Terrestrial Biome - Desert
Desert biomes cover about one fifth (20 percent) of the earth's land area. There are four different types of desert biomes - hot and dry, semi arid, coastal and cold deserts. The different desert types are scattered around the world on different continents. The four major North American deserts are the Chihuahuan, Sonoran, Mojave and Great Basin, these are hot and dry deserts.
Others outside the U.S. include the Southern Asian realm, Neotropical (South and Central America), Ethiopian (Africa) and Australian deserts.
Some deserts get both very hot during the day and very cold during the night, when temperatures can drop well below freezing. Some deserts, however, are always cold, for example, the Gobi Desert in Asia and the desert on the continent of Antarctica. As with all biomes, the desert climate is determined by geographic conditions. Geographic conditions such as location, high atmospheric pressure and proximity of mountain ranges determine just what type of desert it is.
Hot and Dry Deserts
These deserts are hot and dry all year round. These receive very little rainfall in winter months. The largest hot and dry desert is northern Africa's Sahara Desert, it covers roughly 3,500,000 square miles (9,065,000 square kilometres).
Semi Arid Deserts
The major deserts of this type include the sagebrush of Utah, Montana and Great Basin. They also include the Nearctic realm (North America, Newfoundland, Greenland, Russia, Europe and northern Asia). The summers are moderately long and dry and like hot deserts, the winters normally bring low concentrations of rainfall. Summer temperatures usually average between 21 - 27° Centigrade. Temperature do not normally go above 38° Centigrade and evening temperatures are cool, at around 10° Centigrade. Cool nights help both plants and animals by reducing moisture loss from transpiration, sweating and breathing.
These deserts occur in moderately cool to warm areas such as the Nearctic and Neotropical realm. A good example is the Atacama of Chile. The cool winters of coastal deserts are followed by moderately long, warm summers. The average summer temperature ranges from 13 - 24° Centigrade and winter temperatures are 5° Centigrade or below. The maximum annual temperature is about 35° Centigrade and the minimum is about -4° Centigrade. In Chile, the temperature ranges from -2 to 5° Centigrade in July and 21 - 25° Centigrade in January. The average rainfall measures 8 - 13 centimetres in many areas. The maximum annual precipitation over a long period of years has been 37 centimetres with a minimum of 5 centimetres.
These deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer. They occur in the Antarctic, Greenland and the Nearctic realm. Cold deserts have short, moist and moderately warm summers with fairly long, cold winters. The mean winter temperature is between -2 to 4° Centigrade and the mean summer temperature is between 21 - 26° Centigrade. The winters receive quite a bit of snow. The Antarctic desert is the largest cold desert in the world, measuring 14,000,000 kilometres squared.
Animals that live in the Desert Biome
Different animals live in the different types of deserts. Animals that live in the desert have adaptations to cope with the lack of water, the extreme temperatures and the shortage of food. To avoid daytime heat, many desert animals are nocturnal. They burrow beneath the surface or hide in the shade during the day, emerging at night to eat. Many desert animals do not have to drink at all, they get all the water they need from their food. Most desert animals are small.
Rarer, but important, are physiological adaptations such as aestivation (dormancy during summer), the absence of sweat glands, the concentration of urine, localized deposits of fat in tails or humps and salt glands to secrete salt without loosing fluids.
Reptiles with their waterproof skin, production of uric acid instead of urine, hard-shelled eggs and ability to gain body heat directly from the sun and to retreat to shade or underground to avoid heat are exceptionally well adapted to drylands and, not surprisingly, diverse there.
There are relatively few large mammals in deserts because most are not capable of storing sufficient water and withstanding the heat. Deserts often provide little shelter from the sun for large animals. The dominant animals of warm deserts are nonmammalian vertebrates, such as reptiles.
Below are just a few of the animals that inhabit the Desert biome. The animals below are featured in our World Wildlife section.
- Average life span in the wild:
- 5 to 7 years
- Head and body, 25 to 36 in (60 to 90 cm); Tail, 8 to 10 in (20-25 cm)
- 12 to 35 lbs (5 to 16 kg)
- Group name:
The so-called "Big Five" group of animals includes the elephant, rhino, buffalo, lion and leopard. Some years back a scientist suggested a "Small Five" group of animals, consisting of the aardvark, ratel, porcupine, pangolin and the naked mole-rat. Although at first this may seem a humorous suggestion, it is a reminder that many other interesting, lesser-known animals exist.
The crested porcupine is the largest and heaviest of African rodents. The head is roundish and rather domed, with a blunt muzzle and small eyes and ears. The legs are short and sturdy, and each foot has five toes, all equipped with powerful claws.
The porcupine is, of course, easily recognized by its most notable feature—its quills. Quill length on different parts of the body varies, from 1 inch up to 12 inches on the back. Usually the quills lie flat against the body, but if danger threatens, the porcupine raises and spreads them. Scales on quill tips lodge in the skin like fishhooks and are difficult to pull out. New quills grow in to replace lost ones.
^ Back to top
Porcupines are most common in hilly, rocky country, but they can adapt to most habitats. Excessively moist forests and the most barren of deserts seem to be the only exceptions. They have even been found on Mt. Kilimanjaro, as high up as 11,480 feet.
^ Back to top
Natural shelters among roots and rocks are modified by porcupines to suit their needs. They will inhabit holes made by other animals but also dig their own. These burrows are most commonly occupied in family units.
The porcupine warns potential enemies of its defense system when alarmed. It will stamp its feet, click its teeth and growl or hiss while vibrating specialized quills that produce a characteristic rattle. If an enemy persists, the porcupine runs backward until it rams its attacker. The reverse charge is most effective because the hindquarters are the most heavily armed and the quills are directed to the rear.
Not much is known about the breeding habits of porcupines in the wild, but the gestation period of the African crested is about 112 days. Between one and four young are born in a grass-lined burrow. They are well-developed and have their eyes open at birth. The young leave home for the first time at about 2 weeks of age as their quills, soft at birth, begin to harden. They are quite playful and, outside the burrow, they run and chase one another. The young are suckled for 6 to 8 weeks, when they begin to eat vegetable matter. Porcupines readily adapt to captivity and become quite tame, some living as long as 20 years.
When porcupine populations close to cultivated areas surge, they can become serious agricultural pests. They are smoked out of their burrows and hunted with spears, nets or dogs, practices that have eliminated them from densely settled areas.
^ Back to top
Porcupines primarily eat roots, tubers, bark and fallen fruit but have a fondness, too, for cultivated root crops such as cassava, potatoes and carrots. Sometimes porcupines will take carrion back to the burrow to nibble on.
^ Back to top
Especially in heavily settled areas, porcupines can be serious agricultural threats and porcupines can do a lot of crop damage in a single night. They are hunted using dogs, spears or nets, or smoked out of their burrows.
Did You Know?
- The word porcupine means "quill pig" in Latin; however, porcupines are large rodents and not related to pigs at all.
- Porcupine quills have long been a favorite ornament and good-luck charm in Africa. The hollow rattle quills serve as musical instruments and were once used as containers for gold dust.