Keystone species

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Not to be confused with foundation species.

The jaguar: a keystone, flagship, and umbrella species, and an apex predator
ecosystems

A keystone species is a

ecological community, affecting many other organisms 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, are also apex predators
.

The role that a keystone species plays in its ecosystem is analogous to the role of a 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 or productivity. It became a popular concept in conservation biology, alongside 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

Mytilus californianus
), the seastar's prey

The concept of the keystone species was introduced in 1969 by zoologist

marine invertebrates of the intertidal zone (between the high and low tide lines), including starfish and mussels. He removed the starfish from an area, and documented the effects on the ecosystem.[3] In his 1966 paper, Food Web Complexity and Species Diversity, Paine had described such a system in Makah Bay in Washington.[4]
In his 1969 paper, Paine proposed the keystone species concept, using
Mytilus californianus, a species of mussel, as a primary example.[1] 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. 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.[5][6]

Definitions

A keystone species was defined by Paine as a species that has a disproportionately large effect on its environment relative to its abundance.[7] It has been defined operationally by Davic in 2003 as "a strongly interacting species whose top-down effect on species diversity and competition is large relative to its biomass dominance within a functional group."[8]

A classic keystone species is a

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 Eurasian watermilfoil in North American waters.[9] 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.[7]

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

indicator species, and umbrella species. For example, the jaguar is a charismatic big cat which meets all of these definitions:[10]

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[10]

Predators

Sea otters and kelp forests

Sea urchins like this purple sea urchin can damage kelp forests by chewing through kelp holdfasts
The sea otter is an important predator of sea urchins, making it a keystone species for the kelp forests.

Sea otters protect kelp forests 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 holdfasts 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.[11][12][13][14]

The wolf, Yellowstone's apex predator

Riparian willow recovery at Blacktail Creek, Yellowstone National Park, after reintroduction of wolves.[vague]
Further information: 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.[15]

The elimination of the

trophic pyramid.[16] 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 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.[17]

Sea stars and other non-apex predators

As described by Paine in 1966, some

sea stars (e.g., Pisaster ochraceus) may prey on sea urchins, mussels, and other shellfish that have no other natural predators.[18] If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species.[19] The recent onset of sea star wasting disease
around the United States has indirectly caused mussel populations to dominate in many intertidal habitats.

These creatures need not be

sea anemones. Sea otters are prey for orca.[20]

The

mammalian jungle ecosystem with its consumption of 87 different species of prey.[21] The lion is another keystone species.[22]

Acorn banksia, Banksia prionotes, is periodically the sole source of nectar for important pollinators, honeyeaters.

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

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.[23][24]

Engineers

Prairie dog town. Drawing by Josiah Gregg, 1844
Further information: Ecosystem engineer and Niche construction

A term used alongside keystone is ecosystem engineer.[5] In North America, the prairie dog is an ecosystem engineer. Prairie dog burrows provide the nesting areas for mountain plovers and burrowing owls. Prairie dog tunnel systems also help channel rainwater into the water table to prevent 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.[25] 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.[26]

Beaver dam, an animal construction which has a transformative effect on the environment

The

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.[27]

In the African

elephants, shape their environment. The elephants destroy trees, making room for the grass species and creating habitat for various small animal species.[28][29] Without these animals, much of the savanna would turn into woodland.[30]
In the
wallows that are utilized by a wide variety of species.[31][32]
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.[33]

In the

gnus in these grasslands reduces wildfire likelihood, which in turn promotes tree growth. The documentary The Serengeti Rules documents this in detail.[34]

Limitations

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 pollinators 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.[3]

See also

References

  1. ^
    S2CID 83780992
    .
  2. ^ "Keystone Species Hypothesis". University of Washington. Archived from the original on 2011-01-10. Retrieved 2011-02-03.
  3. ^
    JSTOR 1312122
    .
  4. S2CID 85265656
    .
  5. ^
    S2CID 11030284
    .
  6. ^ HHMI, BioInteractive (29 May 2017). "Some Animals Are More Equal than Others: Keystone Species and Trophic Cascades – HHMI (2016)". Retrieved 6 June 2017.
  7. ^
    doi:10.1046/j.1523-1739.1995.09040962.x
    .
  8. hdl:10535/2966
    . Retrieved 2011-02-03.
  9. doi:10.1034/j.1600-0706.2000.910222.x
    .
  10. ^
    ISBN 978-1-55963-817-3
    .
  11. S2CID 84866250
    .
  12. JSTOR 1938786
    .
  13. JSTOR 1313259
    .
  14. ^ Brown, Tina M. (14 March 2013). "My Turn: Southeast Alaska's sea otters: The restoration of an ecosystem". Juneau Empire. Archived from the original on 23 April 2018. Retrieved 23 April 2018.
  15. ISBN 978-0-471-38914-9
    .
  16. ISSN 0021-8790
    .
  17. doi:10.1641/0006-3568(2004)054[0755:WATEOF]2.0.CO;2
    .
  18. ISSN 1948-6596
    .
  19. S2CID 85265656
    .
  20. S2CID 8925215
    .
  21. ISBN 978-2-8317-0045-8. {{cite book}}: |work= ignored (help
    )
  22. S2CID 53686934
    .
  23. ISBN 978-0-642-21423-2
    .
  24. doi:10.1046/j.1523-1739.1995.09040747.x
    .
  25. ^ "Prairie Dogs". Wildlife Species Guide. Nebraska Game and Park Commission. Archived from the original on 19 August 2009. Retrieved 10 November 2013.
  26. ^ Rosmarino, Nicole (2007). "Associated Species : Prairie Dogs are a Keystone Species of the Great Plains". Prairie Dog Coalition. Archived from the original on 10 November 2013. Retrieved 10 November 2013.
  27. S2CID 5940275
    .
  28. PMID 18376543
    .
  29. PMID 27870025
    .
  30. ISBN 1-85799-473-6
    .
  31. ^ "How the overlooked peccary engineers the Amazon, an interview with Harald Beck". 20 September 2010.
  32. ^ "Where Peccaries Wallow, Other Animals Follow". National Geographic Society. 27 September 2014. Archived from the original on April 18, 2020.
  33. ^ Gruber, Karl (26 September 2014). "Single keystone species may be the key to reef health". Australian Geographic.
  34. ^ How Wildebeest Saved the Serengeti

Further reading

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