No organism or a species live alone and there are associates influencing each other and organizing themselves into communities. The organisms of any community besides interacting among themselves always have functional relationship with the external world or the environment. This “structural and functional system of communities of living organisms and their environment is called ecological system or in short the ecosystem”. The concept of ecosystem was first proposed by A G Tansley (1935). The fundamental principle of ecosystem is that at any place where organisms live, there is a continuous interaction between plants, animals and their environment to produce and exchange materials. OR In other words, an ecosystem can be defined as “The biotic (living) community and its physical (non-living) environment in which matter cycles and energy flows is called ecosystem.” An ecosystem is the smallest unit ofbiosphere (The regions of the surface and atmosphere of the planet occupied by living organisms). A pond, lake, desert, grassland, forest are common examples of ecosystems.


The ecosystem is generally divided into, natural ecosystem and artificial ecosystem based on the nature that is the interference of man.


This system function itself under natural conditions without any interference of humans. On the basis of a particular type of habitat (the physical environment in which organism lives), it is further subdivided as terrestrial ecosystem and aquatic ecosystem. Terrestrial ecosystem is often defined by the vegetation type that dominates the community. Terrestrial vegetation has a rapid change of oxygen, water and carbon dioxide. It includes grassland ecosystem, forest ecosystem, desert ecosystem, cropland ecosystem. Aquatic ecosystemincludes Fresh Water Ecosystem (Pond ecosystem) and Marine Ecosystem (Deep Seas, Estuaries and Sea shores). Aquatic ecosystem is sub-divided into two, Running Water (Lotic) ecosystem, in this there is a greater horizontal movement of water. These are called channel type habitats. Examples: streams and rivers. Stationary Water (Lentic) ecosystem in these the circulation of water is slow and usually of vertical type. Examples: ponds, lakes, ditch, swamp, etc.


Artificial ecosystems are maintained by man himself fully or partially through planned manipulations.  For example, man tries to control the biotic community and physic-chemical environment. The examples of such ecosystems are:

  • pond constructed as a part of waste water treatment plant.
  • Cropland ecosystem such as a field of maize, wheat, rice, etc.
  • Micro ecosystem such as those made in laboratories for a planned study.


The structure of an ecosystem is formed of two components, namely, abiotic factors and biotic factors. Abiotic components constitute the non-living components of the ecosystem and are composed of Physical or Climate factors such as soil, air, water, sunlight, temperature, pressure and humidity, and Chemical factors constituting the inorganic and organic substances. The inorganic substances include Oxygen, Carbon, Hydrogen, Nitrogen Phosphorous, Potassium, Calcium, Sodium, Sulphur etc. that are involved in mineral (nutrients) cycle. The organic substances include carbohydrates and proteins. Biotic components include the living components of the ecosystem and are made of many different populations of species, which are interdependent upon each other in the ecosystem. The biotic factors of an ecosystem are classified into three main groups. They are producers, consumers, and decomposers.


Producers are the organisms which can prepare their own food from simple inorganic substances like carbon dioxide and water in the presence of sunlight. Terrestrial ecosystems have trees, shrubs, herbs grasses and mosses that contribute within varying degrees to the production. Algae of various types are the most important producers of aquatic ecosystem, although in estuaries and mashes, grasses may be important as producers.  The members of autotrophic (Self Feeding) components are self-nourishing. These are of two types; the first one is Phototrophs, which prepare food through photosynthesis by using solar radiation. e.g. Green plants, Phytoplankton etc. The second one is Chemotrophs, which prepare food through chemosynthesis from inorganic substances by oxidation. e.g. Some Bacteria.


Consumers are the living members of the ecosystem which consume the food produced by the producers i.e. heterotrophs, means feed on others. They are further divided into three types. Herbivores, they eat the producers like plants and algae. They are also called primary consumers, for e.g. Rabbit, Deer, Elephant, etc., Carnivores, they kill and eat the herbivores. As these carnivores directly depend on herbivores, they are specifically called as primary carnivores or secondary consumers. Fox, wolf, etc., are the secondary consumers in a terrestrial ecosystem. The carnivores which kill and eat the primary carnivores or secondary consumers are called as secondary carnivores or tertiary consumer, for example, lion, tiger, etc., There is an another category called Omnivores:  An animal (Consumer) thateats a variety of food of both plant and animal is known as omnivores. e.g., Humans.


The decomposers are the organisms which decompose the dead bodies of plantsanimals and their waste products. They feed on organic compound of dead or living protoplasm of plants and animals for their food and energy. They secrete enzyme which digest the dead organisms and the debris and convert them into smaller molecules. These substances which are released into the environment are consumed by the producers. If there were no decomposers, then the dead bodies of plants and animals would have been kept as it is for ages and the component constituting the bodies of plants and animal would never had returned to their original pools like soil, air and water. e.g. Fungi and certain Bacteria.