Alligator

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Alligators
Temporal range: Oligocene-Recent, 37–0Ma
An American (top) and Chinese alligator (bottom)
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Clade:Sauropsida
Clade:Crocodylomorpha
Order:Crocodilia
Family:Alligatoridae
Subfamily:Alligatorinae
Genus:Alligator
Daudin, 1809
Type species
Alligator mississipiensis
Daudin, 1802 (originally Crocodylus)
Species
 
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Alligators
Temporal range: Oligocene-Recent, 37–0Ma
An American (top) and Chinese alligator (bottom)
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Clade:Sauropsida
Clade:Crocodylomorpha
Order:Crocodilia
Family:Alligatoridae
Subfamily:Alligatorinae
Genus:Alligator
Daudin, 1809
Type species
Alligator mississipiensis
Daudin, 1802 (originally Crocodylus)
Species

An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two living alligator species: the American alligator (Alligator mississippiensis) and the Chinese alligator (Alligator sinensis). In addition, several extinct species of alligator are known from fossil remains. Alligators first appeared during the Oligocene epoch about 37 million years ago.[1]

The name alligator is an anglicized form of el lagarto, the Spanish term for "the lizard", which early Spanish explorers and settlers in Florida called the alligator.

Species (Extant)

Description

A large adult American alligator's weight and length is 360 kg (790 lb) and 4.0 m (13.1 ft) long[citation needed], but can grow to 4.4 m (14 ft) long and weigh over 450 kg (990 lb).[2] The largest ever recorded was found in Louisiana and measured 5.84 m (19.2 ft).[3] The Chinese alligator is smaller, rarely exceeding 2.1 m (6.9 ft) in length.

There is no measured average lifespan for an alligator.[4] In 1937, a one year-old specimen was brought to the Belgrade Zoo in Serbia from Germany. It is now 76 years old.[5] Although there are no valid records about its date of birth, this alligator in the Belgrade Zoo, officially named Muja (eng. Mooya), is considered the oldest alligator living in captivity. [6]

Habitat

Alligators of various ages in Everglades National Park
Head of Alligator mississippiensis
Eye of Alligator mississippiensis

Alligators are native only to the United States and China.[citation needed]

American alligators are found in the southeast United States: all of Florida and Louisiana, the southern parts of Georgia, Alabama and Mississippi, coastal South and North Carolina, Eastern Texas, the southeast corner of Oklahoma and the southern tip of Arkansas. According to the 2005 Scholastic Book of World Records, Louisiana is the state with the largest alligator population.[7] The majority of American alligators inhabit Florida and Louisiana, with over a million alligators in each state. Southern Florida is the only place where both alligators and crocodiles live side by side.[citation needed]

American alligators live in freshwater environments, such as ponds, marshes, wetlands, rivers, lakes, and swamps, as well as in brackish environments.[8] When they construct gator holes in the wetlands, they increase plant diversity and also provide habitat for other animals during drought periods.[9] They are therefore considered an important species for maintaining ecological diversity in wetlands.[10] Further west, in Louisiana, heavy grazing by nutria (coypu) and muskrat are causing severe damage to coastal wetlands. Large alligators feed extensively on nutria, and provide a vital ecological service by reducing nutria numbers.[11]

The Chinese alligator currently is found only in the Yangtze River valley[citation needed] and is extremely endangered, with only a few dozen believed to be left in the wild. Indeed, far more Chinese alligators live in zoos around the world than can be found in the wild. Rockefeller Wildlife Refuge in southern Louisiana has several in captivity in an attempt to preserve the species. Miami MetroZoo in Florida also has a breeding pair of Chinese alligators.

Behavior

Large male alligators are solitary territorial animals. Smaller alligators can often be found in large numbers close to each other. The largest of the species (both males and females), will defend prime territory; smaller alligators have a higher tolerance of other alligators within a similar size class.

Although alligators have a heavy body and a slow metabolism, they are capable of short bursts of speed, especially in very short lunges. Alligators' main prey are smaller animals that they can kill and eat with a single bite. Alligators may kill larger prey by grabbing it and dragging it into the water to drown. Alligators consume food that can not be eaten in one bite by allowing it to rot, or by biting and then spinning or convulsing wildly until bite-size chunks are torn off. This is referred to as a "death roll." Critical to the alligator's ability to initiate a death roll, the tail must flex to a significant angle relative to its body. An alligator with an immobilized tail cannot perform a death roll.[12]

Most of the muscle in an alligator's jaw evolved to bite and grip prey. The muscles that close the jaws are exceptionally powerful, but the muscles for opening their jaws are comparatively weak. As a result, an adult human can hold an alligator's jaws shut barehanded. It is common today to use several wraps of duct tape to prevent an adult alligator from opening its jaws when handled or transported.[13]

