17: Mutualism and Commensalism

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Page ID: 78226

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Learning Objectives

Introduce and explore the types of mutualisms and commensalisms
Explore theories that explain the evolution of mutualisms
Discuss hypotheses regarding the maintenance of mutualistic relationships

Summary

A commensal relationship occurs when one species benefits from a close prolonged interaction, while the other neither benefits nor is harmed. Commensal relationships come many forms including: phoresis, inquilinism, and metabiosis. A mutualism occurs when two species benefit from their interaction, and can be generalized into three types: resource-resource, service-resource, and service-service. Many mutualisms are thought to have evolved from antagonistic interactions, such as parasite-host relationships. Reciprocal evolutionary responses are most likely important to the evolution of symbiotic mutualisms, like some plant-pollinator interactions, and may be important mechanisms for diversification, though evidence for this is mixed. The maintenance of mutualisms can be undermined by cheating, however, the destabilizing effect of cheating can be minimized by host sanctioning.