Mutualism (biology)

Mutualism describes the ecological interaction between two or more species where each species benefits[1]. Mutualism is thought to be the most common type of ecological interaction, and it is often dominant in most communities worldwide. Prominent examples include most vascular plants engaged in mutualistic interactions with mycorrhizae, flowering plants being pollinated by animals, vascular plants being dispersed by animals, and corals with zooxanthellae, among many others. Mutualism can be contrasted with interspecific competition, in which each species experiences reduced fitness, and exploitation, or parasitism, in which one species benefits at the "expense" of the other.

Mutualism is often conflated with two other types of ecological phenomena: cooperation and symbiosis. Cooperation refers to increases in fitness through within-species (intraspecific) interactions. Symbiosis involves two species living in close proximity and may be mutualistic, parasitic, or commensal, so symbiotic relationships are not always mutualistic.

Mutualism plays a key part in ecology. For example, mutualistic interactions are vital for terrestrial ecosystem function as more than 48% of land plants rely on mycorrhizal relationships with fungi to provide them with inorganic compounds and trace elements. As another example, the estimate of tropical forest trees with seed dispersal mutualisms with animals ranges from 70–90%. In addition, mutualism is thought to have driven the evolution of much of the biological diversity we see, such as flower forms (important for pollination mutualisms) and co-evolution between groups of species.[2] However, mutualism has historically received less attention than other interactions such as predation and parasitism.[3]

The term mutualism was introduced by Pierre-Joseph van Beneden in his 1876 book Animal Parasites and Messmates.[4][5]

Hummingbird hawkmoth a
Hummingbird hawkmoth drinking from Dianthus, with pollination being a classic example of mutualism


Mutualistic relationships can be thought of as a form of "biological barter"[6] in mycorrhizal associations between plant roots and fungi, with the plant providing carbohydrates to the fungus in return for primarily phosphate but also nitrogenous compounds. Other examples include rhizobia bacteria that fix nitrogen for leguminous plants (family Fabaceae) in return for energy-containing carbohydrates.[7]

Service-resource relationships

Impala mutualim with birds wide
The red-billed oxpecker eats ticks on the impala's coat, in a cleaning symbiosis.

Service-resource relationships are common. Three important types are pollination, cleaning symbiosis, and zoochory.

In pollination, a plant trades food resources in the form of nectar or pollen for the service of pollen dispersal.

Phagophiles feed (resource) on ectoparasites, thereby providing anti-pest service, as in cleaning symbiosis. Elacatinus and Gobiosoma, genera of gobies, also feed on ectoparasites of their clients while cleaning them.[8]

Zoochory is the dispersal of the seeds of plants by animals. This is similar to pollination in that the plant produces food resources (for example, fleshy fruit, overabundance of seeds) for animals that disperse the seeds (service).

Another type is ant protection of aphids, where the aphids trade sugar-rich honeydew (a by-product of their mode of feeding on plant sap) in return for defense against predators such as ladybugs.

Service-service relationships

Common clownfish curves dnsmpl
Ocellaris clownfish and Ritter's sea anemones is a mutual service-service symbiosis, the fish driving off butterflyfish and the anemone's tentacles protecting the fish from predators.

Strict service-service interactions are very rare, for reasons that are far from clear.[6] One example is the relationship between sea anemones and anemone fish in the family Pomacentridae: the anemones provide the fish with protection from predators (which cannot tolerate the stings of the anemone's tentacles) and the fish defend the anemones against butterflyfish (family Chaetodontidae), which eat anemones. However, in common with many mutualisms, there is more than one aspect to it: in the anemonefish-anemone mutualism, waste ammonia from the fish feed the symbiotic algae that are found in the anemone's tentacles.[9][10] Therefore, what appears to be a service-service mutualism in fact has a service-resource component. A second example is that of the relationship between some ants in the genus Pseudomyrmex and trees in the genus Acacia, such as the whistling thorn and bullhorn acacia. The ants nest inside the plant's thorns. In exchange for shelter, the ants protect acacias from attack by herbivores (which they frequently eat, introducing a resource component to this service-service relationship) and competition from other plants by trimming back vegetation that would shade the acacia. In addition, another service-resource component is present, as the ants regularly feed on lipid-rich food-bodies called Beltian bodies that are on the Acacia plant.[11]

In the neotropics, the ant Myrmelachista schumanni makes its nest in special cavities in Duroia hirsute. Plants in the vicinity that belong to other species are killed with formic acid. This selective gardening can be so aggressive that small areas of the rainforest are dominated by Duroia hirsute. These peculiar patches are known by local people as "devil's gardens".[12]

