View source for Keystone species

{{Short description|Species with a large effect on its environment}}
{{distinguish|foundation species}}
{{good article}}
[[File:Junior-Jaguar-Belize-Zoo.jpg|thumb|The [[jaguar]]: a keystone, [[flagship species|flagship]], and 
[[umbrella species]], and an [[apex predator]] ]]
[[File:American Beaver.jpg|thumb|The [[beaver]]: a keystone species, and [[habitat]] creator, [[Environmental impacts of beavers|responsible for ecological effects]] such as the creation of [[lakes]], [[canals]] and [[wetlands]] irrigating large forests and creating [[ecosystems]] ]]
A '''keystone species''' is a [[species]] that has a disproportionately large effect on its [[natural environment]] relative to its abundance. The concept was introduced in 1969 by the zoologist [[Robert T. Paine (zoologist)|Robert T. Paine]]. Keystone species play a critical role in maintaining the structure of an [[ecological community]], affecting many other [[organism]]s in an [[ecosystem]] and helping to determine the types and numbers of various other species in the community. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. Some keystone species, such as the [[wolf]] and [[lion]], are also [[apex predator]]s.

The role that a keystone species plays in its ecosystem is analogous to the role of a [[keystone (architecture)|keystone]] in an [[arch]]. While the keystone is under the least pressure of any of the stones in an arch, the arch still collapses without it. Similarly, an ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of [[biomass (ecology)|biomass]] or [[Productivity (ecology)|productivity]].
It became a popular concept in [[conservation biology]], alongside [[flagship species|flagship]] and [[umbrella species]]. Although the concept is valued as a descriptor for particularly strong inter-species interactions, and has allowed easier communication between ecologists and conservation policy-makers, it has been criticized for oversimplifying complex ecological systems.

== History ==

{{multiple image
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|caption1 = Ochre seastars (''[[Pisaster ochraceus]]''), a keystone [[predator]]
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|caption2 = California mussels (''[[Mytilus californianus]]''), the seastar's prey
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[[File:Keystone species.jpg|thumb|Keystone species will disrupt the environment if removed, And when kept they regulate the environment.]]
The concept of the keystone species was introduced in 1969 by zoologist [[Robert T. Paine (zoologist)|Robert T. Paine]].<ref name="paine1969">{{cite journal |last=Paine |first=R. T. |year=1969 |title=A Note on Trophic Complexity and Community Stability |journal=The American Naturalist |volume=103 |issue=929 |pages=91–93 |doi=10.1086/282586 |jstor=2459472 |bibcode=1969ANat..103...91P |s2cid=83780992 }}</ref><ref>{{cite web|title=Keystone Species Hypothesis |url=http://www.washington.edu/research/pathbreakers/1969g.html |publisher=University of Washington |access-date=2011-02-03 |url-status=dead |archive-url=https://web.archive.org/web/20110110060757/http://www.washington.edu/research/pathbreakers/1969g.html |archive-date=2011-01-10}}</ref> Paine developed the concept to explain his observations and experiments on the relationships between [[marine invertebrate]]s of the [[intertidal zone]] (between the high and low tide lines), including [[starfish]] and [[mussel]]s. He removed the starfish from an area, and documented the effects on the ecosystem.<ref name="mills1993"/> In his 1966 paper, ''Food Web Complexity and Species Diversity'', Paine had described such a system in [[Neah Bay, Washington|Makah Bay]] in [[Washington (state)|Washington]].<ref name="paine1966">{{cite journal |last=Paine |first=R. T. |year=1966 |title=Food Web Complexity and Species Diversity |journal=The American Naturalist |volume=100 |issue=910 |pages=65–75 |doi=10.1086/282400 |jstor=2459379 |bibcode=1966ANat..100...65P |s2cid=85265656 }}</ref>
In his 1969 paper, Paine proposed the keystone species concept, using ''[[Pisaster ochraceus]]'', a species of starfish generally known as ochre starfish, and ''[[Mytilus californianus]]'', a species of mussel, as a primary example.<ref name="paine1969"/> The ochre starfish is a generalist predator and feeds on chitons, limpets, snails, barnacles, echinoids, and even decapod crustacea. The favourite food for these starfish is the mussel which is a dominant competitor for the space on the rocks. The ochre starfish keeps the population numbers of the mussels in check along with the other preys allowing the other seaweeds, sponges, and anemones, that ochre starfish do not consume, to co-exist. When Paine removed the ochre starfish, the mussels quickly outgrew the other species crowding them out. At the start, the rock pools held 15 rock-clinging species. Three years later there were 8 such species; and ten years later the pools were largely occupied by a single species, mussels. The concept became popular in conservation, and was deployed in a range of contexts and mobilized to engender support for conservation, especially where human activities had damaged ecosystems, such as by removing keystone predators.<ref name="Barua Metaphor">{{cite journal |last=Barua |first=Maan |title=Mobilizing metaphors: the popular use of keystone, flagship and umbrella species concepts |journal=Biodiversity and Conservation |volume=20 |issue=7 |year=2011 |doi=10.1007/s10531-011-0035-y |pages=1427–1440|bibcode=2011BiCon..20.1427B |s2cid=11030284 }}</ref><ref>{{cite web |last=Sezen |first=Uzay |title=Some Animals Are More Equal than Others: Keystone Species and Trophic Cascades |website=Nature Documentaries |date=29 May 2017 |url=http://naturedocumentaries.org/14877/animals-equal-others-keystone-species-trophic-cascades-hhmi-2016/ |access-date=6 June 2017}}</ref><ref name="Evans 2024">{{cite web |last=Ogwen |first=Lesley Evans |title=Ecologists Struggle to Get a Grip on 'Keystone Species' |url=https://www.quantamagazine.org/ecologists-struggle-to-get-a-grip-on-keystone-species-20240424/ |publisher=Quanta Magazine |access-date=1 May 2024 |date=24 April 2024}}</ref>

