Ecology

The word "Ecology" was coined by a German biologist in 1869 and is derived from the Greek word, "Oikos" meaning "House". Ecology is the branch of science that deals with the study of interactions between living organisms and their physical environment. Both are closely inter-related and they have continuous interaction so that any change in the environment has an effect on the living organisms and vice-versa. Any unit of biosystem that includes all the organisms which function together (biotic community) in a given area where they interact with the physical environment is known as ecosystem.

The ecosystem is the functional unit in ecology as it consists of both the biotic community (living organisms) and the abiotic environment. The latter has close interaction essential for maintenance of life processes. The interaction is conducted by energy flow (solar energy) in the system and cycling of materials (natural cycles).

From the biological point of view, the ecosystem has the

following constituents:

(i) Inorganic substances (carbon, nitrogen, carbon dioxide, water, etc.) involved in natural cycles. (ii) Organic compounds (proteins, carbohydrates, humic substances) etc.

(iii) Air, water and substrate environment including the climatic regime and other physical factors. (iv) Producers, autotrophic (i.e., self-sustaining organisms) green plants that can manufacture food from simple inorganic substances.

(v) Heterotrophic (i.e., that depend on others for nourishment) organisms, mainly bacteria, fungi and animals which live on other organisms or particulate organic matter.

(vi) Micro-consumers, decomposers, mainly bacteria, fungi which obtain their energy by breaking down dead tissues or by absorbing dissolved organic matter, extracted from plants or other organisms. The decomposers releaseinorganic nutrients that are utilised by producers. They also supply food for macro-consumers or heterotrophic organisms. Bacteria, fungi (and animals) often excrete hormone-like substances that inhibit or stimulate other biotic components of the ecosystem.

Typical profiles of a grassland ecosystem and of a pond ecosystem are shown in Figure. 

The common features of all ecosystems-terrestrial, freshwater, marine and agricultural-are the interactions between the autotrophic and the heterotrophic components. The major autotrophic metabolism occurs in the upper "green belt" stratum where solar energy is available while the intense heterotrophic metabolism occurs in the lower "brown belt" where organic matter accumulates in soils and sediments.