Mutualism: Definition, Types & Specificity

Mutualism is the symbiotic relationship between two species of different types where both members are benefitted. They help each other with their growth, reproduction, or survival.

It is characterized by the type of benefits, degree of dependency, specificity, or duration of interaction. Based on the degree of dependency, mutualism can be obligate or facultative.

Obligate mutualism is where the participating species cannot survive without each other. So they live in a close association.
Facultative mutualism is also known as protocooperation where the species do not depend on each other for their survival. For eg., Sea anemone lives on hermit crabs only for their transportation and protection from enemies. Another example is birds feeding on fruits on trees. The birds get food and the seeds get dispersed.

Facultative mutualism is more significant for the conservation of biodiversity as species are generally involved directly or indirectly in such symbiotic relationships. In addition, the participating foundation species will have better chances of developing resistance to the ongoing environmental changes and human activities. Thus they are better able to survive and thereby preserve the biodiversity.

Symbiosis

Symbiosis is a long-term ecological relationship between organisms of different species known as symbionts where they get mutual benefits. It can be an obligatory relationship where both members could be dependent on the other for their survival or facultative.

When one species lives inside the other one, it is called endosymbiosis. When one species lives outside the other organism, it is endosymbiotic. In mutualism, the members are in a beneficial relationship and do not harm each other.

Mutualism Depending on Degree of Specificity

Mutualism could be species-specific or just between two diverse partners. They are called specialists and generalists, respectively. Based on the type of service, mutualism can be,

Dispersive if one partner helps with the seed or pollen dispersal for the other while the second partner provides resources for the other partners’ growth.
Defensive where one party protects the other from herbivores or parasites. In exchange, the other party provides shelter and nutrients for the former.
Resource-based mutualism is where they provide different resources to each other.

A Few Examples of Mutualism

Coral Reef provides protective shelter to Zooxanthellae algae. In return, the algae supplies oxygen and helps with waste removal.
Lichens are the association of heterotrophic fungi and photoautotrophic algae such as Cyanobacteria. The algae supplies organic compounds via photosynthesis while fungi provide an environment for growth.
Nitrogen-fixing bacteria fix nitrogen for the plants where they live and the plants provide shelter.
Mycorrhizae is the association between fungi and plant roots. The plant provides shelter and organic compounds while the fungi provide inorganic nutrients for the plants.

References

Angelini, C., & Eklöf, J. S. (2020). Facultative mutualisms: A double‐edged sword for foundation species in the face of anthropogenic global change. Ecology and Evolution, 11(1), 29-44. https://doi.org/10.1002/ece3.7044