ECOSYSTEMPlants, animals and human beings live in association with a wide variety of other plants and animals. These communities of organisms are not mere ad boc collections of individuals or populations but they represent a highly ordered dynamic and complex organisation. Such complex natural organisation with their living and non-living environments that controls them and from which the living organisms derive their sustenance are technically called as "ecosystem" or an "ecological system".The interaction between living organisms and their environment is very much a two way process: organisms affect and are in turn affected by their surroundings. Professor Arthur Tansley, a British botanist, in 1935 proposed the term ecosystem and defined it as the "system resulting from the integration of all living and non-living factors of the environment". He regarded ecosystem as nQt only the organism complex but also the whole complex of physical factors forming the environment.The concept of this interacting system has proved extremely valuable and the ecosystem is regarded as a basic unit for ecological studies.