Most people picture the desert as a dry, hot and empty sort of place, devoid of much life except perhaps the occasional rattlesnake or vulture. But this image of the desert is not really an accurate one. Because of nature’s amazing ability to create adaptation, or adjustment to various environmental conditions, there is quite a variety of plant and animal life in the world’s deserts.
A desert is basically defined as a region that has less precipitation than most other types of biomes, or areas with similar climactic characteristics, geology and vegetation. To be more precise, a desert is an area that has an average of less than ten inches of rainfall per year, and where the yearly evaporation is more than ten inches a year. Deserts comprise about a third of the earth’s land surface, and are usually found within a belt of 30 degrees north and south latitude, where wind patterns carry down dry air from the earth’s upper atmosphere.
Animals and plants that inhabit deserts must somehow be able to survive in their arid conditions, where there are also extreme variations in temperature from day to night. Many desert plants are able to store water in their roots, leaves, stems or fruit. Plants that are able to do this are called succulents. One well-known example is the saguaro cactus, the state flower of Arizona. This cactus has a remarkable ability to collect and store water. The plant’s outer pulp has vertical ribs, or pleats, which can expand like an accordion as it absorbs water. After a rainstorm, it can store enough water to last for a year, and as a result of the stored water, its weight can increase by as much as 2000 lb. The interior framework of the plant supports it as its weight increases. Clusters of downward-pointing spines also help the plant to survive by directing rainwater to its base, near the roots. During the day, when the cactus is exposed to intense sunlight, microscopic pores close to conserve water. At night when the temperature drops, the pores open to allow entry of carbon dioxide for photosynthesis.
The saguaro cactus also serves as a home for a number of desert animals. Woodpeckers drill holes in it to create nests, which are later used by owls and other birds. The inside of the cactus is cooler by day and warmer by night, which makes it a good home for these creatures. As saguaro cacti grow, they are sometimes sheltered by “nurse trees”, such as the palo verde or the mesquite. These sheltering plants protect the cactus from hot sunlight during the day. A successful saguaro cactus can grow to be as old as 200 years.
Drought tolerance is another means by which plants survive in the desert. Some desert plants become dormant, or have little metabolic activity, during very dry periods. They may shed leaves to reduce transpiration, or water loss into the atmosphere. Desert plants also have much more extensive root systems than plants of similar size in a wetter climate. For example, the mesquite tree may have roots that reach as deep as 200 feet into the ground, well into the water table. Although many desert plants may not have such deep roots, their roots are still very extensive in that they reach at least as far out around the plant as it is tall.
Desert animals, too, have adapted their bodies and habits to the arid desert climate. Many of them get all of their water from the food they eat. Some are nocturnal, only coming out of their lairs during the cool, dark nights to avoid exposure to intense sunlight. The kangaroo rat, found in the Sonoran and Mojave deserts, is able to convert dry seeds that it eats into water. These rats dig dens with openings at the base of plants such as the creosote bush, and during the day, they block off the entrances to the dens. They can then spend most of the day sleeping underground in the humid burrows, coming out at night to feed when it is cooler.
One animal closely associated with desert living is the camel. Camels are well known for their ability to survive in desert conditions. Arabian camels, also known as dromedaries, have a large hump of fat on their backs. This fat can be broken down into water and energy when sustenance is not available. Since camels do not sweat even in high temperatures, they can conserve water for long periods of time. However, when water is available, a camel can drink 30 gallons of water in about 13 minutes. To keep them from inhaling blowing desert sand, they are able to close their nostrils, and they have bushy eyebrows and long eyelashes to protect their eyes as well.
Desert animals are even more vulnerable to temperature extremes than plants. For this reason, many of them are crepuscular, meaning they are only active at dusk and dawn. This is especially true of lizards and mammals. Other desert animals have mechanisms by which they dissipate heat absorbed from their environments. Desert jackrabbits have very large ears with many blood vessels, which release heat when the rabbit is resting in the shade. Black vultures excrete urine on their legs, cooling them by evaporation. This is called urohydrosis.
Most non-desert species of animals lose a great deal of water in their urine and feces. Since desert animals must conserve water, they have developed other methods of discarding body wastes. Some desert birds have salt glands located near their eyes, which excrete salts that are unmixed with water. Camels and kangaroos can convert urea into a usable protein instead of excreting it, reducing the need to urinate. The feces of desert animals are often hard, dry pellets, with almost no water content.
Some desert animals, such as the desert bighorn sheep, dissipate heat by the simple mechanisms of panting and sweating. With their hard hooves and horns, they can remove the spines from cacti, then obtain some of the water they need from the juicy insides.
The desert environment is an excellent example of the interplay and symbiosis of its inhabitants. The amazing intelligence of nature is displayed by the variety of adaptations that take place each day under its blazing sun. Humans would do well to learn from the harmony it creates in the midst of some of the harshest conditions on earth.