In some of these relationships, the cost of the ant’s protection can be quite expensive. Cordia sp. trees in the Amazonian rainforest have a kind of partnership with Allomerus sp. ants, which make their nests in modified leaves. To increase the amount of living space available, the ants will destroy the tree’s flower buds. The flowers die and leaves develop instead, providing the ants with more dwellings. Another type of Allomerus sp. ant lives with the Hirtella sp. tree in the same forests, but in this relationship the tree has turned the tables on the ants. When the tree is ready to produce flowers, the ant abodes on certain branches begin to wither and shrink, forcing the occupants to flee, leaving the tree’s flowers to develop free from ant attack.[12]

The term "species group" can be used to describe the manner in which individual organisms group together. In this non-taxonomic context one can refer to "same-species groups" and "mixed-species groups." While same-species groups are the norm, examples of mixed-species groups abound. For example, zebra (Equus burchelli) and wildebeest (Connochaetes taurinus) can remain in association during periods of long distance migration across the Serengeti as a strategy for thwarting predators. Cercopithecus mitis and Cercopithecus ascanius, species of monkey in the Kakamega Forest of Kenya, can stay in close proximity and travel along exactly the same routes through the forest for periods of up to 12 hours. These mixed-species groups cannot be explained by the coincidence of sharing the same habitat. Rather, they are created by the active behavioural choice of at least one of the species in question.[13]

Mathematical modeling

Mathematical treatments of mutualisms, like the study of mutualisms in general, has lagged behind those of predation, or predator-prey, consumer-resource, interactions. In models of mutualisms, the terms "type I" and "type II" functional responses refer to the linear and saturating relationships, respectively, between benefit provided to an individual of species 1 (y-axis) on the density of species 2 (x-axis).

Type I functional response

One of the simplest frameworks for modeling species interactions is the Lotka–Volterra equations.[14] In this model, the change in population density of the two mutualists is quantified as:


  • = the population densities.
  • = the intrinsic growth rate of the population.
  • = the negative effect of within-species crowding.
  • = the beneficial effect of a mutualistic partner's density.

Mutualism is in essence the logistic growth equation + mutualistic interaction. The mutualistic interaction term represents the increase in population growth of species one as a result of the presence of greater numbers of species two, and vice versa. As the mutualistic term is always positive, it may lead to unrealistic unbounded growth as it happens with the simple model.[15] So, it is important to include a saturation mechanism to avoid the problem.

Type II functional response

In 1989, David Hamilton Wright modified the Lotka–Volterra equations by adding a new term, βM/K, to represent a mutualistic relationship.[16] Wright also considered the concept of saturation, which means that with higher densities, there are decreasing benefits of further increases of the mutualist population. Without saturation, species' densities would increase indefinitely. Because that isn't possible due to environmental constraints and carrying capacity, a model that includes saturation would be more accurate. Wright's mathematical theory is based on the premise of a simple two-species mutualism model in which the benefits of mutualism become saturated due to limits posed by handling time. Wright defines handling time as the time needed to process a food item, from the initial interaction to the start of a search for new food items and assumes that processing of food and searching for food are mutually exclusive. Mutualists that display foraging behavior are exposed to the restrictions on handling time. Mutualism can be associated with symbiosis.

Handling time interactions In 1959, C. S. Holling performed his classic disc experiment that assumed the following: that (1), the number of food items captured is proportional to the allotted searching time; and (2), that there is a variable of handling time that exists separately from the notion of search time. He then developed an equation for the Type II functional response, which showed that the feeding rate is equivalent to


  • a=the instantaneous discovery rate
  • x=food item density
  • TH=handling time

The equation that incorporates Type II functional response and mutualism is:


  • N and M=densities of the two mutualists
  • r=intrinsic rate of increase of N
  • c=coefficient measuring negative intraspecific interaction. This is equivalent to inverse of the carrying capacity, 1/K, of N, in the logistic equation.
  • a=instantaneous discovery rate
  • b=coefficient converting encounters with M to new units of N

or, equivalently,


  • X=1/a TH
  • β=b/TH

This model is most effectively applied to free-living species that encounter a number of individuals of the mutualist part in the course of their existences. Wright notes that models of biological mutualism tend to be similar qualitatively, in that the featured isoclines generally have a positive decreasing slope, and by and large similar isocline diagrams. Mutualistic interactions are best visualized as positively sloped isoclines, which can be explained by the fact that the saturation of benefits accorded to mutualism or restrictions posed by outside factors contribute to a decreasing slope.

