How do organisms living in different habitat manage with stressful conditions?

During the course of millions of years of their existence, many organisms have evolved a relatively constant internal environment, which allows all the biochemical reactions to proceed with maximum efficiency.

Their constant internal environment (maintained by homoestasis) could be in terms of optimal temperature, osmotic concentration of body fluids etc.

Other organisms cope with the situation by the following :

$(a)$ Regulation : Homeostasis is maintained in organisms by physiological and/ or behavioural means to ensure a constant body temperature (thermoregulation),osmotic concentration(osmoregulation) etc.

$(b)$ Conformation : A constant internal environment can not be maintained by most of the animals and nearly all plants.

Their body temperature changes with the ambient temperature.

There is change in osmotic concentration of body fluids of aquatic animals with ambient water or osmotic concentration.

Thermoregulation is energetically expensive for many organisms particularly for small organisms like shrews and humming birds.

Heat loss or heat gain is a function of surface area.

- Small animals have a larger suface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism.

Because of this very small animal are rarely found in polar regions.

$(c)$ Migrate : The organisms can move away temporarily from the stressful habitat to a more hospitable area and return when stressful period is over.

It is like man living in hot regions move to hill stations during summer.

Many animals, particularly birds, during winter undertake long distance migrations to more hospitable areas.

Every winter the famous Keolado National Park (Bharatpur)in Rajasthan host thousands of migratory birds coming from Siberia and other extremely cold northern regions.