Desert Tortoise: Gopherus Agassizii


1. Niche
2. Why the Desert Tortoise is Threatened
3. Conservation Efforts
4. Interesting Facts
5. Bibliography

Niche


Location & Habitat

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The range of the Desert Tortoise stretches across multiple states (downloaded on 10/14/09)
The Desert Tortoise is found in the Southwestern U.S., more specifically in the Mojave and Sonoran deserts, which cover areas in California, Nevada, Arizona, Utah, and Mexico. The tortoise mainly stays in semi - arid (arid meaning barren) grasslands, canyons, and rocky hillsides that are below 4,000 ft. Concerning habitats, the tortoise will dig and live in burrows that reach up to ten meters in length and a foot in diameter. Therefore, the tortoise must have suitable terrain for burrowing, meaning the soil must be supple enough to dig through but sturdy enough to not collapse. The tortoise will not stay in one burrow its whole life, as its home range is roughly 131 acres.

Diet

The tortoise is an herbivore, with a diet that consists mainly of herbs, grasses, shrubs, and an assortment of annual wildflowers. If necessary, the tortoise will eat dry foliage. When rain is abundant, however, the tortoise will drink fresh water that has collected on rocks, but will also resort to digging for water that can be found underground.

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A desert tortoise in the Mojave Desert (downloaded on 10/6/09)
Activity

In general, the Desert Tortoise is most active during the late winter and early spring months. The tortoises will be active above ground from mid morning to late afternoon during these seasons, and spend the rest of their day and night in burrows. In fact, the Desert Tortoise will spend 95 percent of its life underground, though it can survive in aboveground temperatures that range from 65 - 140 degrees Fahrenheit. In Summer, the best time to see a tortoise is during a thunderstorm, as the rain and thunder will cause a flurry of aboveground tortoise activity.

Social Behavior

Desert Tortoises are very aggressive. Tortoises aren't solitary, but their large home range prohibits them from permanently living in a pack. Tortoises do establish hierarchies within their own species, however. Though tortoise fights do occur, the hierarchies are maintained through visual and chemical signs rather than physical contact.
A battle between two tortoises is very loud and can potentially be deadly, as the fight doesn't end until one of two things happen. Either one tortoise loses loses interest in the quarrel, or one tortoise is flipped on its back. If the flipped tortoise cannot right itself, it may die due to suffocation or severe
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Two male tortoises fight (downloaded on 10/14/09)
hyperthermia.

Competitive Relationships

Since the Desert Tortoise is an herbivore, it does not prey on other animal species. Predators include foxes, gila monsters, and coyotes, who prey on young desert tortoises.

Symbiotic Relationships

The Desert Tortoise may maintain a commensal relationships with animals such as gopher frogs and snakes. These other, smaller species will live in burrows that tortoises have dug, either with the tortoise or after the tortoise has abandoned the burrow. Through the burrows other species gain protection from the desert, while the tortoises are not affected; thus the relationship is commensal.

Reproduction
Sexual maturity of a Desert Tortoise is determined by size rather than age, though generally most tortoises are generally the right size when they between the age of 15 and 20. To be "officially" sexually mature, a female must be approximately seven inches mid - carapace, or shell, length. Females lay eggs sometime between mid- April and the beginning of July, and the size of a clutch (a clutch is to tortoises what a litter is to puppies) depends on the size of the Female. Clutches can have anywhere from one to 14 eggs, and females may lay two or three clutches per year. Only a few Desert Tortoise hatchlings out of every hundred grow to be adults.
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A female desert tortoise lays her eggs (downloaded on 10/6/09)
Tortoise eggs resemble white ping - pong balls, and may hatch anywhere between 70 and 120 days of conception. The timing of the hatching depends on the location of the nest and the amount of warmth the nest receives. Warmth is supported by soil temperature only, as the mother leaves the nest after she lays her eggs. The sex of the clutch is also determined by temperature; if the nest is between 79 and 87 degrees Fahrenheit, the hatchlings will all be males. If the nest is between 88 and 90 degrees Fahrenheit, the nest will produce females.

