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Mutualism, Commensalism and Amensalism

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Mutualism, Commensalism and Amensalism - Lesson Summary

In every habitat, microbes, plants and animals interact in various ways to form a community. When populations of two different species interact, it leads to interspecific interactions. Such interactions may benefit, harm or have a neutral effect on one or both species. In mutualism, both species benefit from interaction, while in commensalism, the interspecific interaction is beneficial to one species and neutral to the other. In the case of amensalism, one species is harmed and the other remains unaffected.
Plants and animals show diverse and fascinating examples of mutualism.  In lichens, algal and fungal partners live together by mutually benefitting each other. The algal partner provides food to the fungal partner and, in return, the fungal partner provides shelter to the algal partner. Mutual relationships are also seen between plants and animals. Mutualism is also seen in many orchids that have evolved to attract the right pollinator insect and ensure that pollination takes place.
Apart from mutualism, another interspecific interaction is commensalism seen in plants, animals and the aquatic world. Commensalism is seen in leguminous plants such as pea, beans and lentils which are associated with the nitrogen-fixing bacteria, Rhizobium. The bacteria in the root nodules live symbiotically with the host plant. They obtain nutrition from the host plant and, in return, fix atmospheric free nitrogen as nitrites and nitrates.
Among animals, commensalism can be seen between cattle egrets and cattle.
Apart from commensalism and mutualism, amensalism is another interspecific interaction seen in nature. In this interaction, one species is harmed and the other remains unaffected. Usually in this type of interaction, an organism oozes a chemical compound, which is detrimental to another organism. The black walnut tree exudes a substance called juglone into the soil, which damages the roots of neighbouring plants, thereby preventing other plants from growing nearby. Another common example of amensalism is shown by Penicillium, a bread mold, which secretes penicillin, a chemical that kills or stops the growth of bacteria. In this manner, various species exhibit interspecific interactions like amensalism, commensalism and mutualism, that aid in their overall survival and reproduction.


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