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Keystone species

The science of Conservation Biology tries to find reasons why biodiversity should be preserved. Biodiversity is the variety of life at three levels: ecosystems, species and genes. Here we focus on the species level. There are many species in the world, between 10 million and 20 million perhaps. Of these, only about 2 million have so far been catalogued by scientists (botanists, entomologists, etc.). Species are disappearing faster than we have time to get to know them. Some ecosystems are characterised by the large number of species they contain (‘species richness’). Other ecosystems (or the same ones) are characterised by the uniqueness of the species they contain (‘endemic species’ in a desert, for instance). Are some species more valuable than others? Are there ‘redundant’ species? These would be species that fulfill no singular function in ecosystems. Nevertheless, we might believe they have a right to live.

It is in the context of such questions in Conservation Biology and in the Economics of Biodiversity that the notion of ‘keystone species’ is pertinent. The term has its origins in Robert Paine’s studies in 1969 of marine biology in California. When the top predator in the ecosystem he studied (a starfish) disappeared, the whole ensemble of species collapsed, hence the architectural analogy with the keystone in an arch.

Keystone species are those whose importance is disproportionately large relative to their abundance. An ecosystem may experience a complete shift if a keystone species is removed, even though that species seemed to be a small part of the ecosystem as measured by its frequency or by its biomass. Another example of a keystone species would be a predator that ingests numerous individuals of an herbivorous species that would otherwise eliminate many plants, but a keystone species is not always a top predator. If bees disappear, pollination would be negatively affected. Other species are keystone because of their ‘engineering’ roles, burrowing and making tunnels which are used by other species, such as prairie dogs in America.

For further reading:

Paine, R. (1995) A conversation on refining the concept of keystone species, Conservation Biology, 9 (4) 962-964.

This glossary entry is based on a contribution by Jampel Dell Angelo


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