Size

The weight of an adult Desert Tortoise is generally 8 - 15 pounds, with a carapace 9 - 15 inches in length and a height of four to six inches.

Why the Desert Tortoise is Threatened


The Endangered Species Act (ESA) of 1973 is a law that mandates the conservation of threatened and endangered species. The species that require conservation are on a government issued list, updated every year. Currently there are 1574 endangered species and 351 threatened species on the list. The law prohibits federal agencies, in addition to state governments, from jeopardizing the existence of the endangered or threatened species in any way.

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The Desert Tortoise is a species of reptile that is over 60 million years old (downloaded on 10/6/09)
The Desert Tortoise was listed as "threatened" under the Endangered Species Act in 1990. The animal has suffered great population losses in the past several decades due to both natural and artificial reasons. As the Mojave desert is becoming more urbanized, infrastructure, including mining, building roads, and military activities, takes the place of the Desert Tortoises' natural habitat. In addition, the tortoises are commonly killed by vehicles or taken from their natural habitats by people (collected as pets). The Desert Tortoise's population is declining because of natural causes as well. Populations of predators of the Desert Tortoise have increased in the past decades, and disease has raged among Desert Tortoise populations, also causing their decline. The current population of the Desert Tortoise is unknown, though the population is declining at a slower rate according to the Nevada Fish and Wildlife Office. The Wildlife Office cautions that the species is still threatened and is to be treated as such.

Conservation Efforts


There are many organizations dedicated to conserving the Desert Tortoise population, including the Desert Tortoise Recovery Office, the Desert Tortoise Preserve, and the Desert Tortoise Council among others. The primary goal of these organizations is to thoroughly monitor the habitats, threats, and population of the Desert Tortoise, and effectively use that information to preserve the tortoise population. In addition, the ESA protects the Desert Tortoise under it's law. The conservation efforts appear to be working, according to the Nevada Fish and Wildlife Office, as the decline in population of the tortoise has recently slowed.

Other Facts


  • The desert tortoise conserves water in its bladder (within its shell) and can rely on this water in times of severe drought. In fact, adult tortoises can survive for up to one year without fresh water.
  • Tortoises were alive 60 million years ago - when the Dinosaurs still roamed the earth! While the Dinosaurs went extinct due to climate change, tortoises adapted.
  • The lifespan of a Desert Tortoise is 80 - 100 years.

Bibliography



  1. Berry, K. H. (1999, November 1). Commonly asked questions about the desert tortoise and answers. In Tortoise Tracks . Retrieved October 5, 2009, from Desert Tortoise Preserve Committee website: [[@http://www.tortoise-tracks.org/‌gopherus/‌tortques.html]]
  2. Burge, B., & Royo, A. R. (n.d.). The Desert Tortoise . Retrieved 2009, from Desert USA website: [[@http://www.desertusa.com/‌june96/‌du_tort.html]]
  3. Commensalism and Mutualism . (2008 , April 9). Symbiosis . Retrieved October 14, 2009 , from Marietta College website: [[@http://www.marietta.edu/‌~biol/‌biomes/‌symbiosis.html]]
  4. Corwin, J. (2009 , May 27). Jeff Corwin Desert Tortoise [Video file]. Retrieved from Animal Planet database.
  5. Desert Tortoise . (2009 , September 21). Retrieved October 14, 2009 , from National Park Service website: [[@http://www.nps.gov/‌archive/‌moja/‌planning/‌tort.htm]]
  6. Desert Tortoise Recovery Office. (2009, September 18). Nevada Fish & Wildlife Office . Retrieved October 6, 2009, from U.S. Fish & Wildlife Service website: [[@http://www.fws.gov/‌nevada/‌desert_tortoise/]]
  7. Englin, J. E., Mitchell, G., Crites, A., & Baker, J. (n.d.). History and Habitat of the Desert Tortoise . University of Nevada Cooperative Extension .