Symbiosis

Abstract

The term “symbiosis” does not have the same meaning to all biologists. Here we use it in the literal sense of “living together,” that is, to describe any physically close association between different species irrespective of the functional significance. Such a general term is necessary because there are many cases where the functional nature of the relationship is not yet understood. Symbiosis thus includes “parasitism,” in which one member of the association, the host, suffers while the parasite gains from the association; “mutualism” in which both components gain from the association; and “commensalism” in which the association is neutral from the viewpoint of one of the components. In the real world, there are gradients between these classes of symbiotic associations; the degree of benefit or harm involved may vary, according to environmental conditions or the genotypes of the components.