What is mutualism?

Mutualism is the ecological interaction in which both participants advantage and that is obligatory for their survival. Mutualism is a harmonious (positive) ecological interaction. Mutualism is also called as symbiosis. Examples of mutualism are: the association among microorganisms that digest cellulose and the ruminants or insects within which they live; the lichens, produced by algae or cyanobacteria that make organic material for the fungi and absorb water with their help; nitrifying bacteria of the genus Rhizobium that associated to leguminous plants vary nitrogen to these plants.