The total species assemblage of the subsystems of an ecosystems as well as that of the individual subsystems is termed a community. This rather arbitrary term may also be used for smaller groups of interacting species. The extent to which a specific community, or communities, is associated with an ecosystem depends upon the coherence of its boundaries. In a continuous gradient extending from one ecosystem type to another it may be very difficult to delimit discrete plant or animal communities. Nonetheless, we can usually functionally define a community and measure its gross activity (e.g. decomposition) as well as its interaction with other communities (e.g. the interactions between plant and animal communities).

At a finer level of ecological resolution, we see that a community is composed of populations of individual species. Once we have physically defined the limits of the population we can deduce something about its dynamics or resistance to disturbance by measuring inputs and outputs of energy or nutrients (e.g. for an ant nest) or immigration and emigration. The internal dynamics of a population are primarily determined by balance of birth rates and death rates. The ultimate factors regulating these parameters are other organisms (competitors, predators and parasites) as well as the abiotic environment, particularly the weather (short term temperature, wind and rain conditions) and climate (long term averages of the same measurements).

Most interactions between organisms and their environment, both biotic and abiotic, tend to reach a state of equilibrium over ecological or evolutionary time scales.

Physicochemical processes in the biogeochemical cycles, such as the composition of the earth's atmosphere, also establish equilibrium points under natural conditions. The mechanism by which these phenomena are regulated is known as homeostasis and operates through negative and positive feedback loops controlling deviations from an equilibrium point.

A population with a predominance of positive feedback would show exponential growth, and then die out as resources become limiting. The operation of strongly negative feedback loops would cause the population to decline to extinction. Perfect density dependent homeostasis, in which positive and negative feedback loops respond instantly to changes in state would result in stable equilibrium, as with a sensitive thermostat. Ecological systems rarely, if ever, achieve stable equilibrium and exhibit varying degrees of fluctuation about an environmentally determined equilibrium point with respect to time. This is an inherent consequence of the complexity of the regulatory mechanism in the environment and the time delays in their operation.

Homeostatic mechanisms operate at all levels in communities, from the population to the biosphere, and their identification is of paramount inportance in understanding how an ecological system will respond to disturbance. The extent to which an ecosysem will withstand different degrees of perturbation may be described in terms of neighbourhood (or local) and global stability.  A system returning to equilibrium after small disturbances exhibits local stability, for example grass biomass in a mown meadow. If large perturbations are accommodated by the system's homeostasis, it is said to have global stability. Large and repeated additions of fertilizers to a large lake, for example, will cause only temporary effects and induced eutrophication (nutrient enrichment) which will prove reversible over decades year period.

Communities may exhibit local but not global stability. Animals and plants tend to alter their environment so that it becomes more suitable for other species. For example, the formation of soil by mosses colonizing bare rocks allows grasses and other plants to become established, eventually eliminating the moss, and finally trees will follow grasses. This is the process of ecological succession and the final community, the climax, will show global stability: if a woodland is cut down or burnt and reverted to grassland it is likely to be re-established under the same environmental conditions.

Cultural ecology can be approached from the community by asking the following questions of any of its component species: