By the time Stanford biology graduate student Paula Spaeth and I finally dried off, calmed down and met for dinner at the Elk Lake Lodge in Montana’s remote Centennial Valley last summer, we had to smile at the irony. We had separately endured a rainy, 15-mile drive on an unpaved road, sometimes bumper-deep in mud and out of cell-phone range. Outside, meanwhile, it was now snowing—a full-on white Christmas in June. I had flown in from California to learn firsthand from Spaeth, who’d been holed up in a chilly tent all week with her chihuahua puppy, what it’s like to do field research on global warming. The short answer this evening: “Miserable.”
Say global warming, and most people think of melting polar or glacial ice or unusually hot summers. Spaeth’s research project—trapping rodents in this conifer- and aspen-filled valley—exemplifies the breadth of climate change research being done by Stanford faculty and students. Thanks to some pivotal research by Spaeth’s adviser, associate professor of biological sciences Elizabeth Hadly, the animal processes Spaeth is exploring today can be viewed against a backdrop of 3,000 years of fossil DNA and climate data. That data suggests that climate change prompts genetic change, making some species more vulnerable to extinction.
Spaeth is studying two different neighbor species of mouse-sized rodents called voles: the montane, found in warmer, wetter environs, and the long-tailed vole, which lives in relatively cooler, drier areas. According to Hadly’s findings, vole populations decline as the temperature warms, but some species adapt better than others. Spaeth is going another step, trying to unravel the species’ interactions amidst the changes.
The weather clears the next day. Spaeth, 26, an upbeat fifth-year PhD student and former track star at Brown University, shows me what looks like a small piece of roof flashing and pops it into a box shape. She puts peanut butter and oats inside and, in milder weather, sets traps out in grid patterns on the sloping meadows and systematically removes species from the two climatic habitats. So far, Spaeth says, she’s found that if you remove montane voles from their preferred warmer, wetter area, the long-tailed voles soon arrive and set up house. Remove long-tailed voles, however, and the montane voles stay put and do not enter the other species’ territory. Montane voles appear to be more sensitive to climate, in other words, while long-tailed voles are more sensitive to the presence of the other species.
This work adds to growing evidence that the complexity of species’ responses to climate change will spell vast disruptions. Hadly is concerned that such complexity is overlooked by those who suggest warming trends will have generalized, benign impacts on animals—simply broadening their territorial reach, for example. She explains that warming together with habitat disturbance such as human development, dams, roads and agricultural planting “will lead to the demise of some species and a loss of diversity in others. The animals won’t be able to move.”
For more than seven years, Hadly has been excavating a cave in the Lamar Valley of Yellowstone Park, about 60 miles from the Centennial Valley, in Wyoming. It has a fossil record of animals that is 3,000 years old—a period characterized by postglacial warming, or the warming after an ice age, and several warming and cooling periods. Throughout those millennia, a rodent called a woodrat has been using that cave to store scat from animals who eat voles and other small animals, scat containing teeth and bones rich in DNA. “I wouldn’t have a dissertation if those rats weren’t collecting all that poop for thousands of years,” Spaeth says, laughing.
After extracting that DNA and matching it up to climate data for the stratum in which it’s found, Hadly’s data suggest that species who migrate and interbreed stand a better chance of surviving, even if their populations dwindle. Species who stay put will inbreed: their gene pool will shrink and become less diverse, leaving them vulnerable to viruses or animals that migrate into their turf and wipe them out directly or by eating their food.
What do the data augur? Separate studies have shown that winters in Yellowstone are getting shorter, and winter snow depth has steadily fallen since 1948. In this environment, climatic warming is likely to dry out the dense, verdant grasslands voles like both for food and as a shield from predators. Armed with her own and Spaeth’s findings, Hadly says, “You can make some serious predictions that voles are going to decrease in abundance, and the remaining voles will mostly be long-tailed.” As voles decline, so will an important food source for larger animals and birds of prey.
J.O’C.H
