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Citation. Tilman, D.; Pacala, S. 1993. The maintenance of species richness in plant communities. Pages 13-25 in Ricklefs, R. and D. Schluter, Eds., Species Diversity in Ecological Communities, University of Chicago Press, Chicago. [1193 LTER]
Introduction. In 1959, G. E. Hutchinson posed one of the major conceptual dilemmas of ecology: How is it that numerous species are able to persist in the same habitat? Although many natural habitats are species-rich, classical models predicted that an environment should be dominated by one or a few species. Hutchinson offered a broad outline of potential solutions to this paradox of diversity. He pointed out that the classical models assumed that interactions went to equilibrium, that food webs were composed of just two trophic levels, and that habitats were spatially homogeneous. He asserted that each of these assumptions was violated in nature, and that these violations might allow numerous species to coexist. This idea spawned theoretical and experimental studies which have now offered numerous alternative solutions to the paradox of diversity. In this chapter we summarize and critique these alternative theories and briefly mention relevant observational and experimental data. Our goals are to point out the many alternative mechanisms that can maintain biodiversity and to suggest ways to test for these. Although most theories apply to organisms on any trophic level, we focus on the maintenance of species-rich terrestrial plant communities.
Keywords. species richness, habitat, trophic levels, homogeneous, coexistence, biodiversity