A keystone species is defined as one that has a critical role in determining and maintaining the overall relationship of plants and animals within an ecosystem. If a keystone species is removed or declines, the nature of the ecosystem will change dramatically.
Sea Otters — A Classic Keystone Species
The classic tale of a keystone species is that of the sea otter, which was once found in abundance along the West Coast of North America. The story goes something like this: 1. European and Russian trappers hunt sea otters to near extinction in the 18th and 19th centuries. 2. The decline of the sea otters, which are essential to keeping sea urchins in check, allows sea urchin populations to explode. 3. The burgeoning sea urchins feast on and decimate the kelp beds, which are critical habitat for spawning fish. 4. Fish begin to decline for lack of spawning habitat; this affects fishermen's catches. 5. Finally, an international treaty is enacted to protect sea otters. 6. In areas where the otters recovered, urchin populations are once again kept down, the kelp beds recover, fish nurseries recover, and fish catches rise again. The news today is not completely happy for sea otters—they are still struggling to maintain their populations where they were able to re-establish themselves, and their range along the West Coast, which once stretched from Baja to Alaska, never did recover to anywhere near what it was. But the tale does serve to perfectly illustrate the concept of how a keystone species is essential for keeping an ecosystem in balance.
Other examples of keystone species are the prairie dog in the US Southwest, the banner-tailed kangaroo rat in the Chihuahuan Desert grassland (also in the Southwest), and the red-naped sapsucker in Colorado. But not all keystone species are cute and furry or feathered: Certain species of truffles are thought to be keystone fungal species, and oysters and other shellfish are considered keystone species in a...
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