makes such a hit-and-fly predator as a bald eagle^[26] an apex predator.

Ecological role

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^[27].

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.^[28] Feral cats^[29] and dogs ^[30]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 (or very capable unarmed) humans and larger members of its species, often proves essential to preserving the ecosystems in which it lives ^[31].

The removal of top-level predators—often through human agency—can radically cause (or disrupt) trophic cascades.^[32][33] 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. ^[34]

See also

• List of apex predators

References