Ecology is the study of interactions between the organisms and their environment.
Now, the ecologists feel that the two components of nature–organisms and environment, are not only related but both these components function in an orderly manner as a definite system.
In fact, the two components, organisms and environment are not distinct.
For a particular organism, other organisms can constitute a part of its environments.
Similarly, environment can also be modified and influenced by organisms, thus, organisms and environment are interacting parts of a system.
Therefore, the term ecosystem is now used to describe such a system.
The word Eco-system is a short form of ecological system.
The term was first used by A.G. Tansley in 1935.
An ecosystem can be defined as a system of regularly interacting and interdependent components forming a unified whole.
In other words, any segment of the landscape that includes biotic and abiotic components is known as ecosystem, if all its components are integrated with each other.
For example, a lake or pond is an eco-system when it is considered in its totality and not just a water body.
In that sense, pond is a representative of small ecosystem and biosphere is considered as the largest ecosystem.
Basically, the concept revolves around two aspects.
(1) First, it studies inter-action among the various components and sub-components and
(2) Second, flow of energy among various components of Eco-system which is the essential determinants of how a biological community functions.
Ecosystem can be studied with the following:
 Energy flow
 Food Chain