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Keystone Species are Essential to Ecosystems and Biodiversity

We know that one of the architectural devices perfected by the Ancient Romans was the picture of duck in a keystone archway arch. We're less certain about whether arches were ever the subject of a song by top Roman rap-poet Cicero Doggy Dogg.

In any event, just as the keystone is essential to the physical integrity of a stone arch, 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:

  • European and Russian trappers hunt sea otters to near extinction in the 18th and 19th centuries.
  • The decline of the sea otters, which are essential to keeping sea urchins in check, allows sea urchin populations to explode.
  • The burgeoning sea urchins feast on and decimate the kelp beds, which are critical habitat for spawning fish.picture of sea otter
  • Fish begin to decline for lack of spawning habitat; this affects fishermen's catches.
  • Finally, an international treaty is enacted to protect sea otters.
  • 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.

picture of two prairie dogs 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 variety of estuarine ecosystems.

Keystone Species — The Big Picture

It takes a great deal of study for scientists to understand the complexities and nuances of ecosystems and their keystone species, and there is still much work to be done.



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The important thing for us non-brainiacs to understand is the general concept of keystone species, the need to protect them, and the fact that there are many keystone species that have yet to be identified by scientists.

It's also worth considering the related concept of general species interaction. Even when an ecosystem does not radically change upon decline or loss of a particular species, it does change to some degree. This is often a natural process of evolution. But when the species losses are caused by external factors, the changes to the ecosystem cannot be passed off as "natural." Unnatural causes of habitat and ecosystem change include:

  • overhunting, overfishing, or overharvesting;
  • pollution;
  • habitat encroachment from housing developments, agriculture, ranching, mining operations, or logging;
  • invasion of non-native species (which are often introduced inadvertently via shipping or intentionally via illegal trade in exotic species);
  • disappearance of predator species (which allows populations of prey species to explode);
  • habitat change due to unnatural temperature changes in the environment (such as with global warming).

According to noted biologist E.O. Wilson, we are now seeing species extinctions at 1,000 times the normal rate, and there is no disagreement among biodiversity scientists that this is human-caused. How many of these lost species will turn out to have been keystone species? How much habitat change can our natural world withstand before a domino effect causes truly disastrous results?

Such unanswered or abstract questions may have a hard time competing with our everyday needs, but they're questions that are worth keeping in mind. And now, back to the keystone species in our house, the television.

Publish date: 22-JUN-2004

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Songs for a Better Planet


The Future of Life

by Edward O. Wilson



E. O. Wilson, the eminent Harvard biologist, naturalist and Pulitzer Prize-winning author, thinks that species conservation is not just an end in itself, but rather a necessity for ensuring the future of ALL life on the planet. Each species is a strand in the book cover for E O Wilson, The Future of Life hyper-complicated web of life, and as more and more species disappear due to global warming, pollution, habitat encroachment, and other causes, the web is in more and more danger of collapsing and taking us all down with it. But he does not simply preach doom and gloom. He encourages the world to get behind workable solutions to take better care of the environment in which all life must survive. Developing a sensible land use and conservation policy is a central theme of the book, as are economic evaluations of the "services" that the earth's natural areas and species provide to us bottom-line-focused members of humanity. You may be surprised to learn that these services are roughly twice as valuable as the output of all the world's economies combined. The Future of Life is a good place to start if you still have any doubts about the value of preserving other species.

Read more reviews, see sample pages, or get purchase info for this book at

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"Each one [of the Earth's 5 million invertebrate species] plays a role in its ecosystem. It's like we're tearing the cogs out of a great machine. The machine might work after you tear out ten cogs, but what happens when you tear out a hundred?"

— Scott Black,
Xerces Society,
quoted in Sierra


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