The type II functional response is visualized as the graph of vs. M.

Structure of networks

Mutualistic networks made up out of the interaction between plants and pollinators were found to have a similar structure in very different ecosystems on different continents, consisting of entirely different species.[17] The structure of these mutualistic networks may have large consequences for the way in which pollinator communities respond to increasingly harsh conditions and on the community carrying capacity.[18]

Mathematical models that examine the consequences of this network structure for the stability of pollinator communities suggest that the specific way in which plant-pollinator networks are organized minimizes competition between pollinators,[19] reduce the spread of indirect effects and thus enhance ecosystem stability[20] and may even lead to strong indirect facilitation between pollinators when conditions are harsh.[21] This means that pollinator species together can survive under harsh conditions. But it also means that pollinator species collapse simultaneously when conditions pass a critical point.[22] This simultaneous collapse occurs, because pollinator species depend on each other when surviving under difficult conditions.[21]

Such a community-wide collapse, involving many pollinator species, can occur suddenly when increasingly harsh conditions pass a critical point and recovery from such a collapse might not be easy. The improvement in conditions needed for pollinators to recover could be substantially larger than the improvement needed to return to conditions at which the pollinator community collapsed.[21]


Backing sheep at sheepdog competition
Dogs and sheep were among the first animals to be domesticated.

Humans are involved in mutualisms with other species: their gut flora is essential for efficient digestion.[23] Infestations of head lice might have been beneficial for humans by fostering an immune response that helps to reduce the threat of body louse borne lethal diseases.[24]

Some relationships between humans and domesticated animals and plants are to different degrees mutualistic. For example, agricultural varieties of maize provide food for humans and are unable to reproduce without human intervention because the leafy sheath does not fall open, and the seedhead (the "corn on the cob") does not shatter to scatter the seeds naturally.[25]

In traditional agriculture, some plants have mutualist as companion plants, providing each other with shelter, soil fertility and/or natural pest control. For example, beans may grow up cornstalks as a trellis, while fixing nitrogen in the soil for the corn, a phenomenon that is used in Three Sisters farming.[26]

One researcher has proposed that the key advantage Homo sapiens had over Neanderthals in competing over similar habitats was the former's mutualism with dogs.[27]

Evolution of Mutualism

Mutualism breakdown

Mutualisms are not static, and can be lost by evolution [28]. Sachs and Simms (2006) suggest that this can occur via 4 main pathways:

  1. One mutualist shifts to parasitism, and no longer benefits its partner [28]
  2. One partner abandons the mutualism and lives autonomously [28]
  3. One partner may go extinct [28]
  4. A partner may be switched to another species [29].

There are many examples of mutualism breakdown. For example, plant lineages inhabiting nutrient-rich environments have evolutionarily abandoned mycorrhizal mutualisms many times independently. [30]

Measuring and defining mutualism

Measuring the exact fitness benefit to the individuals in a mutualistic relationship is not always straightforward, particularly when the individuals can receive benefits from a variety of species, for example most plant-pollinator mutualisms. It is therefore common to categorise mutualisms according to the closeness of the association, using terms such as obligate and facultative. Defining "closeness", however, is also problematic. It can refer to mutual dependency (the species cannot live without one another) or the biological intimacy of the relationship in relation to physical closeness (e.g., one species living within the tissues of the other species).[6]

