Climate changes, and there goes the neighborhood

Ranges of rattlers and voles likely to shift drastically with warming

3:58pm, October 15, 2010
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PITTSBURGH ― Rattlesnakes and voles could be facing real estate meltdowns of their own, as climate change forecloses habitats or shifts livable conditions into new regions at speeds as much as a thousand times faster than prehistoric averages.

Even if global average temperatures increase by only 1.1 degrees Celsius by 2100, a level of warming considered virtually inevitable by climate scientists, 11 species of rattlesnakes across North America will have to cope with their ranges dislocating by 430 meters per year on average, paleobiogeographer Michelle Lawing of Indiana University in Bloomington said October 10 at the Society of Vertebrate Paleontology’s annual meeting.

If a more extreme scenario of 6.4 degrees C of warming  turns out to be accurate, shrinkage and shifts for rattlesnake ranges will average 2,420 meters annually, she and David Polly, also of Indiana, have predicted.

At that pace the warming could simply outrun rattlesnakes’ ability to adapt, Lawing said. She and Polly calculate that during the past 230,000 years, a period that includes three ice ages, rattlesnake ranges have shifted an average of only 2.3 meters annually.

Lawing and Polly estimated how snake ranges varied during past climate dramas by characterizing the temperatures and precipitation patterns that prevail in the species’ ranges today and then figuring out where those conditions would have existed in the past. Rattlesnakes made a good case study, Lawing said, because reptiles depend on their environment for heating and cooling and may be especially sensitive to climate disruptions. Finding relevant snake fossils to study is difficult, Lawing said, but those found so far do fit within the ranges predicted for their time.

Christian Kammerer of the American Museum of Natural History in New York City raised the question of whether rattlesnakes will basically just shift north as climate warms, a pattern already detected in some marine organisms along the West Coast. It’s unlikely to be that simple, Lawing said, because on land precipitation changes are also a factor, and snake ranges appear to be contracting as well as moving.

A story similar to the snakes’ appears in the history of range change for voles scurrying along the West Coast, paleoecologist Jenny McGuire of the National Evolutionary Synthesis Center in Durham, N.C., said in an October 11 presentation.

During  the past century’s warming, long-tailed voles in Yosemite National Park have moved up mountain slopes an average of 6 meters per year after 700 years of range movements of only 1.2 meters per year, McGuire reported. Her work incorporated data from fossil sites, where she had to work out a way to distinguish among five vole species just by the shape of their first lower molars.

Closely related vole species have responded to climate changes in individual ways. While long-tailed voles retreated, California voles appeared not to have changed their range much at all during the past 800 years.

Yet when she scrutinized teeth from California voles further, McGuire found that a form that is apparently adapted to drier conditions has replaced other forms of the species over most of the state. The diversity of California voles that once existed statewide now remains mostly around San Francisco.

Checking the fossil record is important for verifying ideas about past niches, because modeling them rests on assumptions that can go awry, says paleoecologist Rebecca Terry of Stanford University. For example, working backward from a species' current address assumes that the modern population occupies all of its prime habitat and has not lost ground to people.

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