Definition and evolution of communities

Ecological community is not a term that is used uniformly by all authors, and there is much disagreement about how communities may have evolved. In this section, I discuss definitions given for ecological communities and their evolution.

Giller and Gee (1987) review the different ways the term community is used, and the problems arising from these different usages. Fauth et al. (1996) defined communities as all species co-occurring at the same time, irrespective of taxon; guilds are species that use the same class of resources. They defined assemblages as groups of species of one taxon (e.g., birds) within a community. According to Cornell (2001), communities are collections of species living contemporaneously in the same place, consisting of individuals that are spatially interspersed, with the potential of direct or indirect interaction. Following Whittaker, Levin (1992) points out that “communities” and “ecosystems” are arbitrary subdivisions of a “gradation of local assemblages.” Communities are not well integrated units, because species within them respond individualistically to the environment. Lawton (2000) asks: how many species constitute a community? There is no logical break between populations of single species and of many, and there is a tendency to take several species of a single taxon as comprising a community. Lawton points out that entire communities are almost impossible to study, with the exception of some in very simple habitats such as water-filled tree holes.