Homeotherms and Poikilotherms

There is a group of animals that have homeostatic mechanisms for maintaining the temperature of the internal environment within very narrow limits. They can do this even though there may be large changes in the environmental temperature. Such animals, humans, other mammals and birds, are called homeotherms. Humans can therefore function quite efficiently in both cold and hot environments.
Another group of organisms known as poikilotherms have not developed mechanisms for regulating the temperature of their internal environment. Their internal temperature therefore changes with temperature changes in the external environment. Lizards and snakes are examples of poikilotherms.
activity	Watch the following two animations and explain the differences in the behaviour of the lizard and the kookaburra.



Did you notice that the kookaburra could catch the lizard on a cold day when it was less active? When poikilotherms such as lizards are exposed to a cold environment their internal temperature also falls. This makes the enzymes less efficient and so the animals become less active. On the other hand, homiotherms such as the kookaburra are not effected as much by changes in environmental temperature.