Alligators are generally timid towards humans and tend to walk or swim away if one approaches. This has led some people to the practice of approaching alligators and their nests in a manner that may provoke the animals into attacking. In the state of Florida, it is illegal to feed wild alligators at any time. If fed, the alligators will eventually lose their fear of humans and will learn to associate humans with food, thereby becoming a greater danger to people.[14]

Diet

The type of food eaten by alligators depends upon their age and size. When young, alligators eat fish, insects, snails, crustaceans, and worms. As they mature, progressively larger prey is taken, including larger fish such as gar, turtles, various mammals, particularly nutria and muskrat,[8] as well as birds, deer and other reptiles.[15][16] Their stomachs also often contain gizzard stones. They will even consume carrion if they are sufficiently hungry. In some cases, larger alligators are known to ambush dogs, Florida panther and black bears, making it the apex predator throughout its distribution. In this role as a top predator, it may determine the abundance of prey species including turtles and nutria[17][18] As humans encroach onto their habitat, attacks are few but not unknown. Alligators, unlike the large crocodiles, do not immediately regard a human upon encounter as prey, but may still attack in self-defense if provoked.

Reproduction

Alligator eggs and young
Baby alligators
A rare albino American alligator.
An albino alligator swimming.

Alligators generally mature at a length of 6 feet (1.8 m). The mating season is in late spring. In April and May, alligators form so-called "bellowing choruses". Large groups of animals bellow together for a few minutes a few times a day, usually one-three hours after sunrise. The bellows of male American alligators are accompanied by powerful blasts of infrasound.[19] Another form of male display is a loud head-slap.[20] Recently it was discovered that on spring nights alligators gather in large numbers for group courtship, the so-called "alligator dances".[21]

In summer, the female builds a nest of vegetation where the decomposition of the vegetation provides the heat needed to incubate the eggs. The sex of the offspring is determined by the temperature in the nest and is fixed within 7 to 21 days of the start of incubation. Incubation temperatures of 86 °F (30 °C) or lower produce a clutch of females; those of 93 °F (34 °C) or higher produce entirely males. Nests constructed on leaves are hotter than those constructed on wet marsh and, thus, the former tend to produce males and the latter, females. The natural sex ratio at hatching is five females to one male. Females hatched from eggs incubated at 86 °F (30 °C) weigh significantly more than males hatched from eggs incubated at 93 °F (34 °C).[22] The mother will defend the nest from predators and will assist the hatchlings to water. She will provide protection to the young for about a year if they remain in the area. The largest threat to the young are adult alligators. Baby alligators have an egg tooth that helps them get out of their egg during hatching time. Predation by adults on young can account for a mortality rate of up to fifty percent in the first year. In the past, immediately following the outlawing of alligator hunting, populations rebounded quickly due to the suppressed number of adults preying upon juveniles, increasing survival among the young alligators.

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Alligator bellow, ogg/Vorbis format.

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Anatomy

Alligators, much like birds, have been shown to exhibit unidirectional movement of air through their lungs.[23] All other amniotes are believed to exhibit bidirectional, or tidal breathing. For a tidal breathing animal, such as a mammal, air flows into and out of the lungs through branching bronchi which terminate in small dead-end chambers called alveoli. As the alveoli represent dead-ends to flow, the inspired air must move back out the same way that it came in. In contrast air in alligator lungs makes a circuit moving in only one direction through the parabronchi. The air first enters the outer branch, moves through the parabronchi, and exits the lung through the inner branch. Extensive vasculature around the parabronchi are where oxygen exchange takes place.[24]

They have muscular flat tails that propel them while swimming.

There are two kinds of white alligators, albino and leucistic. These alligators are practically impossible to find in the wild. They could survive only in captivity and are few in number.[25][26] The Aquarium of the Americas in New Orleans has leucistic alligators found in a Louisiana swamp in 1987.[26]

Human uses

Alligators are raised commercially for their meat and skin, which is used for bags and shoes. They also provide economic benefits through the ecotourism industry. Visitors may take swamp tours, in which alligators are a feature. Their most important economic benefit to humans may be the control of nutria and muskrats.[27] Louisiana spends millions of dollars of bounty money to control nutria.[citation needed] This service is provided by alligators.

