A Bear's Necessities
By DAVID QUAMMEN
Bozeman, Mont.
Op-Ed Contributor
The grizzly bears of Yellowstone Park are a national treasure, owned by nobody, preserved in trust for everybody, like the gold reserves of Fort Knox, the memory of Louis Armstrong and the clear air over western Nebraska on a breezy spring day. For 31 years, those bears have been listed as "threatened," and therefore protected from hunting and certain other tribulations under the Endangered Species Act. But recently the Interior Department has proposed removing them from the list, and this year, after a period for public comment that ends on Feb. 15, Interior Secretary Gale Norton will make a decision. That decision, though political, will in some degree be informed by science. The scientific question is, How safe are Yellowstone's grizzlies from extinction? The political question is, How safe do Americans want them to be?
The good news from Yellowstone comes in comparing two approximate numbers: roughly 200 bears in 1975, roughly 600 bears today. But to understand what those numbers mean, and what they don't mean, you need a few other facts.
The grizzlies of Yellowstone Park are part of a bear population in a larger area, known as the Greater Yellowstone Ecosystem, which encompasses also Grand Teton National Park, parts of six national forests and some other lands under public and private ownership. That ecosystem, so far as bears are concerned, is an island. It's surrounded by landscape inhospitable to grizzly bears: farms, ranches, fences, Interstate highways, golf courses, trophy houses, malls, railroad lines and towns like the one where I live.
Grizzlies from elsewhere do not immigrate to this ecological island. The Yellowstone bears are isolated, marooned, and have been for many years. It's nice to know that, under those circumstances, because of concerted management and conservation efforts by some good, hard-working people, the population has increased threefold, from very small to smallish. But it's also important to remember that insularity itself carries heightened risk. Why? Because any smallish, isolated population is especially vulnerable to bad luck - like a failure of its food sources, an epidemic disease or a coincidence of both.
Concrete examples of such bad luck come easily to mind. The wolves of Yellowstone - to consider another controversial species, reintroduced to the park in 1995 - have been experiencing drastically high pup mortality this last year, possibly because of a lethal virus. Of 69 wolf pups born in 2005, only 22 have survived: bad luck for the Yellowstone wolves, which until recently seemed to be thriving. Meanwhile, the white bark pines of Yellowstone are dying from a combination of fungal infection and bark-burrowing beetles. That's bad luck for Yellowstone's grizzlies, for whom pine nuts are a crucial food in autumn.
Now imagine the Yellowstone grizzlies in a year when a bear-killing virus arrives, the pine nuts are gone, and the cutthroat trout (another major food source, hurt by competition with lake trout, a non-native transplant) don't spawn. The population could quickly drop back to 200. Such fluctuations are common among wild animal populations. The difference with insular populations is that because they lack any supply of immigrants, they are more likely to fluctuate all the way to zero.
And then there's genetics. As the number of bears in the Yellowstone population fell to its low point of 200 in the early 1970's, collective genetic diversity fell too. The degree of loss can only be estimated, but the estimates raise concern. The important points to understand here are that small (and smallish) populations inexorably lose genetic diversity with each passing generation, through a random process called genetic drift, and that when sheer population size rebounds, genetic diversity does not rebound with it.
Genetic impoverishment becomes worse, not better, with each generation when a small population remains small. Inbreeding adds to the consequences of such impoverishment. And we can assume that the 600 Yellowstone grizzlies are now roughly as inbred as if they'd descended from 200 cousins, second cousins and cousins once or twice removed, left to mate together on a desert island 30 years ago.
The Interior Department has recognized this genetic concern and suggested dealing with it by periodically importing a female bear from elsewhere. That might help, or it might not, but the very suggestion reminds us that Yellowstone's grizzly population is constrained, marginal, genetically depauperate and threatened (yes, "threatened" is the right word) by various combinations of possible and inevitable trouble. And I haven't even mentioned the loss of bear habitat within the ecosystem because of timber cutting and oil and gas extraction on public lands and development on private lands.
Some people have argued that it's important in principle to de-list the Yellowstone grizzly, in order to show that the Endangered Species Act can yield success stories. That's like arguing that we must claim success in our wars, early and often, in order to preserve faith in America's military. So long as Yellowstone is an island, growing smaller every year, we shouldn't delude ourselves that its grizzlies have "recovered" in any but the most tenuous and misleading numerical sense. Real recovery will come, if ever, only when we radically revise our vision of how humans and grizzly bears might share far bigger areas of North American landscape.
David Quammen is the author, most recently, of "Monster of God: The Man-Eating Predator in the Jungles of History and the Mind."
