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| Summary |
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| Smallest unit of ecological hierarchy is the organism, while smallest and basic unit of taxonomic hierarchy is species. |
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| A group of individuals, having similar structural and functional characters, capable of potential interbreeding is termed as species. In nature all apecies exhibit cooperative and competitive interactions among the members of the species (intraspecific) and also with members of other species (interspecific). |
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| Several members of a species have definite home range where they find food and mate. The boundaries of territories are marked and guarded by its members. |
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| Population is defined as the total number of individuals of a species present in a particular area. Population is characterized by population density, natality rate, mortality rate, age- composition, growth curve, biotic potential etc. Population growth is the difference between the number of individuals added into and lost from the population. It may be positive, negative or zero growth. |
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| The mathematical expression of growth of population is called growth curve, which may be basically 'Sigmoid (S-shaped) and J- shaped curves'. |
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| An association of a number of different species in a common environment that can survive in nature is called biotic community and the relationship between the species in a community has evolved through their interactions based on the requirement and mode of obtaining food and shelter. |
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| Every community in a particular environment undergoes a series of gradual changes till a group of organism become established in the area. This is called ecological succession. There are two kinds of succession Primary succession and Secondary succession. |
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| Succession is brought about both by changes in the living organisms as well as physico- chemical conditions of the environment. The climax community is most complex and stable. Thus ecological succession is an orderly and evolutionary process of community development in a habitat. |
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