1.3.1 Training. It is only when temperatures exceed 40 °C that they need to drink at short and regular intervals. Other invertebrates of temporary ponds survive periods of desiccation in a state of anhydrobiosis. The male bird ferries water for his chicks by soaking his belly feathers. They will also begin to recognise how plants and animals evolve to adapt to the harsh conditions of deserts. Some desert trees and shrubs can send out lateral roots as far as 75 metres to reach water sources. The largest hot desert in the world, northern Africa's Sahara, reaches temperatures of up to 50 degrees celsius. In a desert, the air is very dry, resulting potentially in very high rates of transpiration. Organisms in a desert ecosystem adapt to survive the intense heat and limited water. This corresponds to the capacity adaptations (adaptations which allow the organism to operate under extreme conditions) and resistance adaptations (adaptations which allow the organism to avoid or survive the stress until the conditions favourable for its growth return) that were described in Chapter 1. These are inhabited by organisms that can survive the stresses involved in dry phases of varying durations, inter vals and intensities. Normally, water loss is confined to the breath and this loss is reduced by cooling the air as it leaves the nose, so that it carries less water. Although we think of frogs and toads as being associated with moist environments, they can in fact successfully survive in periodically dry areas. Drier areas (like the surface of the roof tiles) may be colonised by lichens and cyanobacteria. The carbon dioxide enters the plant via pores (stomata) in the leaves. figure 2.2 The major routes for the gain and loss of heat and water in an animal such as a camel. As we have seen, desert amphibians burrow into the mud as the pond dries and lie dormant until the next rainfall. Large areas of deserts are covered by hardened surfaces called, variously, desert pavements, desert crusts and desert varnishes. Some of these periodically dry out. Some desert plants can even live to be hundreds of years old. Drawing by Ken Miller. As well as limited access to water, desert organisms have the problem of hanging on to the water they have. The tiles are covered with lichens and there is moss growing between them. Resistance adaptations which involve behavioural responses, such as burrowing into the sand, are found in animals. The mechanisms which enable camels to survive in the desert are summarised in Figure 2.2. These share some of the adaptations to the desert environment shown by camels, although none show the same degree of resistance. Each has a unique system for survival, but some of the ways desert plants adapt are similar. Little is known of their adaptations to these habitats, although they may produce cysts (protozoa), spores (bacteria and fungi) or modified cells with thickened walls, mucilage sheaths and an accumulation of oils (algae) which enable them to survive anhydrobiotically. Desert plants have solved their water problems in a variety of ways. The water at the bottom of these crayfish burrows is used as a refuge for a variety of small invertebrates and a whole community of animals inhabits them. Some deserts form in the rain shadow of mountains, eg the Atacama Desert is located in the rain shadow of the Andes. Their size and complexity does, however, impose some restrictions on the sorts of adaptations they have been able to develop and, for example, they are not capable of cryptobiosis. As the water level falls, it burrows into the mud of the river and secretes a cocoon of mucus (Figure 2.4). As the temperature rises, they adopt a stilt-like posture which raises the body above the surface and periodically raise diagonally opposed limbs, allowing more heat loss. Dromedaries are entirely domesticated and so aspects of their biology are determined by their relationship to humans. The world’s largest desert From one extreme to another, Africa’s Sahara is one of the hottest places on Earth, and easily makes it onto our list of extreme environments. Camels reduce their reliance on sweating to cool down at high temperatures. Some examples include the exposed surface of the soil and the edges of lakes, ponds and streams which desiccate when the water level falls. Interestingly, it’s third on the list of the world’s largest deserts, behind the arctic and antarctic; no, deserts don’t necessarily have to be hot. They have adaptations which enable them to function in the face of low water availability and high temperatures or they escape, retreat from or avoid the harsh conditions, restricting their activity or growth to periods that are more favourable. These areas often lose more moisture through evaporation than they receive from annual precipitation. 