The term ‘ecology’ has been derived from the Greek ‘Oikos’ meaning place to live; and ‘logos’ meaning discourse or study. Thus, ecology means a study of the habitat of the organism. In fact, the word ‘ecology’ was developed by German naturalist Ernst Haeckel in 1869.

Ecology has been defined in various ways by different authors. But in simple terms ecology may be defined as the science which studies interrelationships between abiotic and biotic components of the biospheric ecosystem on the one hand and among biotic components on the other hand. Haeckel defined ecology as the comprehensive science of the relationship of the organisms to the environment.

Even though various definitions of ecology are given in different ways, but the definition as given by Rieklefs and Miller (2000) is certainly more perfect and comprehensive: “Ecology is the study of the relations of the organisms to one another and to their surroundings.”

However, the gist of all the definitions is the same. So a very simple definition may be as under: ecology is the study of how organisms interact with one another and with their non-living (abiotic) environment.


An environment is an aggregate of all external influences that control the living beings, and ecology seeks to understand the relationship of living organisms and their environment; where they live, how they live there, and why they live there. The Basic Principles of Ecology

The following are considered to be the basic principles of the science of ecology :

(i) All living organisms and their physical environment are inter dependent.

(ii) The environmental components are dynamic so that alteration of any one component affects the other component.


(iii) Each living organism has minimal and maximal levels of tolerance and living organisms can survive within such limits.

(iv) The living organisms can modify environment according to their needs.

(v) The existence of living organisms depends upon the flow of energy from one trophic level to another in succession.