A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. Such species are described as playing 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. A keystone species is a plant or animal that plays a unique and crucial role in the way an ecosystem functions. 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 it has allowed easier communication between ecologists and conservation policy-makers, it has been criticized for oversimplifying complex ecological systems.
The concept of the keystone species was introduced in 1969 by the zoologist Robert T. Paine. Paine developed the concept to explain his observations and experiments on the relationships between 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. In his 1966 paper, Food Web Complexity and Species Diversity, Paine had described such a system in Makah Bay in Washington. In his 1969 paper, Paine proposed the keystone species concept, using Pisaster ochraceus, a species of starfish, and Mytilus californianus, a species of mussel, as a primary example. 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.
A keystone species was defined by Paine as a species that has a disproportionately large effect on its environment relative to its abundance. It has been defined operationally by R. D. 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."
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 Eurasian watermilfoil in North American waters. 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.
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:
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
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.
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 this 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.
The elimination of the gray wolf from Yellowstone National Park had profound impacts on the trophic pyramid. 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 territory for grazing. 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.
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. If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species.
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. The lion is another keystone species.
Keystone mutualists are organisms that participate in mutually beneficial interaction and 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.
A term used alongside keystone is ecosystem engineer. 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. Grazing species such as plains bison, pronghorn, and mule deer have shown a proclivity for grazing on the same land used by prairie dogs.
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.
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.
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.
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.
Acanthosicyos horridus is an unusual melon that occurs only in Namibia; it is locally called naras or nara. It is a dioecious plant found in sand desert but not stony plains, in areas with access to ground water such as ephemeral rivers and paleochannels, where sand accumulating in the shelter of its stems can form hummocks up to 1000–1500 m2 in area and 4 meters in height. Its stems may rise more than a meter above the hummocks, while its system of thick taproots can extend up to 50 m downward. The nara plant is leafless, so modified stems and spines 2–3 centimeters long serve as the photosynthetic "organs" of the plant. The plant can survive many years without water.Nara typically occurs in the absence of other vegetation due to the harshness of the climate, though Eragrostis spinosa and Stipagrostis sabulicola grasses may grow between its hummocks. It is regarded as a keystone species because its nutritious melons, seeds, shoots, and flowers are food sources for beetles, gemsbok, and ostrich, while small mammals such as Rhabdomys pumilio, Desmodillus auricularis, and Thallomys nigricauda take shelter amid the spiny tangle of its stems.Antarctic realm
The Antarctical realm is one of eight terrestrial biogeographic realms. The ecosystem includes Antarctica and several island groups in the southern Atlantic and Indian Oceans. The continent of Antarctica is so cold and dry that it has supported only 2 vascular plants for millions of years, and its flora presently consists of around 250 lichens, 100 mosses, 25-30 liverworts, and around 700 terrestrial and aquatic algal species, which live on the areas of exposed rock and soil around the shore of the continent. Antarctica's two flowering plant species, the Antarctic hair grass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis), are found on the northern and western parts of the Antarctic Peninsula. Antarctica is also home to a diversity of animal life, including penguins, seals, and whales.
Several Antarctic island groups are considered part of the Antarctica realm, including South Georgia and the South Sandwich Islands, South Orkney Islands, the South Shetland Islands, Bouvet Island, the Crozet Islands, Prince Edward Islands, Heard Island, the Kerguelen Islands, and the McDonald Islands. These islands have a somewhat milder climate than Antarctica proper, and support a greater diversity of tundra plants, although they are all too windy and cold to support trees.
Antarctic krill is the keystone species of the ecosystem of the Southern Ocean, and is an important food organism for whales, seals, leopard seals, fur seals, crabeater seals, squid, icefish, penguins, albatrosses and many other birds. The ocean there is so full of phytoplankton because around the ice continent water rises from the depths to the light flooded surface, bringing nutrients from all oceans back to the photic zone.
