Keystone species 230342 221507353 2008-06-24T20:25:50Z 80.99.85.136 M [[Image:Sea otters holding hands.jpg|thumb|right|120px|Sea otters]] A '''keystone species''' is a [[species]] that has a disproportionate 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}}</ref>. Such species affect many other organisms in an ecosystem and help to determine the types and numbers of various others species in a community. Such an organism plays a role in its [[ecosystem]] that is analogous to the role of a [[keystone (architecture)|keystone]] in an [[arch]]. While the keystone feels 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. It has become a very popular concept in [[conservation biology]].<ref name="mills1993">{{cite journal |author=Mills, L.S. |coauthors=Soule, M.E.; Doak, D.F. |year=1993 |title=The Keystone-Species Concept in Ecology and Conservation |journal=BioScience |volume=43 |issue=4 |pages=219–224 |url=http://links.jstor.org/sici?sici=0006-3568(199304)43%3A4%3C219%3ATKCIEA%3E2.0.CO%3B2-E |accessdate=2007-10-04 |doi=10.2307/1312122 }}</ref> ==Definition== [[Image:Elephantreaching.jpg|thumb|right|120px|Elephant on savanna]] The definition given here is somewhat qualitative in nature because there is not yet an accepted, rigorous definition.<ref name="power1996">{{cite journal |author=Power, M.E. |coauthors=Tilman, D.; Estes, J.A.; Menge, B.A.; Bond, W.J.; Mills, L.S.; Daily, G.; Castilla, J.C.; Lubchenco, J.; Paine, R.T. |year=1996 |title=Challenges in the Quest for Keystones |journal=BioScience |volume=46 |issue=8 |pages=609–620 |url=http://links.jstor.org/sici?sici=0006-3568(199609)46%3A8%3C609%3ACITQFK%3E2.0.CO%3B2-7 |accessdate = 2007-10-04 |doi=10.2307/1312990 }}</ref> An issue is how to measure both abundance and impact and at what point to draw the line. Abundance in this context can be measured by biomass or productivity, among other metrics. Impact is even harder to define. It has been suggested that such keystone predators can be identified in [[ecosystems]] by their biomass dominance within ecological [[functional groups]], even though they may be relatively rare in relation to the ecosystem as a whole.<ref name="davic2003">{{cite journal |author=Davic, R.D. |year=2003 |title=Linking Keystone Species and Functional Groups: A New Operational Definition of the Keystone Species Concept |journal=Conservation Ecology |volume=7 |issue=1 |pages=r11 |url=http://www.ecologyandsociety.org/vol7/iss1/resp11/ |accessdate=2007-10-04}}</ref> The term is often misused in places where [[foundation species]] would be more appropriate. A keystone species is not simply one whose disappearance would alter the ecosystem. Removing any abundant species from any ecosystem will drastically alter that ecosystem by definition. What makes the concept of keystone species attractive to conservationists is that a species with a relatively tiny physical footprint can be critical to the health of its ecosystem.<ref name="power1996" /> ==Examples== {{ImageStackRight|140| [[Image:Puget Sound Red Starfish 1280px.jpg|thumb|right|120px|Puget Sound starfish]] [[Image:California mussel (Mytilus californianus) 01.jpg|thumb|right|120px|California Mussels]]}} Without a consensus on its exact definition, we are left to illustrate the concept of keystone species with a list of examples. 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 weevil and its suggested keystone effects on aquatic plant species diversity by prey activities on nuisance Euransian Watermilfoil.<ref name="creed2000">{{cite journal |author=Creed Jr, R.P. |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 |pages=405 }}</ref> ===Predators=== {{ImageStackRight|140| [[Image:Giantkelp2 300.jpg|thumb|right|120px|Kelp forest]] [[Image:Woda-3 ubt.jpeg|thumb|right|120px|Sea urchin]]}} Some [[starfish]] may perform this function by preying on [[sea urchin]]s, [[mussel]]s, 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. In his classic 1966 paper, Dr. Robert Paine described such a system in Mukkaw Bay in Washington State.