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The unified neutral theory of biodiversity and biogeography (here "Unified Theory" or "UNTB") is a hypothesis and the title of a monograph by ecologist Stephen Hubbell. The hypothesis aims to explain the diversity and relative abundance of species in ecological communities, although like other neutral theories of ecology, Hubbell's hypothesis assumes that the differences between members of an ecological community of trophically similar species are "neutral," or irrelevant to their success. This implies that biodiversity arises at random, as each species follows a random walk. The hypothesis has sparked controversy,〔Science Daily (2014). (New biodiversity study throws out controversial scientific theory. May 27 )〕〔Connolly S.R., MacNeil M.A., Caley M.J., Knowlton N., Cripps E., Hisano M., Thibaut L.M., Bhattacharya B.D., Benedetti-Cecchi L., Brainard R.E., Brandt A., Bulleri F., Ellingsen K.E., K (2014). Commonness and rarity in the marine biosphere. Proceedings of the National Academy of Sciences. (Abstract ), (paper ).〕 and some authors consider it a more complex version of other null models that fit the data better.〔 ''Neutrality'' means that at a given trophic level in a food web, species are equivalent in birth rates, death rates, dispersal rates and speciation rates, when measured on a per-capita basis. This can be considered a null hypothesis to niche theory. Hubbell built on earlier neutral concepts, including MacArthur & Wilson's theory of island biogeography〔 and Gould's concepts of symmetry and null models.〔 An ''ecological community'' is a group of trophically similar, sympatric species that actually or potentially compete in a local area for the same or similar resources.〔 Under the Unified Theory, complex ecological interactions are permitted among individuals of an ecological community (such as competition and cooperation), provided that all individuals obey the same rules. Asymmetric phenomena such as parasitism and predation are ruled out by the terms of reference; but cooperative strategies such as swarming, and negative interaction such as competing for limited food or light are allowed (so long as all individuals behave in the same way). The Unified Theory also makes predictions that have profound implications for the management of biodiversity, especially the management of rare species. The theory predicts the existence of a fundamental biodiversity constant, conventionally written ''θ'', that appears to govern species richness on a wide variety of spatial and temporal scales. ==Saturation== Although not strictly necessary for a neutral theory, many stochastic models of biodiversity assume a fixed, finite community size. There are unavoidable physical constraints on the total number of individuals that can be packed into a given space (although space ''per se'' isn't necessarily a resource, it is often a useful surrogate variable for a limiting resource that is distributed over the landscape; examples would include sunlight or hosts, in the case of parasites). If a wide range of species is considered (say, giant sequoia trees and duckweed, two species that have very different saturation densities), then the assumption of constant community size might not be very good, because density would be higher if the smaller species were monodominant. However, because the Unified Theory refers only to communities of trophically similar, competing species, it is unlikely that population density will vary too widely from one place to another. Hubbell considers the fact that population densities are constant and interprets it as a general principle: ''large landscapes are always biotically saturated with individuals''. Hubbell thus treats communities as being of a fixed number of individuals, usually denoted by ''J''. Exceptions to the saturation principle include disturbed ecosystems such as the Serengeti, where saplings are trampled by elephants and Blue wildebeests; or gardens, where certain species are systematically removed. 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「Unified neutral theory of biodiversity」の詳細全文を読む スポンサード リンク
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