== Definitions ==

A keystone species was defined by Paine as a [[species]] that has a disproportionately large effect on its [[natural environment|environment]] relative to its abundance.<ref name="paine1995">{{cite journal |author=Paine, R. T. |year=1995 |title=A Conversation on Refining the Concept of Keystone Species |journal=Conservation Biology |volume=9 |issue=4 |pages=962–964 |doi=10.1046/j.1523-1739.1995.09040962.x|bibcode=1995ConBi...9..962P }}</ref> It has been defined operationally by Davic in 2003 as "a strongly interacting species whose top-down effect on [[biodiversity|species diversity]] and [[competition (biology)|competition]] is large relative to its [[biomass]] dominance within a functional group."<ref name=Davic2003>{{cite journal |title=Linking Keystone Species and Functional Groups: A New Operational Definition of the Keystone Species Concept|url=http://www.consecol.org/vol7/iss1/resp11/ |author=Davic, R. D. |journal=Conservation Ecology |year=2003 |volume=7 |article-number=resp11 |doi=10.5751/ES-00502-0701r11 |hdl=10535/2966 |access-date=2011-02-03|hdl-access=free |url-access=subscription }}</ref>

A classic keystone species is a [[predator]] that prevents a particular [[herbivorous]] species from eliminating dominant [[plant]] species. If prey numbers are low, keystone predators can be even less abundant and still be effective. Yet without the predators, the herbivorous prey would explode in numbers, wipe out the dominant plants, and dramatically alter the character of the ecosystem. The exact scenario changes in each example, but the central idea remains that through a chain of interactions, a non-abundant species has an outsized impact on ecosystem functions. For example, the herbivorous [[weevil]] ''[[Euhrychiopsis lecontei]]'' is thought to have keystone effects on aquatic plant diversity by foraging on nuisance [[Myriophyllum spicatum|Eurasian watermilfoil]] in North American waters.<ref name="creed2000">{{cite journal |author=Creed, R. P. Jr. |year=2000 |title=Is there a new keystone species in North American lakes and rivers? |journal=OIKOS |volume=91 |issue=2 |doi=10.1034/j.1600-0706.2000.910222.x |page=405|bibcode=2000Oikos..91..405C }}</ref> Similarly, the wasp species ''[[Agelaia vicina]]'' has been labeled a keystone species for its unparalleled nest size, colony size, and high rate of brood production. The diversity of its prey and the quantity necessary to sustain its high rate of growth have a direct impact on other species around it.<ref name="paine1995"/>

