Résumé :
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This is a book about a new general theory of biodiversity in a geographical context. I define biodiversity to be synonymous with species richness and relative species abundance in space and time. Species richness is simply the total number of species in a defined space ai a given time, and relative species abundance refers to their commonness or rarity. This is a less inclusive definition of biodiversity than is commonly used in policy circles, but more in keeping with the classical discipline of ecology as the scientific study of the distribution and abundance of species and their causes. Fragments of a general theory of biodiversity abound in ecological theories of island biogeography, metapopulations, and relative species abundance; but in my opinion, there have not yet been any really successfül syntheses. Among the kinds of diversity patterns 1 seek to explain with this new theory are those illustrated in figure 1.1. This graph shows patterns of relative species abundance in a diverse array of ecological communities, ranging from an open-ocean planktonic copepod community, to a tropical bat community, to a community of rainforest trees, to the relative abundances of British breeding birds. Despite its supreme importance and the threat of its global crash, biodiversity remains poorly understood both empirically and theoretically. This ambitious book presents a new, general neutral theory to explain the origin, maintenance, and loss of biodiversity in a biogeographic context. Until now biogeography (the study of the geographic distribution of species) and biodiversity (the study of species richness and relative species abundance) have had largely disjunct intellectual histories. In this book, Stephen Hubbell develops a formal mathematical theory that unifies these two fields. When a speciation process is incorporated into Robert H. MacArthur and Edward O. Wilson's now classical theory of island biogeography, the generalized theory predicts the existence of a universal, dimensionless biodiversity number. In the theory, this fundamental biodiversity number, together with the migration or dispersal rate, completely determines the steady-state distribution of species richness and relative species abundance on local to large geographic spatial scales and short-term to evolutionary timescales. Although neutral, Hubbell's theory is nevertheless able to generate many nonobvious, testable, and remarkably accurate quantitative predictions about biodiversity and biogeography. In many ways, Hubbell's theory is the ecological analog to the neutral theory' of genetic drift in genetics. The Unified Neutral theory of Biogeography and Biodiversity should stimulate research in new theoretical and empirical directions by ecologists, evolutionary biologists, and biogeographers.
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