Living beings normally cannot exist more than a few kilometers below the surface of the earth, or more than a few kilometers above it. Life occupies an incredibly thin ‘skin’ at earth’s surface. This is known as the biosphere. The biosphere includes four major environmental categories or habitats- marine, estuarine, fresh water and terrestrial. The terrestrial habitat is further classified in biomes about which you will study in later units.
All the four habitats have sub-types, which have a typical set of physical and biological features and from different ecosystems. Thus, ecosystem is a natural unit of biosphere, which is composed of abiotic and biotic components whose interactions result in a stable self-perpetuating system.
Among the main abiotic components of an ecosystem are climatic factors such as solar radiation, temperature, wind, water currents, rainfall; physical factors such as light, air, pressure, geomagnetism; and chemical factors such as oxygen, carbon dioxide, acidity, salinity and the availability of inorganic nutrients needed by plants but which affect animals and plants alike. The biotic factors in an ecosystem are the totality of all living organisms and their organic by-products. This includes each and every plant and animal, irrespective of its size, ranging from bacteria in soil and sediment to large mammals.
In considering ecological factors separately for distinguishing and measuring the effects of each, one must remain aware that in nature these factors never act alone. The “real life” of organisms involves the simultaneous and continuous impact of all existing ecological factors.