Genetic research gives a insight to Greater Yellowstone Ecosystem foxes
BILLINGS - Blame the snow and cold.
Thanks to nasty winters, the Greater Yellowstone Ecosystem, including the Beartooth Mountains, have become a genetic island for Rocky Mountain red foxes.
That’s one of the findings from research that Patrick Cross conducted over two years while spending finger-numbing winter days in the Beartooth Mountains trapping the native high-elevation foxes. Cross, a University of Montana graduate student in systems ecology, was working with the Yellowstone Ecological Research Center. For his research, Cross had hypothesized that the foxes may be genetically different from those found in nearby Yellowstone National Park.
Instead, he found that the two populations are related.
“We thought the Beartooth fox would be distinct from Yellowstone’s, but that’s not true,” Cross said. “But GYE foxes are distinct from backyard foxes. That opens more questions. That’s cool. That’s good science. That’s exciting.”
Adaptable species
Rocky Mountain foxes are one of four western subspecies of the red fox (Vulpes vulpes). It’s estimated that their ancestors — V.v. macroura — likely migrated to the region at some time during the last ice age, about 35,000 to 11,500 years ago — known as the Wisconsin glaciation.
The other western fox species are: the Sierra Nevada red fox, the Sacramento Valley fox and the Cascade Range fox. There are 10 recognized red fox subspecies in North America, attesting to their adaptability to a variety of foods, climates and habitats.
The cat-sized canines are also found around the world, but not all of the subspecies are doing well. The U.S. Fish and Wildlife Service is reviewing the status of the Sierra Nevada red fox for a possible endangered species listing. Few of the foxes remain in the high mountains that border California and Nevada. Researchers like Ben Sacks are trying to figure out why.
“Are they confined to these areas because they are not equipped to survive outside those environments, or are there other reasons, like they don’t have to compete with coyotes?” said Sacks, of the veterinary genetics lab at the University of California-Davis. “Right now we sort of have to guess at that.”
In the genes
With some fox populations dipping, researchers have become more interested in identifying different subspecies, their habitat and their genetic history.
Using genetic analysis from foxes captured in the Beartooth Mountains and adjoining Yellowstone National Park, Cross was able to trace the animals’ ancestry with Sacks’ laboratory help. One of the findings was that the GYE animals shared a common ancestor, dated back about 400,000 years ago to an even earlier ice age — the Illinoian glaciation. That ancestor could have moved east to the GYE from Washington’s Cascade Mountains.
Another scenario is that before the last ice age the Cascade red foxes were more widespread but disappeared from the Rocky Mountains between the ice ages. Sacks said that ancestral fox movement isn’t completely clear, but what scientists have shown is that there was connectivity between the species during the last glacial period.
Either way, Cross said there’s pretty strong evidence that the Rocky Mountain and GYE group of foxes were founded in the same population event.
Following the Wisconsin glaciation, however, the Rocky Mountain red foxes became distinct from their Cascade relatives as the boreal forest retreated farther north. Cross can’t precisely say when the foxes moved into the GYE, since the area was slow to lose its ice cap, but suffice it to say that they were well-adapted to making a living in seasonally cold climates.
Elevation protection
One thing that still sets the GYE foxes apart is that unlike some Rocky Mountain red foxes living farther south, the GYE red foxes have not had their DNA swamped by foxes living at lower elevations.
“It probably has to do with mountain ecosystems and foxes’ relationship to it,” Cross said. “So it’s a much more complex story.”
Cross said one possible explanation is that natural selection would give females who go into heat later, or who have a longer gestation period, an advantage in high-elevation habitats. That’s because the female needs the kits to be born late in the spring when snow has receded from her high-mountain home and food is more plentiful.
“Kits born too early would not survive in this environment, and neither would their DNA,” Cross explained.
Climate question
All of this could change in a warming climate as winters become milder and more precipitation falls as rain instead of snow.
“…Climate and habitat conditions show that the region has undergone dramatic changes in the past, and will likely see a substantial reduction in forest cover in the near future, which will likely affect the genetic integrity of this fox population,” Cross wrote in an email.
Cross wrote his master’s thesis on his research and plans to publish the work in a scientific journal this summer. He said there are a number of similar red fox research projects going on in the West, including studies in the Sierras, Cascades and southern Rockies.
He’s also authoring another paper on the high elevation foxes’ habitat use. Of particular interest was their utilization of whitebark pine nuts as a food source when available.
Nut heads
Whitebark pine are in decline across the GYE. The high-elevation pine tree warrants protection under the Endangered Species Act but was precluded from listing by the U.S. Fish and Wildlife Service. One of the threats the trees face is changes brought on by warmer winters.
“One year we found foxes using pine nuts, and lots of them,” Cross said. “The following year there were zero pine nuts.”
Consequently, the foxes changed their habitat use, following squirrels that moved into spruce-fir forests.
“They changed their habitat use behavior in response to whitebark pine nut availability,” Cross said. “That really backs up that pine nut story of how important it is to these foxes.
“Pine nuts and squirrels help explain how foxes do survive at high elevations.”