Arctic fox failed to move north at end of ice age
Study suggests animals may not migrate in response to rising temperatures.
Even the fast-moving arctic fox, used to trekking long distances, failed to retreat to cooler climes when global temperatures rose in the past, a new study suggests. The find dampens hopes that species will be able to adapt to climate change by moving towards the poles.
Comparing DNA from living arctic foxes with that extracted from fossils indicates that, at the end of the last ice age, foxes that lived in mid-latitude Europe simply died out rather than moved north. And the same could be happening now.
"What we're seeing happen to arctic foxes in Scandinavia today is exactly what we think happened in Europe 10,000 years ago," says Love Dalén, an evolutionary biologist now at University College London, UK, and lead author of the study in Proceedings of the National Academy of Sciences1.
Today the arctic fox, Alopex lagopus, is restricted to northern tundra, for example in Scandinavia and Siberia. But around the end of the last ice age, about 10,000 to 12,000 years ago, its range extended south to what is now Belgium, Germany and southwestern Russia.
Because Scandinavia was covered in ice during the last ice age, modern-day foxes there must have descended from populations that lived elsewhere. The foxes could have come from three possible regions: a northeastern part of Siberia that wasn't covered by ice; small coastal refugia nestled in-between glaciers in Scandinavia; or mid-latitude Europe.
Moving nowhere fast
To find out which it was, Dalén and his colleagues compared the mitochondrial DNA sequences of about 80 modern-day foxes from Siberia and Scandinavia to those of fossil samples from mid-latitude Europe. Siberian and Scandinavian foxes turn out to be very closely matched, but both living populations are genetically distinct from the older European populations.
That suggests that today's Scandinavian foxes came from northeastern Siberia, and that the arctic foxes further south in Europe simply died out when the ice retreated.
Robert Wayne, an evolutionary biologist at the University of California, Los Angeles, who was not involved in the study, says he was struck by the finding. "Arctic foxes are amazing in terms of their dispersal abilities, migrating up to 1,000 kilometres or more across pack ice," he says. "You would predict that they would migrate their way out of things."
But animals that aren't used to tracking temperature gradients as part of their normal life-history strategy are unlikely to read a slight change in temperature each year as a cue to move away, says Dalén. "For us humans, it is intuitively simple to shift north if it gets too hot," he says. "But for an arctic fox it's not going to be apparent that going anywhere helps."
Dalén reckons that warmer temperatures may have allowed red foxes to colonize regions that are normally the purview of their arctic cousins. Red foxes chase artic foxes away from carcasses and will even kill their cubs, forcing the animals to take refuge at the tops of mountains, says Dalén. "Today's arctic foxes aren't moving anywhere; they are just becoming more and more isolated in high-altitude patches," he says.
Increased competition may be one of the biggest problems species face as the climate warms, as animals are forced into territories that are already occupied.
For his part, Wayne would like to see a similar study done on the foxes of North America. But whatever happened in Europe thousands of years ago, "tracking didn't occur in this species, and you would have predicted it to," he says. "That leaves an ominous message for other mammals as we go through global warming."
- Dalén L., et al. Proc. Natl Acad. Sci., doi:10.1073/pnas.0701341104 (2007).