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How does commensalism benefit one species without affecting the other?

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Diagram showing energy flow in a food chain from a tree to a caterpillar, then to a bird, and finally to microbes, with red arrows illustrating energy transfer and heat loss at each stage. — community ecology Energy transfer and heat loss along a food chain.

In community ecology, commensalism is a type of interspecific interaction where one species, known as the commensal, derives benefits while the other species, the host, remains unaffected—neither harmed nor helped.12

The commensal benefits by utilizing the host for various needs, including:
* Food: Obtaining nutrients from leftovers or scraps, such as remoras feeding on the remnants of a shark's meal.1
* Shelter and Support: Using the host as a physical home or foundation, such as epiphytes growing on tree branches for structural support.12
* Locomotion: Utilizing the host for transport.12

It is important to note that these ecological categories are not always rigid. The nature of an interaction can shift based on environmental circumstances, the physical condition of the organisms, or the composition of the local community. An interaction that appears commensal in one setting may function as mutualism or antagonism in another, depending on how the species affect each other's survival or reproduction.2