View source for Mutualism (biology)

{{Short description|Mutually beneficial interaction between species}}
{{merge from|Protocooperation|date=November 2024}}
{{about|the biological term|the economic theory and other uses|Mutualism (disambiguation)}}
{{Use dmy dates|date=February 2025}}

[[File:Hummingbird hawkmoth a.jpg|thumb|[[Hummingbird hawkmoth]] drinking from ''[[Dianthus]]'', with [[pollination]] being a classic example of mutualism]]
'''Mutualism''' describes the ecological [[Biological interaction|interaction]] between two or more [[species]] where each species has a net benefit.<ref name=Bronstein15>{{cite book |last=Bronstein |first=J.L. |year=2015 |title=Mutualism |chapter=1. The study of mutualism |pages=3–19 |chapter-url={{GBurl|hbgVDAAAQBAJ|p=3}} |publisher=Oxford University Press |url={{GBurl|hbgVDAAAQBAJ|pg=PR5}} |isbn=978-0-19-166319-2 |oclc=913513762 }}</ref> Mutualism is a common type of [[Ecology|ecological]] interaction.Prominent examples are:
* the nutrient exchange between vascular plants and [[mycorrhizae|mycorrhizal fungi]],
* the [[Fertilisation|fertilization]] of flowering plants by [[pollinators]],
* the ways plants use fruits and [[edible]] seeds to encourage animal aid in [[seed dispersal]], and
* the way [[coral]]s become photosynthetic with the help of the microorganism [[zooxanthellae]].

Mutualism can be contrasted with [[interspecific competition]], in which each species experiences ''reduced'' fitness, and [[Cheating (biology)|exploitation]], and with [[parasitism]], in which one species benefits at the expense of the other.<ref>{{Cite web |title=Classify symbiotic relationships |work=7th grade science |url=https://www.ixl.com/science/grade-7/classify-symbiotic-relationships |access-date=2023-12-04 |publisher=IXL Learning }}</ref> However, mutualism may evolve from interactions that began with imbalanced benefits, such as [[parasitism]].<ref>{{cite web | url=https://yaledailynews.com/blog/2018/02/06/yale-researchers-show-that-mutualism-can-come-from-parasitism/#:~:text=The%20viruses%20and%20bacteria%20originally,benefited%20from%20one%20another%27s%20presence | title=Yale researchers show that mutualism can come from parasitism | date=6 February 2018 }}</ref>

The term ''mutualism'' was introduced by [[Pierre-Joseph van Beneden]] in his 1876 book ''Animal Parasites and Messmates'' to mean "mutual aid among species".<ref>{{cite book |author= Van Beneden, Pierre-Joseph |author-link=Pierre-Joseph van Beneden |year=1876 |title=Animal Parasites and Messmates |location=London |publisher=Henry S. King |url=https://www.biodiversitylibrary.org/bibliography/132633#/summary}}</ref><ref>{{harvnb|Bronstein|2015|loc=§1.2.2.1 Mutualism versus symbiosis. p. 6}}</ref>

Mutualism is often [[conflated]] with two other types of ecological phenomena: cooperation and [[symbiosis]]. [[Cooperation]] most commonly refers to increases in fitness through within-species (intraspecific) interactions, although it has been used (especially in the past) to refer to mutualistic interactions, and it is sometimes used to refer to mutualistic interactions that are not obligate.<ref name=Bronstein15/> [[Symbiosis]] involves two species living in close physical contact over a long period of their existence and may be mutualistic, [[Parasitism|parasitic]], or [[Commensalism|commensal]], so [[Symbiosis|symbiotic relationships]] are not always mutualistic, and mutualistic interactions are not always symbiotic. Despite a different definition between mutualism and symbiosis, they have been largely used interchangeably in the past, and confusion on their use has persisted.<ref>{{cite book |last1=Douglas |first1=Angela E. |title=The Symbiotic Habit |date=December 2014 |publisher=Princeton University Press |location=United States |isbn=978-0-691-11342-5 |oclc=1277051994}}</ref>

Mutualism plays a key part in [[ecology]] and [[evolution]]. For example, mutualistic interactions are vital for terrestrial [[ecosystem]] function as:
* about 80% of land plants species rely on [[mycorrhizal]] relationships with [[fungi]] to provide them with inorganic compounds and trace elements.<ref>{{cite journal |last1=Wang |first1=B. |title=Phylogenetic distribution and evolution of mycorrhizas in land plants |journal=Mycorrhiza |date=2006 |volume=16 |issue=5 |pages=299–363 |doi=10.1007/s00572-005-0033-6 |pmid=16845554 |bibcode=2006Mycor..16..299W |s2cid=30468942 }}</ref>
* estimates of tropical rainforest plants with seed dispersal mutualisms with animals range at least from 70% to 93.5%.<ref name="Jordano2000">{{cite book |last=Jordano |first=P. |chapter=Fruits and frugivory |editor-last=Fenner |editor-first=M. |title=Seeds: the ecology of regeneration in plant communities |publisher=CABI |edition=2nd |date=2000 |isbn=978-0-85199-947-0 |oclc=228171397 |pages=125–166 }}</ref> 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.<ref>{{cite book |first=J.N. |last=Thompson |title=The geographic mosaic of coevolution |publisher=University of Chicago Press |date=2005  |isbn=978-0-226-11869-7 |oclc=646854337 }}</ref>

A prominent example of pollination mutualism is with bees and flowering plants. Bees use these plants as their food source with pollen and nectar. In turn, they transfer pollen to other nearby flowers, inadvertently allowing for cross-pollination. Cross-pollination has become essential in plant reproduction and fruit/seed production. The bees get their nutrients from the plants, and allow for successful fertilization of plants, demonstrating a mutualistic relationship between two seemingly-unlike species.

Mutualism has also been linked to major [[evolution]]ary events, such as the evolution of the eukaryotic cell ([[symbiogenesis]]) and the colonization of land by plants in association with [[mycorrhiza]]l fungi.

==Types==

=== Resource-resource relationships ===
Mutualistic relationships can be thought of as a form of "[[Biology|biological]] barter"<ref name="Ollerton06" /> in [[mycorrhizal]] associations between plant [[root]]s 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]].<ref>{{cite journal |last1=Denison |first1=RF |last2=Kiers |first2=ET |year=2004 |title= Why are most rhizobia beneficial to their plant hosts, rather than parasitic |journal= [[Microbes and Infection]] |volume=6 |issue=13 |pages= 1235–9 |doi= 10.1016/j.micinf.2004.08.005|pmid=15488744 |doi-access=free }}</ref> Metabolite exchange between multiple mutualistic species of [[bacteria]] has also been observed in a process known as [[Syntrophy|cross-feeding]].<ref>{{Cite journal |last=Schink |first=Bernhard |date=2002-12-01 |title=Synergistic interactions in the microbial world |url=https://doi.org/10.1023/A:1020579004534 |journal=Antonie van Leeuwenhoek|volume=81 |issue=1 |pages=257–261 |doi=10.1023/A:1020579004534 |pmid=12448724 |s2cid=9310406 |issn=1572-9699}}</ref><ref>{{Cite journal |last1=Chacón |first1=Jeremy M. |last2=Hammarlund |first2=Sarah P. |last3=Martinson |first3=Jonathan N.V. |last4=Smith |first4=Leno B. |last5=Harcombe |first5=William R. |date=2021-11-02 |title=The Ecology and Evolution of Model Microbial Mutualisms |journal=Annual Review of Ecology, Evolution, and Systematics|volume=52 |issue=1 |pages=363–384 |doi=10.1146/annurev-ecolsys-012121-091753 |s2cid=239694099 |issn=1543-592X|doi-access=free }}</ref>

===Service-resource relationships===
[[File:Impala mutualim with birds wide.jpg|thumb|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 [[Seed dispersal|zoochory]].

In [[pollination]], a plant trades food resources in the form of [[nectar]] or [[pollen]] for the service of pollen dispersal. However, daciniphilous ''[[Bulbophyllum]]'' orchid species trade [[sex pheromone]] precursor or booster components via floral [[synomone]]s/attractants in a true mutualistic interactions with males of [[Dacini]] fruit flies (Diptera: Tephritidae: Dacinae).<ref>See also [[Attractant]] related to synomone; and references therein</ref><ref>{{cite journal |last1=Tan |first1=K.H. |last2=Nishida |first2=R. |title=Mutual reproductive benefits between a wild orchid, ''Bulbophyllum patens'', and Bactrocera fruit flies via a floral synomone |journal=Journal of Chemical Ecology |volume=26 |issue= 2|pages=533–546 |date=2000 |doi=10.1023/A:1005477926244 |bibcode=2000JCEco..26..533T }}</ref>

[[Phagophile]]s feed (resource) on [[ectoparasite]]s, thereby providing anti-pest service, as in [[cleaning symbiosis]].
''[[Elacatinus]]'' and ''[[Gobiosoma]]'', genera of [[Goby|gobies]], feed on ectoparasites of their clients while cleaning them.<ref>{{Cite journal|author1=M.C. Soares |author2=I.M. Côté |author3=S.C. Cardoso & R.Bshary |date=August 2008| title=The cleaning goby mutualism: a system without punishment, partner switching or tactile stimulation | journal =Journal of Zoology| volume =276 |issue =3 | pages =306–312 | doi=10.1111/j.1469-7998.2008.00489.x|url=http://doc.rero.ch/record/28974/files/Soares_Marta_C._-_The_cleaning_goby_mutualism_a_system_without_20120417.pdf }}</ref>

[[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). Plants may advertise these resources using colour<ref>{{Cite journal|last1=Lim|first1=Ganges|last2=Burns|first2=Kevin C.|date=2021-11-24|title=Do fruit reflectance properties affect avian frugivory in New Zealand?|url=https://doi.org/10.1080/0028825X.2021.2001664|journal=New Zealand Journal of Botany|volume=60 |issue=3 |pages=319–329|doi=10.1080/0028825X.2021.2001664|s2cid=244683146|issn=0028-825X}}</ref> and a variety of other fruit characteristics, e.g., scent.  Fruit of the [[aardvark cucumber]] ''(Cucumis humifructus)'' is buried so deeply that the plant is solely reliant upon the [[Aardvark#Head|aardvark's keen sense of smell]] to detect its ripened fruit, extract, consume and then scatter its seeds;<ref>{{cite book|last1=van Rheede van Oudtshoorn|first1=Karen|last2=van Rooyen |first2=Margaretha W. |title=Dispersal Biology of Desert Plants|year=1998|publisher=Springer |isbn=978-3-540-64886-4 |chapter=Restriction of Dispersal Due to Reduction of Dispersal Structures |chapter-url=https://link.springer.com/chapter/10.1007/978-3-662-03561-0_6 |page=118|doi=10.1007/978-3-662-03561-0_6 |url=https://books.google.com/books?id=bdTfBfsl-DcC&q=aardvark|accessdate=2023-01-28}}</ref>  ''C. humifructus's'' geographical range is thus restricted to that of the aardvark's.