The keystone concept is defined by its ecological effects, and these in turn make it important for conservation. In this it overlaps with several other species conservation concepts such as [[flagship species]], [[indicator species]], and [[umbrella species]]. For example, the [[jaguar]] is a charismatic big cat which meets all of these definitions:<ref name=Maehr2001>{{cite book |last1=Maehr |first1=David |last2=Noss |first2=Reed F. |last3=Larkin |first3=Jeffery L. |title=Large Mammal Restoration: Ecological And Sociological Challenges In The 21St Century |url=https://books.google.com/books?id=x3n_pBQFxVQC&pg=PA73 |year=2001 |publisher=Island Press |isbn=978-1-55963-817-3 |page=73}}</ref>

{{blockquote|The jaguar is an umbrella species, flagship species, and wilderness quality indicator. It promotes the goals of carnivore recovery, protecting and restoring connectivity through Madrean woodland and riparian areas, and protecting and restoring riparian areas. ... A reserve system that protects jaguars is an umbrella for many other species. ... the jaguar [is] a keystone in subtropical and tropical America ...|David Maehr et al, 2001<ref name=Maehr2001/>}}

== Predators ==

=== Sea otters and kelp forests ===

{{multiple image
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|caption1 = Sea urchins like this [[Strongylocentrotus purpuratus|purple sea urchin]] can damage kelp forests by chewing through kelp [[holdfast (biology)|holdfast]]s
|image2 = Mother sea otter with rare twin baby pups (9137174915).jpg
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|caption2 = The [[sea otter]] is an important predator of [[sea urchin]]s, making it a keystone species for the kelp forests.
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[[Sea otters]] protect [[kelp forest]]s from damage by sea urchins. When the sea otters of the North American west coast were hunted commercially for their fur, their numbers fell to such low levels – fewer than 1000 in the north Pacific ocean – that they were unable to control the sea urchin population. The urchins, in turn, grazed the [[holdfast (biology)|holdfast]]s of [[kelp]] so heavily that the kelp forests largely disappeared, along with all the species that depended on them. Reintroducing the sea otters has enabled the kelp ecosystem to be restored. For example, in Southeast Alaska some 400 sea otters were released, and they have bred to form a population approaching 25,000.<ref name="Szpak2013">{{cite journal |last1=Szpak |first1=Paul |last2=Orchard |first2=Trevor J. |last3=Salomon |first3=Anne K. |last4=Gröcke |first4=Darren R. |title=Regional ecological variability and impact of the maritime fur trade on nearshore ecosystems in southern Haida Gwaii (British Columbia, Canada): evidence from stable isotope analysis of rockfish (Sebastes spp.) bone collagen |journal=Archaeological and Anthropological Sciences |volume=5 |issue=2 |year=2013 |doi=10.1007/s12520-013-0122-y |pages=159–182|bibcode=2013ArAnS...5..159S |s2cid=84866250 |url=https://durham-repository.worktribe.com/output/1428483 }}</ref><ref name="estes1978">{{cite journal |last=Estes |first=James E. |author2=Smith, Norman S. |author3=Palmisano, John F. |year=1978 |title=Sea otter predation and community organization in the Western Aleutian Islands, Alaska|journal=Ecology |volume=59 |issue=4 |pages=822–833 |doi=10.2307/1938786 |jstor=1938786|bibcode=1978Ecol...59..822E }}</ref><ref name="cohn1998">{{cite journal |last=Cohn |first=J. P. |year=1998 |title=Understanding Sea Otters |journal=BioScience |volume=48 |issue=3 |pages=151–155 |doi=10.2307/1313259 |jstor=1313259|doi-access=free }}</ref><ref>{{cite web |last=Brown |first=Tina M. |title=My Turn: Southeast Alaska's sea otters: The restoration of an ecosystem |url=http://juneauempire.com/opinion/2013-03-14/my-turn-southeast-alaskas-sea-otters-restoration-ecosystem |publisher=Juneau Empire |access-date=23 April 2018 |date=14 March 2013 |archive-url=https://web.archive.org/web/20180423232435/http://juneauempire.com/opinion/2013-03-14/my-turn-southeast-alaskas-sea-otters-restoration-ecosystem |archive-date=23 April 2018 |url-status=dead }}</ref>

