New research led by a University of Colorado Boulder associate professor has found that warming temperatures are pushing the range of small mammals in the state to higher elevations, which could eventually could lead to localized extinctions in cases when they are pushed too high up mountainsides.
CU Boulder announced the research Thursday in a news release. The peer-reviewed study was published this week in the journal Ecology and led by Christy McCain, an associate professor in the Department of Ecology and Evolutionary Biology at CU Boulder.Â
Described in the release as a “mammoth effort,” the study involved more than 40 species of Colorado rodents and shrews, such as the Preble’s jumping mouse and yellow-bellied marmot. It involved more than a decade of field work and also relied on historical records dating back to the 1880s.
The researchers compared their survey results of species’ ranges to roughly 4,500 historical records in museum collections, including at the CU Museum of Natural History, where McCain is curator of vertebrates.
The results were mixed. Ranges haven’t changed in elevation for six of the studied species, and actually shifted downward for 11. But they shifted upward for 26 species, and the average shift was about 430 feet upward.
However, montane mammals — those living at higher elevations, like the golden-mantled ground squirrel — have been particularly affected by warming temperatures. The ranges of exclusively montane species shifted upward in the case of three-quarters of those studied. Those species moved up by more than 1,100 feet on average, which CU said in its news release said is a significant change that, if it continues, “could wind up squeezing many of these animals out of Colorado entirely.”
“It’s frightening,” McCain said in the release. “We’ve been talking about climate change in the Rockies for a long time, but I think we can say that this is a sign that things are now responding and responding quite drastically.”
The study says that other research has shown upward shifts in elevation in the habitat of many small mammals and birds in the West, alpine plants in Europe and the United States, and moths in the Asian tropics.
“Overall, shifts are upward for most species, but individual species also demonstrate unexpected responses like downward shifts or no detectable change,” it says.
It says numerous factors, ranging from the location of a mountain within a species’ geographic range, to the body size and reproductive capacity of a species, can mediate its response to warming temperatures.
The study focuses on two mountain regions, on the Front Range and in the San Juan Mountains. It says temperatures in the state as a whole are estimated to have warmed by nearly 2 degrees Celsius, or about 3.5 degrees Fahrenheit, over the past several decades.
The study found that the pygmy shrew — North America’s smallest mammal, weighing less than a quarter — never was detected above 9,800 feet in elevation in Colorado before 1980. Now it can be found above 11,800 feet. The golden-mantled ground squirrel’s range went up 650 feet, or 200 meters, in elevation on the Front Range, but increased by some 2,300 feet, or 700 meters, in the San Juans.
“I was expecting that we would see something between 100 to 200 meters, but we saw a lot more,” McCain said in the release. “This is way bigger than the change that has been determined in other mountain regions around the world.”
The study concludes, “These data provide clear evidence that small mammals, particularly montane and cold-adapted species, are rapidly and drastically shifting their ranges to higher elevations as temperatures warm regionally.”
If the trend in shifting upward elevation for montane species continues, they will be at risk of local extinction, the research says. It says the land area on Colorado mountains “decreases linearly” above 8,000 feet or so in elevation, so that only about 5% of land area occurs over about 11,100 feet. Also, the amount of land that consists of uninhabitable rock and ice on a mountain dramatically increases as elevation rises, with habitable land above 11,100 feet or so being only 1 or 2% of habitable land on the mountain as a whole.
“Thus, even if mammals and other organisms can track higher, the amount of habitable land at the highest elevations is minimal,” the study says.
McCain calls the findings “a wake-up call.”
“We have to start taking this seriously immediately if we want to have healthy mountains and ecosystems,” she said.
Other coauthors in the study include Tim Szewczyk, a former graduate student at CU Boulder now at the University of Lausanne, and Sarah King of Colorado State University.