Another type is [[ant]] protection of [[aphids]], where the aphids trade [[sugar]]-rich [[Honeydew (secretion)|honeydew]] (a by-product of their mode of feeding on plant [[sap]]) in return for defense against [[predator]]s such as [[ladybug]]s.{{citation needed|date=June 2024}}

===Service-service relationships===
[[Image:Common clownfish curves dnsmpl.jpg|thumb|[[Ocellaris clownfish]] and [[Heteractis magnifica|Ritter's sea anemone]]s live in 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.<ref name="Ollerton06" /> One example is the relationship between [[sea anemone]]s and [[anemone fish]] in the family [[Pomacentridae]]: the anemones provide the fish with protection from [[predator]]s (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 feeds the [[symbiotic]] [[algae]] that are found in the anemone's tentacles.<ref>{{cite journal | last1=Porat | first1=D. | last2=Chadwick-Furman | first2=N. E. | year=2004 | title=Effects of anemonefish on giant sea anemones: expansion behavior, growth, and survival | journal=[[Hydrobiologia]] | volume=530 | issue=1–3| pages=513–520 | doi=10.1007/s10750-004-2688-y | bibcode=2004HyBio.530..513P | s2cid=2251533 }}</ref><ref>{{cite journal | last1=Porat | first1=D. | last2=Chadwick-Furman | first2=N. E. | year=2005 | title=Effects of anemonefish on giant sea anemones: ammonium uptake, zooxanthella content and tissue regeneration | journal=Mar. Freshw. Behav. Phys. | volume=38 | issue=1 | pages=43–51 | doi= 10.1080/10236240500057929| bibcode=2005MFBP...38...43P | s2cid=53051081 }}</ref> 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 when those are small enough, 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.<ref>{{Cite web|url=https://www2.palomar.edu/users/warmstrong/acacia.htm|title=Swollen Thorn Acacias|website=www2.palomar.edu|access-date=2019-02-22|archive-date=27 June 2018|archive-url=https://web.archive.org/web/20180627005136/http://www2.palomar.edu/users/warmstrong/acacia.htm|url-status=dead}}</ref>

In the [[neotropics]], the ant ''[[Myrmelachista schumanni]]'' makes its nest in special cavities in ''[[Duroia hirsuta|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 garden]]s".<ref name="Piper07">[[Ross Piper|Piper, Ross]] (2007), ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals'', [[Greenwood Press (publisher)|Greenwood Press]].</ref>

In some of these relationships, the cost of the ant's protection can be quite expensive. ''[[Cordia]]'' sp. trees in the [[Amazon Rainforest|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.<ref name="Piper07" />

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 [[wikt:migration|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.<ref>{{cite journal |vauthors=Tosh CR, Jackson AL, Ruxton GD |title=Individuals from different-looking animal species may group together to confuse shared predators: simulations with artificial neural networks |journal=Proc. Biol. Sci. |volume=274 |issue=1611 |pages=827–32 |date=March 2007 |pmid=17251090 |pmc=2093981 |doi=10.1098/rspb.2006.3760 }}</ref>

==Evolution==
Mutualistic symbiosis can sometimes evolve from [[parasitism]] or [[commensalism]]. [[Symbiogenesis]], a leading theory on the evolution of [[Eukaryotes]] states the origin of the [[mitochondria]] and [[cell nucleus]] emerged from a parasitic relationship of ancient [[Archaea]] and [[Bacteria]]. Fungi's relationship to plants in the form of [[mycelium]] evolved from parasitism and [[commensalism]]. Under certain conditions species of fungi previously in a state of mutualism can turn parasitic on weak or dying plants.<ref>{{cite journal |last1=Purin |first1=Sonia |last2=Rillig |first2=Matthias C. |title=Parasitism of arbuscular mycorrhizal fungi: reviewing the evidence |journal=FEMS Microbiology Letters |date=February 2008 |volume=279 |issue=1 |pages=8–14 |doi=10.1111/j.1574-6968.2007.01007.x |pmid=18070075 }}</ref> Likewise the symbiotic relationship of [[clown fish]] and [[sea anemone]]s emerged from a commensalist relationship.<ref>{{Cite web|url=https://yaledailynews.com/blog/2018/02/06/yale-researchers-show-that-mutualism-can-come-from-parasitism/#:~:text=The+viruses+and+bacteria+originally,benefited+from+one+another's+presence|title=Yale researchers show that mutualism can come from parasitism|first=Jessica|last=Pevner|date=February 6, 2018|website=Yale Daily News}}</ref><ref>{{cite journal |last1=Titus |first1=Benjamin M. |last2=Benedict |first2=Charlotte |last3=Laroche |first3=Robert |last4=Gusmão |first4=Luciana C. |last5=Van Deusen |first5=Vanessa |last6=Chiodo |first6=Tommaso |last7=Meyer |first7=Christopher P. |last8=Berumen |first8=Michael L. |last9=Bartholomew |first9=Aaron |last10=Yanagi |first10=Kensuke |last11=Reimer |first11=James D. |last12=Fujii |first12=Takuma |last13=Daly |first13=Marymegan |last14=Rodríguez |first14=Estefanía |title=Phylogenetic relationships among the clownfish-hosting sea anemones |journal=Molecular Phylogenetics and Evolution |date=October 2019 |volume=139 |pages=106526 |doi=10.1016/j.ympev.2019.106526 |pmid=31158486 |bibcode=2019MolPE.13906526T }}</ref><ref>{{cite journal |last1=Litsios |first1=Glenn |last2=Sims |first2=Carrie A |last3=Wüest |first3=Rafael O |last4=Pearman |first4=Peter B |last5=Zimmermann |first5=Niklaus E |last6=Salamin |first6=Nicolas |title=Mutualism with sea anemones triggered the adaptive radiation of clownfishes |journal=BMC Evolutionary Biology |date=December 2012 |volume=12 |issue=1 |page=212 |doi=10.1186/1471-2148-12-212 |doi-access=free |pmid=23122007 |pmc=3532366 |bibcode=2012BMCEE..12..212L }}</ref> Once a mutualistic relationship emerges both symbionts are pushed towards [[co-evolution]] with each other.<ref>{{Cite web|url=https://bio.libretexts.org/Courses/Gettysburg_College/01:_Ecology_for_All/17:_Mutualism_and_Commensalism/17.03:_Evolution_of_Mutualisms|title=17.3: Evolution of Mutualisms|date=18 February 2022|website=Biology LibreTexts}}{{full|this is a book chapter|date=January 2025}}</ref><ref>{{cite journal |last1=Johnson |first1=Christopher A. |last2=Smith |first2=Gordon P. |last3=Yule |first3=Kelsey |last4=Davidowitz |first4=Goggy |last5=Bronstein |first5=Judith L. |last6=Ferrière |first6=Régis |title=Coevolutionary transitions from antagonism to mutualism explained by the Co-Opted Antagonist Hypothesis |journal=Nature Communications |date=17 May 2021 |volume=12 |issue=1 |page=2867 |doi=10.1038/s41467-021-23177-x |pmid=34001894 |pmc=8129128 |bibcode=2021NatCo..12.2867J }}</ref>

