Apex predators (also known as alpha, super, top or top-level predators) are predators with little to no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism (which generally excludes parasites and most bacteria). In this context, "apex predator" is usually defined in terms of trophic dynamics. Apex predator species occupy the highest trophic level(s) and have a crucial role in maintaining the health of their ecosystems. One study of marine food webs defined apex predators as greater than trophic level four. The apex predator concept is commonly applied in wildlife management, conservation, and ecotourism.
Food chains are often far shorter on land, with the top of the food chain limited to the third trophic level, as where such predators as the big cats, crocodilians, hyenas, wolves, or giant constrictor snakes prey upon large herbivores. Apex predators do not need to be hypercarnivores. For example, grizzly bears and humans are each apex predators and are omnivores.
Ecological role 
- See also Mesopredator release hypothesis
Apex predators affect prey species' population dynamics. Where two competing species are in an ecologically unstable relationship, apex predators tend to create stability if they prey upon both. Inter-predator relationships are also affected by apex status. Non-native fish, for example, have been known to devastate formerly dominant predators. One lake manipulation study found that when the non-native smallmouth bass was removed, lake trout, the suppressed native apex predator, diversified its prey selection and increased its trophic level.
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. Such wide-ranging effects on lower levels of an ecosystem are termed trophic cascades. The removal of top-level predators, often, recently, through human agency, can radically cause (or disrupt) trophic cascades. A commonly cited example of apex predators affecting an ecosystem is Yellowstone National Park. After the reintroduction of the gray wolf in 1995, researchers noticed drastic changes occurring in the Greater Yellowstone Ecosystem. Elk, the primary prey of the gray wolf, became less abundant and changed their behavior, freeing riparian zones from constant grazing. The respite allowed willows, aspens, and cottonwoods to grow, creating habitat for beaver, moose, and scores of other species. In addition to the effects on prey species, the gray wolf's presence also affected the park's grizzly bear, a vulnerable species. The bears, emerging from hibernation, chose to scavenge off wolf kills after fasting for months. They can also eat wolf kills in autumn to prepare for hibernation. As grizzly bears give birth during hibernation, a greater food supply may improve the mother’s nutrition and increase the number of cubs. Dozens of other species, including eagles, ravens, magpies, coyotes, and black bears, have been documented scavenging from wolf kills. Keystone species are apex predators within functional groups, a concept first described by zoologist Robert Paine to explain the relationship between Pisaster ochraceus, a species of starfish, and Mytilus californianus, a species of mussel.
A killer whale observes a Weddell seal on an ice floe near Rothera Station, along the Antarctic Peninsula. Killer whales are known to sometimes kill other whales while hunting in packs, earning them the title "Wolves of the Sea", and even killing the Great White Shark and leopard seal one-on-one as prey.
The whale shark, the world's largest shark and fish, has a reputation as a "gentle giant" as a filter feeder. Despite having no prey larger than small fish, it has no natural predators and is an apex predator.
- "apex predator". PBS. Retrieved 2010-01-25.
- "predator". Online Etymological Dictionary. Retrieved 2010-01-25.
- Essington, Timothy E.; Beaudreau, Anne H., Wiedenmann, John (December 2005). "Fishing through marine food webs" (PDF). Proceedings of the National Academy of Sciences 103 (9): 3171–3175. doi:10.1073/pnas.0510964103. PMC 1413903. PMID 16481614. Retrieved 2010-01-25.
- Archer, Michael. "Slime Monsters Will Be Human Too," Nature Australia, vol. 22, 1989.
- Lepak, Jesse M.; Kraft, Clifford E., Weidel, Brian C. (March 2006). "Rapid food web recovery in response to removal of an introduced apex predator" (PDF). Canadian Journal of Fisheries and Aquatic Sciences 63 (3): 569-575. ISSN: 0706-652X. Retrieved 2010-01-25.
- 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. PMID 15790855. Retrieved 2010-01-25.
- 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 2010-01-25.
- 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. doi:10.1016/S0169-5347(99)01723-1. PMID 10542455.
- Bystroff, PhD., Chris. "The wolves of Yellowstone" (PDF). 2006-04-17. pg. 2. Retrieved 2010-01-25.
- Wilmers, Christopher C. (2004). "The gray wolf – scavenger complex in Yellowstone National Park" (PDF). p. 56. Retrieved 2010-01-25.
- Levy, Sharon (November 2002). "Top Dogs". Retrieved 2010-01-25.
- Wilmers, Christopher C. (2004). "The gray wolf – scavenger complex in Yellowstone National Park" (PDF). p. 90. Retrieved 2010-01-25.
- Robbins, Jim (May-June 1998). "Weaving a new web: wolves change an ecosystem". Smithsonian Zoogoer (Smithsonian Institution) 27 (3). Archived from the original on 10 February 2010. Retrieved 2010-01-25.
- Wilmers, Christopher C.; Getz, Wayne M. (April 2005). "Gray wolves as climate change buffers in Yellowstone". PLoS Biology 3 (4): e92. doi:10.1371/journal.pbio.0030092. Retrieved 2010-01-25.
- Davic, Robert D (2003). "Linking keystone species and functional groups: a new operational definition of the keystone species concept". Conservation Ecology 7 (1): r11. Retrieved 2010-01-25.
- "Saltwater Crocodile." National Geographic. Retrieved 2010-01-25.
- Whiting, Frances. "Terri fights to halt croc eggs harvest." Australia Zoo. 2007-06-11. Retrieved 2010-01-25.
- "Orcinus orca – Orca (Killer Whale)". Marinebio.org. Retrieved 2012-03-04.