kommensalism

Kommensalism refers to a type of ecological interaction in which one species benefits while the other is neither helped nor harmed to any significant degree. The term is closely related to the more common English spelling commensalism; both derive from Latin commensalis, meaning "sharing a table." In practice, true commensal relationships are sometimes difficult to prove because subtle costs or benefits to the host can be hard to measure.

Typical examples include barnacles that attach to whales or turtles, gaining mobility and access to food particles while the host is largely unaffected, and epiphytic plants such as many orchids that grow on tree branches for support and light without extracting nutrients from the host. Remoras that hitch rides on larger fishes and feed on leftover scraps illustrate another commonly cited case. In human contexts, certain skin and environmental microbes live on the body without producing noticeable effects and are often described as commensal.

Commensalism is distinguished from mutualism, where both partners benefit, and parasitism, where one benefits at the expense of the other. Ecologically, commensal species can influence community structure by facilitating dispersal, providing habitat, or altering resource use. Over evolutionary time, commensal interactions may shift toward mutualism or parasitism as selection changes the balance of costs and benefits for the species involved.