See also


  1. ^ Bronstein, Judith (2015). Mutualism. Oxford University Press.
  2. ^ Thompson, J. N. 2005 The geographic mosaic of coevolution. Chicago, IL: University of Chicago Press.
  3. ^ Bronstein, JL (1994). "Our current understand of mutualism". Quarterly Review of Biology. 69 (1): 31–51. doi:10.1086/418432.
  4. ^ Van Beneden, Pierre-Joseph (1876). Animal Parasites and Messmates. London: Henry S. King.
  5. ^ Bronstein, J. L. (2015). The study of mutualism. Mutualism. Oxford University Press. ISBN 9780199675654.
  6. ^ a b c Ollerton, J. 2006. "Biological Barter": Interactions of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press.
  7. ^ Denison, RF; Kiers, ET (2004). "Why are most rhizobia beneficial to their plant hosts, rather than parasitic". Microbes and Infection. 6 (13): 1235–1239. doi:10.1016/j.micinf.2004.08.005. PMID 15488744.
  8. ^ M.C. Soares; I.M. Côté; S.C. Cardoso & R.Bshary (August 2008). "The cleaning goby mutualism: a system without punishment, partner switching or tactile stimulation" (PDF). Journal of Zoology. 276 (3): 306–312. doi:10.1111/j.1469-7998.2008.00489.x.
  9. ^ Porat, D.; Chadwick-Furman, N. E. (2004). "Effects of anemonefish on giant sea anemones: expansion behavior, growth, and survival". Hydrobiologia. 530 (1–3): 513–520. doi:10.1007/s10750-004-2688-y.
  10. ^ Porat, D.; Chadwick-Furman, N. E. (2005). "Effects of anemonefish on giant sea anemones: ammonium uptake, zooxanthella content and tissue regeneration". Mar. Freshw.Behav. Phys. 38: 43–51. doi:10.1080/102362405000_57929 (inactive 7 July 2019).
  11. ^ "Swollen Thorn Acacias". Retrieved 22 February 2019.
  12. ^ a b Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
  13. ^ Tosh CR, Jackson AL, Ruxton GD (March 2007). "Individuals from different-looking animal species may group together to confuse shared predators: simulations with artificial neural networks". Proc. Biol. Sci. 274 (1611): 827–32. doi:10.1098/rspb.2006.3760. PMC 2093981. PMID 17251090.
  14. ^ May, R., 1981. Models for Two Interacting Populations. In: May, R.M., Theoretical Ecology. Principles and Applications, 2nd ed. pp. 78–104.
  15. ^ García-Algarra, Javier (2014). "Rethinking the logistic approach for population dynamics of mutualistic interactions" (PDF). Journal of Theoretical Biology. 363: 332–343. arXiv:1305.5411. doi:10.1016/j.jtbi.2014.08.039. PMID 25173080.
  16. ^ Wright, David Hamilton (1989). "A Simple, Stable Model of Mutualism Incorporating Handling Time". The American Naturalist. 134 (4): 664–667. doi:10.1086/285003.
  17. ^ Bascompte, J.; Jordano, P.; Melián, C. J.; Olesen, J. M. (2003). "The nested assembly of plant–animal mutualistic networks". Proceedings of the National Academy of Sciences. 100 (16): 9383–9387. Bibcode:2003PNAS..100.9383B. doi:10.1073/pnas.1633576100. PMC 170927. PMID 12881488.
  18. ^ Suweis, S.; Simini, F.; Banavar, J; Maritan, A. (2013). "Emergence of structural and dynamical properties of ecological mutualistic networks". Nature. 500 (7463): 449–452. arXiv:1308.4807. Bibcode:2013Natur.500..449S. doi:10.1038/nature12438. PMID 23969462.
  19. ^ Bastolla, U.; Fortuna, M. A.; Pascual-García, A.; Ferrera, A.; Luque, B.; Bascompte, J. (2009). "The architecture of mutualistic networks minimizes competition and increases biodiversity". Nature. 458 (7241): 1018–1020. Bibcode:2009Natur.458.1018B. doi:10.1038/nature07950. PMID 19396144.
  20. ^ Suweis, S., Grilli, J., Banavar, J. R., Allesina, S., & Maritan, A. (2015) Effect of localization on the stability of mutualistic ecological networks. "Nature Communications", 6
  21. ^ a b c Lever, J. J.; Nes, E. H.; Scheffer, M.; Bascompte, J. (2014). "The sudden collapse of pollinator communities". Ecology Letters. 17 (3): 350–359. doi:10.1111/ele.12236. hdl:10261/91808. PMID 24386999.
  22. ^ Garcia-Algarra, J.; Pasotr, J. M.; Iriondo, J. M.; Galeano, J. (2017). "Ranking of critical species to preserve the functionality of mutualistic networks using the k-core decomposition". PeerJ. 5: e3321. doi:10.7717/peerj.3321. PMC 5438587. PMID 28533969.
  23. ^ Sears CL (October 2005). "A dynamic partnership: celebrating our gut flora". Anaerobe. 11 (5): 247–51. doi:10.1016/j.anaerobe.2005.05.001. PMID 16701579.
  24. ^ Rozsa, L; Apari, P. (2012). "Why infest the loved ones – inherent human behaviour indicates former mutualism with head lice" (PDF). Parasitology. 139 (6): 696–700. doi:10.1017/s0031182012000017. PMID 22309598.
  25. ^ "Symbiosis – Symbioses Between Humans And Other Species". Net Industries. Retrieved 9 December 2012.
  26. ^ Mt. Pleasant, Jane (2006). "The science behind the Three Sisters mound system: An agronomic assessment of an indigenous agricultural system in the northeast". In John E. Staller; Robert H. Tykot; Bruce F. Benz (eds.). Histories of maize: Multidisciplinary approaches to the prehistory, linguistics, biogeography, domestication, and evolution of maize. Amsterdam. pp. 529–537.
  27. ^ Shipman, Pat (2015). The Invaders: How Humans and Their Dogs Drove Neanderthals to Extinction. Cambridge, Maryland: Harvard University Press.
  28. ^ a b c d Sachs JL, Simms EL (2006). "Pathways to mutualism breakdown". TREE. 21 (10): 585–592.
  29. ^ Werner, G. D. A. et al. (2018) ‘Symbiont switching and alternative resource acquisition strategies drive mutualism breakdown’, bioRxiv, p. 242834
  30. ^ Wang, B. and Qiu, Y.-L. (2006) ‘Phylogenetic distribution and evolution of mycorrhizas in land plants.’, Mycorrhiza, 16(5), pp. 299–363.

