Adaptations to Hot and Cold Environments

Warm-blooded animals, endotherms, survive in extreme environments by keeping their internal environments at a relatively constant temperature that is an optimum for enzymes to function. In many cases this internal temperature varies greatly from the outside environment.

An obvious example of this is the camel which is forced to survive in very hot and dry conditions. The extreme heat and variation in it between day and night (and season) is coped with by the camel’s ability to vary its internal temperature by about 8oC. The Bactrian camel found in the Gobi desert has to cope with a temperature of -30oC in the winter which rises to 50oC in summer. In the cold winter the Bactrian will grow dense hair, denser at the colder extremities. Six months later the hair will be shed to allow the camel to cool easily.

The indigenous human environment is relatively constant in temperature so our internal temperature does not vary to such an extent as the camel’s. However, compared with the fluctuations in the camel’s environmental temperature, its internal temperature is relatively constant. This is an example of homeostasis though appears initially not to be because there is still an 8oC fluctuation.

The aridity is coped with not by storing water in the hump but by adaptations that allow for dehydration. Again, this does not appear to be homeostasis because the internal environment is not being kept constant, but is adapted to coping with changes. These adaptations include the camel’s ability to sacrifice tissue fluid for blood plasma and its erythrocytes’ oval shape which allows them to continue circulating when blood is viscous (i.e., when plasma is at low levels).

When water is ingested, it is done so in large amounts. Most animals would not be able to cope with this as osmotic potentials would be too high. However, water is absorbed slowly from a camel’s stomach and intestines giving time for water potentials to attain equilibrium. Camel urine can be as viscous as syrup, their kidneys squeezing every last drop of water out of it. Camel faeces are so dry that it can be instantly burnt as fuel.

As well as the heat and aridity of the desert, the camel must live with sand blowing in its eyes, nose, ears etc. It copes by simple adaptations such as long eyelashes, closing small nostrils and hairy ears. It stores fat in its hump (in a Dromedary, two in a Bactrian) which is metabolised for energy when food is scarce. A healthy, recently well-fed camel will have (a) plump, erect hump(s).

Another arid environment, and technically desert, is the Anatarctic where penguins are up against the cold. Like many animals living in similar conditions, penguins, polar bears and seals all have a thick layer of blubber to insulate their warm internal environment from the cold external one.

A polar bear’s fur keeps it camoflaged against its snowy background while allowing sunlight through to the black skin underneath which will absorb more heat than white skin.

Polar bears are apparently so well insulated that they have trouble in overheating. To counteract this, they don’t warm up by moving and therefore respiring unnecessarily.

A naked human in a cold environment is not sufficiently adapted to cope with it. Unlike the 8oC leeway camels have, human internal body temperature can only vary about 0.8-0.9oC about 37oC. Take this two degrees down and hypothermia will set in. The body will do its best to keep warm by shivering to produce heat, erecting hair to insulate with warmer air, vasoconstriction etc. However, this can be detrimental in that the vasoconstriction will leave the skin more susceptible to frostbite as there is no heat being carried in blood to it.

Te hypothalamus stops working below 30oC so none of the body’s defences are able to function. The heart is starved of oxygen causing it to stop beating regularly, ventricular fibrillation. The body is therefore starved of oxygen. Respiration cannot take places so the body is left even colder.

In the hot environment of the camel, hot and dehydrated humans may suffer from heatstroke. The body will sweat, leading to water loss though so you must keep drinking in hot environments. Blood vessels near the skin will dilate to increase heat loss. However, above 38oC, these normal functions will not be enough. The skin will become red (vasodilatation) and dry (lack of sweat due to lack of water), heart rate will increase and the victim will become dizzy and eventually unconscious.

Animals are adapted to survive in the conditions in which they live. A polar bear will not survive five minutes in the Gobi desert while a camel will not survive in the Antarctic. Equally, but not as obviously, a naked human will not survive in these environments either.