©2006 New York Times
Bozeman, Mont.
Op-Ed Contributor
The grizzly bears of Yellowstone Park are a national treasure, owned by nobody, preserved in trust for everybody, like the gold reserves of Fort Knox, the memory of Louis Armstrong and the clear air over western Nebraska on a breezy spring day. For 31 years, those bears have been listed as "threatened," and therefore protected from hunting and certain other tribulations under the Endangered Species Act. But recently the Interior Department has proposed removing them from the list, and this year, after a period for public comment that ends on Feb. 15, Interior Secretary Gale Norton will make a decision. That decision, though political, will in some degree be informed by science. The scientific question is, How safe are Yellowstone's grizzlies from extinction? The political question is, How safe do Americans want them to be?
The good news from Yellowstone comes in comparing two approximate numbers: roughly 200 bears in 1975, roughly 600 bears today. But to understand what those numbers mean, and what they don't mean, you need a few other facts.
The grizzlies of Yellowstone Park are part of a bear population in a larger area, known as the Greater Yellowstone Ecosystem, which encompasses also Grand Teton National Park, parts of six national forests and some other lands under public and private ownership. That ecosystem, so far as bears are concerned, is an island. It's surrounded by landscape inhospitable to grizzly bears: farms, ranches, fences, Interstate highways, golf courses, trophy houses, malls, railroad lines and towns like the one where I live.
Grizzlies from elsewhere do not immigrate to this ecological island. The Yellowstone bears are isolated, marooned, and have been for many years. It's nice to know that, under those circumstances, because of concerted management and conservation efforts by some good, hard-working people, the population has increased threefold, from very small to smallish. But it's also important to remember that insularity itself carries heightened risk. Why? Because any smallish, isolated population is especially vulnerable to bad luck - like a failure of its food sources, an epidemic disease or a coincidence of both.
Concrete examples of such bad luck come easily to mind. The wolves of Yellowstone - to consider another controversial species, reintroduced to the park in 1995 - have been experiencing drastically high pup mortality this last year, possibly because of a lethal virus. Of 69 wolf pups born in 2005, only 22 have survived: bad luck for the Yellowstone wolves, which until recently seemed to be thriving. Meanwhile, the white bark pines of Yellowstone are dying from a combination of fungal infection and bark-burrowing beetles. That's bad luck for Yellowstone's grizzlies, for whom pine nuts are a crucial food in autumn.
Now imagine the Yellowstone grizzlies in a year when a bear-killing virus arrives, the pine nuts are gone, and the cutthroat trout (another major food source, hurt by competition with lake trout, a non-native transplant) don't spawn. The population could quickly drop back to 200. Such fluctuations are common among wild animal populations. The difference with insular populations is that because they lack any supply of immigrants, they are more likely to fluctuate all the way to zero.
And then there's genetics. As the number of bears in the Yellowstone population fell to its low point of 200 in the early 1970's, collective genetic diversity fell too. The degree of loss can only be estimated, but the estimates raise concern. The important points to understand here are that small (and smallish) populations inexorably lose genetic diversity with each passing generation, through a random process called genetic drift, and that when sheer population size rebounds, genetic diversity does not rebound with it.
Genetic impoverishment becomes worse, not better, with each generation when a small population remains small. Inbreeding adds to the consequences of such impoverishment. And we can assume that the 600 Yellowstone grizzlies are now roughly as inbred as if they'd descended from 200 cousins, second cousins and cousins once or twice removed, left to mate together on a desert island 30 years ago.
The Interior Department has recognized this genetic concern and suggested dealing with it by periodically importing a female bear from elsewhere. That might help, or it might not, but the very suggestion reminds us that Yellowstone's grizzly population is constrained, marginal, genetically depauperate and threatened (yes, "threatened" is the right word) by various combinations of possible and inevitable trouble. And I haven't even mentioned the loss of bear habitat within the ecosystem because of timber cutting and oil and gas extraction on public lands and development on private lands.
Some people have argued that it's important in principle to de-list the Yellowstone grizzly, in order to show that the Endangered Species Act can yield success stories. That's like arguing that we must claim success in our wars, early and often, in order to preserve faith in America's military. So long as Yellowstone is an island, growing smaller every year, we shouldn't delude ourselves that its grizzlies have "recovered" in any but the most tenuous and misleading numerical sense. Real recovery will come, if ever, only when we radically revise our vision of how humans and grizzly bears might share far bigger areas of North American landscape.
David Quammen is the author, most recently, of "Monster of God: The Man-Eating Predator in the Jungles of History and the Mind."
©2006 New York Times
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