Deserts by Middleton Nick

Author:Middleton, Nick [Middleton, Nick]
Language: ru
Format: mobi, pdf
Publisher: OUP Oxford
Published: 2009-03-17T20:00:00+00:00

12. Makgadikgadi salt pan in Botswana is one of the most important flamingo breeding sites in southern Africa

Some of the fish that occur in desert habitats have become adapted to live in salt water. One unusual and well-studied group of desert fishes is the desert pupfish found in springs, sinkholes, and marshes in North American deserts. Some pupfish species live in very extreme conditions, able to tolerate water salinities up to four times that of seawater and water temperatures of 45°C. Pupfish have also been found in water almost devoid of oxygen. These species have enlarged gills but also gulp air at the water’s surface to supplement their meagre intake of oxygen from the water.

Obtaining fresh water in deserts is often a serious challenge for terrestrial creatures and several animals have adaptations to make the most of the limited resources available. In hyper-arid areas where rainfall is extremely rare and unpredictable, the occurrence of fog and dew plays an important role in the water economy of many organisms. Several creatures found in the Namib have developed interesting ways of ‘fog-basking’. One is the sidewinder adder (Bitis peringueyi) which flattens its body against a cool sand surface during foggy periods, so increasing its surface area exposed to water deposition. The snake licks the water droplets off its body, raising its head to swallow using gravity.

Two species of tenebrionid beetles have also developed unique fog-basking behaviour in the Namib. This involves climbing up to the crest of a fog-swept dune at night and assuming a head-down stance, allowing fog to be deposited on their carapaces. The beetles drink drops of moisture that run down towards the mouth, gaining an average of 12% of body weight.

Dew is an important source of water for many desert animals, particularly those that feed on vegetation in the early morning. For most desert snails, dormant much of the year, a heavy dew provides sufficient moisture for them to become active, with high rates of water intake. An example is the snail Trochoidea seetzenii, which is widely distributed in the Negev. The Australian tarantula, Selenocosmia stirlingi, which occurs throughout arid areas in the centre of the continent, traps dew for drinking on a low silk-covered mound at the entrance to its burrow.

Size is a serious issue for desert invertebrates – those animals without a backbone – because these creatures lose water through their surface, and the smaller the organism the larger its surface area relative to its volume. Insects, however, have a waxy, waterproof outer layer to combat this problem. A covering of wax also makes scorpions better adapted to high temperatures and arid conditions than most other animals, although scorpions are not restricted to deserts. A scorpion’s rate of water loss has been measured at just one part per 10,000 of its body moisture, the lowest recorded for any animal. Scorpions are also remarkably tolerant of dehydration, being able to survive losing up to 40% of their body fluid. Despite these capabilities, scorpions typically spend the daylight

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