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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 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.
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. Sea otters once ranged from northern Japan to the Alaskan peninsula and along the west coast of North America to Baja California in Mexico. Until the 1700s, sea otters were abundant throughout the waters of the north Pacific and for centuries native groups, such as the Aleuts, hunted them.
During this time, the worldwide sea otter population numbered between 150,000 to 300,000. By the mid-1700s, Russian hunters had coerced the Aleuts to exploit sea otters for the fur trade, and the once abundant sea otter population plummeted. The otters that remained were chased down by English, French, Japanese and American traders. By the 1900s, the sea otter was nearly extinct with only 1,000 to 2,000 otters left. Only 13 remnant sea otter colonies existed from Russia to Mexico when the International Fur Seal
Treaty, which banned the hunting of sea otters and fur seals, was established in 1911. CALIFORNIA By the 1930s, a small group of 50 to 300 sea otters, a population now known as southern or California sea otters, remained near Big Sur, California. Under the protection of the International Fur Seal Treaty, this small population began a slow and steady climb from nearly extinct to a fairly stable population. From the mid 1970s to the mid 1980s, the southern sea otter population began to decline once again.
About 1,000 sea otters died over a 10 year period due to entrapment in gill nets. When gill net legislation was passed in the late 1980s requiring gill nets to move farther off shore, the sea otter population began to grow again until the mid-1990s. In 1977, the southern sea otter was listed as “threatened” under the Endangered Species Act. From 1995 until the present, southern sea otter numbers have declined in five out of the last six years.
Some of the possible causes include entrapment in fisheries gear, disease, food limitations, and habitat loss and degradation due to contaminants. Sea otter protection is a source of ongoing conflict between the California shellfish (abalone, sea urchins, crab, lobster) industries and conservation groups. While fishermen view the shellfish eating sea otter as a threat to their livelihood, conservation groups and scientists see the sea otter as a keystone species because their activity is central to the nature of their ecosystem.
A sea otter’s effect on the ecosystem is disproportionate to how many sea otters there are. Very few sea otters can have alarge effect. ALASKA In the early 1900s, following the near extinction of the sea otter, remnant sea otter colonies held on in the Aleutian Islands of Alaska, other portions of southwest Alaska, the Alaska peninsula and the northern Gulf of Alaska. Perhaps the most dramatic recovery of the sea otter now known as the northern sea otter occurred in the Aleutian archipelago.
By the mid-1980s, biologists believed that perhaps as much as half of the world’s population of sea otters lived in the Aleutian Islands. Indeed, the entire Alaska sea otter population seemed to be quite abundant until the late 1990s, when sea otters in southwestern Alaska began to suffer dramatic declines. OREGON AND WASHINGTON Northern sea otters from Alaska were transplanted to Oregon and Washington state with the goal of repopulating the sea otters’ former range.
In 1970 and 1971, 93 sea otters from Amchitka Island in Alaska were reintroduced to Oregon. However, sea otters are not presently found in Oregon. From 1969 to 1970, 59 sea otters were relocated from Amchitka Island to Washington. This population grew at an average annual rate of about 11 percent from 1989 to 1999 and scientists estimate that 500 sea otters currently live in Washington. However, this small population is vulnerable to fisheries conflicts, the continuing threat of oil spills and environmental contaminants.