Keystone species: Difference between revisions
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Given that there are many historical definitions<ref>{{cite web | title= Linking Keystone Species and Functional Groups: A New Operational Definition of the Keystone Species Concept| url= http://www.consecol.org/vol7/iss1/resp11/ | work= | author=Robert D. Davic | publisher=Conservation Ecology | date=2003 | accessdate=2011-02-03}}</ref> of the keystone species concept, and without a consensus on its exact definition, a list of examples best illustrates the concept of keystone species. |
Given that there are many historical definitions<ref>{{cite web | title= Linking Keystone Species and Functional Groups: A New Operational Definition of the Keystone Species Concept| url= http://www.consecol.org/vol7/iss1/resp11/ | work= | author=Robert D. Davic | publisher=Conservation Ecology | date=2003 | accessdate=2011-02-03}}</ref> of the keystone species concept, and without a consensus on its exact definition, a list of examples best illustrates the concept of keystone species. |
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A classic keystone species is a small [[predator]] that prevents a particular [[herbivorous]] species from eliminating dominant [[plant]] species. Since the prey numbers are low, the keystone predator numbers can be even lower 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 out-sized impact on ecosystem functions. One example is the [[ |
A classic keystone species is a small [[predator]] that prevents a particular [[herbivorous]] species from eliminating dominant [[plant]] species. Since the prey numbers are low, the keystone predator numbers can be even lower 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 out-sized impact on ecosystem functions. One example is the herbivourous weevil ''[[Euhrychiopsis lecontei]]'' and its suggested keystone effects on aquatic plant species diversity by foraging on nuisance [[Myriophyllum spicatum|Eurasian Watermilfoil]].<ref name="creed2000">{{cite journal |
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|author=Creed Jr, R.P. |
|author=Creed Jr, R.P. |
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Revision as of 22:06, 14 April 2012
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance.[1] Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community.
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 has become a very popular concept in conservation biology.[2]
History
The keystone species concept was coined, in 1969,[3] by the zoologist Robert T. Paine, professor emeritus of the University of Washington, to explain the relationship between Pisaster ochraceus, a species of starfish, and Mytilus californianus, a species of mussel.[4] In his classic 1966 paper, Dr. Robert Paine described such a system in Makah Bay in Washington State.[5] This led to his 1969 paper where he proposed the keystone species concept.[6] The concept has been very popular in conservation, deployed in a range of contexts and mobilized to engender support for conservation.[7]
Examples
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Given that there are many historical definitions[8] of the keystone species concept, and without a consensus on its exact definition, a list of examples best illustrates the concept of keystone species.
A classic keystone species is a small predator that prevents a particular herbivorous species from eliminating dominant plant species. Since the prey numbers are low, the keystone predator numbers can be even lower 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 out-sized impact on ecosystem functions. One example is the herbivourous weevil Euhrychiopsis lecontei and its suggested keystone effects on aquatic plant species diversity by foraging on nuisance Eurasian Watermilfoil.[9]
Predators
As was described by Dr. Robert Paine in his classic 1966 paper, some sea stars may prey on sea urchins, mussels, and other shellfish that have no other natural predators. If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species, while the urchin population annihilates coral reefs.
Similarly, sea otters protect kelp forests from damage by sea urchins. Kelp "roots", called holdfasts, are merely anchors, and not the vast nutrient gathering networks of land plants. Thus the sea urchins only need to eat the roots of the kelp, a tiny fraction of the plant's biomass, to remove it from the ecosystem.[10] [11]
These creatures need not be apex predators. Sea stars are prey for sharks, rays, and sea anemones. Sea otters are prey for orca.[12]
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.[13]
Mutualists
Keystone mutualists are organisms that participate in mutually beneficial interactions, 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 honeyeaters, 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, and some will not grow unless they have been through a cassowary. [14][15]
Engineers
Although the terms 'keystone' and 'engineer' are used interchangeably [7], the latter is better understood as a subset of keystone species.[16] In North America, the grizzly bear is a keystone species—not as a predator but as ecosystem engineers. They transfer nutrients from the oceanic ecosystem to the forest ecosystem. The first stage of the transfer is performed by salmon, rich in nitrogen, sulfur, carbon, and phosphorus, who swim up rivers, sometimes for hundreds of miles. The bears then capture the salmon and carry them onto dry land, dispersing nutrient-rich feces and partially eaten carcasses. It has been estimated that the bears leave up to half of the salmon they harvest on the forest floor.[17]
The prairie dog is also 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.[18] Even grazing species such as Plains bison, pronghorn, and Mule deer have shown a proclivity for grazing on the same land used by prairie dogs.[19] It is believed that they prefer the vegetative conditions after prairie dogs have foraged through the area.
