The Concept of ecosystem: A systematic and orderly study of organisms living in a geographic unit and the interrelations of that unit is called ecological mechanism. According to A.G. Tansley(1935), “The system in which the biotic and abiotic factors of the environment are inter – related, is called the ecosystem”.

Other definitions related to ecosystem are given as follows:

According to R.L. Lindeman (1942): “The system that is produced by physical – chemical – biological processes in a particular time unit of any magnitude, is called the ecosystem”.

According to Fasbert (1963): “The ecosystem is a functional and interactive system, whose structure is formed by one or more organisms and their effective environment”.

According to Odum (1971): “The ecosystem is the basic functional unit of such organisms and their environment, which constantly interacts with other ecosystems and their components”

According to Peter Haggett (1975): “Ecosystem is such an ecological system in which plants and organisms are linked to their environment through the nutritional chain.”

According to Arthur N. Strahler (1976): “The ecosystem is a group of components that interact with groups of organisms. This activity involves investing in substances and energy, which create biological structures.”

According to Park (1980): “The ecosystem is the gross of all the natural organisms and elements within a certain area.”

An ecosystem is the basic unit of ecological study whose size and extent can vary. For example, if one ecosystem is an entire global supplemental ecosystem, then the second ecosystem may be as small as a cage built in a zoo or limited to a lake. Ecosystems can be either natural or man-made.