A biological community is an association or assemblage of populations of organisms living in a localized area or habitat. The community is a level of organization incorporating individual organisms, species, and populations. A population is an assemblage of one species, and the community is a collage of one or more populations. Communities may be large or small, ranging from the microscopic to the level of biome and biosphere.

"Community," as contrasted conceptually to ecosystem, does not necessarily include consideration of the physical environment or the habitat of a particular group of organisms, though it is of course impossible to understand fully the dynamics of a community without reference to the resources on which it exists. The term ecosystem was coined to incorporate study of a community together with its physical environment. Still, communities are adaptive systems, inseparable from and evolving in response to changing environmental conditions...