Can animals evolve quickly enough to survive global warming?
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Michelle Nijhuis
In recent years, Westerners have seen and heard a great deal about the effects of climate change on wildlife. Pikas are increasingly isolated on shrinking islands of mountaintop habitat in the Great Basin; mice, chipmunks and squirrels are retreating toward the ridgelines of Yosemite National Park; and numerous species, from butterflies and hummingbirds to an array of mammals, appear to be shifting uphill and northward.
The evidence has sparked a lively and emotional debate among conservation scientists. When threatened species can't relocate to more hospitable habitats, should we move them ourselves? The idea, known as "assisted colonization" or "assisted migration," is controversial for a lot of reasons, but a growing number of researchers see it as a necessary conservation strategy for at least some species.
As part of "Hot Times," our continuing series on climate change and the West, Hillary Rosner examines other strategies available to Western wildlife -- and to conservationists. Some species may be able to adapt to their changing habitats, either by simply tolerating new conditions or by evolving quickly enough to survive them. "Evolution is not just about one species ever-so-slowly transforming into another," Rosner writes. "It's also about much smaller, much faster changes that can determine whether a species will endure or perish as its world shifts."
Late last year, Rosner accompanied Montana biologist Scott Mills and his students into the Seeley-Swan Valley, where Mills studies seasonal coat color changes in snowshoe hares. For hares, coat color is a matter of survival: Brown hares on snowy ground and white hares on brown ground are both easy pickings for predators. In recent years, hunters and other observers have reported increasing numbers of hares out of sync with the season. But by tracking a group of Seeley-Swan hares throughout the year, Mills is finding that individual animals may be able to adjust the rate of their coat change to match variations in snowfall -- literally outfitting themselves for survival in a changing world.
For the hares, it's hopeful news. For us, it raises some new -- and sticky -- questions. If evolution can occur rapidly enough to protect some species from climate change, do conservationists have a responsibility to practice so-called "evolutionary rescue"? That is, should they encourage the reproduction of especially adaptable individual animals, or introduce resilient subspecies into new habitats? There are countless questions, both scientific and ethical, and no clear answers.
It's easy, and tempting, to say that humans have meddled enough, and that natural systems should simply be left alone to adapt as well as they can. But our power over the West's climate and habitat, for both good and ill, is outsized and growing. We can pursue answers to the many questions raised by climate change, and do our best to direct our influence intelligently. But stepping back is not an option.
