Washington Post has us – well, not exactly preparing for the end of the world, but definitely on our guard. When polar bears start mating with grizzlies, it’s definitely a sign that the Arctic isn’t what it used to be:
Textbooks say these two species aren’t supposed to inhabit the same environments. Polar bears are marine mammals; grizzlies are terrestrial. But as the Arctic warms, sea ice is shrinking and the tundra is expanding. And the bears’ disparate populations are meeting, mating and creating a new breed that’s capable of reproducing.
Bears sharing both species’ DNA have been recorded several times over the past decade. So why are these two species linking up?
It’s called flexible mate choice: The bears are mating with the best possible partners as opposed to not mating at all, and they’re mating because they share relatively close territories and the same branches of the same evolutionary tree.
Intraspecies mixing between the two happened thousands of years ago, thanks to the advance and retreat of glaciers, and of late, it has been boosted by climate change. Scientists say it’s also probably been assisted by policies that protect both bears from culling and hunting, affording further opportunities for mingling.
[Steven Amstrup, chief scientist at Polar Bears International], like other experts, characterizes this “new” bear relationship as more beneficial to grizzlies than polar bears. That’s because there are more grizzlies than polar bears and because grizzly territory is expanding while polar bear territory is contracting. What that adds up to is a good chance grizzlies could essentially dilute the polar bear population until it doesn’t exist at all….