Further references

Further reading

Ant–fungus mutualism

Ant–fungus mutualism is a symbiosis seen in certain ant and fungal species, in which ants actively cultivate fungus much like humans farm crops as a food source. In some species, the ants and fungi are dependent on each other for survival. The leafcutter ant is a well-known example of this symbiosis. A mutualism with fungi is also noted in some species of termites in Africa.

Biotic component

Biotic components, or biotic factors, can be described as any living component that affects another organism or shapes the ecosystem. This includes both animals that consume other organisms within their ecosystem, and the organism that is being consumed. Biotic factors also include human influence, pathogens, and disease outbreaks. Each biotic factor needs the proper amount of energy and nutrition to function day to day.

Biotic components are typically sorted into three main categories:

Producers, otherwise known as autotrophs, convert energy (through the process of photosynthesis) into food.

Consumers, otherwise known as heterotrophs, depend upon producers (and occasionally other consumers) for food.

Decomposers, otherwise known as detritivores, break down chemicals from producers and consumers (usually antibiotic) into simpler form which can be reused.

Cleaning symbiosis

Cleaning symbiosis is a mutually beneficial association between individuals of two species, where one (the cleaner) removes and eats parasites and other materials from the surface of the other (the client). Cleaning symbiosis is well-known among marine fish, where some small species of cleaner fish, notably wrasses but also species in other genera, are specialised to feed almost exclusively by cleaning larger fish and other marine animals. Other cleaning symbioses exist between birds and mammals, and in other groups.

Cleaning behaviour was first described by the Greek historian Herodotus in about 420 BC, though his example (birds serving crocodiles) appears to occur only rarely.

The role of cleaning symbioses has been debated by biologists for over thirty years. Some believe that cleaning represents selfless co-operation, essentially pure mutualism, increasing the fitness of both individuals. Others such as Robert Trivers hold that it illustrates mutual selfishness, reciprocal altruism. Others again believe that cleaning behaviour is simply one-sided exploitation, a form of parasitism.

Cheating, where either a cleaner sometimes harms its client, or a predatory species mimics a cleaner, also occurs. Predatory cheating is analogous to Batesian mimicry, as where a harmless hoverfly mimics a stinging wasp, though with the tables turned. Some genuine cleaner fish, such as gobies and wrasse, have the same colours and patterns, in an example of convergent evolution. Mutual resemblance among cleaner fish is analogous to Müllerian mimicry, as where stinging bees and wasps mimic each other.


A domatium (plural: domatia, from the Latin "domus", meaning home) is a tiny chamber produced by plants that houses arthropods.Ideally domatia differ from galls in that they are produced by the plant rather than being induced by their inhabitants, but the distinction is not sharp; the development of many types of domatia is influenced and promoted by the inhabitants. Most domatia are inhabited either by mites or ants, in what can be a mutualist relationship, but other arthropods such as thrips may take parasitic advantage of the protection offered by this structure.

Domatia occupied by ants are called myrmecodomatia. An important class of myrmecodomatia comprise large, hollow spines of certain acacias such as Acacia sphaerocephala, in which ants of the genera Pseudomyrmex and Tetraponera make their nests. Plants that provide myrmecodomatia are called myrmecophytes. The variety of the plants that provide myrmecodomatia, and the ranges of forms of such domatia are considerable. Some plants, such as Myrmecodia, grow large bulbous structures riddled with channels in which their ants may establish themselves, both for mutual protection and for the nutritive benefit of the ants' wastes.

