Difference Between Mutualism and Commensalism

The key difference between mutualism and commensalism is that mutualism is a relationship where both species are benefitted, while commensalism is a relationship where one species is benefitted while the other is neither benefited nor harmed.

Many interactions between species are present in the ecosystem in order for organisms to survive and continue the cycle of life. These interactions or relationships are known as symbiosis. Symbiotic relationships are of three types; they are mutualism, parasitism, and commensalism. Relationships take place between two or more species. Mutualism is the relationship in which both organisms are benefitted, while parasitism is where one organism is benefitted and the other is harmed. Commensalism is where one organism is benefitted while the other organisms are neither benefited nor harmed.

CONTENTS

1. Overview and Key Difference
2. What is Mutualism 
3. What is Commensalism
4. Similarities – Mutualism and Commensalism
5. Mutualism vs Commensalism in Tabular Form
6. Summary – Mutualism vs Commensalism

What is Mutualism?

Mutualism is the association between two different species where each of them benefits from the relationship. Such associations develop between organisms with a wide variety of different living requirements. It is a common type of ecological interaction. Mutualism often combines two types of ecological phenomena: cooperation and symbiosis. Cooperation refers to the increase in fitness through intraspecific interactions that take place within species. Symbiosis involves two species living in close physical contact over a long period of time.

Mutualism plays an important role in ecology and evolution. There are different types of mutualistic relationships. The most common example of mutualism is mycorrhizal associations between plant roots and fungi, where the plant provides carbohydrates to the fungus mainly in return for phosphates and nitrogenous products. Another example is the Rhizobium bacterium that fixes nitrogen for leguminous plants in return for carbohydrates. This type is known as resource-resource relationships. Pollination is also an example where plant gives food in the form of nectar and pollen for the pollen dispersal by insects. Phagophiles feed on ectoparasites by destroying pests, and this provides cleaning symbiosis. Zoochory is another example where the dispersal of seeds takes place through animals. This is known as service-resource relationships. Service-service relationships are rare. However, this type of mutualistic relationship takes place between sea anemone and anemone fish, where anemone provides the fish with protection from predators, and the fish defends the anemones against other fish which eat them.

What is Commensalism?

Commensalism is a biological relationship between individuals of two species in which one species gets benefits without harming or benefiting the other. Usually, the commensal or the species that benefits obtain nutrients, support, shelter, or locomotion from the host species, which remains unaffected. This type of relationship often takes place between a large host and a small commensal.

The commensal species usually show structural adaptation consistent with its habits. The best examples of commensalism are remora, which rides attached to sharks and other fish. The evolution of remoras is seen on top of their heads with a flat, oval, sucking dish-like structure. This helps them to adhere to the bodies of the host. Another example includes bird species such as the great egret, which feeds on insects turned up by grazing mammals on the soil. Various lice, flies, and fleas are also commensals as they feed harmlessly on the feathers of birds or sloughed-off flaked skin of mammals.

What are the Similarities Between Mutualism and Commensalism?

• Mutualism and commensalism are biological relationships.
• Moreover, both are observed in prokaryotes and eukaryotes.
• They occur between two species.
• In both relationships, neither of the species is harmed.
• Both have common benefits, like defense and support.

What is the Difference Between Mutualism and Commensalism?

Mutualism is a relationship where both species are benefitted, while commensalism is a relationship where one species is benefitted while the other is neither benefited nor harmed. Thus, this is the key difference between mutualism and commensalism. Mutualism is an obligatory relationship, while commensalism is non-obligatory. The most common benefit of mutualism is satisfying nutrient needs among the two species, while in commensalism, the most common benefit is related to shelter and habitat.

The below infographic presents the differences between mutualism and commensalism in tabular form for side-by-side comparison.

Summary – Mutualism vs Commensalism

Mutualism and commensalism are two types of symbiotic relationships that are observed in ecosystems. In mutualism, both species are benefitted, while in commensalism, one species is benefitted while the other is neither benefited nor harmed. The most common examples of mutualism are mycorrhizal associations between plant roots and fungi, Rhizobium bacteria and leguminous plants, bees and flowers, humans and digestive bacteria, and sea anemone and anemone fish. Commensalism often takes place between a large host and a small commensal. The most common examples of commensalism are remora and sharks, birds and insects, lice, flies, and birds and mammals, and hermit crabs and gastropods. So, this summarizes the difference between mutualism and commensalism.

Reference:

1. “Commensalism.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.
2. “Mutualism.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.

Image Courtesy:

1. “Mutualistic mycorrhiza en” By Nefronus – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “An example of commensalism – A zebra and an egret” By Jorge Láscar (CC BY 2.0) via Flickr