International Encyclopedia of Systems and Cybernetics

"That part of the actual environment relevant to the unit's survival (i.e. its continued organizational closure without desintegration) (R. HARNDEN, 1990, p.299). He writes: "… niche has to be separated out from environment in the same process that structured mechanisms relevant to survival become visible in terms of the observer… The first step in handling any complexity is to reduce the general noise of the total environment. Indeed, that is precisely how perceptual and cognitive processes function (e.g. Gestalt)" (p.300).

In short, the niche is the specific sector in the general environment wherefrom the basic determinisms of the system do emerge. J.J. GIBSON distinguishes clearly "habitat", from "niche": "A niche refers more to how an animal lives than to where it lives. I suggest that a niche is a set of affordances" (1986, p.128).

In a more specific way and, somewhat surprisingly, giving to the term quite an active sense, the UNESCO – UNEP "Glossary of environmental education terms" defines the ecological niche as follows: "The role, status and position of a species in the environment, its activities and relationships to the biotic and abiotic environment" (1983, p.9).

S. MARTINEZ observes: "… what is important is the extent to which any growth niche is linked and in what ways to others by invasion, exchange, or incorporation, perhaps even a random encounter" (1993, p.401).

Niches are not static since its occupants – plants, animals and also human populations, trades, products, techniques or concepts – cross-fertilize, evolve and co-evolve.

Clearly, "niche" is more an ethological than an ecological concept, even if both are interdependent.