Competition is the state of affairs that exists between two or more organisms or groups of organisms when a shared resource is limited. For example, there may be direct competition over the amount of living space, food supply, or the availability of mates. There are two main types: intraspecific competition between members of the same species, and interspecific competition between different species. The usual outcome is the classic "survival of the fittest", with at least a temporary reduction in the numbers of the less fit organism, and for this reason competition is a significant force in the process of evolution.