Large animals that inhabit the desert have evolved a number of adaptations for reducing the effects of extreme heat. One adaptation is to be light in color, and to reflect rather than absorb the Sun's rays. Desert mammals also depart from the normal mammalian practice of maintaining a constant body temperature. Instead of trying to keep down the body temperature deep inside the body, which would involve the expenditure of water and energy, desert mammals allow their temperatures to rise to __what would normally be fever height__, and temperatures as high as 46 degrees Celsius have been measured in Grant's gazelles. The overheated body then cools down during __the cold desert night__, and indeed the temperature may fall unusually low by dawn, as low as 34 degrees Celsius in the camel. This is an advantage since the heat of the first few hours of daylight is absorbed in warming up the body, and an excessive buildup of heat does not begin until well into the day. Another strategy of large desert animals is to tolerate the loss of body water to a point that would be fatal for non-adapted animals. The camel can lose up to 30 percent of its body weight as water without harm to itself, whereas human beings die after losing only 12 to 13 percent of their body weight. An equally important adaptation is the ability to replenish this water loss at one drink__. Desert animals can __drink prodigious
__volumes in a short time__, and camels have been known to imbibe over 100 liters in a
few minutes. A very dehydrated person, on the other hand, cannot drink enough water
__to rehydrate at one session__, because the human stomach is not sufficiently big and
because a too rapid dilution of the body fluids causes death from __water intoxication__.
The tolerance of water loss is of obvious advantage in the desert, as animals do not
have to remain near a water hole but can obtain food from grazing sparse and far-flung
pastures. Desert-adapted mammals have the further ability to feed normally when
__extremely dehydrated__, it is a common experience in people that appetite is lost even under
conditions of moderate thirst.
đang được dịch, vui lòng đợi..
