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Species use restricted ecological niches, and the niches of all species are segregated, often with much overlap, by the use of different habitats, different geographic areas and seasons, and different food resources, to mention only a few of the many niche dimensions. The causes of niche restriction and segregation are important problems in evolutionary ecology. ==Background== Two ecological paradigms deal with the problem. The first paradigm predominates in what may be called “classical” ecology. It assumes that niche space is largely saturated with individuals and species, leading to strong competition. Niches are restricted because “neighbouring” species, i.e., species with similar ecological characteristics such as similar habitats or food preferences, prevent expansion into other niches or even narrow niches down. This continual struggle for existence is an important assumption of natural selection introduced by Darwin as an explanation for evolution. The other paradigm assumes that niche space is to a large degree vacant, i.e., that there are many vacant niches. It is based on many empirical studies 〔Rohde, K. 1980. Warum sind ökologische Nischen begrenzt? Zwischenartlicher Antagonismus oder innerartlicher Zusammenhalt? Naturwissenschaftliche Rundschau, 33, 98-102.〕〔Rohde, K. 2005a. Eine neue Ökologie. Aktuelle Probleme der evolutionären Ökologie. Naturwissenschaftliche Rundschau, 58, 420-426.〕〔K. Rohde: Nonequilibrium Ecology, Cambridge University Press, Cambridge, 2005b, 223 pp. auf http://www.cambridge.org/9780521674553〕 and theoretical investigations especially of Kauffman 1993.〔Kauffman, S.A. 1993. The origins of order. Self-organization and selection in evolution. Oxford University Press, New York Oxford.〕 Causes of vacant niches may be evolutionary contingencies or brief or long-lasting environmental disturbances. Both paradigms agree that species are never “universal” in the sense that they occupy all possible niches; they are always specialized, although the degree of specialization varies. For example, there is no universal parasite which infects all host species and microhabitats within or on them. However, the degree of host specificity varies strongly. Thus, ''Toxoplasma'' (Protista) infects numerous vertebrates including humans, ''Enterobius vermicularis'' infects only humans. The following mechanisms for niche restriction and segregation have been proposed: 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Niche segregation」の詳細全文を読む スポンサード リンク
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