Which ecological relationship describes a scenario in which one species benefits while the other species is unaffected?

• A. Commensalism
• B. Mutualism
• C. Parasitism
• D. Predation

Answer: (A)

Commensalism is when one species benefits and the other is unaffected. In this type of relationship, the beneficiary gains something like food, transport, or habitat, while the other species experiences neither benefit nor harm. For example, barnacles attached to a whale gain access to moving water that brings food particles, while the whale itself isn’t helped or hurt in a meaningful way. This neutrality for the host distinguishes commensalism from other interactions. By contrast, mutualism benefits both partners, parasitism benefits one at the expense of the other, and predation involves one organism killing and consuming another.