Keystone Species

9 Key excerpts on "Keystone Species"

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  Conservation of Rare or Little-Known Species

  Biological, Social, and Economic Considerations

  • Martin G. Raphael, Randy Molina, Martin G. Raphael, Randy Molina(Authors)
  • 2013(Publication Date)
  • Island Press

    (Publisher)

  Keystone Species are species that regulate local species diversity in lower trophic levels, and whose removal results in significant shifts (increases or decreases) in the presence, distribution, or abundance of other species (Bond 1994). The term “keystone” was initially suggested by Paine (1966, 1974) in experiments in which mussels released from starfish predation took over the intertidal environment, and in doing so, reduced or excluded other species. Paine thus defined a keystone as a species (like the starfish) that kept other species in the system by keeping mussel populations in check. The main assumption of the keystone approach is that some individual species disproportionately affect the distribution and abundance of either resources for other species or other species directly. The effect is directly causal from the Keystone Species’ behaviors and is not just correlational. Further, the removal or decline in Keystone Species results in significant (and presumably undesired) changes in those resources or other species, and only a relatively few species within an ecosystem have such effects. Since Paine’s (1969) experiments, numerous species in many environments have been proposed as Keystone Species, including the coyote (Canis latrans) as a keystone terrestrial vertebrate predator (Henke and Bryant 1999), salamanders as keystone aquatic invertebrate predators (Wilbur 1997), and prairie dogs (Cynomys spp.) as keystone providers of ground burrows for other animals (Van Putten and Miller 1999). Even rare species can play keystone roles in some systems. Lyons and Schwartz (2001) reported that experimental removal of rare plant species, as compared with the same removal of dominants, led to greater invasion by an exotic grass species. However, this is not to say that all rare species play equally influential roles on community structure

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  Infectious Disease Ecology

  Effects of Ecosystems on Disease and of Disease on Ecosystems

  • Richard S. Ostfeld, Felicia Keesing, Valerie T. Eviner, Richard S. Ostfeld, Felicia Keesing, Valerie T. Eviner, Richard Ostfeld, Felicia Keesing, Valerie Eviner(Authors)
  • 2010(Publication Date)
  • Princeton University Press

    (Publisher)

  temporal variation specifically in the context of disease effects on both sea otters and black-tailed prairie dogs. Refinement of the Keystone Concept As a result of broad usage of the term “Keystone Species” in the ecologi- cal literature during the years following Paine’s publications, some ecol- ogists thought the keystone concept was losing its distinct meaning (e.g., Mills et al. 1993). In response to this concern, and because of the per- ceived need to incorporate the Keystone Species concept into biological conservation efforts, a group of ecologists met to consider the concept and arrive at an operational defi nition of a Keystone Species. This group proposed an expanded definition that included interactions other than trophic interactions: “a Keystone Species is a species whose impacts on its community or ecosystem are large, and much larger than would be expected from its abundance” (Power and Mills 1995: 184). Kotliar (2000), using prairie dogs as an example of a keystone spe- cies, questioned the emphasis on low species relative abundance put forth by Power and Mills (1995). She suggested that ecologists abandon the duality of the keystone versus non-Keystone Species construct and in- stead focus on the relationship between the abundance of a species and its importance in the community. Kotliar further argued that Keystone Species should be identified as those that play unique versus redundant roles in ecological communities. We discuss the issue of species unique- ness versus redundancy later in reference to the American chestnut. These expanded views characterize as keystones those species that are relatively rare but have large and unique effects on communities and ecosystems. This distinguishes them from dominant species, which may have similarly strong interactions but are more abundant members of communities.

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  Marine Conservation Ecology

  • John Roff, Mark Zacharias, John Roff(Authors)
  • 2013(Publication Date)
  • Routledge

    (Publisher)

  He found that removal of Pisaster from an intertidal community resulted in the mussel (Mytilus) becoming a competitive dominant; therefore Pisaster appeared to exert an influence disproportionate to its abundance and biomass. He theorized that certain species are either directly or indirectly responsible for biological community structure, composition and biomass, and therefore biodiversity (Paine, 1969). The removal of a keystone has a significant impact on a community, and consequently there is an impetus to identify and conserve them. The concept holds considerable allure for managers and conservationists, as the notion of protecting and managing just a few species to the benefit of the entire community or ecosystem could make a seemingly impossible task manageable (Navarrete and Menge, 1996). A number of criteria should be met before any species can be considered a keystone. While there is debate surrounding what constitutes a keystone, their general characteristics are supplied in Table 9.1. The Keystone Species concept has become an accepted and central organizing theme of population level ecology and conservation, and many species have been proposed as keystones in the marine environment (Table 9.2). The concept has, however, been ill defined, which has led to the christening of a number of species as key-stones that are probably not (Hurlburt, 1997; Simberloff, 1998). The Oxford Dictionary of Ecology defines a Keystone Species as: ‘The species, the presence or abundance of which can be used to assess the extent to which resources of an area or habitat are being exploited’ (Allaby, 1996). Roughgarden's (1983) definition of a Keystone Species was one ‘…whose removal leads to a still further loss of species from the community.’ Terborgh (1986) discussed keystone resources, which are those resources that comprise a small percentage of diversity or biomass, but are essential to community structure and/or diversity