=== The wolf, Yellowstone's apex predator ===

[[File:Fig. 1 -Riparian willow recovery (26485120926) horiz.jpg|thumb|upright=2<!--double image-->|Riparian willow recovery at Blacktail Creek, [[Yellowstone National Park]], showing effect of the reintroduction of wolves]]

{{further|Apex predator}}

Keystone predators may increase the [[biodiversity]] of communities by preventing a single species from becoming dominant. They can have a profound influence on the balance of organisms in a particular [[ecosystem]]. Introduction or removal of a keystone predator, or changes in its population density, can have drastic cascading effects on the equilibrium of many other populations in the ecosystem. For example, grazers of a grassland may prevent a single dominant species from taking over.<ref>{{cite book |last1=Botkin |first1=D. |last2=Keller |first2=E. |date=2003 |title=Environmental Science: Earth as a living planet |publisher=John Wiley & Sons |isbn=978-0-471-38914-9 |page=2}}</ref>

The elimination of the [[gray wolf]] from the [[Greater Yellowstone Ecosystem]] had profound impacts on the [[trophic pyramid]].<ref>{{Cite journal |last1=Wilmers |first1=Christopher C. |last2=Crabtree |first2=Robert L. |last3=Smith |first3=Douglas W. |last4=Murphy |first4=Kerry M. |last5=Getz |first5=Wayne M. |date=November 2003 |title=Trophic facilitation by introduced top predators: grey wolf subsidies to scavengers in Yellowstone National Park |journal=Journal of Animal Ecology |language=en |volume=72 |issue=6 |pages=909–916 |doi=10.1046/j.1365-2656.2003.00766.x |issn=0021-8790|doi-access=free |bibcode=2003JAnEc..72..909W }}</ref> Without predation, herbivores began to over-graze many woody browse species, affecting the area's plant populations. In addition, wolves often kept animals from grazing in riparian areas, which protected beavers from having their food sources encroached upon. The removal of wolves had a direct effect on beaver populations, as their habitat became grazing territory. Increased browsing on willows and conifers along Blacktail Creek due to a lack of predation caused channel incision because the [[Environmental impacts of beavers|beavers helped slow the water down]], allowing soil to stay in place. Furthermore, predation keeps hydrological features such as creeks and streams in normal working order. When wolves were reintroduced, the beaver population and the whole riparian ecosystem recovered dramatically within a few years.<ref name="Ripple2004">{{cite journal |last1=Ripple |first1=William J. |last2=Beschta |first2=Robert L. |title=Wolves and the Ecology of Fear: Can Predation Risk Structure Ecosystems? |journal=BioScience |publisher=Oxford University Press  |volume=54 |issue=8 |year=2004 |doi=10.1641/0006-3568(2004)054[0755:WATEOF]2.0.CO;2 |page=755 |doi-access=free }}</ref>

=== Sea stars and other non-apex predators ===

As described by Paine in 1966, some [[sea stars]] (e.g., ''[[Pisaster ochraceus]]'') may prey on [[sea urchin]]s, [[mussel]]s, and other [[shellfish]] that have no other natural predators.<ref>{{Cite journal |last1=Cottee-Jones |first1=Henry Eden W |last2=Whittaker |first2=Robert J. |date=2012-09-28 |title=perspective: The keystone species concept: a critical appraisal |url=https://escholarship.org/uc/item/15d2b65t |journal=Frontiers of Biogeography |volume=4 |issue=3 |doi=10.21425/F54312533 |issn=1948-6596|doi-access=free }}</ref> If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species.<ref name="paine1966" /> 

These creatures need not be [[apex predator]]s. Sea stars are prey for [[sharks]], [[Ray (fish)|rays]], and [[sea anemones]]. Sea otters are prey for [[orca]].<ref name="estes1998">{{cite journal |last1=Estes |first1=J. A. |author2=Tinker, M. T. |author3=Williams, T. M. |author4= Doak, D. F. |date=1998-10-16 |title=Killer whale predation on sea otters linking oceanic and nearshore ecosystems |journal=Science |volume=282 |issue=5388 |pages=473–476 |doi=10.1126/science.282.5388.473 |bibcode=1998Sci...282..473E |pmid=9774274|s2cid=8925215 }}</ref>