==Mathematical modeling==
Mathematical treatments of mutualisms, like the study of mutualisms in general, have lagged behind those for [[predation]], or predator-prey, consumer-resource, interactions. In models of mutualisms, the terms "type I" and "type II" [[functional response]]s refer to the linear and saturating relationships, respectively, between the ''benefit'' provided to an individual of species 1 ([[dependent and independent variables|dependent variable]]) and the ''density'' of species 2 (independent variable).{{citation needed|date=June 2024}}

===Type I functional response===
One of the simplest frameworks for modeling species interactions is the [[Lotka–Volterra equation]]s.<ref name=May1981>May, R., 1981. Models for Two Interacting Populations. In: May, R.M., Theoretical Ecology. Principles and Applications, 2nd ed. pp. 78–104.</ref> In this model, the changes in population densities of the two mutualists are quantified as:

:<math>
\begin{align}
\frac{dN_1}{dt} &=r_1 N_1 - \alpha_{11} N_1^2 + \beta _{12}N_1N_2 \\[8pt]
\frac{dN_2}{dt} &=r_2 N_2 - \alpha_{22} N_2^2 + \beta _{21}N_1N_2
\end{align}
</math>

where
* <math>N_i</math> = the population density of species ''i''.
* <math>r_i</math> = the intrinsic growth rate of the population of species ''i''.
* <math>\alpha _{ii}</math> = the negative effect of within-species crowding on species ''i''.
* <math>\beta _{ij}</math> = the beneficial effect of the density of species ''j'' on species ''i''.
Mutualism is in essence the [[Logistic function|logistic growth equation]] modified for mutualistic interaction. The mutualistic interaction term represents the increase in population growth of one species as a result of the presence of greater numbers of another species. As the mutualistic interactive term β is always positive, this simple model may lead to unrealistic unbounded growth.<ref name="G-Alg">{{cite journal | last1=García-Algarra| first1=Javier | year=2014| title=Rethinking the logistic approach for population dynamics of mutualistic interactions | url=http://ifisc.uib-csic.es/~jramasco/text/ecol_eqs.pdf| journal=[[Journal of Theoretical Biology]] | volume=363 | pages=332–343 | doi=10.1016/j.jtbi.2014.08.039| pmid=25173080 | arxiv=1305.5411| bibcode=2014JThBi.363..332G | s2cid=15940333 }}</ref> So it may be more realistic to include a further term in the formula, representing a saturation mechanism, to avoid this occurring.

===Type II functional response===
In 1989, David Hamilton Wright modified the above Lotka–Volterra equations by adding a new term, ''βM''/''K'', to represent a mutualistic relationship.<ref name="Wright">{{cite journal | last1=Wright | first1=David Hamilton | year=1989 | title=A Simple, Stable Model of Mutualism Incorporating Handling Time | journal=[[The American Naturalist]] | volume=134 | issue=4| pages=664–7 | doi=10.1086/285003| bibcode=1989ANat..134..664W | s2cid=83502337 }}</ref> Wright also considered the concept of saturation, which means that with higher densities, there is a decrease in the benefits of further increases of the mutualist population. Without saturation, depending on the size of parameter α, species densities would increase indefinitely. Because that is not 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.{{citation needed|date=June 2024}}

;Handling time interactions

In 1959, [[C. S. Holling]] performed his classic disc experiment that assumed that
# the number of food items captured is proportional to the allotted [[Search time|searching time]]; and
# that there is a [[handling time]] variable 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

::<math>\cfrac{ax}{1+axT_H}</math>

where
* ''a'' = the instantaneous discovery rate
* ''x'' = food item density
* ''T''<sub>''H''</sub> = handling time

