At present ecological studies are made at an Ecosystem level. At this level, the units of study are quite large. This approach has the view that living organisms and their non-living environment are inseparably interrelated and interact with each other. A.G. Tansley (in 1935) defined the Ecosystem as ‘the system resulting from the integrations of all the loving and non-living actors of the environment’. Thus he regarded the Ecosystems as including not only the organism complex but also the whole complex of physical factors forming the environment.
The abiotic environmental components include basic inorganic elements and compounds such as water and carbon dioxide, calcium and oxygen, carbonates and phosphates besides such physical factors as soil, rainfall, temperature, moisture, winds, currents, and solar radiation with its concomitants of light and heat.
The biotic environmental factors comprise plants, animals, and microbes; They interact in a fundamentally energy-dependent fashion. In the words of Helena Curtis “The scientific study of the interactions of organisms with their physical environment and with each other, is called ecology”. According to Herreid II “It mainly concerns with the directive influences of abiotic and biotic environmental factors over the growth, distribution behaviour and survival of organisms.
- Ernst Haeckel (1866) defined ecology “as the body of knowledge concerning the economy of nature the investigation of the total relations of animal to its inorganic and organic environment.
- Frederick Clements (1916) considered ecology to be “the science of community.
- British ecologist Charles Elton (1927) defined ecology as “the scientific natural history concerned with the sociology and economics of animals.”
- Taylor (1936) defines ecology as “the science of the relations of all organisms to all their environments.”
- Taylor (1936) defined ecology as “the science of the relations of all organisms to all their environments.”
- Allee (1949), considered ecology as “the science of inter-relations batwing living organisms and their environment, including both the physical and biotic environments, and emphasizing inter-species as well as intra-species relations.
- G.L. Clarke (1954) defined ecology as “the study of interrelations of plants and animals with their environment which may include the influences of other plants and animals present as well as those of the physical features.”
- Woodbury (1955) regarded ecology as “the science which in investigates organisms in relation to their environment: a philosophy in which the world of life is interpreted in terms of natural processes.
- A. Macfadyen (1957) defined ecology as “ a science, which concerns itself with the inter-relationships of living organisms, plants and animals, and their environments.”
- S.C. Kendeigh (1961, 1974) defined ecology as “the study of animals and plants in their relation to each other and to their environment.” Certain modern ecologists have provided somewhat broader definitions of ecology.
- M.E. Clark (1973) considers ecology as “a study of ecosystems of the totality of the reciprocal interactions between living organisms and their physical surroundings.
- Pinaka (1973) defined ecology as “the scientific study of the relationships of living organisms with each other and with their environments.” He adds that “it is the science of biological interactions among individuals, populations, and communities; and it is also the science of ecosystems-the inter-relations of biotic communities with their non-living environments.
- R.L. Smith (1977), considers ecology as “a multidisciplinary science which deals with the organism and its place to live and which focuses on the ecosystems.”
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