The [[jaguar]], whose numbers in Central and South America have been classified as [[near threatened]], acts as a keystone predator by its widely varied diet, helping to balance the [[mammalian]] jungle ecosystem with its consumption of 87 different species of prey.<ref>{{cite book |editor1=Nowell, K. |editor2=Jackson, P. |date=1996 |title=Wild Cats, Status Survey and Conservation Action Plan |publisher=IUCN/SSC Cat Specialist Group |chapter=''Panthera onca'' |isbn=978-2-8317-0045-8 |pages=118–122 |url=https://portals.iucn.org/library/node/6998}}</ref> The [[lion]] is another keystone species.<ref name="HaleKoprowski2018">{{cite journal |last1=Hale |first1=Sarah L. |last2=Koprowski |first2=John L. |title=Ecosystem-level effects of keystone species reintroduction: a literature review |journal=Restoration Ecology |volume=26 |issue=3 |pages=439–445 |date=February 2018 |doi=10.1111/rec.12684 |bibcode=2018ResEc..26..439H |s2cid=53686934 }}</ref>

[[File:Banksia prionotes 3 gnangarra.jpg|thumb|Acorn banksia, ''[[Banksia prionotes]]'', is periodically the sole source of nectar for important [[pollinator]]s, [[honeyeater]]s.]]

== Mutualists ==

Keystone mutualists are organisms that participate in mutually beneficial interaction, the loss of which would have a profound impact upon the ecosystem as a whole. For example, in the [[Avon Wheatbelt]] region of [[Western Australia]], there is a period of each year when ''[[Banksia prionotes]]'' (acorn banksia) is the sole source of [[nectar]] for [[honeyeater]]s, which play an important role in [[pollination]] of numerous plant species. Therefore, the loss of this one species of tree would probably cause the honeyeater population to collapse, with profound implications for the entire ecosystem. Another example is [[frugivores]], such as the [[cassowary]], which spreads the seeds of many different trees. Some seeds will not grow unless they have been through a cassowary.<ref name="Lambeck 1999">{{cite book |title=Landscape Planning for Biodiversity Conservation in Agricultural Regions: A Case Study from the Wheatbelt of Western Australia |version=Biodiversity Technical Paper No. 2 |first=Robert J. |last=Lambeck |publisher=[[CSIRO]] Division of Wildlife and Ecology |year=1999 |isbn=978-0-642-21423-2}}</ref><ref name="Walker 1995">{{cite journal |title=Conserving Biological Diversity through Ecosystem Resilience |first=Brian |last=Walker |journal=Conservation Biology |volume=9 |issue=4 |year=1995 |pages=747–752 |doi=10.1046/j.1523-1739.1995.09040747.x|bibcode=1995ConBi...9..747W }}</ref>

== Ecosystem engineers ==

[[File:PrairieDogTownGregg.jpg|thumb|left|[[Prairie dog]] town. Drawing by [[Josiah Gregg]], 1844]]

{{further|Ecosystem engineer|Niche construction}}

A term used alongside keystone is [[ecosystem engineer]].<ref name="Barua Metaphor"/> In [[North America]], the [[prairie dog]] is an ecosystem engineer. Prairie dog burrows provide the nesting areas for [[mountain plover]]s and [[burrowing owl]]s. Prairie dog tunnel systems also help channel rainwater into the [[water table]] to prevent [[surface runoff|runoff]] and [[erosion]], and can also serve to change the composition of the soil in a region by increasing [[aeration]] and reversing soil compaction that can be a result of cattle grazing. Prairie dogs also trim the vegetation around their colonies, perhaps to remove any cover for predators.<ref name="NGPC">{{cite web |url=http://www.ngpc.state.ne.us/wildlife/prairiedogs.asp  |title=Prairie Dogs |website=Wildlife Species Guide |publisher=Nebraska Game and Park Commission |access-date=10 November 2013 |url-status=dead |archive-url=https://web.archive.org/web/20090819031734/http://www.ngpc.state.ne.us/wildlife/prairiedogs.asp |archive-date=19 August 2009}}</ref> Grazing species such as [[plains bison]], which is another keystone species, the [[pronghorn]], and the [[mule deer]] have shown a proclivity for grazing on the same land used by prairie dogs.<ref name="Rosmarino2007">{{cite web |url=http://www.prairiedogcoalition.org/pd-associated-species.php |last=Rosmarino |first=Nicole |year=2007 |title=Associated Species : Prairie Dogs are a Keystone Species of the Great Plains |publisher=Prairie Dog Coalition |access-date=10 November 2013 |url-status=dead |archive-url=https://web.archive.org/web/20131110163932/http://www.prairiedogcoalition.org/pd-associated-species.php |archive-date=10 November 2013}}</ref>

