A UNIFIED CONCEPT OF THE ECOLOGICAL NICHE

The modern concept of ecological niche contains two basic meanings: (a) The "conditions of existence" or the hypervolume delimited by the range of values of the environmental variables permitting the indefinite persistence of the species; (b) what the species does, its role, its way of relating to other species, environment and space within the biological community. This duality has generated conceptual difficulties. Using a general systems approach, the concept of niche is characterized in an coherent and unitary manner. The ecological niche (N) is defined as the total relation established by a species or biological population between the set of input or environmental variables (X), the set of internal variables (Z) (not considered previously) and the set of output or response variables (Y): N=R (X,Z,Y). This definition is complete at each resolution level. Previous definitions of niche are shown to be particular cases, associated to differences in the resolution level and viewpoint adopted. Theoretical and practical implications are discussed,