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The Saltwater Crocodile is the largest living reptile[1] and is the dominant predator throughout its range.[2]

Apex predators (also known as alpha, super-, or top-level predators) are predators that have virtually no predators of their own, residing at the top of their food chain.[3] Apex predator species are often at the top of long food chains, where they have a crucial role in maintaining the health of ecosystems.

Contents

Definition

Predation in its zoological sense is the killing and consumption of another organism, which excludes bacteria and parasites from the apex predator concept. Predation has been defined in this sense since 1932.[4] The apex predator concept is commonly applied in wildlife management and conservation, as well as eco-tourism. In these contexts it has been defined in terms of trophic levels. Trophic levels are "hierarchical strata of a food web characterized by organisms which are the same number of steps removed from the primary producers."[5] Primary, secondary, tertiary, and higher level consumers occupy successive trophic levels. One study of marine food webs defined apex predators as greater than trophic level four.[6]

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 need not be hypercarnivores. For example, grizzly bears and humans[7] are each apex predators, and yet they are omnivores that eat considerable vegetable material as well as much meat. Some animals may be superpredators in some environments but not others, such as dogs and domestic cats, both of which can ravage ecosystems.

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.[8]

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.[9] 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.[10][11] 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.[12] 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.[13][14] They can also eat wolf kills in autumn to prepare for hibernation.[15] As grizzly bears give birth during hibernation, a greater food supply may improve the mother’s nutrition and increase the number of cubs.[16] Dozens of other species, including eagles, ravens, magpies, coyotes, and black bears, have been documented scavenging from wolf kills.[17] Keystone species, as first defined by Robert Paine for Seastars are apex predators within functional groups.[18]

See also

References

  1. ^ "Saltwater Crocodile." National Geographic. Retrieved 2010-01-25.
  2. ^ Whiting, Frances. "Terri fights to halt croc eggs harvest." Australia Zoo. 2007-06-11. Retrieved 2010-01-25.
  3. ^ "apex predator". PBS. http://www.pbs.org/kqed/oceanadventures/glossary/. Retrieved 2010-01-25. 
  4. ^ "predator". Online Etymological Dictionary. http://www.etymonline.com/index.php?search=predation&searchmode=none. Retrieved 2010-01-25. 
  5. ^ "Trophic level". Merriam-Webster Dictionary. http://www.merriam-webster.com/dictionary/trophic+level. Retrieved 2010-01-25. 
  6. ^ 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. http://www.pnas.org/content/103/9/3171.full.pdf. Retrieved 2010-01-25. 
  7. ^ Archer, Michael. "Slime Monsters Will Be Human Too," Nature Australia, vol. 22, 1989.
  8. ^ 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.
  9. ^ 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. http://www.sciencemag.org/cgi/content/abstract/307/5717/1959. Retrieved 2010-01-25. 
  10. ^ 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. http://stanford.sea.edu/research/EganTellez_Research_Project.pdf. Retrieved 2010-01-25. 
  11. ^ 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. http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&list_uids=10542455&cmd=Retrieve&indexed=google. Retrieved 2010-01-25. 
  12. ^ Bystroff, PhD., Chris. "The wolves of Yellowstone" (PDF). 2006-04-17. pg. 2. Retrieved 2010-01-25.
  13. ^ Wilmers, Christopher C. (2004). "The gray wolf - scavenger complex in Yellowstone National Park" (PDF). p. 56. http://www.cnr.berkeley.edu/~getz/dissertation/WilmersDis.pdf. Retrieved 2010-01-25. 
  14. ^ Levy, Sharon (November 2002). "Top Dogs". http://www.newscientist.com/article/mg17623675.300-top-dogs.html. Retrieved 2010-01-25. 
  15. ^ Wilmers, Christopher C. (2004). "The gray wolf - scavenger complex in Yellowstone National Park" (PDF). p. 90. http://www.cnr.berkeley.edu/~getz/dissertation/WilmersDis.pdf. Retrieved 2010-01-25. 
  16. ^ Robbins, Jim (May-June 1998). "Weaving a new web: wolves change an ecosystem". Smithsonian Zoogoer. Smithsonian Institution. http://nationalzoo.si.edu/Publications/ZooGoer/1998/3/weavingwolfweb.cfm. Retrieved 2010-01-25. 
  17. ^ 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.
  18. ^ 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.







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