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Beta diversity
The term beta diversity (β-diversity) was introduced by R. H. Whittaker〔Whittaker, R. H. (1960) Vegetation of the Siskiyou Mountains, Oregon and California. Ecological Monographs, 30, 279–338.〕 together with the terms alpha diversity (α-diversity) and gamma diversity (γ-diversity). The idea was that the total species diversity in a landscape (γ) is determined by two different things, the mean species diversity at the habitat level (α) and the differentiation among habitats (β). Whittaker proposed several ways of quantifying differentiation, and subsequent generations of ecologists have invented more. As a result, the definition of beta diversity has become quite contentious.〔Tuomisto, H. (2010) A diversity of beta diversities: straightening up a concept gone awry. Part 1. Defining beta diversity as a function of alpha and gamma diversity. Ecography 33: 2–22. 〕〔Tuomisto, H. (2010) A diversity of beta diversities: straightening up a concept gone awry. Part 2. Quantifying beta diversity and related phenomena. Ecography, 33, 23-45. 〕 Some use beta diversity as a broad umbrella term that can refer to any of several indices related to compositional heterogeneity.〔Koleff, P., Gaston, K. J. and Lennon, J. J. (2003) Measuring beta diversity for presence–absence data. Journal of Animal Ecology 72, 367–382. 〕〔Anderson, M. J. et al. (2011) Navigating the multiple meanings of β diversity: a roadmap for the practicing ecologist. Ecology Letters 14, 19–28. 〕〔Gorelick, R. (2011) Commentary: Do we have a consistent terminology for species diversity? The fallacy of true diversity. Oecologia 167, 885-888. 〕 Others argue that such broad usage should be avoided because it leads to confusion. Instead, they propose that the term beta diversity be used to refer to one phenomenon only (true beta diversity), and that other formulations be referred to by other names.〔〔〔Tuomisto, H. 2010. A consistent terminology for quantifying species diversity? Yes, it does exist. Oecologia 4: 853–860. 〕〔Jurasinski, G. and Koch, M. (2011) Commentary: do we have a consistent terminology for species diversity? We are on the way. Oecologia, 167, 893-902. 〕〔Moreno, C. E: and Rodríguez, P. (2011) Commentary: Do we have a consistent terminology for species diversity? Back to basics and toward a unifying framework. Oecologia, 167, 889-892. 〕〔Tuomisto, H. (2011) Commentary: do we have a consistent terminology for species diversity? Yes, if we choose to use it. Oecologia, 167, 903-911. 〕
==Beta diversity in the strict sense (True beta diversity)==
Gamma diversity and alpha diversity can be calculated directly from species inventory data.〔〔Jost L (2006) Entropy and diversity. Oikos 113, 363–375. 〕 The simplest of Whittaker's original definitions of beta diversity is
β = γ/α
Here gamma diversity is the total species diversity of a landscape and alpha diversity is the mean species diversity per habitat. Because the limits among habitats and landscapes are diffuse and to some degree subjective, it has been proposed that gamma diversity can be quantified for any inventory dataset and that alpha and beta diversity can be quantified whenever the dataset is divided into subunits. Then gamma diversity is the total species diversity in the dataset and alpha diversity the mean species diversity per subunit. Beta diversity quantifies how many subunits there would be if the total species diversity of the dataset and the mean species diversity per subunit remained the same, but the subunits shared no species.〔〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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