Symbiotic Relationships


There are 3 types of symbiotic relationships in ecology – commensalism, mutualism and neutral.

Commensalism describes an interaction where the abundance of one species in the relationship increases as a result of the interaction whilst the other is unaffected. This can be described as a ‘+ 0’ interaction.

A mutualistic relationship between two species is where both benefit from the relationship and can be described as a ‘+ +’ interaction. In some mutualistic relationships, the organisms are not able to survive solely by themselves and consequently experience a tight relationship, whereas others are able to live independently experiencing a loose relationship.

An example of a mutualistic relationship can be seen between cleaner fish and other fish species. The cleaner fish remove parasites from other fish by feeding upon them, providing the cleaner fish with food, whilst also increasing the health of the fish they “clean” therefore benefiting both species. This relationship can be described as loose because each animal can survive by itself.

A neutral relationship, however, is an interaction that neither benefits nor harms either species involved in the interaction.


Figure 1 – Two cleaner fish feeding from a larger fish

‘Epinephelus tukula is cleaned by two Labroides dimidiatus’, graphic, 2005, Richard Ling. Source:


Key Terms:

Organism – An individual animal, plant, or single-celled life form.

Parasite – An organism which lives solely off another, gaining nutrients and energy at the other organism’s expense

Symbiotic relationship – An interaction between two or more species

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