Why species stay or go in response to climate change
Washington: In two new studies, researchers have provided a clearer picture of why some species move according to climate change, and where they go.
UC Berkeley researchers found that the Ash-throated Flycatcher, a low-elevation species, shifted its range down slope in response to climate change.
One study finds that changes in precipitation have been underappreciated as a factor in driving bird species out of their normal range.
In the other study, the researchers found a sharp decrease in range for the Belding’s ground squirrel, but noted some surprising areas where the species found refuge.
The two studies exemplify the type of research being explored through the Berkeley Initiative in Global Change Biology, or BiGCB, an ambitious effort to better understand and predict how plants and animals will respond to changing environmental conditions by studying how they have responded to earlier periods of climate change.
The first study’s findings challenge the conventional reliance on temperature as the only climate-related force impacting where species live.
The authors noted that as many as 25 percent of species have shifted in directions that were not predicted in response to temperature changes, yet few attempts have been made to investigate this.
“Our results redefine the fundamental model of how species should respond to future climate change,” Morgan Tingley, lead author of the study, said.
“We find that precipitation changes can have a major, opposing influence to temperature in a species’ range shift. Climate change may actually be tearing communities of organisms apart,” Tingley said.
The findings are based upon data gathered from the Grinnell Resurvey Project, which retraces the steps of Joseph Grinnell, founder of the UC Berkeley Museum of Vertebrate Zoology, in his surveys of Sierra Nevada wildlife from the early 1900s.
The resurvey project, which began in 2003, was led by Craig Moritz, former UC Berkeley professor of integrative biology, and his colleagues at the Museum of Vertebrate Zoology.
For the bird study, the researchers included 99 species in 77 historic survey sites in Lassen Volcanic, Yosemite and Sequoia national parks, as well as in several national forests.
In the century that has passed since the original Grinnell survey, summer and winter temperatures have increased an average of 1-2 degrees Celsius in the Sierra Nevada. Yosemite experienced the most warming — with average temperatures increasing by 3 degrees Celsius — while parts of Lassen actually got cooler and much wetter.
Among the bird species that moved upslope are the Savannah Sparrow, which shifted upward by 2,503 meters, and other meadow species such as the Red-winged Blackbird and Western Meadowlark.
The ones that shifted their range downslope include both low-elevation species like the Ash-throated Flycatcher and Western Scrub-Jay, and high-elevation species like the Cassin’s Finch and Red-breasted Nuthatch.
“Temperature did not explain the majority of these shifts,” Tingley said.
“Only when we included precipitation as an explanatory variable did our models adequately explain the movement patterns we observed,” he said.
The researchers found that while rising temperatures tended to push birds to cooler regions upslope, increased precipitation, which is more common at higher elevations, pulled them downslope.
“We believe many species may feel this divergent pressure from temperature and precipitation, and in the end, only one wins,” Tingley said.
Notably, more than half of the bird species in each of the three study regions did not shift their range despite pressures from climate change.
“Moving is a sign of adaptation, which is good from a conservation standpoint,” Tingley said.
“More worrisome are the species that have not shifted. How are they adapting? Are they moving, but we just can’t detect it? Or are they slowly declining as environmental conditions gradually become less ideal where they live?” he said.
The Belding’s ground squirrel has disappeared from 42 percent of the sites in the California Mountains where they were recorded in the early 1900s, but noted that some human-modified areas provided an artificial oasis for the squirrel.
The answers are complex, as illustrated by the second UC Berkeley paper about range changes for a species of squirrel found in the mountains of the western United States.
In that paper, researchers again used information obtained from the Grinnell Resurvey Project. Through visual observations and trapping surveys conducted throughout the mountains of California, they discovered that the Belding’s ground squirrel had disappeared from 42 percent of the sites where they were recorded in the early 1900s.
Extinctions were particularly common at sites with high average winter temperatures and large increases in precipitation over the last century.
“Taken together, these two studies indicate that many species have been responding to recent climate change, yet the complexities of a species’ ecological needs and their responses to habitat modification by humans can result in unanticipated responses,” Steven Beissinger, senior author on both studies, said.
The first study has been published online in the journal Global Change Biology and the second in the journal Proceedings of the Royal Society B.
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