Symbiosis: Mutualism, Commensalism and Parasitism

Symbiosis: Mutualism, Commensalism and Parasitism

The species in an ecosystem will interact in different ways. These interactions may have positive, neutral or negative impacts on the species involved.

The term symbiosis can be used to broadly refer to these types of relationships as it directly translates to mean living together (sym: with; bio: life).

Symbiosis is the ecological relationship between two or more organisms living closely together with some form of feeding relationship involved. The three main symbiotic relationships are:

Mutualism, where both organisms benefit.

Commensalism, where one organism benefits while the other organism is not harmed.

Parasitism, where one organism benefits and causes harm to the other organism.


This is a beneficial relationship to both partners of different species living together. For example a bee and a pollinating flower. The bee gains nectar from the flower for survival, as it uses the bee to carry its pollen to other flowers. So both organisms living together benefit from their existence.


The association of two or more partners living together, where only one benefits from the partnership and the other remains unharmed.  An example of this is the relationship between a sea anemone with and a clown fish. The anemone travels with the fish on route to its destination and the fish remains unharmed.


Parasites are completely dependent on a host for survival. The relationship is beneficial to one, and harmful to the other.  Parasites may live outside or inside a host; they are called ectoparasites (the prefix ecto means outside) and endoparasites (theprefix endo means inside). An example of the endoparasite is the tapeworms which live in the digestive systems of its host. Examples of ectoparasites are ticks and lice.


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