Protocooperation is the ecological interaction in which both participants benefit but which is not obligatory for their survival. Protocooperation is a harmonious (positive) interspecific ecological interaction. Examples of protocooperation are: the action of the spur-winged plover that using its beak eats residuals from crocodile teeth; the removal of ectoparasites from the back of bovines by some birds that eat the parasites; the hermit crab that live inside shells over which sea anemones live (these offer protection to the crab and gain mobility to obtain food).