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Keystone species

A keystone species is one whose impact on its community or ecosystem is disproportionately large relative to its abundance [8]. The classic example is a starfish (Pisaster ochraceus) in the rocky intertidal of the Pacific Northwest:

Kangaroo rats (members of the genus Dipodymys) play a similar role in the Chihuahuan desert of southeastern Arizona [2].

If we're going to focus on conserving whole systems, it might make sense to begin with a focus on keystone species. After all, ensuring that they persist and, more importantly, that their ecological role persists would, it seems, guarantee that the system as a whole will persist relatively intact. Although the idea of keystone species is intuitively appealing, it has been much criticized in the ecological literature.1 Why?

McCann et al. [6] also point out that it may be the weak trophic interactions that are most important in stabilizing food webs. Weak links dampen the oscillations in population size characteristically associated with resource-consumer dynamics, which tends to keep both resource population sizes and consumer population sizes bounded away from zero and decreasing the chance they will become extinct. Thus, strong links may have the greatest influence on overall community dynamics and structure, but it's the abundance of weak links that allow communities to persist.

In spite of its limitations, the keystone species concept has some usefulness in the same way that elasticity coefficients in a Leslie or Lefkovitch matrix are useful. It directs attention to those aspects of the system where management efforts are likely to have the greatest impact. Of course, identifying those aspects is not an easy task.


next up previous
Next: Evolutionary consequences of species Up: Species Interactions and Biodiversity Previous: Introduction
Kent Holsinger 2005-10-11