Often domatia are formed on the lower surface of leaves, at the juncture of the midrib and the veins. They usually consist of small depressions partly enclosed by leaf tissue or hairs. Many members of the Lauraceae family develop leaf domatia. Domatia are also found in some rainforest tree species in the families Alangiaceae, Elaeocarpaceae, Fabaceae, Icacinaceae, Meliaceae, Rubiaceae, Sapindaceae and Simaroubaceae.


Endogenosymbiosis is an evolutionary process, proposed by the evolutionary and environmental biologist Roberto Cazzolla Gatti, in which "gene carriers" (viruses, retroviruses and bacteriophages) and symbiotic prokaryotic cells (bacteria or archaea) could share parts or all of their genomes in an endogenous symbiotic relationship with their hosts.


In zoology, an inquiline (from Latin inquilinus, "lodger" or "tenant") is an animal that lives commensally in the nest, burrow, or dwelling place of an animal of another species. For example, some organisms such as insects may live in the homes of gophers and feed on debris, fungi, roots, etc. The most widely distributed types of inquiline are those found in association with the nests of social insects, especially ants and termites – a single colony may support dozens of different inquiline species. The distinctions between parasites, social parasites, and inquilines are subtle, and many species may fulfill the criteria for more than one of these, as inquilines do exhibit many of the same characteristics as parasites. However, parasites are specifically not inquilines, because by definition they have a deleterious effect on the host species, while inquilines do not.In the specific case of termites, the term "inquiline" is restricted to termite species that inhabit other termite species' nests whereas other arthropods cohabiting termitaria are called "termitophiles".

Inquilines are known especially among the gall wasps (Cynipidae family). In the sub-family Synerginae this mode of life predominates. These insects are similar in structure to the true gall-inducing wasps, but they do not produce galls, instead depositing their eggs within those of other species. They infest certain species of galls, such as those of the blackberry and some oak galls, in large numbers, and sometimes more than one kind occur in a single gall. Perhaps the most remarkable feature of these inquilines is their frequent close resemblance to the insect that produces the gall they infest.The term inquiline has also been applied to aquatic invertebrates that spend all or part of their life cycles in phytotelmata, water-filled structures produced by plants. For example, Wyeomyia smithii, Metriocnemus knabi, and Habrotrocha rosa are three invertebrates that make up part of the microecosystem within the pitchers of Sarracenia purpurea. Some species of pitcher plants like the Nepenthes and Cephalotus produce acidic, toxic or digestive fluids and host a limited diversity of inquilines. Other pitcher plant species like the Sarracenia or Heliamphora host diverse organisms and depend to a large extent on their symbionts for prey utilization.

Mutual aid

Mutual aid may refer to:

Billion Dollar Gift and Mutual Aid: Canada's gift of $4 billion to Britain in the Second World War

Mutual aid (organization theory), a tenet of organization theories

Mutual aid (emergency services), an agreement between emergency responders

Mutual Aid: A Factor of Evolution, a biology book by anarchist Peter Kropotkin

Mutual aid, in social work with groups

Mutual aid society, various organizations formed for the benefit of members


Mutualism may refer to:

Mutualism (biology), positive interactions between species

Mutualism (economic theory), associated with Pierre-Joseph Proudhon

Mutualism (movement), social movement promoting mutual organizations

Mutualisms and conservation

Conservation is the maintenance of biological diversity. Conservation can focus on preserving diversity at genetic, species, community or whole ecosystem levels. This article will examine conservation at the species level, because mutualisms involve interactions between species. The ultimate goal of conservation at this level is to prevent the extinction of species. However, species conservation has the broader aim of maintaining the abundance and distribution of all species, not only those threatened with extinction (van Dyke 2008). Determining the value of conserving particular species can be done through the use of evolutionary significant units, which essentially attempt to prioritise the conservation of the species which are rarest, fastest declining, and most distinct genotypically and phenotypically (Moritz 1994, Fraser and Bernatchez 2001).

