Introduction: Natural world around us shows amazing diversity of forms and complexity of relations. To understand these, we have to study levels of organization in the living world viz. macromolecules, cells, tissues, organs, individual organism, population, communities, biomes. Ecology is a study of the interactions among organisms and between the organisms and their physical (abiotic) environment. Term ecology was first used by Reiter but E. Haeckel.
Ecological grouping of organisms is nothing but ecological hierarchy. There are four sequential levels with increasing complexity of ecological (biological) organizations viz, Organism, Populations, Communities and Biomes.
Individual organism is the basic unit of ecological hierarchy.
Organisms of same kind inhabiting a geographical area constitute population. Several populations of
different species in a particular area constitute community that
interact with one another in several ways.
There are six major groups of terrestrial biomes. We shall explore first two levels viz, organism and populations.