[[File:BeaverDam 8409.jpg|thumb|Beaver dam, an [[structures built by animals|animal construction]] which has a transformative effect on the environment]]

The [[beaver]] is a well known ecosystem engineer and keystone species. It transforms its territory from a stream to a pond or swamp. Beavers affect the environment first altering the edges of [[riparian]] areas by cutting down older trees to use for their dams. This allows younger trees to take their place. Beaver dams alter the riparian area they are established in. Depending on topography, soils, and many factors, these dams change the riparian edges of streams and rivers into wetlands, meadows, or riverine forests. These dams have been shown to be beneficial to a myriad of species including amphibians, salmon, and song birds.<ref name="wright2002">{{cite journal |last1=Wright |first1=J. P. |author2=Jones, C. G. |author3=Flecker, A. S. |year=2002 |title=An ecosystem engineer, the beaver, increases species richness at the landscape scale |journal=Oecologia |volume=132 |issue=1 |pages=96–101 |doi=10.1007/s00442-002-0929-1|pmid=28547281 |bibcode=2002Oecol.132...96W |s2cid=5940275 }}</ref>

In the African [[savanna]], the larger herbivores, especially the [[elephants]], shape their environment. The elephants destroy trees, making room for the grass species and creating habitat for various small animal species.<ref>{{Cite journal |last=Pringle |first=Robert M. |date=2008 |title=Elephants as agents of habitat creation for small vertebrates at the patch scale |url=http://doi.wiley.com/10.1890/07-0776.1 |journal=Ecology |volume=89 |issue=1 |pages=26–33 |doi=10.1890/07-0776.1 |pmid=18376543 |bibcode=2008Ecol...89...26P |issn=0012-9658|url-access=subscription }}</ref><ref>{{Cite journal |last1=Coverdale |first1=Tyler C. |last2=Kartzinel |first2=Tyler R. |last3=Grabowski |first3=Kathryn L. |last4=Shriver |first4=Robert K. |last5=Hassan |first5=Abdikadir A. |last6=Goheen |first6=Jacob R. |last7=Palmer |first7=Todd M. |last8=Pringle |first8=Robert M. |date=2016 |title=Elephants in the understory: opposing direct and indirect effects of consumption and ecosystem engineering by megaherbivores |url=https://onlinelibrary.wiley.com/doi/10.1002/ecy.1557 |journal=Ecology |language=en |volume=97 |issue=11 |pages=3219–3230 |doi=10.1002/ecy.1557 |pmid=27870025 |bibcode=2016Ecol...97.3219C |issn=0012-9658|url-access=subscription }}</ref> Without these animals, much of the savanna would turn into [[woodland]].<ref name="leakey1995">{{cite book |last1=Leakey |first1=Richard |author1-link=Richard Leakey |first2=Roger |last2=Lewin |author2-link=Roger Lewin |title=The sixth extinction: biodiversity and its survival |year=1999 |publisher=Phoenix |isbn=1-85799-473-6 |pages=216–217 |chapter=11 The modern elephant story |orig-year=1995}}</ref>
In the [[Amazon river basin]], [[peccaries]] produce and maintain [[wallow]]s that are utilized by a wide variety of species.<ref>{{Cite web|url=https://news.mongabay.com/2010/09/how-the-overlooked-peccary-engineers-the-amazon-an-interview-with-harald-beck/|title = How the overlooked peccary engineers the Amazon, an interview with Harald Beck|date = 20 September 2010}}</ref><ref>{{Cite web|url=https://www.nationalgeographic.com/news/2014/9/140927-peccary-wallow-amazon-rainforest-camera-trap-biodiversity-science/|archive-url=https://web.archive.org/web/20200418080154/https://www.nationalgeographic.com/news/2014/9/140927-peccary-wallow-amazon-rainforest-camera-trap-biodiversity-science/|url-status=dead|archive-date=April 18, 2020|title=Where Peccaries Wallow, Other Animals Follow|website=[[National Geographic Society]] |date=27 September 2014}}</ref>
Australian studies have found that [[parrotfish]] on the [[Great Barrier Reef]] are the only reef fish that consistently scrape and clean the coral on the reef. Without these animals, the Great Barrier Reef would be under severe strain.<ref>{{cite web |last=Gruber |first=Karl |url=http://www.australiangeographic.com.au/news/2014/09/single-keystone-species-may-be-key-to-reef-health/ |title=Single keystone species may be the key to reef health |publisher=Australian Geographic |date=26 September 2014}}</ref>