Another ecosystem engineering keystone species is the beaver, which transforms its territory from a stream to a pond or swamp.[20]
In the African savanna, the larger herbivores, especially the elephants, shape their environment. The elephants destroy trees, making room for the grass species. Without these animals, much of the savannah would turn into woodland.[21]
See also
- Foundation species
- Ecosystem engineer
- Indicator species
- Flagship species
- Indigenous
- Introduced species
- Umbrella species
References
- ^ Paine, R.T. (1995). "A Conversation on Refining the Concept of Keystone Species". Conservation Biology. 9 (4): 962–964. doi:10.1046/j.1523-1739.1995.09040962.x.
- ^ Mills, L.S. (1993). "The Keystone-Species Concept in Ecology and Conservation". BioScience. 43 (4). BioScience, Vol. 43, No. 4: 219–224. doi:10.2307/1312122. JSTOR 1312122.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ "Keystone Species Hypothesis". University of Washington. Retrieved 2011-02-03.
- ^ Stolzenberg, William (2008). Where the Wild Things Were: Life, death and ecological wreckage in a land of vanishing predators. Bloomsbury USA. ISBN 1-59691-299-5.
- ^ Paine, R.T. (1966). "Food Web Complexity and Species Diversity". The American Naturalist. 100 (910): 65–75. doi:10.1086/282400. JSTOR 2459379.
- ^ Paine, R.T. (1969). "A Note on Trophic Complexity and Community Stability". The American Naturalist. 103 (929): 91–93. doi:10.1086/282586. JSTOR 2459472.
- ^ a b Barua, M. (2011) Mobilizing metaphors: the popular use of keystone, flagship and umbrella species concepts. Biodiversity and Conservation, 20: 1427-1440.
- ^ Robert D. Davic (2003). "Linking Keystone Species and Functional Groups: A New Operational Definition of the Keystone Species Concept". Conservation Ecology. Retrieved 2011-02-03.
- ^ Creed Jr, R.P. (2000). "Is there a new keystone species in North American lakes and rivers?". OIKOS. 91 (2): 405. doi:10.1034/j.1600-0706.2000.910222.x.
- ^ Estes, James E. (1978). "Sea otter predation and community organization in the Western Aleutian Islands, Alaska". Ecology. 59 (4). Ecology, Vol. 59, No. 4: 822–833. doi:10.2307/1938786. JSTOR 1938786.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Cohn, J.P. (1998). "Understanding Sea Otters". BioScience. 48 (3). BioScience, Vol. 48, No. 3: 151–155. doi:10.2307/1313259. JSTOR 1313259.
- ^ Estes, J.A. (1998-10-16). "Killer whale predation on sea otters linking oceanic and nearshore ecosystems". Science. 282 (5388): 473–476. Bibcode:1998Sci...282..473E. doi:10.1126/science.282.5388.473. PMID 9774274.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Nowell, K. and Jackson, P. (compilers and editors) 1996. Wild Cats, Status Survey and Conservation Action Plan. IUCN/SSC Cat Specialist Group. IUCN, Gland, Switzerland. (see Panthera Onca, pp 118–122)
- ^ Lambeck, Robert J. (1999). "Landscape Planning for Biodiversity Conservation in Agricultural Regions: A Case Study from the Wheatbelt of Western Australia". Biodiversity Technical Paper No. 2. CSIRO Division of Wildlife and Ecology.
{{cite journal}}: Cite journal requires|journal=(help) - ^ Walker, Brian (1995). "Conserving Biological Diversity through Ecosystem Resilience". Conservation Biology. 9 (4): 747–752. doi:10.1046/j.1523-1739.1995.09040747.x.
- ^ Caro, T. (2010) Conservation by Proxy. Island Press, Washington DC.
- ^ Reichman, Tom. "Salmon nutrients, nitrogen isotopes and coastal forest" (PDF). Salmon nutrients, nitrogen isotopes and coastal forest. University of Victoria. Retrieved 3 June 2011.
- ^ Nebraska Game and Park Commission: the Prairie Dog.
- ^ Prairie Dog Coalition – Associated Species
- ^ Wright, J.P. (2002). "An ecosystem engineer, the beaver, increases species richness at the landscape scale" (PDF). Oecologia. 132 (1): 96–101. doi:10.1007/s00442-002-0929-1. Retrieved 2007-10-04.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Leakey, Richard (1999) [1995]. "11 The modern elephant story". The sixth extinction: biodiversity and its survival. London: Phoenix. pp. 216–217. ISBN 1-85799-473-6.
{{cite book}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help)