Competition between individuals or species occurs when there are limited resources that must be shared. It is an interaction in which one organism deprives another of resources, for example food; water; nesting space, and causes a reduction in fitness i.e. reduced growth, fewer progeny, and greater risk of death of the weaker species (employees.csbsju.edu). Competition is expresed by either exploitation, in which one organism will 'use up' shared resources, or interference whereby animals keep others away from resources by fighting or by aggressive displays (Krebs & Davies, 1993). When exhibited between two different species it is called interspecific competition, and intraspecific when between individuals of the same species. For competitive exclusion to occur interspecific competition must be greater than intraspecific (Begon et al., 1996).
Competitive exclusion or Gause's Principle is the most severe outcome of interspecific competition that leads to the extinction or removal from the habitat of the weaker species (Reitz & Trumble, 2002).
It occurs when two species share a very similar or identical niche within the habitat, in that they use the same resources in the same ways. The more similar the needs shared by the species the more intense the competition (Oosting, 1956). Inevitably one of the two species will always have a slight advantage over the other, either by better utilization or defence of resources, and therefore out-competes the weaker species, causing exclusion from the habitat, by either extinction of the species, or extinction from the area. This principle can often be observed when non-native invading species drive native species to extinction, or competitive displacement, through their superior competitive ability (www.tiem.utk.edu), and absence of environmental stops. For example, red squirrel populations in Britain have plummeted mainly due to competitive exclusion (also influenced by other factors such as disease, and habitat disappearance). The...