Deserts and animal life

Deserts are typically defined by their annual rainfall, climate, plants and animals. Most deserts are found in bands along 30 degrees north and south latitudes. The rain shadow effect causes other deserts. This is when mountain ranges block rainfall and inhibit the growth of vegetation. Deserts are biomes where less than twenty-five to fifty centimeters of precipitation drops each year. There may be no vegetation or widely spaced vegetation combined with large areas of bare ground. The plants tend to be spaced evenly, as if planted by hand. The desert is a land of extreme heat and dryness. It is often very hot in the daytime and somewhat chilly or even cold at night. The desert is dry most of the year; even the wettest deserts get only ten inches or less precipitation per year. The scarce precipitation comes from a few very large rains or snows. Due to such extreme conditions, deserts often have names like “Death Valley,” “the empty quarter,” and “the place from which there is no return.” Overall, about one-fifth of the earth’s land surface is desert.

Depending upon whether the precipitation comes from rain or snow, deserts can be divided into hot (rain) or cold (snow) deserts. The deserts of Arabia, Australia, Chihuahua, Kalahari, Monte, Sonora, and Thar are all considered hot deserts. Cold deserts include the Atacama, Gobi, Basin, Iranian, Namib, and Turkestan deserts. Regardless of desert type, organisms living within these biomes are required to adapt to the scarcity of water and large range of temperatures.

Global climate change threatens to have immense impacts on plant and animal life in these environments. While deserts may be considered fixed in size, they are actually growing larger. Scientists have noted that deserts are expanding towards their respective poles at a rate of 30 miles per decade. Expanding deserts are thought to comprise much of the 12 million hectares of arable land lost each year. In addition, deserts are projected to become much greater in temperature. By the latter half of the twenty-first century, many of these regions are projected to contain “ultra-extreme” temperatures. Despite the many adaptations plant and animal species have undergone to survive in this environment, global climate change may prove to be decisive in threatening ecosystems in this region. Desert environments may in fact be the most vulnerable to changing climatic conditions. Studies undertaken in deserts in multiple global locations show similar patterns where rising temperatures and reduced rainfall are leading to the loss of desert habitats.

Plant Life in Deserts

Desert plant life includes wildflowers, cacti and succulents, and grasses and trees. The desert is renowned for its explosions of spring wildflowers and the succulent cactus that adorn its landscapes. Desert wildflowers assume a variety of shapes and colors; some are beautiful, while others are poisonous. Apache plume (Fallugia paradoxa) is an evergreen shrub that grows up to six feet, with small grayish, downy leaves, and round white flowers with yellow centers. Jimson weed (genus Datura) has large, white, trumpet-shaped flowers that bloom from March through November. This foul-smelling flower opens after dusk and closes by midmorning of the following day. All parts of datura plants are poisonous and can be fatal if ingested. Desert dandelion (Malacothrix glabrata) grows six to fourteen inches high with three- to five-inch leaves. In spring, this bright wildflower will form broad, brilliant patches of gold across the sandy desert floor. Many other species, including desert lily, desert paintbrush, ghost flower, and prickly poppies, help contribute to the beauty of the desert’s spring.

The pleated shape of the barrel cactus (genus Ferocactus) allows it to expand when it rains to store water in its spongy tissue. It shrinks in size during dry times as the stored water is consumed. The fishhook cactus (Mammillaria microcarpa) has fishhook-shaped spines that divert heat and shade the growing tip of the plant. Prickly pear cactus (genus Opuntia) includes about a dozen species, all with modified stems and leaves for water storage, photosynthesis, and flower production. The saguaro cactus (Carnegiea gigantea) is equipped with a green stem to store water and perform photosynthesis, and large nets of roots that collect water after rain.

The Crucifixion thorn tree (Chaparro amargosa) exhibits no leaves but has intricately branched, thick, rigid, sharp spines, which perform photosynthesis and conserve water. The Joshua tree (Yucca brevifolia) grows only in the Mojave Desert. This picturesque, spike-leafed evergreen can grow to forty feet tall, with a diameter of one to three feet. Poison ivy (Toxicodendron rydbergii) is a small, woody shrub that lacks the climbing, vinelike structure of its better-known eastern relative, T. radican. At least ten species and subspecies bear the common name “poison ivy,” a notoriously poisonous plant. Plants that live in the desert help animals by providing them with food, water, and shade.

Animal Life in Deserts

Animals living in the desert include mammals, birds and fish, reptiles and amphibians, and insects and spiders. A few examples of mammals include bats, bighorn sheep, bobcats, and coyotes. Desert bats, members of the suborder Micro chioptera, are often considered to be flying mice, but they are more closely related to primates. Bats are unique among mammals because they can fly. Most bat species also possess a system of acoustic orientation, technically known as echolocation. The bighorn sheep lives in dry, desert mountain ranges and foothills near rocky cliffs. Its body is compact and muscular; the muzzle is narrow and pointed; the ears, short and pointed; the tail, very short. The fur is deerlike and usually a shade of brown, with whitish rump patches. Bighorns are grazers, consuming grasses, sedges, and other low-lying plants. The bobcat (Felis rufus) has long legs, large paws, and a short tail (six to seven inches long), with average body weight of fifteen to twenty pounds. However, it is quite fierce and is equipped to kill animals as large as deer. The desert coyote (Canis latrans), a member of the dog family, weighs about twenty pounds, less than half the weight of its mountain kin, which can weigh up to fifty pounds. Its body color is light gray or tan, which helps it survive in the desert.

