Introduction

Summary

Ecology has long been shaped by ideas that stress the sharing of resources and the competition for those resources, and by the assumption that populations and communities typically exist under equilibrium conditions in habitats saturated with both individuals and species. This view can be traced back to Linnaeus, who considered an equilibrium in nature; Adam Smith, who contributed the idea that competition can lead to equilibrium in a community; and Malthus, who suggested that greater growth in demand than in supply would lead to competition for limited resources. Among well known ecologists, Hutchinson (1948) took it for granted that stability (owing to “self-correcting mechanisms”) is characteristic of most ecological systems and permits their persistence, and, according to Dobshansky (1957, cited by Cooper 2001): “natural selection, and hence the evolutionary process, are the outcome of competition; and therefore are governed by density-dependent factors.” Some ecologists were always aware of the possibility of nonequilibria, but the majority ignored it, especially in connection with theory in ecology. In several widely used older ecological texts, competition and equilibria are discussed in depth, but nonequilibria are not mentioned at all or only in a very cursory fashion (e.g., Pielou 1969; MacArthur 1972; Cody and Diamond 1975; Ehrlich et al. 1977). This has changed somewhat in recent years, particularly in population ecology (e.g., Chesson and Case 1986; Diamond and Case 1986; DeAngelis and Waterhouse 1987; Krebs 2001). Nevertheless, many workers still seem to be pre-occupied with looking for evidence of competition and equilibria.