Two groups of animals—arthropods and reptiles—are particularly well adapted
to the desert environment and play a dominant role in its food chains. In the
desert environment arthropods, whose hard body casings help to conserve
precious body water, are represented mainly by insects, such as grasshoppers,
flies, beetles, bugs, ants, and termites, and arachnids, such as spiders, scorpions,
and mites. The principal types of reptile found in deserts are lizards and snakes,
whose scaly covering, like the arthropods’ carapace, restricts water loss, unlike
the thinner, more exposed skin of amphibians, birds, and mammals, all of which
flourish less well in arid conditions.
Bodily water conservation is only one reason why arthropods and reptiles are
so successful in arid habitats, however. Body temperature, too, plays a crucial
role. Deserts are places not only of extreme heat but also of extreme cold, with
nocturnal temperatures that can often dip toward freezing. Both temperature
extremes present life-threatening challenges to the maintenance of
steady body temperature, in particular for warm-blooded vertebrates such as
mammals and birds. To survive the desert night, mammals, for example, must
find sufficient and continuing food supplies to act as fuel to maintain a healthy
body temperature—from 35°C to 43°C (95–110°F) according to the species—
and food, like water, is in short supply in the desert. Moreover, during scorching
daylight hours mammals’ cooling systems are triggered to prevent overheating,
involving the loss of precious body fluids as the animal sweats or pants.
Unlike mammals, arthropods and reptiles are not warm-blooded but
poikilothermic; that is, they have a variable body temperature that is generally
slightly higher than the ambient temperature. For example, in the desert sun their
body temperature may exceed the 40°C (104°F) or so of a bird or mammal.
Many poikilothermic animals can regulate their body temperatures by
behavioral means, seeking out shade and cooling breezes when it is too hot and
basking on a heat-retaining rock when it is too cool. The great advantage of
poikilotherms is that they require far less energy and, hence, food compared to
warm-blooded animals. Some experts estimate that poikilothermic animals like
reptiles and arthropods need about five or six times less food than mammals
relative to their body weight.