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

:<math>
\frac{dN}{dt}=N\left[r(1-cN)+\cfrac{baM}{1+aT_H M}\right]
</math>

where
* ''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 function#Logistic differential equation|logistic equation]].
* ''a'' = instantaneous discovery rate
* ''b'' = coefficient converting encounters with ''M'' to new units of ''N''

or, equivalently,

:<math>
\frac{dN}{dt}=N[r(1-cN)+\beta M/(X+M)]
</math>

where
* ''X'' = 1/''aT''<sub>H</sub>
* ''β'' = ''b''/''T''<sub>H</sub>

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 [[isocline]]s 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 <math>\cfrac{baM}{1+aT_H M}</math> ''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.<ref>{{cite journal | last1=Bascompte | first1=J. | last2=Jordano | first2=P. | last3=Melián | first3=C. J. | last4=Olesen | first4=J. M. | year=2003 | title=The nested assembly of plant–animal mutualistic networks | journal=Proceedings of the National Academy of Sciences | volume=100 | issue=16| pages=9383–7 | doi=10.1073/pnas.1633576100 | pmid=12881488 | pmc=170927| bibcode=2003PNAS..100.9383B | doi-access=free }}</ref> 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.<ref>{{cite journal | last1=Suweis | first1=S. | last2=Simini | first2=F. | last3=Banavar | first3=J | last4=Maritan | first4=A. | year=2013 | title=Emergence of structural and dynamical properties of ecological mutualistic networks | journal=Nature | volume=500 | issue=7463| pages=449–452 | doi=10.1038/nature12438 | pmid=23969462| arxiv=1308.4807 | bibcode=2013Natur.500..449S | s2cid=4412384 }}</ref>

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,<ref>{{cite journal | last1=Bastolla | first1=U. | last2=Fortuna | first2=M. A. | last3=Pascual-García | first3=A. | last4=Ferrera | first4=A. | last5=Luque | first5=B. | last6=Bascompte | first6=J. | year=2009 | title=The architecture of mutualistic networks minimizes competition and increases biodiversity | journal=Nature | volume=458 | issue=7241| pages=1018–20 | doi=10.1038/nature07950 | pmid=19396144| bibcode=2009Natur.458.1018B | s2cid=4395634 }}</ref> reduce the spread of indirect effects and thus enhance ecosystem stability<ref>{{cite journal |vauthors=Suweis S, Grilli J, Banavar JR, Allesina S, Maritan A |title=Effect of localization on the stability of mutualistic ecological networks |journal=Nat Commun |volume=6 |pages=10179 |date=December 2015 |pmid=26674106 |pmc=4703855 |doi=10.1038/ncomms10179 |bibcode=2015NatCo...610179S }}</ref> and may even lead to strong indirect facilitation between pollinators when conditions are harsh.<ref name=Lever_et_al>{{cite journal | last1=Lever | first1=J. J. | last2=Nes | first2=E. H. | last3=Scheffer | first3=M. | last4=Bascompte | first4=J. | year=2014 | title=The sudden collapse of pollinator communities | journal=Ecology Letters | volume=17 | issue=3| pages=350–9 | doi=10.1111/ele.12236| pmid=24386999 | bibcode=2014EcolL..17..350L | hdl=10261/91808 | hdl-access=free }}</ref> 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.<ref name=Garcia_et_al>{{cite journal | last1=Garcia-Algarra | first1=J. | last2=Pasotr | first2=J. M. | last3=Iriondo | first3=J. M. | last4=Galeano | first4=J. | year=2017 | title=Ranking of critical species to preserve the functionality of mutualistic networks using the k-core decomposition | journal=PeerJ | volume=5 | pages=e3321 | doi=10.7717/peerj.3321| pmid=28533969 | pmc=5438587 | doi-access=free }}</ref> This simultaneous collapse occurs, because pollinator species depend on each other when surviving under difficult conditions.<ref name=Lever_et_al />

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.<ref name=Lever_et_al />

==Humans==
[[Image:Backing sheep at sheepdog competition.jpg|right|upright|thumb|[[Dog]]s and [[sheep]] were among the first animals to be [[Domestication|domesticated]].]]

Humans are involved in mutualisms with other species: their [[gut flora]] is essential for efficient [[digestion]].<ref name=Sears>{{cite journal |author=Sears CL |title=A dynamic partnership: celebrating our gut flora |journal=Anaerobe |volume=11 |issue=5 |pages=247–51 |date=October 2005 |pmid=16701579 |doi=10.1016/j.anaerobe.2005.05.001 }}</ref> 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.<ref name="mutualism">{{cite journal| last=Rozsa| first=L |author2=Apari, P. | url =http://www.zoologia.hu/list/Why_infest.pdf | title =Why infest the loved ones – inherent human behaviour indicates former mutualism with head lice| journal =Parasitology | volume=139 | issue=6 | pages=696–700| year=2012 | doi=10.1017/s0031182012000017 | pmid=22309598| s2cid=206247019 }}</ref>

Some relationships between humans and [[domestication|domesticated]] animals and plants are to different degrees mutualistic.{{citation needed|date=February 2025}} For example, domesticated [[cereal]]s that provide food for humans have lost the ability to spread seeds by [[Shattering (agriculture)|shattering]], a strategy that wild grains use to spread their seeds.<ref>{{cite journal |last1=Liu |first1=Hangqin |last2=Fang |first2=Xiaojian |last3=Zhou |first3=Leina |last4=Li |first4=Yan |last5=Zhu |first5=Can |last6=Liu |first6=Jiacheng |last7=Song |first7=Yang |last8=Jian |first8=Xing |last9=Xu |first9=Min |last10=Dong |first10=Li |last11=Lin |first11=Zhongwei |title=Transposon Insertion Drove the Loss of Natural Seed Shattering during Foxtail Millet Domestication |journal=[[Molecular Biology and Evolution]] |date=June 2022 |volume=39 |issue=6 |doi=10.1093/molbev/msac078|pmc=9167939 }}</ref>

