Apex_predators

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. 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. Such non-predators as elephants and hippopotamuses that prove more dangerous to humans than bears, hyenas, crocodilians, giant snakes, or the big cats are not apex predators because they are 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 a predator of extreme efficiency must adapt its behavior to the presence of killers even more formidable than themselves. Such an animal that has predators throughout its range and must alter its behavior to avoid being preyed upon is not an apex predator. The giant panda, even if exempt from predation due to its size and its bear-like defenses, is so slightly predatory that it has no effect upon any prey species.

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. 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" (American Heritage Dictionary, 2006. <http://dictionary.reference.com/browse/trophic%20level>). 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" (American Heritage Science Dictionary, 2002. <http://dictionary.reference.com/browse/trophic%20level>). One study of marine food webs defined apex predators as greater than trophic level fourEssington, Timothy E.; Beaudreau, Anne H.; Wiedenmann, John (2005 2005). "Fishing through marine food webs" (PDF). Proceedings of the National Academy of Sciences 103 (9): 3171–3175. Retrieved on 2007-11-24. ; 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. lionsAWF: Wildlife: Lion, tigersAnimal Info - Tiger, and African wild dogs ADW: Lycaon pictus: Informationthat 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 [http://animaldiversity.ummz.umich.edu/site/accounts/information/Canis_lupus_familiaris.html

ADW: Canis lupus familiaris: Information] 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.Canadian Eskimo Dog History In most seas, the orcaKiller Whale, Killer Whale Profile, Facts, Information, Photos, Pictures, Sounds, Habitats, Reports, News - National Geographic has such a role.

Apex predators include a wide variety of animals, all at least part-time predators such as grizzly bears,Grizzly Bear - Defenders of Wildlife, wolvesADW: Canis lupus: Information Tasmanian Devil,http://www.parks.tas.gov.au/wildlife/mammals/devil_faq.html and (as mature adults) snapping turtles,ADW: Chelydra serpentina: Information as well as such obligate carnivores as the great white shark,Great White Shark, Carcharodon carcharias at MarineBio.org tiger sharkFlorida Museum of Natural History Ichthyology Department the giant otter,Mammals - Giant Otter great horned owl,All About Birds: Great Horned Owl and the Komodo dragon.Komodo Dragon 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,[1] whale shark,Florida Museum of Natural History Ichthyology Department: Whale Shark snow leopardhttp://www.animalinfo.org/species/carnivor/unciunci.htm that dwells in the Himalayas, or the Baikal seal of the distinct ecosystem of Lake Baikal[2] (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.Electric Eel [3] Social organization allows driver ants and army antsBBC - Science & Nature - Articles - Ants can\'t hurt you, can they? to prey upon animals far larger than themselves while driving off even humans until the swarm passes. BBC - Nature Wildfacts - Driver ant, locally known as \'Siafu\'. Inaccessibility of its home makes such a hit-and-fly predator as a bald eagleADW: Haliaeetus leucocephalus: Information 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 bothTasku, Cheon; Ohta, Shigemi (August 2004). "Suppression of ecological competition by an apex predator". Physical Review 70 (2). doi:10.1103/PhysRevE.70.021913. Retrieved on 2007-11-24. .

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.Croll, D. A.; Maron, J. L.; et al. (March 2005). "Introduced Predators Transform Subarctic Islands from Grassland to Tundra". Science 307 (5717): 1959 - 1961. doi:10.1126/science.1108485. Retrieved on 2007-11-24.  Feral catsThe Great Australian Cat Dilemma and dogs BBC NEWS | Science/Nature | Dog doubts over Tasmanian tigerhave 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 Crocodilian Species - American Alligator (Alligator mississippiensis).

The removal of top-level predators—often through human agency—can radically cause (or disrupt) trophic cascades.Egan, Logan Zane; Téllez, Jesús Javier (June 2005). Effects of preferential primary consumer fishing on lower trophic level herbivores in the Line Islands (PDF). Stanford at Sea. Stanford University. Retrieved on 2007-11-24.Pace, M. L.; Cole, J. J.; et al. (December 1999). "Trophic cascades revealed in diverse ecosystems". Trends in Ecology and Evolution 14 (12): 483-488. Retrieved on 2007-11-24.  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. AIMS Crown-of-Thorns Starfish - Contents

See also

• List of Apex Predators

References

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