Keystone Species

A keystone species is a particular species that has a great influence on the structure or functioning of its ecological community. This influence is far out of proportion to the relative biomass or productivity of the keystone species within its community. Most keystone species are top predators, although a few are influential because they play a critical role as herbivores or in nutrient cycling.

In engineering, the keystone is a wedge-shaped stone that occurs at the top of a self-supporting stone arch or dome. The keystone is extremely important in the physical integrity of the structure, and if it is removed, the arch or dome will collapse. The keystone metaphor in ecology is used to refer to species that have a similarly critical influence on the functioning or structure of their community.

The importance of particular keystone species can often be deduced by careful examination of their interactions with other species or by measuring their functional attributes, especially those important in nutrient cycles. The role of keystone species can also be demonstrated by conducting experiments in which these organisms are removed from their community, and the resulting ecological changes are monitored.