As mountaintop dwellers, American pikas (Ochotona princeps) are particularly susceptible to climate change, but recent research suggests a population in California’s Sierra Nevada Mountains were driven to extirpation from the center of their distribution area by more than 60 years of warming temperatures.
Writing in the journal PLOS ONE, the researchers found evidence of pikas once occupying a vast area where they no longer exist, and they warned that pikas may future warming may cause pikas to disappear from a much larger area of the Sierra Nevadas than previous research has suggested.
The historic area of pika extinction is the largest recorded in the modern era, said Joseph Steward, a conservation biologist and PhD candidate at the University of California Santa Cruz.
“It’s a huge area that no longer has pikas anymore, and this is a novel example of the species disappearing from the center of their distribution,” said Stewart, the lead author of the study. “There’s been evidence of climate change nibbling away or eroding their distribution, but not extinction from climate change in the center of an area of contiguous distribution.”
Stewart and his colleagues were looking at the area surrounding Mount Pluto, which occupies 64 square miles in the northern Sierra Nevada Mountains. They surveyed the area from 2011 to 2016 to collect baseline data on where the pikas had been.
“It’s not only a survey of where they are right now,” Stewart said. “We can fill in gaps from where they were in the past by looking for their scat. We can rewind the clock and look at what the climate was like when there were pikas at these sites.”
Collecting their scat, which resembled tiny peppercorns, they used radiocarbon dating to track the pikas’ retreat. The radiocarbon data suggested the pikas likely disappeared from many of the lower elevation sites before 1955, when above-ground nuclear testing caused a spike in atmospheric radiation. Starting at low-elevation talus slopes by the Truckee River, the team found old pika scat at altitudes below where they expected pika to persist. Working their way to the peak, they found the most recent pika scat was from 1991, when they were extirpated from the region.
“We progressively worked our way up the mountain to be extra certain they were gone from this huge area,” Stewart said.
All signs for the cause of their extinction point to climate change, he said. When temperatures are too warm, pikas can’t forage, Stewart said, resulting in less energy. Pikas appear to have shifted upward in altitude along with warming trends, just as evidence suggests they did after the last Ice Ages, he said.
“Despite an abundance of suitable rocky habitat climate warming appears to have precipitated their demise,” he and his team wrote.
The evidence paints a bleak future for pikas in California. Projecting climate conditions into the future, they found that by 2050, suitable climate conditions for pikas in the Lake Tahoe area will be reduced 97 percent. Previous research suggested pikas might disappear from smaller pockets of habitat, about 28 square kilometers or smaller. Stewart’s team believes they will be extirpated from areas as large as 165 square kilometers.
The pikas’ disappearance points to other impacts from climate change, Stewart said.
“Hopefully since pikas have grabbed the headlines, as charismatic as they are, they will be an ambassador species for this issue,” he said.