mutualism

Mutualism is a type of symbiotic interaction in which two or more species benefit from the association. Benefits can be ecological, such as improved nutrition, protection from predators, or increased access to resources, and the relationship may be obligate or facultative. In obligate mutualism, at least one partner cannot survive or reproduce efficiently without the other; in facultative mutualism, the partners benefit but can live independently.

Common mutualisms include pollination, where flowering plants provide nectar and pollen to pollinators such as bees, birds, or bats, which in turn facilitate plant reproduction; seed dispersal, where animals transport and deposit seeds; mycorrhizal associations in which fungi colonize plant roots and improve water and nutrient uptake while receiving carbohydrates; and the lichen symbiosis between fungi and photosynthetic algae or cyanobacteria. In marine systems, corals host photosynthetic algae that supply energy, while algae gain a protected habitat. Microbial mutualisms occur in guts, where bacteria aid digestion and synthesize vitamins for the host, and bacteria receive a nutrient-rich environment.

Mutualisms can be context-dependent and influenced by environmental conditions. They are maintained by net benefits, though costs such as resource use or the risk of cheating by partners can occur. Organisms may evolve mechanisms to sanction non-cooperating partners or to preferentially associate with more mutualistic partners. Mutualistic interactions influence community structure, nutrient cycling, and the evolution of species.