Among the first to use the term niche was Grinnell (1917, 1924, 1928). He viewed the niche as the functional role and position of an organism in its community.
Grinnell considered the niche essentially a behavioural unit, although he also emphasized it as the ultimate distributional unit (thereby including spatial features of the physical environment).
Later Elton (1927) defined an animal’s niche as “its place in the biotic environment, its relations to food and enemies” (his italics) and as “the status of an organism in its community.” Further, he said that “the niche of an animal can be defined to a large extent-by its size and food habits.” Others, such as Dice (1952), use the term to refer to a subdivision of habitat; thus Dice states that “the term (niche) does not include, except indirectly, any consideration of the function the species serves in the community.”
Clark (1954) distinguished two separate meanings for the term niche, the “functional niche” and the “place niche.” Clark noted that different species of animals and plants fulfill different functions in the ecological complex, and that the same functional niche may be filled by quite different species in different geographical regions. The idea of “ecological equivalents” was first stressed by Grinnell in 1921.
The most influential modem treatment of niche is that of Hutchinson (1957a). Using set theory, he treats the niche somewhat more formally and defines it as the total range of conditions under which the individual (or population) lives and replaces itself. Hutchinson’s examples for niche coordinates are nonbehavioural and have thus emphasized the niche as a place in space rather like a microhabitat or the “habitat niche” of Allee etc.
The emphasis is unfortunate to the extent that it tends to exclude the “behavioural niche” from consideration. Hutchinson’s distinction between the fundamental and the realized niche is one of the most explicit statements that an animal’s potential niche is seldom fully utilized at a given moment in time or a particular place in space. This distinction has proven useful in clarifying the roles of other species, both competitors and predators, in determining the niche of an organism.
More recently Odum (1959) defined the ecological niche as “the position or status of an organism which its community and ecosystem resulting from the organism’s structural adaptations, physiological responses, and specific behaviour (inherited and/or learned).” He emphasized that “the ecological niche of an organism depends not only on where it lives but also on what it does.”
The place an organism lives, or where one would go to find it, is its habitat. For Odum the habitat is the organism’s “address” while the niche is its “profession.” Weatherly (1963) suggested that the definition of niche be restricted to “the nutritional role of the animal in its ecosystem, that is, its relations to all the foods available to it.” Some ecologists prefer, however, to define the term niche more broadly and to subdivide it into components such as the “food niche” or the “place niche.”
Because concepts of the ecological niche have taken on so many different forms, it is often difficult to be sure exactly what a particular ecologist means when this entity is invoked. Some therefore avoid using the word altogether and insist that we can get along perfectly well without it. However, no one denies that there is a broad zone of interaction between the traditional entities of “environment” and organismic unit”; the major problem is to specify precisely in any given case just what subset of this enormous subject matter should be considered the “ecological niche.”
The niche concept has gradually become inextricably linked to the phenomenon of interspecific competition, and it is increasingly becoming identified with patterns of resource utilization. Niche relationships among competing species are frequently visualized and modeled with bell-shaped utilization curves along a continuous resource gradient, such as prey size or height above ground.
Emphasis on resource use is operationally tractable and has generated a rich theoretical literature on niche relationships in competitive communities. In this chapter we consider in detail various aspects of this theory; including niche breadth, niche overlap, and niche dimensionality.