commensalism

A type of interaction between two different species in which one species (the commensal) derives benefit from a common food supply, while the other species (the host) is not adversely affected.

Commensalism is an interaction between two living organisms, where one organism benefits and the other is neither harmed nor helped. Originally it was used to describe the use of waste food by second animals, like the carcass eaters who follow hunting animals, but wait until they have finished their meal. Other forms of commensalism include:

Phoresy: Using a second organism for transportation. Inquilinism: Using a second organism for housing. Examples are epiphytic plants (such as many orchids) which grow on trees, or birds that live in holes in trees. Metabiosis: A more indirect dependency, in which the second organism uses something the first created, however after the death of the first.

Some biologists argue that any close interaction between two organisms is unlikely to be completely neutral for either party, and that relationships identified as commensal are likely mutualistic or parasitic in a subtle way that has not been detected. For example, epiphytes are "nutritional pirates" that may intercept substantial amounts of mineral nutrients that would otherwise go to the host plant.