Keystone Species

The term KEYSTONE was introduced to the fields of ecology and conservation biology in 1969 by Robert T. Paine, a professor of zoology at the University of Washington. A keystone denotes one stone at the top center of an arch or vault that provides critical structural support. Due to the keystone's strategic location, if removed, the entire arch will collapse to the ground. This in essence explains the role of keystone plant and animal species—they are the central critical piece holding other associated species together.

Similarly, in the natural world there are keystone resources (natural resources like food, water, mineral deposits, shelter, mineral deposits, among others) on which a variety of species depend. When a keystone resource is threatened, lost or become unavailable, it needs to be supplemented by artificial means such as the setting up of wildlife feeding stations, artificial waterholes, salt licks, and the creation of wildlife refuges to arrest the loss of important wildlife habitat.

Keystone species have become an important concept in conservation biology because of the disproportionate influence they have in relation to their abundance in the environment. In a biological community, they can hold power over other species by determining which species propagate and which do not. This has led to the prioritization of keystone species for conservation.

Ironically, the keystone function of a plant or animal is usually recognized when the species is removed or lost from an ecosystem. As a result of Robert Paine's groundbreaking research on the ecology of the sea otter and the biodiversity of marine communities in the Pacific Northwest, we know that sea otters play a keystone role by consuming and regulating sea urchins. Sea urchins feed on forests of giant kelp and bull kelp, and an explosion in sea urchin populations can destroy kelp forests. This helps maintain marine biodiversity, allowing California sea lions, harbor seals, sea otters, and many other species to feed and shelter in the kelp.

Top carnivores are some of the most visible keystone species. Wolves are threatened around the world for different reasons; they can seriously affect rural milk and dairy economies by destroying [Page 984]livestock, and in parts of Asia, wolves are hunted in the belief that they are child-lifters. In areas from where the endangered gray wolf was exterminated, populations of deer have increased, resulting in overgrazed habitats that cannot support other herbivores and insects.

Examples of other keystone species include pollinators and seed dispersers in tropical forests such as bats essential to the reproduction of many trees; species called ecosystem engineers (e.g., beavers) because the new wetland habitats they create are used by other species; elephants, which help maintain grasslands by browsing on and removing trees and bushes that would otherwise shade out grasses; and disease-causing organisms that multiply and regulate excessive animal populations.

Animals are not the only keystone species. Fig trees comprise a small proportion of all trees in a forest but produce a copious and continuous supply of fruits critical to many birds and small animals, especially during a drought. Adding new information to the knowledge base on keystone species is an ongoing activity that helps continuously improve wildlife and forest management. For example, fig trees and keystone resources, like den trees and fallen trees that shelter many animals and provide unique humid environments for plant regeneration, are now often retained during forest logging operations.

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