<ref name="paine1966">{{cite journal |author=Paine, R.T. |year=1966 |title=Food Web Complexity and Species Diversity |journal=The American Naturalist |volume=100 |issue=910 |pages=65–75 |url=http://links.jstor.org/sici?sici=0003-0147(196601/02)100:910%3C65:FWCASD%3E2.0.CO;2-D |accessdate=2007-10-04 |doi=10.1086/282400 }}</ref> This led to his 1969 paper where he proposed the keystone species concept.<ref name="paine1969">{{cite journal |author=Paine, R.T. |year=1969 |title=A Note on Trophic Complexity and Community Stability |journal=The American Naturalist |volume=103 |issue=929 |pages=91–93 |url=http://links.jstor.org/sici?sici=0003-0147(196901%2F02)103%3A929%3C91%3AANOTCA%3E2.0.CO%3B2-U |accessdate = 2007-10-04 |doi=10.1086/282586 }}</ref> Similarly, [[sea otters]] in [[kelp forest]]s keep sea urchins in check. Kelp roots are merely anchors, and not the vast nutrient gathering networks of land plants. Thus the urchins only need to eat the roots of the kelp, a tiny fraction of the plant's biomass, to remove it from the ecosystem.<ref name="estes1978">{{cite journal |last=Estes |first=James E. |coauthors=Norman S. Smith, John F. Palmisano |year=1978 |title=Sea otter predation and community organization in the Western Aleutian Islands, Alaska |journal=Ecology |volume=59 |issue=4 |pages=822–833 |url=http://links.jstor.org/sici?sici=0012-9658(197822)59%3A4%3C822%3ASOPACO%3E2.0.CO%3B2-N |accessdate=2007-10-04 |doi=10.2307/1938786}}</ref> <ref name="cohn1998"> {{cite journal |author=Cohn, J.P. |year=1998 |title=Understanding Sea Otters |journal=BioScience |volume=48 |issue=3 |pages=151–155 |url=http://links.jstor.org/sici?sici=0006-3568(199803)48%3A3%3C151%3AUSO%3E2.0.CO%3B2-G |accessdate=2007-10-04 |doi=10.2307/1313259 }}</ref> These creatures need not be [[apex predator]]s. Sea stars are prey for sharks, rays, and sea anemones. Sea otters are prey for [[orca]].<ref name="estes1998">{{cite journal |author=Estes, J.A. |coauthors=Tinker, M.T.; Williams, T.M.; 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 |url=http://adsabs.harvard.edu/abs/1998Sci...282..473E |accessdate = 2007-10-04 |pmid=9774274}}</ref> ===Engineers=== {{ImageStackRight|140| [[Image:Grizzly In Water.jpg|thumb|right|120px|Grizzly bear in water]] [[Image:BeaverDam 8409.jpg|thumb|right|120px|Beaver dam lake]]}} In [[North America]], the [[grizzly bear]] is a keystone species - not as a predator but as [[ecosystem engineer]]s. They transfer nutrients from the [[ocean]]ic ecosystem to the [[forest]] ecosystem. The first stage of the transfer is performed by [[salmon]], rich in nitrogen and potassium, 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.{{Fact|date=October 2007}} Another ecosystem engineering keystone species is the [[beaver]], which transforms its territory from a stream to a pond or swamp.<ref name="wright2002">{{cite journal |author=Wright, J.P. |coauthors=Jones, C.G.; 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 |url=http://www.springerlink.com/index/0637GF0979LRU90J.pdf |accessdate = 2007-10-04 |doi=10.1007/s00442-002-0929-1 }}</ref> 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 savanna would turn into [[woodland]].<ref name="leakey1995">{{cite book |last=Leakey |first=Richard |authorlink=Richard Leakey |coauthors=[[Roger Lewin]] |title=The sixth extinction: biodiversity and its survival |origdate=1995 |accessdate=2007-10-28 |year=1999 |publisher=Phoenix |location=London |isbn=1-85799-473-6 |pages=pp. 216-217 |chapter=11 The modern elephant story}}</ref> ==References== {{Reflist}} ==See also== *[[Foundation species]] *[[Indicator species]] *[[Flagship species]] *[[Indigenous (ecology)|Indigenous]] *[[Introduced species]] ==External links== *[http://www.washington.edu/research/pathbreakers/1969g.html A summary of Paine's original hypothesis from the University of Washington's Pathbreaker series] [[Category:Community ecology]] [[ja:キーストーン種]] [[ko:키스톤 종]] [[fi:Avainlaji]] [[hu:kulcsfaj]] [[tr:Kilittaşı türler]]