Adaptations
Every organism can live and reproduce within a certain range of climatic conditions. Organisms that live in hot or cold environments have behavioural and physiological features that enable them to survive extremes of temperature. ks a survival strategy organisms eithertolerate these extreme conditions or evolve ways of avoiding them altogether. For example, plants cope up with high temperatures in the desert by developing a thick layer of cuticle,succulence i.e., water storage tissue in the leaves and stems. In many cacti the stem is green and carry out the functions of leaf and makes food by photosynthesis. These plants also have physiological adaptations. The stomata remain closed during the day to prevent the loss of water due to transpiration. CO2 diffusion cannot occur in stomata1 closure in the day. To carry on photosynthesis these plants have evolved special physiological adaptation. During night when their stomata open they trap CO2 and store it in the form of four carbon acid. The CO2 trapped in the leaf at night is subsequently released during the day and used in photosynthesis. This type of metabolism is called crusstulacean acid metabolism (CAM). The details will be covered in physiology course. Comparative study of plant responses to constant favourable temperature region verses alternating temperature shows that seed germination, vegetative growth or fruit production is best under the latter conditions. This shows that plants are adjusted to natural rythmic diurnal cycle temperature changes. The regulation of plant responses to periodic thermal changes is called thermoperiodism.
Animals have advantage over plants as they can move from one place to another. They cope with temperature stress by regulating their internal and external environment by physiological and behavioural means. Probably you know that birds and mammals are capable of maintaining constant body temperature. They do so by using the energy of metabolism released during cellular respiration. They are called homeotherms or endotherms because they control constant body temperature by internal means. The body fat, feather, fur or hair etc. help to retain this heat. Some animals use a number of behavioural mechanisms to regulate their body temperature. This type of regulation is termed as behavioural thermoregulation. For instance, they can move to shady areas or take a dip inawater during the hot period of the day. The desert animals such as snakes, lizards, scorpions, and rats are mostly nocturnal i.e. they remain hiding during the day to avoid the scorching sun and roam in search of food at night or early in the morning when temperature is generally low. Reptiles like lizard and snake are considered cold blooded because they cannot control their body temperature. However, experiments on these animals have revealed that they can also control their body temperature effectively by behavioural means.
In colder climates animals have adaptations to gather heat. Birds warm up their bddy by increasing the muscular activity in their wings by shivering. The chameleons change their colour to black, thus increasing their heat absorbing capacity, the ectotherms bask in the sun. The animals also manipulate by exposing a certain portion of their body so as to acquire desirable heat.
Another way to avoid adverse climatic conditions is through migration. Probably you know that birds of northern or colder regions migrate to warmer southern regions during the winter season. Fishes also swim long distances until they reach water masses which have suitable temperature for their survival.
Some animals such as bats, hedgehogs, ground-squirrels, lizards reduce their metabolic activity and thus enter into hibernation to minimise their energy needs during winter. To overcome high temperature during summer insects, lungfish, amphibians etc. also suspend their activities and lead dormant life. This state is called aestivation.