Relationship between organisms and their environment are based on certain principles which are summarized as follows:
1. Everything influencing the life processes of an organism constitutes its environment.
2. Environment in a habitat may be considered into biotic and abiotic components and the activities of the organisms are influenced by the combined effects of various environmental factors.
3. An organism is a biotic component of the environment and the materials and energy required for the maintenance of the body and sustenance of life of organisms constitute the abiotic environment.
4. An organism cannot exist in vacuum.
5. Life is the energy exchange process between the organism and environment and death means cessation of the exchange process.
6. The environmental requirements of different organisms differ from individual to individual and also with age and need.
7. Life activities are influenced by that environmental component which occurs in minimum quantity. This is Liebig’s law of limiting factor. Liebig stated that the growth of a plant is dependent on the amount of the food stuff which is presented to it in minimum quantity.
8. Life activities of an organism are influenced by the minimum or maximum quantity of the environmental components or factors, as for example, nutrients, light, temperature, moisture Based on this principle Shelford founded the law of tolerance.
9. Tolerance limits of an individual for different environmental factors may be different.
10. An organism may show different tolerance limit for a particular environmental factor in different habitats and at different age and stage of life history.
11. Organisms having wide tolerance limits for many environmental factors are widely distributed.
12. An organism is a product of nature (genetic set-up) and nurture (environmental upbringing). The inherited qualities are unfolded in proper environment.
13. Organisms react with the external stimuli caused by the environmental changes. The reactions may be exhibited by movements (migration) or adaptational changes in the body or physiological activities. All such adaptations have survival value.
14. Widely distributed species are adapted to various habitat conditions by evolving ecotypes.
15. Every habitat has potential to support a certain number of organisms. This is known as carrying capacity of the habitat. Knowledge of carrying capacity is essential for proper management of the habitat.
16. The biotic and abiotic components of the environment are in constant flux in any habitat which induce ecological succession with the passage of time and change in the environment.
17. Sun is the only source of energy in our earth’s environment and the life depends on solar energy. Organisms live through exchange of energy.
18. Energy is neither created nor destroyed. It can be transformed from one form to the other.
19. During transformation of energy from one form to the other a large amount is dissipated into the environment mainly as heat energy.
20. Every living thing that we see has potential energy in huge quantity. One gm. dry weight of body tissue contains 4—5 kcal of energy stored in it.
21. Solar energy reaching the earth’s surface is not lost but only transformed from one form to the other. A very small amount (1 to 3 per cent) of solar energy is trapped by green plants and converted into chemical energy.
22. Energy flow from the sun to the plants, to the other organisms and then to the space is always unidirectional.
23. Energy and space relationships of the organisms cause niche differentiation within the habitat which brings about ecological stability in the community life. In any habitat a community is born, it grows with passage of time and through succession it is stabilized to form a climax community.
24. Life on the earth exists in a thin mantle or layer around the earth. This layer forms the biosphere.
25. The biosphere is not uniform structure and it consists of several life supporting habitats called ecosms or ecosystems.
26. An ecosystem has producers (plants), consumers (animals), and decomposers constituting the biotic component, and life supporting matter and energy which constitute the abiotic component.
27. In any ecosystem the stability is conditioned by:
(i) Fixation and transfer of energy in the organisms at various levels.
(ii) Conversion of abiotic components (nutrients and energy) into organic structures which adds to the biomass. The abiotic components are replenished through weathering of the lithosphere, atmospheric movements and biogeochemical cycling’s of nutrients.
28. Energy flow, synthesis of matter and balanced relationship of biotic and abiotic components in an ecosystem are regulated through ecological processes.