In ecology, commensalism is a class of relationships between two organisms where one organism benefits from the other without affecting it. 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 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”. Originally, the term was used to describe the use of waste food by second animals, like the carcass eaters that follow hunting animals, but wait until they have finished their meal. Commensalism, in biology, a relation between individuals of two species in which one species obtains food or other benefits from the other without either harming or benefiting the latter. (This kind of relation can be contrasted with mutualism, in which both species benefit.) 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. Both remoras and pilot fishes feed on the leftovers of their hosts’ meals. A commensal relation based on shelter is seen in clown fishes (Amphiprion percula), which live unharmed among the stinging tentacles of sea anemones, where they are protected from predators. Numerous birds feed on the insects turned up by grazing mammals, while other birds obtain soil organisms stirred up by the plow. Various biting lice, fleas, and louse flies are commensals in that they feed harmlessly on the feathers of birds and on sloughed-off flakes of skin from mammals Pierre-Joseph van Beneden introduced the term “Commensalism” in 1876.
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