21: Mutualism

Mutualism: A positive interaction between two species in which each species receives benefits that only the other species can provide.
Generalist – interacts with many species.
Specialist – interacts with one or a few species.
Mutualisms can provide water, nutrients, and places to live
Obligate mutualists — Two species that provide fitness benefits to each other and require each other to persist.
Facultative mutualists — Two species that provide fitness benefits to each other, but whose interaction is not critical to the persistence of either species.

Mycorrhizal fungi — Fungi that surround plant roots and help plants obtain water and minerals.
Endomycorrhizal fungi — Fungi characterized by hyphal threads that extend far out into the soil and penetrate root cells between the cell wall and the cell membrane.
Ectomycorrhizal fungi — Fungi characterized by hyphae that surround the roots of plants and enter between root cells but rarely enter the cells.
Mutualisms can aid in defense against enemies
Mutualisms can facilitate pollination and seed dispersal
Mutualisms can change when conditions change
- Shifting from mutualism to negative interactions
- Dealing with cheaters in mutualisms
Mutualisms can affect species distributions, communities, and ecosystems
- Effects on species distributions
- Mutualism’s effects on communities
- Mutualism’s effects on ecosystem function
Summary
- Mutualism can provide water, nutrients and places to live.
- Mutualistic relationships can become negative interactions.