Mutualism Among Free‐living Species


Mutualisms are interspecific interactions resulting in benefits to both participants. In symbiotic mutualisms, the species live together for most of their lives. In nonsymbiotic mutualisms, members of the interacting species live apart most of the time and interact intermittently. Common mutualisms among free‐living species include various plant–animal mutualisms, such as pollination and seed dispersal, and a number of animal–animal mutualisms such as cleaning and parasite‐removal services (e.g. oxpeckers and cleaning wrasses). The evolutionary stability of these mutualisms is a topic of current research interest, in which mutualism may easily slip into unbalanced relationships wherein one partner exploits the other.

Key Concepts:

  • Mutualisms among free‐living species are ecologically important, providing critical services for the maintenance of populations and functioning of ecosystems.

  • Mutualisms among free‐living species may be evolutionarily more labile than symbiotic mutualisms, in which the former may more commonly ‘degenerate’ into exploitative relationships.

  • A key factor in the ecology and evolution of mutualisms among free‐living species is signalling between spatially distant organisms, usually with behaviour, volatile chemicals and/or colour. The degree of honesty (or dishonesty) of such signalling is another topic of current research interest.

Keywords: ecology; evolution; mutualism

Figure 1.

A Trigona sp. bee (Hymenoptera: Apidae) collecting resin and picking up pollen from a male flower of the tropical tree Clusia sp. (Clusiaceae). This is a pollination mutualism in which the plant provides resin that bees collect to use in construction of their nests. The mutualism may have originated by modification of a pre‐existing system of plant defence against herbivores with latex or resin. (Photograph: W.S. Armbruster.)

Figure 2.

Tropical Ectatoma sp. ants (Hymenoptera: Formicidae) collecting nectar in their mandibles from extrafloral (leaf) nectaries of an Inga sp. sapling (Leguminosae). These ants facultatively visit numerous species of plants that secrete nectar from vegetative structures; the ants provide some measure of protection against herbivorous insects. (Photograph: W.S. Armbruster.)



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Further Reading

Armbruster WS (1992) Phylogeny and the evolution of plant–animal interactions. BioScience 42: 12–20.

Boucher DH (1985) The Biology of Mutualism: Ecology and Evolution. New York: Oxford University Press.

Heinrich B and Raven PH (1972) Energetics and pollination ecology. Science 176: 597–602.

Herrera CM and Pellmyr O (eds) (2002) Plant–Animal Interactions: An Evolutionary Approach. Oxford, UK: Blackwell Science.

Schaeffer HM and Ruxton GD (2011) Plant–Animal Communication. Oxford, UK: Oxford University Press.

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How to Cite close
Armbruster, WS, and Rosenqvist, G(Dec 2011) Mutualism Among Free‐living Species. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0003287.pub2]