On August 20, 2014, scientists confirmed the existence of microorganisms living 800 metres (2,600 feet) below the ice of Antarctica.Antarctic silverfish
The Antarctic silverfish (Pleuragramma antarcticum) is a species of notothen native to the Southern Ocean and the only truly pelagic fish in the waters near Antarctica. It is a keystone species in the ecosystem of the Southern Ocean.While widely distributed around the Antarctic, the species appears to have largely disappeared from the western side of the northern Antarctic Peninsula, based on a 2010 research cruise funded by the National Science Foundation under the US Antarctic Program.Apex predator
An apex predator, also known as an alpha predator or top predator, is a predator at the top of a food chain, with no natural predators.Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic levels. Food chains are often far shorter on land, usually limited to being secondary consumers – for example, wolves prey mostly upon large herbivores (primary consumers), which eat plants (primary producers). The apex predator concept is applied in wildlife management, conservation and ecotourism.
Apex predators have a long evolutionary history, dating at least to the Cambrian period when animals such as Anomalocaris dominated the seas.
Humans have for many centuries interacted with apex predators including the wolf, birds of prey and cormorants to hunt game animals, birds, and fish respectively. More recently, ecotourism such as with the tiger shark has become popular, and rewilding with predators such as the lynx has been proposed.Beaver dam
Beaver dams or beaver impoundments are dams built by beavers to provide ponds as protection against predators such as coyotes, wolves, and bears, and to provide easy access to food during winter. These structures modify the natural environment in such a way that the overall ecosystem builds upon the change, making beavers a keystone species. Beavers work at night and are prolific builders, carrying mud and stones with their fore-paws and timber between their teeth.Cultural keystone species
The cultural keystone species concept, first proposed by Sergio Cristancho and Joanne Vining in 2000 and later described by ethnobotanist Ann Garibaldi and ethnobiologist Nancy Turner in 2004, is a "metaphorical parallel" to the ecological keystone species concept, and may be useful for biodiversity conservation and ecological restoration. Cultural keystone species are species of exceptional significance to a culture or a people, and can be identified by their prevalence in language, cultural practices (e.g. ceremonies), traditions, diet, medicines, material items, and histories of a community. These species influence social systems and culture and are a key feature of a community's identity.Ecological extinction
Ecological extinction is "the reduction of a species to such low abundance that, although it is still present in the community, it no longer interacts significantly with other species".Ecological extinction stands out because it is the interaction ecology of a species that is important for conservation work. They state that "unless the species interacts significantly with other species in the community (e.g. it is an important predator, competitor, symbiont, mutualist, or prey) its loss may result in little to no adjustment to the abundance and population structure of other species".This view stems from the neutral model of communities that assumes there is little to no interaction within species unless otherwise proven.
Estes, Duggins, and Rathburn (1989) recognize two other distinct types of extinction:
Global extinction is defined as "the ubiquitous disappearance of a species".
Local extinction is characterized by "the disappearance of a species from part of its natural range".Ecology
Ecology (from Greek: οἶκος, "house", or "environment"; -λογία, "study of") is the branch of biology which studies the interactions among organisms and their environment. Objects of study include interactions of organisms with each other and with abiotic components of their environment. Topics of interest include the biodiversity, distribution, biomass, and populations of organisms, as well as cooperation and competition within and between species. Ecosystems are dynamically interacting systems of organisms, the communities they make up, and the non-living components of their environment. Ecosystem processes, such as primary production, pedogenesis, nutrient cycling, and niche construction, regulate the flux of energy and matter through an environment. These processes are sustained by organisms with specific life history traits. Biodiversity means the varieties of species, genes, and ecosystems, enhances certain ecosystem services.
Ecology is not synonymous with environmentalism, natural history, or environmental science. It overlaps with the closely related sciences of evolutionary biology, genetics, and ethology. An important focus for ecologists is to improve the understanding of how biodiversity affects ecological function. Ecologists seek to explain:
Life processes, interactions, and adaptations
The movement of materials and energy through living communities
The successional development of ecosystems
The abundance and distribution of organisms and biodiversity in the context of the environment.Ecology has practical applications in conservation biology, wetland management, natural resource management (agroecology, agriculture, forestry, agroforestry, fisheries), city planning (urban ecology), community health, economics, basic and applied science, and human social interaction (human ecology). For example, the Circles of Sustainability approach treats ecology as more than the environment 'out there'. It is not treated as separate from humans. Organisms (including humans) and resources compose ecosystems which, in turn, maintain biophysical feedback mechanisms that moderate processes acting on living (biotic) and non-living (abiotic) components of the planet. Ecosystems sustain life-supporting functions and produce natural capital like biomass production (food, fuel, fiber, and medicine), the regulation of climate, global biogeochemical cycles, water filtration, soil formation, erosion control, flood protection, and many other natural features of scientific, historical, economic, or intrinsic value.
