Ecological Dominants vs. Keystone Species: A Call for Reason

Robert D. Davic

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• Literature Cited

Published: March 10, 2000

I agree with the viewpoint that it is unwise to diffuse Paine's (1966) concept of "keystone species" due to its importance in ecosystem diagnosis. Sensu Paine, a keystone species has a very limited function in an ecosystem: by selective predation on competitively dominant prey species, the keystone species has the potential to maintain high species diversity within the functional groups of the prey community. Bond (1993) clearly shows the importance of conserving Paine's concept, because it can then be linked directly to the seral stages of ecological succession and to subsequent changes in species adundance. Bond also documents numerous examples of keystone species that meet the narrow Paine definition.

I suggest a re-evaluation of the term "ecological dominants" introduced by Odum (1971) as a way to preserve the original concept of the keystone species. I urge ecologists to use the general term "ecologically dominant species" to call attention to species that are important to ecosystem structure and function in whatever form (e.g., a "key species"), while reserving the term "keystone species" for those species whose role in nature includes the potential to affect the abundance of competitively dominant prey. For it is the actions in the lower trophic levels that allow for keystone predation effects: they are a bottom-up, not a top-down, ecosystem property. Without competitive interactions within the prey functional group, the keystone concept is meaningless.

As stated by Schulze and Mooney (1993), keystone species may be regarded as functional groups with no redundant representation. They conclude that a major research challenge for ecologists is to predict which species in a community are keystone species or have keystone effects (according to the narrow, bottom-up definition), or which species may become so under conditions of environmental change. I hold that ecologists can respond to this challenge only if Paine's narrow concept of keystone predation is preserved. If numerous ecosystem functional responses are viewed as being "keystone effects," then the concept becomes a non-concept, similar to the problem ecologists have created with so-called "species diversity."

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Bond, W. J. 1993. Keystone species. Pages 237-253 in E.-D. Shultze and H. A. Mooney, editors. Biodiversity and ecosystem function. Springer-verlag, Berlin, Germany.

Odum, E. P. 1971. Fundamentals of ecology. Third edition. W. B. Saunders, Philadelphia, PA, USA.

Paine, R. T. 1966. Food web complexity and species diversity. American Naturalist 100: 65-75.

Schulze, E.-D., and H. A. Mooney. 1993. Ecosystem function of biodiversity: a summary. Pages 497-510 in E.-D. Shulze and H. A. Mooney, editors. Biodiversity and ecosystem function. Springer-verlag, Berlin, Germany.

Vanclay, J. K. 1999. On the nature of keystone species. Conservation Ecology 3(1): r3. [online] URL: http://www.consecol.org/Journal/vol3/iss1/resp3