Commensalism

In commensalism one partner gains while the other is left neither better nor worse off.

An epiphytic orchid perched on a mango branch gains support and light; the mango tree gains nothing apparent.

Barnacles growing on the back of a whale benefit; the whale gains nothing apparent.

Cattle egrets forage close to grazing cattle, because the moving cattle stir up insects from the vegetation that the egrets would otherwise struggle to find.

The clown fish lives among the stinging tentacles of a sea anemone and is protected from predators, which avoid the tentacles. The anemone does not appear to gain anything.