The word "ecology" ("Ökologie") was coined in 1866 by the German scientist Ernst Haeckel. Ecological thought is derivative of established currents in philosophy, particularly from ethics and politics. Ancient Greek philosophers such as Hippocrates and Aristotle laid the foundations of ecology in their studies on natural history. Modern ecology became a much more rigorous science in the late 19th century. Evolutionary concepts relating to adaptation and natural selection became the cornerstones of modern ecological theory.Ecosystem engineer
An ecosystem engineer is any organism that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on the species richness and landscape-level heterogeneity of an area. As a result, ecosystem engineers are important for maintaining the health and stability of the environment they are living in. Since all organisms impact the environment they live in in one way or another, it has been proposed that the term "ecosystem engineers" be used only for keystone species whose behavior very strongly affects other organisms.Keystone
Keystone may refer to:
Keystone (architecture), a central stone or other piece at the apex of an arch or vault
The keystone effect, caused by projecting an image onto a surface at an angle, or by photography at an angle
Keystone (cask), a fitting used in ale casks
Keystone module, a type of data connector mounted in walls and patch panels
Keystone species, species that have a larger effect on their environment than is purely due to their abundance
Operation Keystone during World War II
The Keystone asterism in the Hercules constellation
Keystone Press Awards
Keystone (limestone), quarried in the Florida Keys
Keystone, a variety of screwdriver blade
Keystone Initiative, a medical protocol to reduce infection rates
Keystone Bituminous Coal Ass'n v. DeBenedictis, a leading American Supreme Court case on regulatory takingMangrove crab
Mangrove crabs are crabs that live among mangroves, and may belong to many different species and even families. They have been shown to be ecologically significant in many ways. They keep much of the energy within the forest by burying and consuming leaf litter. Along with burrowing in the ground, at high tide and in the face of predators these crustaceans can climb trees to protect themselves. The hermit crab and the mangrove crab are the only crustaceans that can climb trees as a defense mechanism. Furthermore, their feces may form the basis of a coprophagous food chain contributing to mangrove secondary production.Mangrove crab larvae are the major source of food for juvenile fish inhabiting the adjacent waterways, indicating that crabs also help nearshore fisheries. The adult crabs are food for threatened species such as the crab plover.Their burrows alter the topography and sediment grain size of the mangrove, and help aerate the sediment. Removing crabs from an area causes significant increases in sulfides and ammonium concentrations, which in turn affects the productivity and reproductive output of the vegetation, supporting the hypothesis that mangrove crabs are a keystone species.Marine worm
Any worm that lives in a marine environment is considered a marine worm. Marine worms are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida (segmented worms), Chaetognatha, Hemichordata, and Phoronida. For a list of marine animals that have been called "sea worms", see sea worm.
Many of these worms have specialized tentacles used for exchanging oxygen and carbon dioxide and also may be used for reproduction.
Some marine worms are tube worms, of which the giant tube worm lives in waters near underwater volcanoes, and can withstand temperatures up to 90 degrees Celsius or about 194 degrees Fahrenheit.
Some worms can live in the trench. These worms were first discovered in the Pacific Ocean off the Galápagos Islands.
