If there were such a thing as a living, breathing barometer for climate change, it would probably be the American pika (Ochotona princeps). The thickly-furred bodies of these chatty, mountain-dwelling mammals—which resemble tiny rabbits with rounded mouse ears—tend to run hot, but aren’t efficient at giving off heat.
That makes them extremely sensitive to high temperatures—a tough trait to have in a warming world.
One answer might seem obvious: genetics. That is, after all, a central tenet of biology—that evolution occurs as diverse populations encounter environmental pressures, sparing individuals with adaptive mutations while others perish. It’s survival of the fittest, a lesson taught in high school science classrooms around the world. Consider, for instance, the rapid diversification of Darwin’s finches, or the high stakes of adequate camouflage in mice.
In theory, climate responses should be no exception, says Adam Smith, an ecologist and computational biologist at the Missouri Botanical Garden’s Center for Conservation and Sustainable Development. Climate, like any other aspect of the environment, favors certain traits over others. And when certain members of a species fare better than their kin, he says, it’s pretty much always chalked up to differences in their DNA.
But as Smith and his colleagues report today in the journal Nature Climate Change, American pikas might just break this age-old rule. In predicting how pint-sized pikas respond to climate, they found, genetics takes a backseat to geography.
In other words, a pika’s wellbeing may have more to do with the resources in its environment—like boulders and plants—than the traits it’s inherited. That’s almost like saying the quality of a cake is dictated more by the shape of the pan it’s baked in than the ingredients that went into it. Or, put in terms of human health, that a person’s longevity depends more on what shops are available in their neighborhood than the contents of their genome (sorry, 23andMe).
And it’s not at all what Smith and his 70 co-authors expected to find.
Smith and a handful of his colleagues—the self-described “pika brain trust”—have spent years trying to dissect the key factors that dictate pika survival in the wild. And most of them expected that this latest paper would simply confirm that evolution was the predominant force at play in the piecemeal disappearances of pika populations.
There was, however, one skeptic among the bunch: United States Geological Survey ecologist Erik Beever. After spending the better part of 25 years chasing after the grapefruit-sized balls of floof, Beever had a nagging suspicion that there was more to the bigger pika picture than genetics alone. With so much variation in survival, he mused, there had to be some contribution from the creatures’ physical surroundings—that is, their ecological context.
The rest of the brain trust was dubious, Beever recalls. But he convinced his colleagues to humor him.
Parsing out the predictive power of these different theories would require a near-complete portrait of pika survival in North America over time. So the brain trust reached out to colleagues and collaborators for data. More than 70 researchers responded to the call—and soon, Smith, the group’s resident computational biologist, found himself saddled with more than 14,500 records of pika sightings in North America, spanning about three decades.
Smith spent the next year crunching the numbers. He first sorted the pika populations into groups based on four different criteria: their genetic lineages; the elevation they lived at; the mountain ranges they occupied; or their “ecoregions,” or areas that offered defined sets of resources to their inhabitants, such as types of vegetation or soil, or the shade offered by nearby rocks.
Then, he looked at how groups of pikas within each subdivision scheme responded to each of 20 different climate-related variables, such as temperature, humidity, and precipitation. The best of the four models, Smith reasoned, would be the one where the fates of the pikas—measured by their abundance in the wild between 1990 and 2015—could be most accurately predicted on a group-by-group basis.
If, for instance, genetics prevailed (as most of the team expected), then pikas within a given lineage should exhibit similar responses, while those that were only distantly related wouldn’t.
For a few climate variables, that turned out to be true. But in the end, the most consistently predictive model—the one that sorted the pikas into the most coherently climate-responsive groups—was actually the ecoregion schematic. It was a gratifying result for Beever. “A small part of me was happy to see I wasn’t crazy,” he says.
In retrospect, the finding makes a lot of sense, Smith says. Ecoregions are reflective of what’s available in a given habitat—and for a territorial homebody like a pika, which might spend its entire life within a couple hundred feet of its birthplace, securing good real estate is crucial for survival. These ecological neighborhoods are what provide pikas with water-rich plants to munch on in times of prolonged drought, or the piles of broken rock to scurry under to escape the heat.
Pikas’ extreme context dependence almost makes them the plants of the mammal world, says Meagan Oldfather, an ecologist at the University of Colorado Boulder who wasn’t involved in the study, but authored a related commentary praising its design. “They’re really reliant on specific structures in their landscape,” she says.
That has important implications for conservation, Oldfather says. With so many ecological factors to take into account, there won’t be a one-size-fits-all solution for pika populations. A strategy that works well in one area could be irrelevant, or even disastrous, in another.
That might sound grim. But there’s a flipside, too: Paying closer attention to habitats could help researchers identify important ecosystem elements that help pikas thrive in unlikely places, Smith says. While pikas have dwindled in some areas, other populations are still going strong, and researchers are now exploring ways to enhance the resilience of the groups most in peril, Smith says. In light of these findings, future interventions might include installing water guzzlers—essentially, giant versions of the bottles in hamster cages—in certain habitats, or outfitting others with dead logs to provide extra shade.
And ecoregional influences probably aren’t a pika-specific phenomenon, Beever says. Whether it’s because they’re relatively immobile, or because they have very specific habitat requirements, plenty of other species have deep ties to their surroundings. Which means they could need more tailored conservation efforts, too. “We think this is going to be the norm, rather than the exception,” Beever says.
Of course, none of this invalidates the contribution of genetics—even for pikas, Smith says. In many parts of the world, pika species have shifted to higher elevations to beat the heat, and may be tapping into genes that make them more tolerant of low-oxygen conditions to do so. (In the race against temperature, however, pikas will probably stop climbing first.)
Rather, this study underscores a simple fact on a complex topic: Biology lacks hard and fast rules—and the few it’s retained keep getting broken, Beever suggests. It’s why we still study it: There’s no all-encompassing explanation for how life manifests in the face of change.
“Evolution is still the basis for understanding biological variation,” Smith says. “But we also need to take into account local circumstances when understanding how species respond to climate.”