In the [[Serengeti]], the presence of sufficient [[gnu]]s in these grasslands reduces [[wildfire]] likelihood, which in turn promotes tree growth. The documentary [[The Serengeti Rules]] documents this in detail.<ref>[https://www.pbs.org/wnet/nature/how-wildebeest-saved-serengeti-az7odc/19932/ How Wildebeest Saved the Serengeti]</ref>
<!--please do not add examples here, this is NOT A LIST of all possible engineers-->

== Limitations ==

=== Depends on context ===

The community ecologist Bruce Menge states that the keystone concept has been stretched far beyond Paine's original concept.  That stretching can be quantified: the researcher Ishana Shukla has listed 230 species identified as keystones in some 157 studies in the 50 years since Paine's paper. Menge's own work has shown that the purple ''Pisaster'' sea star that Paine had studied was a powerful keystone species in places exposed to strong wave action, but was far less important in sheltered places. Paine had indeed stated that in Alaska, without the relevant mussel species as prey, the predatory ''Pisaster'' was "just another sea star". In other words, the extent to which a species could be described as a keystone depended on the ecological context.<ref name="Evans 2024"/>

=== Multiple meanings ===

Although the concept of the keystone species has a value in describing particularly strong inter-species interactions, and for allowing easier communication between ecologists and conservation policy-makers, it has been criticized by L. S. Mills and colleagues for oversimplifying complex ecological systems. The term has been applied widely in different ecosystems and to predators, prey, and plants (primary producers), inevitably with differing ecological meanings. For instance, removing a predator may allow other animals to increase to the point where they wipe out other species; removing a prey species may cause predator populations to crash, or may allow predators to drive other prey species to extinction; and removing a plant species may result in the loss of animals that depend on it, like [[pollinator]]s and seed dispersers. Beavers too have been called keystone, not for eating other species but for modifying the environment in ways that affected other species. The term has thus been given quite different meanings in different cases. In Mills's view, Paine's work showed that a few species could sometimes have extremely strong interactions within a particular ecosystem, but that does not automatically imply that other ecosystems have a similar structure.<ref name="mills1993">{{cite journal |last1=Mills |first1=L. S. |last2=Soule |first2=M. E. |last3=Doak |first3=D. F. |year=1993 |title=The Keystone-Species Concept in Ecology and Conservation |journal=BioScience |volume=43 |issue=4 |pages=219–224 |doi=10.2307/1312122 |jstor=1312122|url=https://zenodo.org/record/8204920 }}</ref>

== See also ==

* [[Cultural keystone species]]
* [[Ecosystem service]]
* [[Foundation species]]
* [[Indigenous (ecology)|Indigenous]]
* [[Introduced species]]
* [[Rewilding]]
* [[Sentinel species]]

== References ==

{{reflist|30em}}

== Further reading ==

* {{cite book |last=Caro |first=Tim |author-link=Tim Caro |title=Conservation by proxy: indicator, umbrella, keystone, flagship, and other surrogate species |date=2010 |publisher=Island Press |location=Washington, DC |isbn=9781597261920 |ref=none}}
{{Conservation of species}}{{modelling ecosystems}}

[[Category:Biodiversity]]
[[Category:Community ecology]]
[[Category:Conservation biology]]
[[Category:Ecology terminology]]
[[Category:Habitat]]