In [[traditional agriculture]], some plants have mutualistic relationships as [[Companion planting|companion plants]], providing each other with shelter, soil fertility or natural [[pest control]]. For example, [[bean]]s may grow up [[Maize|corn]]stalks as a trellis, while fixing nitrogen in the soil for the corn, a phenomenon that is used in [[Three Sisters (agriculture)|Three Sisters farming]].<ref name="Mount Pleasant 2006">{{cite book |author-link=Jane Mount Pleasant |last=Mount Pleasant |first=Jane |editor1=Staller, John E. |editor2=Tykot, Robert H. |editor3=Benz, Bruce F. |title=Histories of Maize: Multidisciplinary Approaches to the Prehistory, Linguistics, Biogeography, Domestication, and Evolution of Maize |chapter=The science behind the Three Sisters mound system: An agronomic assessment of an indigenous agricultural system in the northeast |publisher=Left Coast Press |year=2006 |pages=529–537 |isbn=978-1-59874-782-9 |oclc=785782398}}</ref>

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.<ref>{{cite book | title=The Invaders: How Humans and Their Dogs Drove Neanderthals to Extinction | publisher=Harvard University Press | author=Shipman, Pat | year=2015 |doi=10.4159/9780674425385 | isbn=978-0-674-42538-5 |oclc=898113099}}</ref>

===Intestinal microbiota===

The [[gut microbiota|microbiota in the human intestine]] coevolved with the human species, and this relationship is considered to be a mutualism that is beneficial both to the human host and the bacteria in the gut population.<ref>{{cite journal |vauthors=Bäckhed F, Ley RE, Sonnenburg JL, Peterson DA, Gordon JI |title=Host-bacterial mutualism in the human intestine |journal=Science |volume=307 |issue=5717 |pages=1915–20 |date=March 2005 |pmid=15790844 |doi=10.1126/science.1104816 |bibcode=2005Sci...307.1915B }}</ref> The [[mucous membrane|mucous layer]] of the intestine contains [[commensalism|commensal]] bacteria that produce [[bacteriocin]]s, modify the pH of the intestinal contents, and compete for nutrition to inhibit colonization by pathogens.<ref name="Genua2021">{{cite journal |vauthors=Genua F, Raghunathan V, Jenab M, Gallagher WM, Hughes DJ |title=The Role of Gut Barrier Dysfunction and Microbiome Dysbiosis in Colorectal Cancer Development |journal=Front Oncol |volume=11 |pages=626349 |date=2021 |pmid=33937029 |pmc=8082020 |doi=10.3389/fonc.2021.626349 |doi-access=free
}}</ref> The gut microbiota, containing trillions of [[microorganism]]s, possesses the metabolic capacity to produce and regulate multiple compounds that reach the circulation and act to influence the function of distal organs and systems.<ref>{{cite journal |vauthors=Clarke G, Stilling RM, Kennedy PJ, Stanton C, Cryan JF, Dinan TG |title=Minireview: Gut microbiota: the neglected endocrine organ |journal=Mol Endocrinol |volume=28 |issue=8 |pages=1221–38 |date=August 2014 |pmid=24892638 |pmc=5414803 |doi=10.1210/me.2014-1108 }}</ref> Breakdown of the protective mucosal barrier of the gut can contribute to the development of [[colorectal cancer|colon cancer]].<ref name = Genua2021/>

==Evolution of mutualism==
===Evolution by type===
Every generation of every organism needs nutrients {{endash}} and similar nutrients {{endash}} more than they need particular defensive characteristics, as the fitness benefit of these vary heavily especially by environment. This may be the reason that hosts are more likely to evolve to become dependent on vertically transmitted bacterial mutualists which provide nutrients than those providing defensive benefits. This pattern is generalized beyond bacteria by Yamada et al. 2015's demonstration that undernourished ''[[Drosophila melanogaster|Drosophila]]'' are heavily dependent on their fungal symbiont ''[[Issatchenkia]] [[Issatchenkia orientalis|orientalis]]'' for amino acids.<ref name="Biedermann-Vega-2020">{{cite journal | last1=Biedermann | first1=Peter H.W. | last2=Vega | first2=Fernando E. | title=Ecology and Evolution of Insect–Fungus Mutualisms | journal=[[Annual Review of Entomology]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=65 | issue=1 | date=2020-01-07 | issn=0066-4170 | doi=10.1146/annurev-ento-011019-024910 | pages=431–455| pmid=31610133 | s2cid=204704243 | doi-access=free }}</ref>

===Mutualism breakdown===

Mutualisms are not static, and can be lost by evolution.<ref name=SachsSimms2006>{{cite journal | last1=Sachs | first1=JL | last2=Simms | first2=EL |title=Pathways to mutualism breakdown|journal=TREE|volume=21 |issue=10 |pages=585–592 |date=2006 |doi=10.1016/j.tree.2006.06.018|pmid=16828927| bibcode=2006TEcoE..21..585S }}</ref> Sachs and Simms (2006) suggest that this can occur via four main pathways:
# One mutualist shifts to parasitism, and no longer benefits its partner,<ref name=SachsSimms2006 /> such as headlice<ref name="RÓZSA-2012">{{Cite journal |last1=RÓZSA |first1=LAJOS |last2=APARI |first2=PÉTER |date=2012-02-06 |title=Why infest the loved ones – inherent human behaviour indicates former mutualism with head lice |url=http://dx.doi.org/10.1017/s0031182012000017 |journal=Parasitology |volume=139 |issue=6 |pages=696–700 |doi=10.1017/s0031182012000017 |pmid=22309598 |s2cid=206247019 |issn=0031-1820|url-access=subscription }}</ref>
# One partner abandons the mutualism and lives autonomously<ref name=SachsSimms2006 />
# One partner may go extinct<ref name=SachsSimms2006 />
# A partner may be switched to another species<ref name="Werner-et-al-2018">{{cite journal | last1=Werner | first1=Gijsbert D. A. | last2=Cornelissen | first2=Johannes H. C. | last3=Cornwell | first3=William K. | last4=Soudzilovskaia | first4=Nadejda A. | last5=Kattge | first5=Jens | last6=West | first6=Stuart A. | last7=Kiers | first7=E. Toby | title=Symbiont switching and alternative resource acquisition strategies drive mutualism breakdown | journal=[[Proceedings of the National Academy of Sciences]] | publisher=[[National Academy of Sciences]] | volume=115 | issue=20 | date=2018-04-30 | issn=0027-8424 | doi=10.1073/pnas.1721629115 | pages=5229–34 | pmid=29712857 | pmc=5960305 | bibcode=2018PNAS..115.5229W | s2cid=14055644| doi-access=free }}</ref>

