Aridland
Extreme temperatures and low rainfall typify the aridlands of the world. These regions range from the semi-arid scrub forests of the Middle East, which receive an annual rainfall of ten to twelve inches (25 to 30 cm), to the Asian Gobi Desert, where the driest areas receive less than three inches (8 cm) of rain per year. In between lie regions known as Mediterranean, where summer drought places heavy demands on the plant and animal species that live there.
Survival for most aridland plant life depends on an array of structures that gather and retain moisture, including extensive root systems, shiny succulent leaves
that hold moisture, and even, in the case of the welwitschia of the Namib Desert, leaves with the ability to absorb humidity from nighttime mist.
Mammals, too, are ingeniously adapted to withstand the difficult conditions. The camel, for example, uses its hump to store fat, which, during prolonged dry periods, is metabolized to produce water. The body temperature of the camel and another large aridland mammal, the gemsbok, fluctuates rapidly in response to external temperature changes, allowing them to expend less energy staying warm when temperatures drop at night. Equally important, water is not wasted in cooling the body during the scorching heat of day.
Many small aridland mammals are nocturnal, responding to the heat by spending the day burrowed in soil or sand. Some, such as the lesser Egyptian jerboa, the African jird, and the Ord's kangaroo rat, have developed common physical traits to cope, showing convergent evolution at work. These rodents all have enlarged hindlegs and long tails to help them hop on shifting sands.
Ready for the first mammal? Check out the Aoudad.
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