|1.||Three concepts of the ecological niche|
|2.||The recess/role niche and seeking ecological equivalents|
|3.||The population-persistence niche and mechanistically representing competition|
|4.||The resource-utilization niche and understanding the evolution of species differences|
|5.||Environmental niche modeling and analyzing niches on a macroscale|
It may come as something of a surprise that ecological niche, a term so common in the popular media, has three distinct meanings among scientists, each with an associated conceptual basis: these are the recess/role niche, the population-persistence niche, and the resource-utilization niche.
character displacement. The situation in which two species are more different in geographic locations where they overlap than between locations where they occur alone
community. Those species populations occurring at some location
competition. Ecological interaction inwhich two or more species negatively affect one another by consuming common resources or by other harmful means
convergence. Development of increasing similarity over time, usually applied to species somewhat unrelated evolutionarily
niche dimension. Environmental variable along which a species’ niche is characterized, e.g., food size, and typically represented as the axis of a graph
polymorphism. The existence of two or more forms, differing in morphology or some other way, in the same population
population. Those individuals of a species occurring at some location
population growth rate r. The per capita rate at which a population changes size, typically computed as the birthrate minus the death rate
The first use of “ecological niche” appeared in a report on ladybugs written by R. H. Johnson nearly a century ago, although the term was used shortly thereafter by the zoologist Joseph Grinnell, who is generally given credit for its original development. The meaning was very close to figurative usage: the ecological niche of a species is its “role,” “place,” or more literally “recess” (in the sense of a “nook” or “cubbyhole”) in an ecological community. Thus, the California thrasher, one of Grinnell’s major examples, is a bird of the chaparral community that feeds mostly on the ground by working over the surface litter and eating both animal and plant items of a suitable size. Escape from predators is similarly terrestrial, with the well-camouflaged bird shuffling off through the underbrush on the rare occasions when it is threatened.
The idea that there exists a set of characteristic habitat and food types with accompanying behavioral, morphological, and physiological adaptations leads to the notion of ecological equivalents. These are defined as two or more species with very similar niche characteristics that occur in completely different localities. An example from Grinnell’s writings is the kangaroo rat of North America, which “corresponds exactly” to the jerboa (another desert rodent species) of the Sahara. The existence of ecological equivalents would imply that rather invariant rules determine the niches available for occupancy in a particular kind of environment, e.g., a desert. Moreover, niches can be empty in the sense that a suitable species does not occur within a