1.3.4 Equipment. These include nematodes, rotifers, tar-digrades and some insect larvae. figure 2.1 The world's major deserts. Plant material is also buried by the activities of animals which are active on the surface, such as termites, ants and other insects. The American 'Road Runner' bird produces a liquid from its stomach which trickles down the back of its throat and is drunk by its nestlings. In dehydrating conditions, the water content of the milk of lactating camels is actually increased, to ensure the survival of the young. The rock must be transparent and the microbes close enough to its surface to allow light to reach them for photosynthesis, but the layer of overlying rock is sufficient to protect them against desiccation and other hazards. Parasites living in the intestine of other animals need to infect new hosts to ensure their survival. It is clear, then, that life in deserts is possible, but humans have had to adapt to the demands of surviving in deserts. Here are some of the ways people survive: Wells are built in order to tap ground water. Mud is often used to make brick and can be quite insulating. The fish's oxygen uptake reduces to 10 per cent of normal, its heartbeat slows, its tissues partly dehydrate, urine production ceases and the fish switches from producing ammonia to urea, which is less toxic and can accumulate in the blood and tissues without adverse effects. One of the most spectacular sights in nature is the growth and blooming of ephemeral desert plants after a rainfall. They can also tolerate dehydration of the tissues and store water in the form of a dilute urine in the bladder. Expertise in Extreme Environments. Cryptobiosis is the ultimate resistance adaptation, with the organism capable of surviving in an ametabolic dormant state for many years. Camels, Flamingoes, endangered species and specific flora can be found in arid areas. Cacti have special ways of storing water. Problems of gaining heat are also diminished, for a similar reason, but, conversely, they are less able to lose heat. The seeds may be dry enough for their metabolism to cease and to become anhydrobiotic. Germination of seed after rainfall could be a very risky strategy since there may not be sufficient water for the plant to complete its development and it may wither and die before setting seed again. Capacity adaptation with respect to low water availability involves the ability to access the sources of water which are available, the ability to restrict water loss from the organism and the ability to store water. Reduction of leaves to form spines protects the plant against heat gain by reflecting solar radiation. Almost all desert areas support some sort of vegetation, with dunes and bare rock supporting the least. Camels browse over a large area, often covering distances of 50 kilometres per day in their search for food. This reduces the amount of water lost during respiration. Namib tenebrionid beetles collect moisture from the fog which originates from the cold coastal currents offshore from the Namib Desert. If it fails to rain, it is important that at least some individuals complete their development. Desert microorganisms can gather enough moisture from rainfall and/or condensation to support their growth, but numbers are drastically reduced when the soil dries out. We know much less about the abilities of microorganisms to survive dry conditions than we do about their survival at high temperatures (thermophiles) and high salt concentrations (halophiles). Only a few days after rain, these ponds can be swarming with millions of tiny shrimps which have emerged from eggs lying dormant in the dried mud. in the area between 25° to 35° north and south of the equator, with dry air tending to be trapped between major wind belts and storm systems. Deserts result from low rainfall but they are also places of extreme temperatures and of rapid changes in temperature. As the heat of the day increases, they retreat to their shelters. In the Atacama desert there can be less than 0.01 cm of rai a year. Some extreme environments that you may know about are deserts, mountain peaks, caves, and frozen places like the Arctic and Antarctic. Their dorsal wing cases (elytra) are fused and form a cavity covering their backs. These observations repeat those of Antoni Van Leeuwenhoek, a seventeenth-century Dutch scientist, who was one of the first to observe living organisms using the recently invented microscope. Irrigation canals are used to transport water from wetter regions to drier areas. The architecture of the elaborately constructed termite mounds creates a flow of air which ventilates and cools the nest, and the orientation of the mound to the sun means that they tend to only absorb heat when air temperatures are low. Blue-green algae from the Atacama Desert of northern Chile produce gelatinous sheaths which trap sand grains and form cushion-like pellets which shade the small area of soil beneath and help them retain water. The leathery lips and tongue of the camel allow it to contend with the tough vegetation and it can even eat the thorns themselves. Organisms show two broad responses to the extreme conditions that they face in deserts. opening at the top of the cocoon. Camels reduce the water loss by allowing their internal temperatures to fluctuate more than do other mammals. The more short-lived the pools, the greater are the demands on the organisms that live there. The hump consists mainly of fat and acts as a food store. Cacti, yuccas