Mutualisms can be defined as "interspecific interactions in which each of two partner species receives a net benefit" (Bronstein et al. 2004). Here net benefit is defined as, a short-term increase in inclusive fitness (IF). Incorporating the concept of genetic relatedness (through IF) is essential because many mutualisms involve the eusocial insects, where the majority of individuals are not reproductively active. The short-term component is chosen because it is operationally useful, even though the role of long-term adaptation is not considered (de Mazancourt et al. 2005). This definition of mutualism should be suffice for this article, although it neglects discussion of the many subtitles of IF theory applied to mutualisms, and the difficulties of examining short-term compared to long-term benefits, which are discussed in Foster and Wenselneers (2006) and de Mazancourt et al. (2005) respectively. Mutualisms can be broadly divided into two categories. Firstly, obligate mutualism, where two mutualistic partners are completely interdependent for survival and reproduction. Secondly, facultative mutualism, where two mutualistic partners both benefit from the mutualism, but can theoretically survive in each other's absence.

Mutualisms are remarkably common, in fact all organisms are believed to be involved in a mutualism at some point during their lives (Bronstein et al. 2004). This is particularly likely to be true for the definition of mutualism adopted here, where herbivory can paradoxically be mutualistic, for example in a situation where a plant overcompensates by producing more biomass when grazed on. Therefore, any species identified as particularly important to conserve will probably have mutualistic partners. It is beyond the purview of this article to discuss all these mutualisms, so the focus will be on specifically animal-plant mutualisms.

Mycorrhiza helper bacteria

Mycorrhiza helper bacteria (MHB) are a group of organisms that form symbiotic associations with both ectomycorrhiza and arbuscular mycorrhiza. MHBs are diverse and belong to different bacterial phyla including both gram-negative and gram-positive bacteria. Some of the most common types are Pseudomonas and Streptomyces. MHBs have specific interactions with fungi, but not with the plants. MHB enhance mycorrhizal function, increase mycorrhizal growth, provide nutrients to the fungus and plant, improve soil conductance, select to aid pathogens, and help promote defense mechanisms.


Myrmecochory ( (sometimes myrmechory); from Ancient Greek: μύρμηξ, romanized: mýrmēks and χορεία khoreíā "circular dance") is seed dispersal by ants, an ecologically significant ant-plant interaction with worldwide distribution. Most myrmecochorous plants produce seeds with elaiosomes, a term encompassing various external appendages or "food bodies" rich in lipids, amino acid, or other nutrients that are attractive to ants. The seed with its attached elaiosome is collectively known as a diaspore. Seed dispersal by ants is typically accomplished when foraging workers carry diaspores back to the ant colony after which the elaiosome is removed or fed directly to ant larvae. Once the elaiosome is consumed the seed is usually discarded in underground middens or ejected from the nest. Although diaspores are seldom distributed far from the parent plant, myrmecochores also benefit from this predominantly mutualistic interaction through dispersal to favourable locations for germination as well as escape from seed predation.


Myrmecophily ( mur-mə-KOF-il-ee; literally "ant-love") is the term applied to positive interspecies associations between ants and a variety of other organisms such as plants, other arthropods, and fungi. Myrmecophily refers to mutualistic associations with ants, though in its more general use the term may also refer to commensal or even parasitic interactions.

The term myrmecophile is used mainly for animals that associate with ants. There are an estimated 10,000 species of ants (Formicidae), with a higher diversity in the tropics. In most terrestrial ecosystems ants are ecologically and numerically dominant, being the main invertebrate predators. As a result, ants play a key role in controlling arthropod richness, abundance, and community structure. There is evidence that the evolution of myrmecophilous interactions has contributed to the abundance and ecological success of ants, by ensuring a dependable and energy-rich food supply and thus providing a competitive advantage for ants over other invertebrate predators. Most myrmecophilous associations are opportunistic, unspecialized, and facultative (meaning both species are capable of surviving without the interaction), though obligate mutualisms (those in which one or both species are dependent on the interaction for survival) have also been observed for many species.

Myrmecophily in Staphylinidae

Many species of Staphylinidae (commonly known as “rove beetles”) have developed complex interspecies relationships with ants, known as myrmecophily. Rove Beetles are among the most rich and diverse families of myrmecophilous beetles, with a wide variety of relationships with ants. Ant associations range from near free-living species which prey only on ants, to obligate inquilines of ants, which exhibit extreme morphological and chemical adaptations to the harsh environments of ant nests. Some species are fully integrated into the host colony, and are cleaned and fed by ants. Many of these, including species in tribe Clavigerini, are myrmecophagous, placating their hosts with glandular secretions while eating the brood


Myrmecophytes (mər′mek•ə‚fīt; literally "ant-plant") are plants that live in a mutualistic association with a colony of ants. There are over 100 different genera of myrmecophytes. These plants possess structural adaptations that provide ants with food and/or shelter. These specialized structures include domatia, food bodies, and extrafloral nectaries. In exchange for food and shelter, ants aid the myrmecophyte in pollination, seed dispersal, gathering of essential nutrients, and/or defense. Specifically, domatia adapted to ants may be called myrmecodomatia.

