Regulate : Some organisms can maintain homeostasis by physiological (sometimes behavioural also) means which ensures constant body temperature, constant osmotic concentration, etc. All birds and mammals and a very few lower vertebrate and invertebrate species are indeed capable of such regulation ( thermoregulation and osmoregulation ). Evolutionary biologists believe that the ‘success’ of mammals is largely due to their ability to maintain a constant body temperature and thrive whether they live in Antarctica or the Sahara desert. The mechanisms used by most mammals to regulate their body temperature are similar to the ones that we humans use. We maintain a constant body temperature of 370° C . Plants , on the other hand, do not have such mechanisms to maintain internal temperatures. Conform : An overwhelming majority ( 99 per cent ) of animals and nearly all plants cannot maintain a constant internal environment . Their body temperature changes with the ambient temperature . In aquatic animals, the osmotic concentration of the body fluids changes with that of the ambient air, water osmotic concentration. These animals and plants are simply conformers. Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and hummingbirds. Heat loss or heat gain is a function of surface area. Since small animals have a larger surface 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. This is the main reason why very small animals are rarely found in polar regions. Migrate : The organism can move away temporarily from the stressful habitat to a more hospitable area and return when the stressful period is over. Many animals , particularly birds , during winter undertake long-distance migrations to more hospitable areas. Every winter the famous Keoladeo National Park ( Bharatpur ) in Rajasthan host thousands of migratory birds coming from Siberia and other extremely cold northern regions . Suspend : In bacteria, fungi and lower plants , various kinds of thick-walled spores are formed which help them to survive unfavourable conditions –these germinate on availability of suitable environment. In higher plants, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal – they germinate to form new plants under favourable moisture and temperature conditions. They do so by reducing their metabolic activity and going into a state of ‘ dormancy ’. In animals, the organism, if unable to migrate, might avoid the stress by escaping in time. The familiar case of bears hibernating during winter is an example of an escape in time. Some snails and fish go into aestivation to avoid summer-related problems-heat and desiccation. Under unfavourable conditions , many zooplankton species in lakes and ponds are known to enter diapause, a stage of suspended development .