From California to Costa Rica, rising temperatures could be driving species to higher elevations
As temperatures rose, these species tended to edge upward to
higher and cooler ground, says Craig Moritz, director of the
The possibility that climate change is pushing around sensitive species has been worrying biologists, so Moritz and his colleagues found a way to test the idea over an unusually long time. They resurrected the museum’s trove of field notes and revisted sites of a mammal survey that started in 1914.
Tropical biologists are still describing lots of new species
and often don’t have such luxurious long-term data, says Robert Colwell of the
Rising temperatures that push species uphill could suck some
of the current native biodiversity out of the tropical lowlands, Colwell and
his colleagues warn. Their paper and the
European scientists have found long-term data sets to check
for species shifts, so Moritz says he was delighted to work out a way to use a
rich record in
From 1914 through 1920, pioneering ecologist Joseph Grinnell
painstakingly surveyed small mammals along a line, or transect, running through
Since Grinnell’s time, the region’s monthly average minimum temperatures have risen about 3 degrees Celsius. Today’s surveyors put together enough details to see if that warming correlated with a rise in the upper ends of the ranges of 28 small mammal species.
Overall, species’ range limits seemed to have crept up the slopes, Moritz and his colleagues reported. But some creatures, such as the deer mouse, didn’t seem to have moved, and a few even retreated a bit.
“This opens up a lot of questions in community ecology,” Moritz says. For one thing, he would like to know why the pinyon mouse seems to have shifted upward when the deer mouse apparently hasn’t.
Jonathan Lenoir, who
has been studying plant range shifts in European mountains, says he would like
to know whether there’s a difference in sensitivity to temperature between
low-elevation and high-elevation mammal species in the
Grinnell’s copious old
notes provided an unusually strong basis for re-surveying, comments Richard
Condit of the Smithsonian Tropical Research Institute in
Such attrition could develop, Colwell explains, because average temperatures at a particular elevation don’t change much across the tropics. At other latitudes, species shifting up a slope merely clear the way for neighbors from warmer zones to move in behind them. For the tropics, though, there’s no warmer zone to supply warm-adapted neighbors.
Colwell is not predicting a barren landscape, but a loss of current diversity. “I expect the lowlands to get simplified,” he says.
To get a rough sense of the risk, Colwell and his colleagues estimated ranges from transect samples of four species groups — ants, geometrid moths, members of the coffee family and plants growing on tree branches. According to these records, about half have such narrow ranges now that they may have to colonize a completely new zone if temperatures increase as predicted.
Condit protests that lots of factors besides temperature draw borders for a species, so there’s no way to know just from current ranges what warming will do to species.
“This is crude, and we acknowledge that in the paper,” Colwell says. He adds that he hopes this first pass at the problem will lead to more experiments — and inspire conservationists to protect corridors for species to migrate upward in case the worst does come to pass.
Colwell, Robert et al. 2008. Global warming, elevational range shifts, and lowland biotic attrition in the wet tropics. Science vol 322 (Oct. 10) p. 258 – 261.
Moritz, Craig et al. 2008. Impact of climate change on small-mammal communities in Yosemite National Park, USA. Science vol. 322( Oct 10) p. 261 -264.
Information about Joseph Grinnell, including examples of his notes:
Lenoir, Jonathan et al. 2008. A Significant Upward Shift in Plant Species Optimum Elevation During the 20th Century. Science Vol. 320. no. 5884 (June 27) pp. 1768 - 1771
Svenning, Jens-Christian and Richard Condit. 2008. Biodiversity in a Warmer World. Science vol 322(Oct. 10), p. 206 -207.