Müllerian mimicry

Müllerian mimicry is a natural phenomenon in which two or more unprofitable (often, distasteful) species, that may or may not be closely related and share one or more common predators, have come to mimic each other's honest warning signals, to their mutual benefit, since predators can learn to avoid all of them with fewer experiences. It is named after the German naturalist Fritz Müller, who first proposed the concept in 1878, supporting his theory with the first mathematical model of frequency-dependent selection, one of the first such models anywhere in biology.Müllerian mimicry was first identified in tropical butterflies that shared colourful wing patterns, but it is found in many groups of insects such as bumblebees, and other animals including poison frogs and coral snakes. The mimicry need not be visual; for example, many snakes share auditory warning signals. Similarly, the defences involved are not limited to toxicity; anything that tends to deter predators, such as foul taste, sharp spines, or defensive behaviour can make a species unprofitable enough to predators to allow Müllerian mimicry to develop.

Once a pair of Müllerian mimics has formed, other mimics may join them by advergent evolution (one species changing to conform to the appearance of the pair, rather than mutual convergence), forming mimicry rings. Large rings are found for example in velvet ants. Since the frequency of mimics is negatively correlated with survivability, rarer mimics are likely to adapt to resemble commoner models, favouring both advergence and larger Müllerian mimicry rings. Where mimics are not strongly protected by venom or other defences, honest Müllerian mimicry grades into bluffing Batesian mimicry.

Pollination network

A pollination network is a bipartite mutualistic network in which plants and pollinators are the nodes, and the pollination interactions form the links between these nodes. The pollination network is bipartite as interactions only exist between two distinct, non-overlapping sets of species, but not within the set: a pollinator can never be pollinated, unlike in a predator-prey network where a predator can be depredated. A pollination network is two-modal, i.e., it includes only links connecting plant and animal communities.

Seed dispersal syndrome

A seed dispersal syndrome is a mutualistic plant-animal interaction. Seed dispersal syndromes are morphological characters of seeds correlated to particular seed dispersal agents. Dispersal is the event by which individuals move from the site of their parents to establish in a new area. A seed disperser is the vector by which a seed moves from its parent to the resting place where the individual will establish, for instance an animal. Similar to the term syndrome, a diaspore is a morphological functional unit of a seed for dispersal purposes.Characteristics for seed dispersal syndromes are commonly fruit colour, mass, and persistence. These syndrome characteristics are often associated with the fruit that carries the seeds. Fruits are packages for seeds, composed of nutritious tissues to feed animals. However, fruit pulp is not commonly used as a seed dispersal syndrome because pulp nutritional value does not enhance seed dispersal success. Animals interact with these fruits because they are a common food source for them. Although, not all seed dispersal syndromes have fruits because not all seeds are dispersed by animals. Suitable biological and environmental conditions of dispersal syndromes are needed for seed dispersal and invasion success such as temperature and moisture.

Seed dispersal syndromes are parallel to pollination syndromes, which are defined as floral characteristics that attract organisms as pollinators. They are considered parallels because they are both plant-animal interactions, which increase the reproductive success of a plant. However, seed dispersal syndromes are more common in gymnosperms, while pollination syndromes are found in angiosperms.

Seeds disperse to increase the reproductive success of the plant. The farther away a seed is from a parent, the better its chances of survival and germination. Therefore, a plant should select certain traits to increase dispersal by a vector (i.e. bird) to increase the reproductive success of the plant.

Trophic mutualism

Trophic mutualism is a key type of ecological mutualism. Specifically, "trophic mutualism" refers to the transfer of energy and nutrients between two species. This is also sometimes known as resource-to-resource mutualism. Trophic mutualism often occurs between an autotroph and a heterotroph. Although there are many examples of trophic mutualisms, the heterotroph is generally a fungus or bacteria. This mutualism can be both obligate and opportunistic.

Patterns of evolution
Biological swarming
Animal migration
Swarm algorithms
Collective motion
Swarm robotics
Related topics
Food webs
Example webs
Ecology: Modelling ecosystems: Other components


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