A semantic taxonomy for diversity measures
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A semantic taxonomy for diversity measures Carlo Ricotta
Received: 27 October 2006 / Accepted 6 March 2007 / Published online: 8 May 2007 Ó Springer Science+Business Media, B.V. 2007
Abstract Community diversity has been studied extensively in relation to its effects on ecosystem functioning. Testing the consequences of diversity on ecosystem processes will require measures to be available based on a rigorous conceptualization of their very meaning. In the last decades, literally dozens of measures of diversity have been proposed. However, rather than using unrelated metrics, we need to identify their separate components so that possible links between them and ecosystem functioning can be examined using an agreed-upon language. In this paper, first, a short overview on new and old measures of community diversity is presented. Next, I propose a general framework in which most of the existing measures of diversity are sorted into four interrelated semantic classes: richness, abundance-weighted diversity, evenness and divergence. In this view, this paper constitutes an attempt to organize the very large number of existing diversity measures avoiding ambiguities in the meaning of the different facets of community diversity. Keywords Complexity Compositional diversity matrix Divergence Evenness Pairwise species distances Richness 1 Introduction The compositional diversity of a species assemblage is a central concept in ecology that has been studied extensively for many decades in relation to its possible connection with ecosystem functioning and organization. Classical examples include the diversity-productivity (McCann 2000) and the diversity-stability debate
C. Ricotta (&) Department of Plant Biology, University of Rome ‘‘La Sapienza’’, Piazzale Aldo Moro 5, 00185 Rome, Italy e-mail: [email protected]
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(Tilman et al. 1996; Hooper and Vitousek 1997; Hector et al. 1999). More recently the influence of species diversity on exotic invasions has received increasingly attention (Stohlgren et al. 1999; Fridley et al. 2004; Fargione and Tilman 2005). However, an unambiguous characterization of the concept of community diversity has proved elusive (see Ricotta 2005a). This observation has led to the classical comments by Hurlbert (1971) on the ‘‘non-concept of diversity’’ and by Poole (1974) that diversity measures are ‘‘answers to which questions have not yet been found’’. One reason for this ambiguity is that traditional measures of diversity like the Shannon index or the Simpson index combine in non-standard way the two components of species richness and their relative abundances (called variously evenness, equitability or dominance). High species richness and evenness, that occurs when species are equal in abundance, are both equated with high diversity. Also, traditional measures are computed solely from species relative abundances without incorporating ecological differences between species. However, a community composed of ecologically dissimilar taxa is intuitively more diverse
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