DESERTS

Desert biomes receive very little rain and cover about one-fifth of the planet's surface. They are divided into four sub-habitats based on their location, aridity, climate and temperature: arid deserts, semi-arid deserts, coastal deserts and cold deserts.

 Arid deserts are hot and dry and are located at low latitudes throughout the world. Temperatures are warm all year and hottest during the summer. Arid deserts receive little rainfall, and most rain that does fall usually evaporates. Arid deserts are located in North America, South America, Central America, Africa, Australia and Southern Asia.

 Semi-arid deserts are usually not as hot and dry as arid deserts. They have long, dry summers and cool winters with some rain. Semi arid deserts are found in North America, Europe, Asia, Newfoundland and Greenland.

 Coastal deserts are usually located on the western edges of continents at approximately 23°N and 23°S latitude, the Tropic of Cancer and the Tropic of Capricorn. Cold ocean currents run parallel to the coast, producing heavy fogs. Despite high humidity in coastal deserts, it rarely rains.

 Cold deserts have low temperatures and long winters and are found above the treelines of mountain ranges and in the Arctic and Antarctic. They experience more rain than other deserts. Many locations of the tundra are cold deserts.

Desert animals include coyotes, kangaroo rats, spiders, meerkats, roadrunners, reptiles, toads, snakes, pronghorn, birds and bats.

 

 Dry and baron landscapes, deserts receive intense sunshine and little rain. They are places of extremes, with a greater range of temperatures throughout the day than any other habitats. Temperatures range from boiling in the middle of the day, to freezing at night.

The two main types of deserts are true deserts (hot deserts) and semi-deserts.

True deserts are located on either side of the tropics.

Semi-deserts occur on every continent, usually far from the tropics. Semi-deserts receive at least twice as much rain each year than true deserts.

Deserts are formed from large fluctuations in temperature between day and night which puts strain on rocks. The stress causes the rocks to break into pieces. Occasional downpours of rain cause flash floods. The rain falling on hot rocks can cause them to shatter. The rubble is strewn over the ground and further eroded by the wind. Wind-blown sand grains further break down stones, causing more sand. Rocks are smoothed down, and the wind sorts sand into deposits. The grains end up as sheets of sand.

Other deserts are flat, stony plains where all the fine material has been blown away leaving an area of smooth stones. These deserts are called desert pavements and little further erosion takes place. Some deserts include rock outcrops, exposed bedrock and clays once deposited by flowing water. Oases occur where there are underground sources of water in the form of springs and seepages from aquifers.
 
A unique desert is the Gobi desert in Asia which is located across China and stretches up to the Siberian Mountains where winters are very cold. Despite the cold winters, the mountains block rain-clouds from reaching the desert area.

A variety of plants and animals live in desert habitats. Plants tend to be tough and wiry with small or no leaves. Some plants germinate, bloom and die in the course of a few weeks after rainfall. Some long-lived plants survive for years with deep roots that tap into underground moisture.

Most animals are nocturnal, coming above ground or out of the shade at night when temperatures are cooler. Reptiles, insects and small birds are the most common animals in true deserts. Mammals are more common in semi-deserts, where plant life is more plentiful.

 

 Animals of the deserts are adapted to dry and arid conditions. They are efficient at conserving water, extracting most of their needs from their food and concentrating their urine. The addax antelope, dik-dik, Grant's gazelle and oryx never need to drink. The thorny devil in Australia sucks water through channels in its body located from its feet to its mouth. The camel minimizes its water loss by producing concentrated urine and dry dung, and is able to lose 40% of its body weight through water loss without dying of dehydration. Camels have humps of fatty tissue that concentrate body fat in one area, minimizing the insulating effect fat would have if distributed over their whole bodies. Birds are able to fly to areas of greater food availability as the desert blooms after local rainfall, and can fly to faraway waterholes. Carnivores obtain much of their water needs from the body fluids of their prey.

Flies, beetles, ants, termites, locusts, millipedes, scorpions and spiders have hard cuticles which are impervious to water and many lay their eggs underground where their young develop away from the surface temperature extremes. Some arthropods make use of the ephemeral pools that form after rain and complete their life cycle in a matter of days.

Reptiles do not sweat, so they shelter during the heat of the day. In the first part of the night, as the ground radiates the heat absorbed during the day, they emerge and search for prey. Some snakes move sidewards to navigate high sand-dunes. Even amphibians have adapted to desert habitats, spending the hot dry months in deep burrows where they shed their skins numerous times to create cocoons around them to retain moisture.

Some animals remain in a state of dormancy for long periods, becoming active again when the rare rains fall. They then reproduce rapidly while conditions are favorable before returning to dormancy.

Deserts habitats have been the least affected by human activities, remaining relatively untouched. Threats do include extraction of oil from the sand and grazing farm animals that deplete desert plants, threatening wildlife that rely on those plants. Desertification can be caused by tilling for agriculture, overgrazing and deforestation.

 

DESERT FACTS

WHAT IS A DESERT?

Approximately one-third of the Earth's land surface is desert, arid land with meager rainfall that supports only sparse vegetation and a limited population of people and animals. Deserts stark, sometimes mysterious worlds have been portrayed as fascinating environments of adventure and exploration from narratives such as that of Lawrence of Arabia to movies such as "Dune." These arid regions are called deserts because they are dry. They may be hot, they may be cold.