There are many examples of mutualism breakdown. For example, plant lineages inhabiting nutrient-rich environments have evolutionarily abandoned mycorrhizal mutualisms many times independently.<ref name="Wang-Qiu-2006">{{cite journal | last1=Wang | first1=B. | last2=Qiu | first2=Y.-L. | title=Phylogenetic distribution and evolution of mycorrhizas in land plants | journal=Mycorrhiza | publisher=[[International Mycorrhiza Society]] ([[Springer Science+Business Media|Springer]]) | volume=16 | issue=5 | date=2006-05-06 | issn=0940-6360 | doi=10.1007/s00572-005-0033-6 | pages=299–363 | pmid=16845554 | bibcode=2006Mycor..16..299W | s2cid=30468942}}</ref> Evolutionarily, headlice may have been mutualistic as they allow for early immunity to various body-louse borne disease; however, as these diseases became eradicated, the relationship has become less mutualistic and more parasitic.<ref name="RÓZSA-2012" />

==Measuring and defining mutualism==

Measuring the exact [[Fitness (biology)|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 mutualism|obligate]] and [[WIKT:facultative|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).<ref name="Ollerton06">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.</ref> =)

==See also==
* [[Arbuscular mycorrhiza]]
* [[Co-adaptation]]
* [[Coevolution]]
* [[Ecological facilitation]]
* [[Frugivore]]
* [[Greater honeyguide]] – has a mutualism with humans
* [[Interspecies communication]]
* [[Müllerian mimicry]]
* [[Mutualisms and conservation]]
* ''[[Mutual Aid: A Factor of Evolution]]''
* [[Symbiogenesis]]
* [[Plant–animal interaction]]