A variety of birds reside in the desert due to the abundance of insects and spiders. Golden eagles (Aquila chrysaetos) get their name from the golden feathers on the back of their neck. They are birds of the open country, building large stick nests in trees or cliff walls where they have plenty of room to maneuver. Adults weigh 9 to 12.5 pounds, with females usually larger than males. Ravens (Corvus corax) are the largest birds of the crow family, averaging twenty-four inches tall, with a wingspan of forty-six to fifty-six inches. Ravens are strong fliers that can soar like a hawk, and may form large flocks of over several hundred individuals during their autumn migration. The American turkey (Meleagris gallopavo), the largest upland game bird in North America, is thirty-six to forty-eight inches long, with four- to five-foot wingspans. Males average ten inches longer than females, which are paler and of a more buff color. Turkeys inhabit a variety of habitats from open grassland and fields to open woodlands and mature deciduous or coniferous forests.

Many species of reptiles and amphibians live in desert, including the black-collared lizard (genus Crotaphytus), bullfrog (Rana catesbeiana), desert dinosaur (orders Saurischia and Ornithischia), desert iguana (Dispsosaurus dorsalis), rattlesnake (genus Crotalus), and many others. Insects and spiders include dragonflies (suborder Anisoptera), scorpions (order Scorpionida), and black widow spiders (Latrodectus hesperus). It is nothing short of a miracle that such an abundance of lives, both plants and animals, can survive in the extreme conditions of the desert.

Animal Survival in the Desert

Among the thousands of desert animal species, there are many remarkable behavioral and structural adaptations developed for avoiding excess heat. Equally ingenious are the diverse mechanisms various animal species have developed to acquire, conserve, recycle, and actually manufacture water.

Certain species of birds, such as the Phanopepla, breed during the relatively cool spring, then leave the desert for cooler areas at higher elevations or along the Pacific coast. The Costa’s hummingbird begins breeding in late winter and leaves in late spring when temperatures become extreme. Many birds, as well as other mammals and reptiles, are crepuscular, meaning they are active only at dusk and again at dawn. Many animals, including bats, many snakes, most rodents, and some larger animals such as foxes and skunks, are nocturnal, restricting all their activities to the cooler temperatures of the night, and sleeping in a cool den, cave, or burrow by day. A few desert animals, such as the round-tailed ground squirrel, sleep away the hottest part of summer and also hibernate in winter to avoid the cold season. Other animals, such as desert toads, remain dormant deep in the ground until the summer rains fill ponds. They then emerge, breed, lay eggs, and replenish their body reserves of food and water for another long period.

Various mechanisms are employed to dissipate heat absorbed by desert animals. Many mammals have long appendages to release body heat into their environment. The enormous ears of jack rabbits, with their many blood vessels, dissipate heat when the animal is resting in a cool, shady location. Their close relatives in cooler regions have much shorter ears. New World vultures, dark in color and thus absorbing considerable heat in the desert, excrete urine on their legs to cool them by evaporation, and circulate the cooled blood back through the body. Many desert animals are paler than their relatives elsewhere, ensuring that they not only suffer less heat absorption, but also are less conspicuous to predators in the bright, pallid surroundings.

The mechanisms by which water is retained by desert animals are even more elaborate. Reptiles and birds excrete metabolic wastes in the form of uric acid, an insoluble white compound, wasting very little water in the process. Other animals retain water by burrowing into moist soil during the dry daylight hours. Some predatory and scavenging animals can obtain their entire water needs from the food they eat. Most mammals, however, need access to a good supply of fresh water at least every few days, if not daily, due to the considerable water loss from excretion of urea, a soluble compound.

Many desert animals obtain water from plants, particularly succulent ones such as cactus and saguaro. Many species of insects thrive in the desert, as they tap plant fluids for water and nectar. The abundance of insect life permits insectivorous birds, bats, and lizards to thrive in the desert. Certain desert animals, such as kangaroo rats, have multiple adaptation mechanisms to acquire and conserve water. First, they live in underground dens that they seal off to block out heat and to recycle the moisture from their own breathing. Second, they have specialized kidneys with extra microscopic projections to extract most of the water from their urine and return it to the bloodstream. Third, and most fascinating of all, they actually manufacture their water metabolically from the digestion of dry seeds. These are just a few examples of the ingenious variety of adaptations animals use to survive in the desert, overcoming the extremes of heat and the paucity of water.

Principal Terms

biome: a terrestrial ecosystem that occupies an extensive geographical area and is characterized by a specific type of plant community, such as deserts

perennial: plants that live for several years

rain shadow: a local dry (desertlike) area created by the modification of rainfall patterns by a mountain range

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