The migration of southern animals into the Arctic is an intriguing development that may result in an addition or subtraction of several pieces to the puzzle that will determine what the Arctic will look like in 50 to 100 years. The new dynamics will include the possibility of displacement of Arctic native species, with fish and animals like Pacific salmon and red fox potentially outcompeting Arctic char and Arctic fox for food and territory. And with sea ice no longer stopping them, killer whales could drive beluga whales and narwhals out of the biological hotspots they depend on in summer. Additional effects could come from diseases carried by southern animals from which some Arctic animals have no immunity.
There is also the potential for a variety of closely related animals - such as grizzlies and polar bears - to interbreed and produce hybrids that could drive some native species to extinction. It's impossible to predict how each of these influences will shape the species that survive in the future Arctic and which ones will not, but we are already seeing evidence of change in a variety of ways.
I first heard of animals interbreeding in the Arctic in the spring of 2006. I was flying in a small plane from Tuktoyaktuk to Inuvik in the western Arctic. I had just spent a few days with scientist Ian Stirling, who was catching and tagging polar bears in the Beaufort Sea. After learning what I had been up to, the pilot told me that an American hunter had shot a strange-looking bear on the sea ice just west of Banks Island a week earlier. The bear apparently had the features of both a grizzly bear and a polar bear. The wildlife officer who investigated was so confused that he seized the dead animal until the origins of its parentage could be proved. Grizzly bears and polar bears have produced hybrids in zoos, but the biology and behavior of the two animals suggested that they would likely make war, not love, in the rare event they met on the sea ice.
In Inuvik, I didn't bother to drop in at the government wildlife office to see if there was truth to anything the pilot had told me. I soon regretted that I hadn't. Back home a few days later, I learned from polar bear biologist Andrew Derocher that an American hunter had shot a polar bear/grizzly cross that spring (photo above).
As it was a first in the modern wild, no one was willing to suggest that this hybrid might signal a trend. It did, however, get Alaska biologist Brendan Kelly wondering whether this kind of hybridization was occurring in other Arctic species.
Kelly was well aware that seals, walruses, and sea lions are more prone to hybridization because they share the same number of chromosomes, which allows them to produce offspring. He also knew that the zones in which hybridization are likely to occur have been limited by sea ice that effectively prevents Atlantic walruses and narwhals, for example, from moving into the Pacific and prevents Pacific salmon and other marine animals from moving into the eastern Arctic.
If you removed continent-sized ice sheets that prevented southern marine mammals from moving north into the Bering and Chukchi Seas and from the Bering and the Chukchi into the Arctic Archipelago, he wondered, what might be the outcome? The question was not an outlandish one because Arctic sea ice receded to a record low in 2007.
In the 1990s, scientists such as Ian Stirling and Andrew Derocher predicted the demise of polar bears at the southern edge of their range as sea ice retreated. (Photo: Edward Struzik)