The Niche Concept Revisited: Mechanistic Models and Community Context

The niche concept is a central organizing aspect of modern ecology. Although its history has often been reviewed, the structure of the concept and its connection to advances in ecological theory has received less recent attention. I review the niche concept using "mechanistic" models of community theory to identify two distinct components. One describes the environmental requirements of organisms and the other describes the per capita impact of organisms on the environment. I argue that these correspond to significant differences between Grinnell's and Elton's concepts distinct from the previously discussed "habitat" vs. "functional" dichotomy. I illustrate the distinction between the requirement and impact components of the niche using models of resource competition and of keystone predators, and I discuss "Gause's axiom" and conventional "niche theory" in the context of these two distinct niche components. I suggest that the niche concept be elucidated by explicit reference to these two distinct components; the "impact" niche (corresponding to Elton's concept) describing instantaneous per—capita effects of species on the environment, and the "requirement" niche describing the responses of species to the environment (corresponding to Hutchinson's definition). This approach connects conventional niche theory with "mechanistic" individual—based ecological models and can help provide a more modern context for the niche concept.