TYPES OF DESERTS

Deserts are classified by their geographical location and dominant weather pattern as trade wind, midlatitude, rain shadow, coastal, monsoon, or polar deserts. Former desert areas presently in nonarid environments are paleodeserts, and extraterrestrial deserts exist on other planets. The trade winds in two belts on the equatorial sides of the Horse Latitudes heat up as they move toward the Equator. These dry winds dissipate cloud cover, allowing more sunlight to heat the land.

DESERT FEATURES

Sand covers only about 20 percent of the Earth's deserts. Most of the sand is in sand sheets and sand seas vast regions of undulating dunes resembling ocean waves "frozen" in an instant of time. Nearly 50 percent of desert surfaces are plains where eolian deflation removal of fine-grained material by the wind has exposed loose gravels consisting predominantly of pebbles but with occasional cobbles. The remaining surfaces of arid lands are composed of exposed bedrock outcrops, desert soils, and fluvial deposits.

DESERTIFICATION

The world's great deserts were formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independent of human activities. Paleodeserts, large sand seas now inactive because they are stabilized by vegetation, extend well beyond the present margins of core deserts, such as the Sahara. In some regions, deserts are separated sharply from surrounding, less arid areas by mountains and other contrasting landforms.

REMOTE SENSING OF ARID LANDS

The world's deserts are generally remote, inaccessible, and inhospitable. Hidden among them, however, are hydrocarbon reservoirs, evaporites, and other mineral deposits, as well as human artifacts preserved for centuries by the arid climate. In these harsh environments, the information and perspective required to increase our understanding of arid-land geology and resources often depends on remote sensing methods. Remote sensing is the collection of information about an object without being in direct physical contact with it.

ANTELOPES IN DOUBLE JEOPARDY

Antelopes are an increasing conservation concern, with one-third of the world's 87 species now listed as threatened. Loss of habitat, game hunting, poaching, and loss of grazing land to cattle farmers are some of the biggest threats to antelope populations. Adding to the threats to antelope populations is changes in climate. For 82 percent of African antelope species, forecasts show a decline in suitable habitat by 2080 due to the effect of climate change.

CAMEL

A camel is either of the two species of large even-toed ungulate in the genus Camelus. The Dromedary is a single hump camel, and the Bactrian Camel is a double hump camel. Both are native to the dry and desert areas of Asia and northern Africa. The average life expectancy of a camel is 30 to 50 years. Humans first domesticated camels approximately 5,000 years ago. Although there are almost 13 million Dromedaries alive today, the species is extinct in the wild. There is, however, a substantial feral population in central parts of Australia, descended from individuals that escaped from captivity in the late 19th century.

TARANTULA

Like all arthropods, the tarantula is an invertebrate that relies on an exoskeleton for muscular support. Like other Arachnida a tarantula’s body comprises two main parts, the prosoma (or cephalothorax) and the opisthosoma (or abdomen). Spiders are invertebrates but are not considered insects because they only have two main body parts instead of three, eight legs instead of six and no antennae. Most spiders also have eight simple eyes, while insects have large, compound eyes. Some have no eyes and others have as many as 12. Spiders, along with ticks, mites, harvestmen and scorpions, are called arachnida.

SCORPION

Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by a pair of grasping pincers (claws) and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger. They have adapted to a wide range of environmental conditions and can now be found on all continents except Antarctica. Scorpions did not occur naturally in Great Britain, New Zealand and some of the islands in Oceania, but now have been accidentally introduced in some of these places by human trade and commerce.

KANGAROO

Kangaroos have powerful hind legs and short, thumbless forelimbs. Kangaroos can travel at speeds up to 30 miles per hour and can leap some 30 feet. Kangaroos use their long tails for balancing. Their bodies are covered in thick, coarse, wooly hair that can be shades of gray, brown or red. Kangaroos are marsupials, which means that females carry newborns, or "joeys," in a pouch on the front of their abdomens.

FENNEC FOX

The fennec fox is a small fox found in the Sahara Desert of North Africa (excluding the coast) which has distinctive oversized ears. The fennec is the smallest canid. The animals are often a sandy color and blend in with their desert surroundings. Their ears, which are the largest in the canid family, serve to help dissipate heat. Their coat can repel sunlight during the day and conserve heat at night. The soles of of a fennec's feet are protected from the hot sand by thick fur.

MEERKAT

The meerkat, or suricate, is a small mammal and a member of the mongoose family. Meerkats live in southern parts of Africa which is dominated by the Kalahari desert. The Kalahari desert has little rainfall and an arid climate with open plains. It spreads across the Southern part of Africa covering over one million square miles and is 10 times the size of Great Britain. The land is covered by a porous or soft sand that in many places is bright orange color.

RATTLESNAKE

Rattlesnakes are a group of venomous (poisonous) snakes that live in a wide range of habitats, and have the scientific name Crotalus cerastes. There are 32 known species of rattlesnakes, and they can be found all over the Americas, ranging from Alberta and British Columbia, Canada, to as far south as Argentina. These fascinating snakes get their name from the rattle at the end of their tails – when the snake shakes the rattle, it makes a loud noise that helps to defend the snake by warning off predators or passing larger animals. It’s basically the snake’s way of saying ‘watch your step!’