See also

References

  1. ^ The Paleobiology Database: Alligatoridae
  2. ^ "American Alligator and our National Parks". Eparks.org. Retrieved 2008-10-14. 
  3. ^ "Louisiana Alligator Advisory Council". Retrieved 2010-03-07. 
  4. ^ Kaku, Michio (March 2011). Physics of the Future: How Science Will Shape Human Destiny And Our Daily Lives by the Year 2100. Doubleday. pp. 150, 151. ISBN 978-0-385-53080-4. 
  5. ^ "Oldest alligator in the world". b92.net. Retrieved 2012-02-08. 
  6. ^ "The oldest alligator living in captivity". shekoos.wordpress.com. 2012-02-22. Retrieved 2013-08-07. 
  7. ^ 2005 Scholastic Book of World Records
  8. ^ a b Dundee, H. A., and D. A. Rossman. 1989. The Amphibians and Reptiles of Louisiana. Baton Rouge: Louisiana State University Press.
  9. ^ Craighead, F. C., Sr. (1968). The role of the alligator in shaping plant communities and maintaining wildlife in the southern Everglades. The Florida Naturalist, 41, 2–7, 69–74.
  10. ^ Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Chapter 4.
  11. ^ Keddy, P.A., L. Gough, J.A. Nyman, T. McFalls, J. Carter and J. Siegrist. 2009. Alligator hunters, pelt traders, and runaway consumption of Gulf coast marshes: A trophic cascade perspective on coastal wetland losses. p. 115-133 in B.R. Silliman, E.D. Grosholz, and M.D. Bertness (eds.) Human Impacts on Salt Marshes. A Global Perspective. University of California Press, Berkeley, CA
  12. ^ Fish, Frank E.; Bostic, Sandra A.; Nicastro, Anthony J.; Beneski, John T. (2007). "Death roll of the alligator: mechanics of twist feeding in water" (PDF). The Journal of Experimental Biology 210 (16): 2811–2818. doi:10.1242/jeb.004267. PMID 17690228. 
  13. ^ Crocodilian Captive Care FAQ: How to properly handle/transport crocodilians etc.
  14. ^ Living with Alligators
  15. ^ Wolfe, J. L., D. K. Bradshaw, and R. H. Chabreck. 1987. Alligator feeding habits: New data and a review. Northeast Gulf Science 9: 1–8.
  16. ^ Gabrey, S. W. 2005. Impacts of the nutria removal program on the diet of American alligators (Alligator mississippiensis) in south Louisiana. Report to Louisiana Department of Wildlife and Fisheries, New Orleans.
  17. ^ Bondavalli, C., and R. E. Ulanowicz. 1998. Unexpected effects of predators upon their prey: The case of the American alligator. Ecosystems 2: 49–63.
  18. ^ Keddy, P.A., L. Gough, J.A. Nyman, T. McFalls, J. Carter and J. Siegrist. 2009. Alligator hunters, pelt traders, and runaway consumption of Gulf coast marshes: A trophic cascade perspective on coastal wetland losses. p. 115-133 in B.R. Silliman, E.D. Grosholz, and M.D. Bertness (eds.) Human Impacts on Salt Marshes. A Global Perspective. University of California Press, Berkeley, CA.
  19. ^ "Can Animals Predict Disaster? - Listening to Infrasound | Nature". PBS. 2004-12-26. Retrieved 2013-11-27. 
  20. ^ Garrick, L. D. and Lang, J. W. (1977). "Social Displays of the American Alligator". American Zoologist 17: 225–239. 
  21. ^ Dinets, V. (2010). "Nocturnal behavior of the American Alligator (Alligator mississippiensis) in the wild during the mating season" (PDF). Herpetological Bulletin 111: 4–11. 
  22. ^ Mark W. J. Ferguson & Ted Joanen (1982). "Temperature of egg incubation determines sex in Alligator mississippiensis". Nature 296 (5860): 850–853. doi:10.1038/296850a0. PMID 7070524. 
  23. ^ Farmer, C. G., and Sanders, K. (January 2010). "Unidirectional Airflow in the Lungs of Alligators". Science 327 (5963): 338–340. doi:10.1126/science.1180219. PMID 20075253. 
  24. ^ Science News; February 13, 2010; Page 11
  25. ^ "White albino alligators". softpedia.com. Retrieved 2008-10-27. 
  26. ^ a b "Mississippi River Gallery". 
  27. ^ Keddy, P. A., Gough, L., Nyman, J. A., McFalls, T., Carter, J., and Siegnist, J. (2009a). Alligator hunters, pelt traders, and runaway consumption of Gulf coast marshes: a trophic cascade perspective on coastal wetland losses. In Human Impacts on Salt Marshes: A Global Perspective, eds. B. R. Silliman, E. D. Grosholz, and M. D. Bertness, pp. 115–33. Berkeley, CA: University of California Press.

External links

The dictionary definition of alligator at Wiktionary