(from Greek, syn: together, bios: livelihood) A mutually beneficial relationship in which members of different SPECIES live together at the same time. (Were it not at the same time the relationship would be better described as RECIPROCAL ALTRUISM.) The benefiting partners could live directly one on another (ectoparasitism); or one species could live within the other (endoparasitism). It is contrasted with the life of a PARASITE: parasitism involves one species living off another, to its own exclusive benefit, though without necessarily (in the short term at least) being detrimental to the host.
(A better contrast for symbiosis might be the more specific form, MUTUAL PARASITISM, in which two species live off each other to the long-term detriment of both.) A related term is COMMENSAL (from Latin, con: together, mensa: table—commensal literally means sharing a table). Commensalism is where two species share an environment, but without necessarily bringing either harm or benefit to each other: foxes and badgers are often commensal.
While symbiosis, as a biological construct, was originally concerned with the cooperation of two species, it as come to be used more liberally in everyday talk to describe mutually beneficial associations between CONSPECIFIC animals; it should not be so improperly used.