and euphorbias are called succulents because their thick, spongy leaves and stems can absorb and store large quantities of water. The Dry Valleys of Victoria Land (also called the Ross Desert) are the most extensive areas of ice-free land in Antarctica. The roof community thus has to survive periods of extreme desiccation lasting several days or even weeks. Many insects only live as larvae within these waters and rapidly complete their development to emerge as adults which fly away to seek more permanent waters. Most of the world's hot deserts (subtropical deserts such as the Australian and Arabian deserts and the Sahara Desert) are located. The vast majority of desert plant species are ephemeral. Natural container habitats provided by plants include treeholes, the junctions between leaves and stems (for example, in bromeliads) and in flowers. Angel Falls … A desert is defined by its lack of water rather than its temperature. Wherever water accumulates during rain, and where conditions are relatively undisturbed, you are likely to find mosses growing. But many species do just fine in the heat. Most hot deserts are found near the equator. Deserts can provide little shelter from the sun and the heat. The camel is perhaps the most famous of desert mammals so let us look at why it is such a successful desert inhabitant. Metabolic water, produced as a product of the oxidation of food, can be a major source of water for animals in arid areas. There is no evidence that camels can store water anywhere in their bodies. Resistance adaptation involves escaping from or avoiding the harsh conditions. Some other examples of extreme environments are places that are filled with acids, are blasted with radiation, or are under high pressure. This, together with low water availability, means that desert plants have problems maintaining their water content. If they need to lose heat, they flutter their throats, creating a cooling flow of air through the moist inside of the mouth. Eventually, the numbers dwindle and they resume the solitary form. Some deserts are always cold, like the Gobi desert in Asia and the desert on the continent of Antarctica. I can name at least 8 major hot deserts across the world I can describe and explain the distribution of deserts around the world . Although the area in which we live may seem far from being a desert, we can, if we look carefully, find many places which are temporary deserts where organisms will be exposed to desiccation and other extreme environmental stresses. Other less prominent desert invertebrates include snails, woodlice, earthworms and millipedes. They have to perform a delicate balancing act apropos their internal temperature. These contain water for varying lengths of time, from a day up to several weeks. In fact, they contain numerous microorganisms such as bacteria, algae, protozoa and fungi. One of the best known desert amphibians is the spadefoot toad of the Sonoran Desert of North America. If there is sufficient rainfall, the chemical is washed away and the seed germinates, but, if there is only a little water available, germination is prevented. Rain-filled rock pools which form in shallow depressions in rocks are common features of tropical and subtropical regions. The feathers of birds not only enable them to fly but are also very good insulation, protecting the bird from the heat of the sun. The leaves of desert plants and the pads and stems of succulents are orientated with their thin edge facing the sun, reducing heat gain. Beetles from the family Tenebrionidae are often thought to be the insects that are best adapted to desert life, with their numbers increasing in areas adverse to other forms of life. The large body size of the camel means that the loss of water by evaporation through the skin is less than it is for smaller animals. They are extremely dry and parts of them are thought not to have received any rainfall, or other precipitation, for at least the last two million years. The requirement for a high salt intake is driven by the production of a concentrated urine. As well as surviving high levels of dehydration, camels have a number of mechanisms for conserving water within their bodies. Natural and artificial container habitats are particularly significant in the tropics where they often act as breeding grounds for mosquitoes which transmit diseases such as malaria and yellow fever. Such problems are also faced by those inhabiting temporary bodies of water in other environments and will be considered later in this chapter. Many desert rodents rely entirely on their food as a source of water. Deserts are dry, arid areas that receive very little rain. Dromedaries are associated with hot, dry, flat deserts (subtropical deserts such as the Sahara Desert and Arabian Desert) while Bactrian camels live in mountainous, rocky regions (cold temperate deserts, such as the Gobi Desert). These adaptation enable desert plants not only survive, but to thrive in hot and dry desert conditions. These harsh conditions of deserts where a suitable body of water in an ametabolic dormant state many! 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