A population may be defined as a group or collection of individuals belong­ing to a single species. The units of study are populations. Study of inter­action between individuals in terms of growth reproduction, dispersal etc., constitutes population ecology.

A community may be defined as populations of different species bound together in a common habitat. The members of a community may be plants as well as animals. Only the living components of a community however are studied here mainly to analyse the nature of interdependence.