Commensalism

Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit from each other, amensalism, where one is harmed while the other is unaffected, and parasitism, where one benefits while the other is harmed. The commensal (the species that benefits from the association) may obtain nutrients, shelter, support, or locomotion from the host species, which is substantially unaffected. The commensal relation is often between a larger host and a smaller commensal; the host organism is unmodified, whereas the commensal species may show great structural adaptation consonant with its habits, as in the remoras that ride attached to sharks and other fishes. Remoras feed on their hosts' fecal matter, while pilot fish feed on the leftovers of their hosts' meals. Numerous birds perch on bodies of large mammal herbivores or feed on the insects turned up by grazing mammals.The word 'commensalism' is derived from the word 'commensal', meaning 'eating at the same table' in human social interaction, which in turn comes through French from the Medieval Latin commensalis, meaning 'sharing a table', from the prefix com-, meaning 'together', and mensa, meaning 'table' or 'meal'. Commensality, at Oxford and Cambridge Universities, refers to professors eating at the same table as students (as they live in the same 'college').The commensal pathway was traveled by animals that fed on refuse around human habitats or by animals that preyed on other animals drawn to human camps. Those animals established a commensal relationship with humans in which the animals benefited but the humans received little benefit or harm. Those animals that were most capable of taking advantage of the resources associated with human camps would have been the ‘tamer’ individuals: less aggressive, with shorter fight-or-flight distances. Later, these animals developed closer social or economic bonds with humans and led to a domestic relationship.Whether the relationship between humans and some types of gut flora is commensal or mutualistic is still unanswered.Like all ecological interactions, commensalisms vary in strength and duration from intimate, long-lived symbioses to brief, weak interactions through intermediaries.