This is a symbiotic relationship in which both members of the association benefit. Mutualistic relationships often allow organisms to obtain food or to avoid pedation. This relationship can be differentiated into:

• facultative, and
  
• obligate mutualism.

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• Facultative Mutualism
  

  In this relationship both organisms benefit by living in close association, but is not essential.

  Examples:
  
  • many ants are found in the vicinity of aphids. The ants feed on the sugary fluid released by the aphids, and the aphids are protected by the ants;
  • small fish of several families, including a wrasse, feed on small organisms and parasites on the bodies of larger fish. These cleaner or barber fish in this manner, and the larger fish are relieved of unwelcome guests on their bodies.

• Obligate Mutualism
  

  As the name implies, an obligatory contact exists between different organisms.

  Examples:
  
  • lichens are plants made up of a fungus and an alga living in close association. They are usually found on rocks and tree trunks. The fungus is attached to the substratum by fungal treads. These fungal treads help to absorb inorganic substances which are then used by the alga during photosynthesis (when organic compounds are made). The fungus obtains organic substances manufactured by the alga;
  • bees and birds visit flowers in search of pollen and nectar. In the process flowers are pollinated.

A bird that pollinates a protea.

Commensalism
Parasitism