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  Self-Organization in Complex Ecosystems

  • Ricard Solé, Jordi Bascompte(Authors)
  • 2012(Publication Date)
  • Princeton University Press

    (Publisher)

  Keystone Species AND EVOLUTIONARY DYNAMICS As discussed at the beginning of this chapter, a specially relevant feature of complex ecologies is the presence of particular species whose removal can cause large effects on the whole community. These are so-called Keystone Species (Paine, 1966; Bond, 1993), and their 232 C H A P T E R S I X T ABLE 6.1. Keystone Species: Types, Including Mode of Action and Specific Examples TYPE MODE OF ACTION EXAMPLE Predators Supress competitors Otters, sea urchins Herbivores Supress competitors Elephants, rabbits Pathogens Supress competitors Myxomatosis virus Mutualists Effective reproduction Pollinators, dispersors Earth movers Physical disturbance Termites System processors Rates of nutrient transfer Mycorrhiza Social predators Modify local succession Army ants identification as a common (perhaps inevitable) ingredient of ecosys-tem architecture has important implications for conservation issues. Indeed, their demise can lead, often through indirect effects, to the loss of many other species. Keystone Species can have different positions in the food web. Al-though top predators and basal species seem obvious candidates, in-termediate species (particularly omnivores) are also as likely as oth-ers to be Keystone Species (see table 6.1). One significant problem, however, is the proper identification of possible candidate species in a given food web. Only the removal of a given node from the eco-logical graph gives a clear answer, and thus species deletion (either from a real or model ecosystem) can provide a direct, clear criterion. However, the effects might not be immediate but strongly delayed (as discussed in chapter 5 in relation to the extinction debt). Be-sides, in many cases the effects can propagate through the food web in a slow path. An example is the demise of jaguars and pumas in Central and South America (Terborgh, 1988; Wilson, 1992).

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  Assessing Ecological Risks of Biotechnology

  • Lev R. Ginzburg(Author)
  • 2013(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  He termed these Keystone Species. His two examples both concerned predatory marine invertebrates—the star-fish, Pisaster ochraceus, in the Pacific rocky intertidal zone and tritons (Char-onia spp.) on the Great Barrier Reef. The starfish, preferring to eat mussels, prevents these from dominating space and eliminating other species (Paine 1966). The tritons might, by favoring as prey the crown-of-thorns starfish (Acanthaster plana), prevent this species from destroying large patches of living coral reef (though other hypotheses than destruction of the tritons are possible for crown-of-thorns, population explosions [Ford 1988]). In 8 Keystone Species and Community Effects of Biological Introduction either case the key is that the Keystone Species prevents a particular prey species from otherwise exerting a dominating influence. The concept of Keystone Species has been generalized—for example, Gilbert (1980) defined keystone mutualists as organisms, typically plants, that provide critical support to a large number of animal species that are, in turn, critical to the existence of other species. The tree Caesuria corymbosa fills this role by maintaining several frugivores that are themselves critical to seed dispersal of a number of other plants (Howe and Westley 1988). Introduced species have played so many different keystone roles that it is necessary to classify them in order to get an overview. I divide them arbitrarily into three categories. First, some species themselves constitute a new structural habitat with diverse microhabitats for many other species. Second are species that create but do not comprise a new structural habitat. Finally, several introduced species have affected many other species (e.g., by direct predation), but have not greatly affected the structural habitat, at least initially.

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  Ecotoxicology

  A Comprehensive Treatment

  • Michael C. Newman, William H. Clements(Authors)
  • 2007(Publication Date)
  • CRC Press

    (Publisher)

  The effects of a species on community structure and function are not necessarily related to its abundance or biomass. Species in the upper right hand quadrant are dominant in the community, but their impact is less than expected based on their abundance or biomass. Species to the left of the diagonal have greater impact than expected and are considered true Keystone Species. (Modified from Figure 3 in Power et al. (1996).) or biomass. Species to the left of the diagonal are defined as true Keystone Species because they have a disproportionate influence on community structure or function. 21.3.1 I DENTIFYING K EYSTONE S PECIES Identifying Keystone Species and quantifying their effects on community structure are not trivial issues, and criticism of the Keystone Species concept is at least partially a result of these difficulties. While manipulating density of an individual species remains the most direct approach for assess-ing its role in a community, conducting experiments at appropriate spatial and temporal scales is logistically challenging. Conclusions about the importance of species interactions relative to abiotic processes are clearly scale dependent. Because the size of study plots and the duration of experiments may influence patterns that we observe, it follows that more attention should be 390 Ecotoxicology: A Comprehensive Treatment given to spatial and temporal scale when interpreting results of manipulative experiments (see Chapter 23). The tremendous success of rocky intertidal ecologists is at least partially a result of the relative ease with which these communities can be manipulated. The reluctance of some ecologists to embrace the Keystone Species concept is likely due to difficulty obtaining experimental evidence in systems that are less amenable to manipulation (Box 21.2).

