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| The chief obstacles to survival in the desert are lack of water, shortage
of food, and extreme temperatures. Mammals, including humans have the ability
to maintain a constant body temperature regardless of external conditions.
This has advantages and disadvantages in the desert. Mammals can endure
a large range of air temperatures, but are unable to tolerate even a small
change in body temperature without encountering problems. |
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| When most mammals get hot they perspire, and the evaporation
of this water cools them down and helps maintain a constant body temperature.
Some mammals use panting to produce the same effect. Both methods work well,
but they have an important drawback for life in the desert. They involve
substantial loss of water. Where water is in short supply, animals must
minimize water loss. Thus, few desert mammals use perspiration or panting
as their main method of keeping cool. |
| Because scarcity of food in the desert limits the number
of large mammals that can be supported, most desert mammals are small. Joshua
Tree National Park is home to 52 species of mammals. Of these, 24 are small
rodents. Being small has its advantages and disadvantages. Rodents can burrow
into the ground or hide in rocky crevices to avoid the mid-day heat. But
their small body size means that they can gain or lose body heat rapidly.
Many of them plug the entrance to their burrows to keep out the hot, desiccating
air. |
| Most small mammals make the most of the positive side of
being small, spending the day in burrows and emerging at night when the
temperature drops to a more comfortable level. The larger mammals, such
as mule deer and mountain sheep stay close enough to springs to be able
to drink daily. |
| A few desert mammals, such as the round-tailed ground squirrel, a diurnal
rodent, enter a state of aestivation when the days become too hot and the
vegetation too dry. They sleep away the hottest part of the summer. They
also hibernate in winter to avoid the cold. |
| Many of our Joshua Tree mammals are paler in color than
their relatives in more moderate environments. Pale colors not only ensure
that the animal will absorb less heat from the environment, but help make
it less conspicuous to predators in the bright, pallid landscape. |
| Most desert mammals are herbivores and derive water directly
from the plants they eat. Some, like kangaroo rats, have extreme adaptations
enabling them to live without ever drinking water. They have super efficient
kidneys that extract most of the water from their urine and return it to
the blood. And much of the water that would be lost in breathing is recaptured
in the nasal cavities by specialized organs. If that weren’t enough, kangaroo
rats actually manufacture water metabolically from the digestion of dry
seeds! |
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last modified: 03/26/02
web editor: Sandra kaye |