In recent years, marine worms (especially those found in the ocean) have been observed ingesting microplastic particles found in the oceans. This trend is concerning many scientists, as marine worms act as an important food source for many fish and wading birds. Marine Worms play as Keystone Species in an ecosystem, and the introduction of plastic in the oceans will not only diminish the growth rates of the marine worms, but also affect the food chain of that ecosystem.Navicula
Navicula is a genus of boat-shaped diatom algae, comprising over 1,200 species. Navicula is Latin for "small ship", and also a term in English for a boat-shaped incense-holder.Diatoms — eukaryotic, primarily aquatic, single-celled photosynthetic organisms — play an important role in global ecology, producing about a quarter of all the oxygen within Earth's biosphere, often serving as foundational organisms, or keystone species in the food chain of many environments where they provide a staple for the diets of many aquatic species.Non-trophic networks
Any action or influence that species have on each other is considered a biological interaction. These interactions between species can be considered in several ways. One such way is to depict interactions in the form of a network, which identifies the members and the patterns that connect them. Species interactions are considered primarily in terms of trophic interactions, which depict which species feed on others.
Currently, ecological networks that integrate non-trophic interactions are being built. The type of interactions they can contain can be classified into six categories: mutualism, commensalism, neutralism, amensalism, antagonism, and competition.
Observing and estimating the fitness costs and benefits of species interactions can be very problematic. The way interactions are interpreted can profoundly affect the ensuing conclusions.Pisaster ochraceus
Pisaster ochraceus, generally known as the purple sea star, ochre sea star, or ochre starfish, is a common starfish found among the waters of the Pacific Ocean. Identified as a keystone species, Pisaster is considered an important indicator for the health of the intertidal zone.Rewilding (conservation biology)
Rewilding is large-scale conservation aimed at restoring and protecting natural processes and core wilderness areas, providing connectivity between such areas, and protecting or reintroducing apex predators and keystone species. Rewilding projects may require ecological restoration or wilderness engineering, particularly to restore connectivity between fragmented protected areas, and reintroduction of predators and keystone species where extirpated. The ultimate goal of rewilding efforts is to create ecosystems requiring passive management by limiting human control of ecosystems. Successful long term rewilding projects should be considered to have little to no human-based ecological management, as successful reintroduction of keystone species creates a self-regulatory and self-sustaining stable ecosystem, with near pre-human levels of biodiversity.Robert T. Paine (zoologist)
Robert Treat "Bob" Paine III (April 13, 1933 – June 13, 2016) was an American ecologist, who spent most of his career at the University of Washington. Paine coined the keystone species concept to explain the relationship between Pisaster ochraceus, a species of starfish, and Mytilus californianus, a species of mussel. Paine's research, and the subsequent work of his students, has been hugely influential in the field of ecology.Salmon run
The salmon run is the time when salmon, which have migrated from the ocean, swim to the upper reaches of rivers where they spawn on gravel beds. After spawning, all Pacific salmon and most Atlantic salmon die, and the salmon life cycle starts over again. The annual run can be a major event for grizzly bears, bald eagles and sport fishermen. Most salmon species migrate during the fall (September through November).Salmon spend their early life in rivers, and then swim out to sea where they live their adult lives and gain most of their body mass. When they have matured, they return to the rivers to spawn. Usually they return with uncanny precision to the natal river where they were born, and even to the very spawning ground of their birth. It is thought that, when they are in the ocean, they use magnetoception to locate the general position of their natal river, and once close to the river, that they use their sense of smell to home in on the river entrance and even their natal spawning ground.
In northwest America, salmon is a keystone species, which means the impact they have on other life is greater than would be expected in relation to their biomass. The death of the salmon has important consequences, since it means significant nutrients in their carcasses, rich in nitrogen, sulfur, carbon and phosphorus, are transferred from the ocean to terrestrial wildlife such as bears and riparian woodlands adjacent to the rivers. This has knock-on effects not only for the next generation of salmon, but to every species living in the riparian zones the salmon reach. The nutrients can also be washed downstream into estuaries where they accumulate and provide much support for estuarine breeding birds.Umbrella species
Umbrella species are species selected for making conservation-related decisions, typically because protecting these species indirectly protects the many other species that make up the ecological community of its habitat. Species conservation can be subjective because it is hard to determine the status of many species. With millions of species of concern, the identification of selected keystone species, flagship species or umbrella species makes conservation decisions easier. Umbrella species can be used to help select the locations of potential reserves, find the minimum size of these conservation areas or reserves, and to determine the composition, structure and processes of ecosystems.