All scientific disciplines tenaciously seek a unified view of their subject. For example, the quest in particle physics and cosmology is to integrate the disparate physical forces in nature into a single, united framework, with as little or no dependence on empirically derived values for the model parameters (Green et al. 1987, Rees 1987). Although the objective is not quite so grand in community ecology, it is just as, or in some respects, more challenging because we have to deal not only with the contemporary dynamics of communities but also with the evolution of organisms. We seek a comprehensive picture of how and why resources are distributed among individuals and populations in the ways that they are, and the effects on population and community dynamics that stem from these distributions (J. Roughgarden cited in Lewin 1986, Hall and Raffaelli 1993). The immense diversity of living organisms and the wide range of physical and climatic variation on Earth, when coupled with organic evolution, have provided a seemingly endless supply of novel circumstances and outcomes. This variety has impeded the progress of the science of community ecology, which many judge to have been almost excruciatingly slow (Oksanen 1991a). Nevertheless, a rich and dynamic variety of new ideas aiming to unify community ecology continues to emerge, such as the ‘macroecology’ (Brown and Maurer 1989) and ‘metapopulation’ (Gilpin and Hanski 1991) concepts of relatively recent vintage.

In any event, one of the most obvious features of ecological communities is that species display manifestly different levels of ecological specialization (McNaughton and Wolf 1970, Futuyma and Moreno 1988).