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  Finding Our Niche

  Toward A Restorative Human Ecology

  • Philip A. Loring(Author)
  • 2020(Publication Date)
  • Fernwood Publishing

    (Publisher)

  The keystone metaphor was first proposed in the mid-twentieth century, a time when scientists were making great advances in the understanding of animal biology and how different animals’ respective biologies interact to create the assemblages we now know as ecosys- tems. Among the leaders of the field was Robert Paine, a scientist from the University of Washington trained in zoology and ecology. In 1966, Paine proposed a hypothesis that would eventually become known as the Keystone Species hypothesis. He wrote, “local species diversity is directly related to the efficiency with which predators prevent the monopolization of the environment by one species.” 1 In other words, Paine was proposing that certain kinds of creatures, particularly grazers, will come to monopolize ecosystems, outcompeting all others to the point where other species are excluded, unless there is a predator pres- ent who can keep the highly efficient grazers in check. With a predator keeping one species from outcompeting others, the less efficient species can find their own niches in which to thrive. Paine famously tested the Keystone Species hypothesis with a series of hands-on experiments in tidal pools involving sea stars (predator) and barnacles (prey). He placed sea stars in some pools and not others, showing convincingly that the sea stars kept a single species of barnacle from dominating the others. Where the sea stars were present, more kinds of barnacles were also present. Where absent, the single-most dominant barnacle species outcompeted the rest. Paine’s concept has been validated and revalidated through all manner of experimental and observational science. One of the most Keystone 63 well-known cases comes not from a controlled experiment but as an accident of ill-advised environmental policy. This is the case of wolves and elk in Yellowstone National Park. In the 1920s, wolves had been virtually eliminated in Yellowstone.

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  Ecological Biomarkers

  Indicators of Ecotoxicological Effects

  • Claude Amiard-Triquet, Jean-Claude Amiard, Philip S. Rainbow(Authors)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  Such species are therefore Keystone Species. The examples that follow illustrate some levels of actions of these Keystone Species. 7.2.1.1 Roles in Food Webs Some species have a particular importance in an ecosystem through their activities of pre-dation or by the biomass that they themselves offer as prey. • Among the approximately 3000 species of fishes present in coral reefs, which are among the most biologically productive and diverse ecosystems in the world and among the world’s most fragile and endangered ecosystems, the humphead parrot-fish Bolbometopon muricatum is the only predator of the coral whose action can be con-sidered significant.

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  Perspectives in Ecological Theory

  • Jonathan Roughgarden, Robert M May, Simon A. Levin, Jonathan Roughgarden, Robert M May, Simon A. Levin, Jonathan Roughgarden, Robert May, Simon Levin(Authors)
  • 2014(Publication Date)
  • Princeton University Press

    (Publisher)

  S E C O N D A R Y E X T I N C T I O N S : W H I C H S P E C I E S A R E I M P O R T A N T ? Some species are likely to be much more important than others and, given that we probably cannot save all the species threatened with extinction, identifying "important" species becomes essential. What makes a species "important"? Spe- cies may be important because, like giant pandas, cheetahs, and rhinos, they are charismatic. Yet other species may be important because they are economically valuable to us. However, species may also be important in preserving commu- nities. Keystone Species are those species whose loss is likely to trigger the greatest number of secondary extinctions. Clearly, special efforts must be made to identify and to preserve Keystone Species, because the fate of so many other species is tied to them. We have discussed in the previous section ecological theory that identifies some species that may be Keystone Species. The loss of predators of generalized herbivores, for example, might be predicted to have major consequences. The experience in the U.S. National Park system, with the eliminations of top preda- tors and great subsequent increases in large herbivores, suggests the need to preserve predators for reasons other than their being charismatic (Chase 1986). C O N C L U S I O N S The human species needs desperately to find a new way to navigate its ship of technology and population. One problem is that we are drowning too many other THEORETICAL ISSUES 303 species in our wake. A successful answer will involve components from all areas of human thought and inquiry. At the strategic level, philosophy, politics, and human psychology will certainly be the most important. But at the tactical and day-to-day level—the crisis level of conservation biology—our knowledge of ecologic, population, and genetic processes will be crucial.

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