|
In biology and ecology, an ecocline or simply cline (from (ギリシア語:κλίνω) "to possess or exhibit gradient, to lean") describes an ecotone in which a series of biocommunities display a continuous gradient.〔For definition and an etymology, see (Merriam-Webster entry for "cline." )〕 The term was coined by the English evolutionary biologist Julian Huxley in 1938. More technically, clines consist of ecotypes or forms of species that exhibit gradual phenotypic and/or genetic differences over a geographical area, typically as a result of environmental heterogeneity. Genetically, clines result from the change of allele frequencies within the gene pool of the group of taxa in question.〔Microsoft Encarta Premium 2009: "cline"〕〔King, Stansfield, Mulligan: ''A dictionary of genetics'', 7th ed. (2006), Oxford University Press:"cline"〕〔Begon, Townsend, Harper, ''Ecology: From individuals to ecosystems'', Blackwell Publishing, 4th ed. (2006), p. 10〕 Clines may manifest in time and/or space.〔Eric R. Pianka: ''Evolutionary Ecology'', 6th ed. (2000), Pearson Education, chapter 4〕 ==Gradient analysis== In ecology, spatial clines have led to gradient analysis where the abundance and distribution of organisms is rendered by sinusoidal curves on the plane. From these curves can be extracted that populations occupy zones of maximum and minimum presence, according to their special needs and tolerances imposed by their environment.〔 Typically, a well-marked cline does not allow for a delineation of subspecies, as it is then impossible, by definition, to draw any further clear dividing lines between populations. In population genetics, a cline could include a spectrum of subspecies, as allele and haplotype frequencies tend to vary over a larger space; moreover, in evolution, genetic lineage sorting usually lags behind the establishment of locally differentiated phenotypes. Regardless, in neither case will such a variation yield different species, as long as the populations, though geographically spread, can interbreed one with another. 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「Cline (biology)」の詳細全文を読む スポンサード リンク
|