What is Commensalism?

• A. A relationship in which both species benefit
• B. A relationship where one species benefits and the other is harmed
• C. A relationship where organisms compete for the same resource
• D. A relationship where one organism benefits and the other is unaffected

Answer: (D)

Commensalism is a relationship in which one organism benefits while the other is unaffected. The benefiting partner gains something—like a ride, food scraps, or a place to live—without causing harm to the other. Classic examples include remora fish hitching rides on sharks or barnacles attaching to whales. The shark or whale isn’t helped or harmed in a meaningful way.

This is different from mutualism, where both species gain, and from parasitism, where one benefits at the expense of the other. It also differs from competition, where both organisms are negatively impacted because they vie for the same limited resources.