Final answer:
Commensalism is a symbiotic relationship where one organism benefits and the other is unaffected. Examples include cattle egrets and grazing mammals, mites hitching rides on insects, and S. epidermidis on human skin. Understanding commensalism helps in distinguishing it from parasitism and mutualism, where the interactions among organisms are different.
Step-by-step explanation:
Commensalism is a type of symbiotic relationship where one organism benefits while the other is not significantly affected. This interaction contrasts with other types of symbiotic relationships like parasitism, where one organism is harmed, and mutualism, where both organisms benefit. An example of commensalism can be observed between cattle egrets and grazing mammals. The egrets eat insects and small mammals that are disturbed by the grazing animals, benefiting from the association without negatively affecting the grazers. Another example is certain mites that hitch rides on larger insects, receiving transportation without impacting the larger insect. Similarly, hermit crabs utilize the shells of dead snails to protect themselves without affecting the deceased snails.
Bacteria like Staphylococcus epidermidis living on human skin demonstrate how commensal relationships can be close to mutualistic relationships, as these bacteria consume dead skin cells without impacting human health and sometimes offer an inherent defense against pathogens. Furthermore, endosymbiosis is another form of close and often mutualistic symbiotic relationship where one organism lives within another, such as gut bacteria producing vitamin K inside the human gut.