Biomes: Desert (1989)

[Music] [Music] A biome is a community composed of living things. The vegetation that develops in a certain climate region and the animal life that has become adapted to [Music] it. Of all the major biomes on Earth, the driest is the desert. There are different desert landscapes. Many have large sand dunes like those in the Namib on the southwest coast of Africa and in the Sahara in the north. Some are stony like the vast plains and parts of the Sahara. Some deserts are even mountainous. Some deserts have cold winters. Others are hot year round. Despite their differences, deserts have one thing in common. Lack of water. The world's major desert biomes are found in two zones north and south of the equator. Most deserts are created by global wind patterns that produce scant and erratic rainfall. Because there is little cloud cover to reflect the sun's heat, daytime temperatures can be hot and nighttime temperatures very cold. Desert plants are pure and more widely scattered than in other biomes. Desert soil is poor and does not retain water very well from whatever rainfalls. Plants like the cactus store water in their swollen stems. Other succulents like the yuckas store water in their leaves. All succulents have waxy coverings that slow water loss by evaporation. There is a remarkable number of animals that have become adapted to the desert. Some animals have adapted for movement in hot sand, like the side winder snake and the sand lizard with its fringed toes. Under the hot, dry surface of the desert, it is much cooler and moistister. In burrows under the sand, many small mammals like the elephant shrew live. Most are nocturnal, but occasionally search for food during the day. Like the elephant shrew, the mircat also lives in underground burrows. Being underground not only protects desert mammals from the heat, but also reduces water loss from their bodies. Mircats stay alert not only for the birds that prey on them, but for the small reptiles and insects that they prey upon in the sand. The mircats will dig them out of their hiding places. In this biome, without a permanent water supply, carnivores have to depend on water in the bodies of the animals they eat. The radle gets food and water from the honey that it often eats, which is why it's also called a honey badger. But it also eats insects, roots, bulbs, and fruits. Some large mammals that have moved in from neighboring grasslands are able to survive in the desert. Steinbach, a kind of antelope, are able to go long periods without water by eating leaves and other parts of plants like underground stems and roots. During the hottest part of the day, mammals like these and other kinds of antelope are unable to escape the heat by going underground. So they seek what shade there is on the desert and spend the hottest hours of the day inactive. As the sun sets, the desert cools and the cast of characters changes. Small mammals become active. Crested porcupines emerge from their burrows to feed. The tiny sama melons they eat are a source of water for many desert animals. Gerbles are also active at night. They never have to drink. They get their water from their food, seeds, and other plant parts. The gecko is a nocturnal hunter. It feeds not only on insects, but also on spiders and other small invertebrates. But under the sand, a golden mole, a small mammal that feeds on the gecko, lies in weight. This time, the gecko escapes the golden mole. Sunrise is the coldest moment in a desert day. Sometimes early in the morning, water is plentiful in the form of fog and [Music] dew for an hour or so. Small animals take advantage of the available moisture. Then the heat of the day arrives and the water evaporates back into the air. The largest mammal of the desert and the best adapted is the camel. Its hump stores fat which can be converted to food and water for the camel. It can also store large amounts of water in the cells that line its stomach. Some antelope like the gmsbach can go for years without actually drinking water. Very rarely, rain clouds form over the desert. [Applause] Desert rains can be violent and intense. The rains change the tempo of life in the desert biome. After a heavy rain, some animals that have stayed inactive underground emerge. This toad has only a few weeks in which to reproduce before the water dries up. Immediately after a rain, there is plenty of water for desert life. Not only for the animals, but for the plants as well. The desert floor erupts with green plants. Annual plants have to germinate, grow, bloom, and go to seed during the few weeks of moisture. [Music] For a short time, there are abundant plants for animals to eat. [Music] Flowers last only a few hours or days, but the fruits that follow are more durable. They extend the season's abundance for weeks or months after a rainfall, providing food and water for many animal species. All too soon, the desert is dry again. The growing season ends and the pave slows and desert life is once again governed by heat and a lack of water. In some places, changing climate is causing deserts to form. But climate is not the only cause of the desert. In many areas, human activities are creating deserts or helping them spread. Use of marginal grassland for farming and overg grazing by domestic animals removes precious plant cover and makes the land more vulnerable to drying out. [Music] Poor use of the land plus long years of drought can allow the desert to advance, extending the area of the desert biome, the driest on Earth. [Music]