==References==
{{reflist}}

==Further references==
{{refbegin}}
* {{cite news | url=https://www.nytimes.com/2016/07/23/science/birds-bees-honeyguides-africa.html | title=African Tribesmen Can Talk Birds into Helping Them Find Honey | newspaper=[[The New York Times]] | date=22 July 2016| author=Angier, Natalie| author-link= Natalie Angier}}
* {{cite journal | last1=Bascompte | first1=J. | last2=Jordano | first2=P. | last3=Melián | first3=C. J. | last4=Olesen | first4=J. M. | year=2003 | title=The nested assembly of plant–animal mutualistic networks | journal=[[Proceedings of the National Academy of Sciences]] | volume=100 | issue=16| pages=9383–7 | doi=10.1073/pnas.1633576100 | pmid=12881488 | pmc=170927| bibcode=2003PNAS..100.9383B | doi-access=free }}
* {{cite journal | last1=Bastolla | first1=U. | last2=Fortuna | first2=M. A. | last3=Pascual-García | first3=A. | last4=Ferrera | first4=A. | last5=Luque | first5=B. | last6=Bascompte | first6=J. | year=2009 | title=The architecture of mutualistic networks minimizes competition and increases biodiversity | journal=Nature | volume=458 | issue=7241| pages=1018–20 | doi=10.1038/nature07950 | pmid=19396144| bibcode=2009Natur.458.1018B | s2cid=4395634 }}
* {{cite journal | last1=Breton | first1=Lorraine M. | last2=Addicott | first2=John F. | year=1992 | title=Density-Dependent Mutualism in an Aphid-Ant Interaction | journal=[[Ecology (journal)|Ecology]] | volume=73 | issue=6| pages=2175–80 | doi=10.2307/1941465| jstor=1941465 | bibcode=1992Ecol...73.2175B }}
* {{cite journal | last1=Bronstein | first1=JL | year=1994 | title=Our current understanding of mutualism | journal=[[Quarterly Review of Biology]] | volume=69 | issue=1| pages=31–51 | doi=10.1086/418432| s2cid=85294431 }}
* {{cite journal | last1=Bronstein | first1=JL | year=2001 | title=The exploitation of mutualisms | journal=[[Ecology Letters]] | volume=4 | issue=3| pages=277–287 | doi=10.1046/j.1461-0248.2001.00218.x| doi-access=free | bibcode=2001EcolL...4..277B }}
* Bronstein JL. 2001. The costs of mutualism. ''[[American Zoologist]]'' 41 (4): 825-839 S
* {{cite journal | last1=Bronstein | first1=JL | last2=Alarcon | first2=R | last3=Geber | first3=M | year=2006 | title=The evolution of plant-insect mutualisms | journal=[[New Phytologist]] | volume=172 | issue=3| pages=412–28 | doi=10.1111/j.1469-8137.2006.01864.x | pmid=17083673| doi-access=free | bibcode=2006NewPh.172..412B }}
* {{cite journal | last1=Denison | first1=RF | last2=Kiers | first2=ET | year=2004 | title=Why are most rhizobia beneficial to their plant hosts, rather than parasitic? | journal=[[Microbes and Infection]] | volume=6 | issue=13| pages=1235–9 | doi=10.1016/j.micinf.2004.08.005| pmid=15488744 | doi-access=free }}
* {{cite journal | last1=DeVries | first1=PJ | last2=Baker | first2=I | year=1989 | title=Butterfly exploitation of an ant-plant mutualism: Adding insult of herbivory | journal=Journal of the New York Entomological Society | volume=97 | issue=3| pages=332–340 }}
* {{cite journal | last1=Hoeksema | first1=J.D. | last2=Bruna | first2=E.M. | year=2000 | title=Pursuing the big questions about interspecific mutualism: a review of theoretical approaches | journal=[[Oecologia]] | volume=125 | issue=3| pages=321–330 | doi=10.1007/s004420000496| pmid=28547326 | bibcode=2000Oecol.125..321H | s2cid=22756212 }}
* {{cite journal | last1=Jahn | first1=G.C. | last2=Beardsley | first2=J.W. | year=2000 | title=Interactions of ants (Hymenoptera: Formicidae) and mealybugs (Homoptera: Pseudococcidae) on pineapple | journal=Proceedings of the Hawaiian Entomological Society | volume=34 | pages=181–5 |hdl=10125/8370 }}
* {{cite journal | last1=Jahn | first1=Gary C. | last2=Beardsley | first2=J. W. | last3=González-Hernández | first3=H. | year=2003 | title=A review of the association of ants with mealybug wilt disease of pineapple | url=https://scholarspace.manoa.hawaii.edu/bitstream/10125/95/1/36_9-28.pdf | journal=Proceedings of the Hawaiian Entomological Society | volume=36 | pages=9–28 |hdl=10125/95 }}
* {{cite journal | last1=Lever | first1=J. J. | last2=Nes | first2=E. H. | last3=Scheffer | first3=M. | last4=Bascompte | first4=J. | year=2014 | title=The sudden collapse of pollinator communities | journal=[[Ecology Letters]] | volume=17 | issue=3| pages=350–9 | doi=10.1111/ele.12236| pmid=24386999 | bibcode=2014EcolL..17..350L | hdl=10261/91808 | hdl-access=free }}
* {{cite journal | last1=Noe | first1=R. | last2=Hammerstein | first2=P. | year=1994 | title=Biological markets: supply and demand determine the effect of partner choice in cooperation, mutualism and mating | journal=[[Behavioral Ecology and Sociobiology]] | volume=35 | issue=1 | pages=1–11 | doi=10.1007/bf00167053| bibcode=1994BEcoS..35....1N | s2cid=37085820 }}
* {{cite book |last=Ollerton |first=J. |chapter="Biological Barter": Patterns of Specialization Compared across Different Mutualisms |editor-last=Waser |editor-first=N.M. |editor2-last=Ollerton |editor2-first=J. |title=Plant-Pollinator Interactions: From Specialization to Generalization |publisher=University of Chicago Press |date=2006 |isbn=978-0-226-87400-5 |pages=411–435 |oclc=1109234356 }}
* {{cite journal | last1=Paszkowski | first1=U | year=2006 | title=Mutualism and parasitism: the yin and yang of plant symbioses | journal=[[Current Opinion in Plant Biology]] | volume=9 | issue=4| pages=364–370 | doi=10.1016/j.pbi.2006.05.008 | pmid=16713732 | bibcode=2006COPB....9..364P }}
* {{cite journal | last1=Porat | first1=D. | last2=Chadwick-Furman | first2=N. E. | year=2004 | title=Effects of anemonefish on giant sea anemones:expansion behavior, growth, and survival | journal=[[Hydrobiologia]] | volume=530 | issue=1–3| pages=513–520 | doi=10.1007/s10750-004-2688-y | bibcode=2004HyBio.530..513P | s2cid=2251533 }}
* {{cite journal | last1=Porat | first1=D. | last2=Chadwick-Furman | first2=N. E. | year=2005 | title=Effects of anemonefish on giant sea anemones: ammonium uptake, zooxanthella content and tissue regeneration | journal=Mar. Freshw. Behav. Phys. | volume=38 | issue=1 | pages=43–51 | doi= 10.1080/10236240500057929| bibcode=2005MFBP...38...43P | s2cid=53051081 }}
* Thompson, J. N. 2005. ''The Geographic Mosaic of Coevolution''. University of Chicago Press. {{ISBN|978-0-226-79762-5}}
* {{cite journal | last1=Wright | first1=David Hamilton | year=1989 | title=A Simple, Stable Model of Mutualism Incorporating Handling Time | journal=[[The American Naturalist]] | volume=134 | issue=4| pages=664–7 | doi=10.1086/285003| bibcode=1989ANat..134..664W | s2cid=83502337 }}
{{refend}}
<!-- Don't add articles here; the list is alphabetical, but it'll be more use to use and cite articles inline to some visible purpose. -->

==Further reading==
{{Commons category|Mutualism (biology)}}
{{Wiktionary}}
* {{cite journal | last1=Boucher | first1=D. G. | last2=James | first2=S. | last3=Keeler | first3=K. | year=1984 | title=The ecology of mutualism | journal=[[Annual Review of Ecology and Systematics]] | volume=13 | pages=315–347 | doi=10.1146/annurev.es.13.110182.001531}}
* {{cite book |first=D.H. |last=Boucher |title=The Biology of Mutualism : Ecology and Evolution |publisher=Oxford University Press |date=1985 |isbn=0-7099-3238-3 |oclc=11971241}}

{{Biological interaction-footer}}
{{evo ecol}}
{{Evolution}}
{{collective animal behaviour}}
{{modelling ecosystems|expanded=none}}
{{Authority control}}

{{DEFAULTSORT:Mutualism (Biology)}}
[[Category:Mutualism (biology)| ]]
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