Inhabitational mutualism is when one mutualist lives within another. Exhabitational mutualism is when the organisms involved are relatively independent physically, but interact directly. Indirect mutualism is the interaction among a set of species to modify the environment. Mutualism can either be symbiotic, nonsymbiotic, or facultative. Symbiotic mutualism is a relationship between different organisms live in direct contact, in which one or both benefit and at least one member of the pair cannot live an independent life without the other.
Mutualism is a type of species interaction.
Other types of species interactions include commensalism, which is an interaction that stimulates one organism but has no effect on the other. Another example is protocooperation, which is an interaction that stimulates both partners, but it is not obligatory because stable growth continues in the absence of the interaction. Common examples of mutualism are mycorrihizae, nitrogen fixation, and pollination. Mycorrhizae are fungal associations with the roots of higher plants. Types of mycorrizae are ectomycorrhizae and endomycorrhizae.