Commensalism

Commensalism is a long-term biological interaction in which one species benefits while the other is neither helped nor harmed. The benefiting organism, the commensal, may gain nutrients, shelter, physical support or transportation from a host species that is left essentially unaffected. Well known examples include remoras that attach to sharks and feed on the waste of their host, pilot fish that eat scraps left over from the meals of a larger animal, and birds that perch on large grazing mammals to feed on the insects the animals disturb. Commensalism is one of several classic types of interspecific interaction alongside mutualism, in which both species benefit, parasitism, in which one benefits at the other's expense, and amensalism, in which one is harmed while the other is unaffected.