By now, it's old news: Melting Arctic ice forces polar bears south, onto drier land and into warmer climates than they are accustomed. That the entire population will make this migration is inevitable, the question is: What will happen when they arrive?
Many researchers have claimed that polar bears will simply adjust their diets to survive in their new habitats. New research, however, shows that this change might not be enough when polar bears face a new competitor: grizzly bears.
To estimate the outcome of direct grizzly/polar bear competition, a team of researchers at UCLA created three-dimensional computer models of the two bears' skulls, based on actual specimens. They then used the model to compare various characteristics of the animals. Graham Slater, a biologist who led the study, explained:
What we found was striking...the polar bear and brown bear can bite equally hard, but the polar bear's skull is a much weaker structure.
What this means, is that polar bears will likely lose out the the grizzlies, who are better adapted to the plant-rich diet common in lower latitudes. The polar bear skull simply isn't strong enough to withstand the constant grinding a plant-based diet requires.
"The result for polar bears," explained Blaire Van Valkenburgh, a senior author of the research, "may be lower weight, smaller and fewer litters, less reproductive success, fewer that would survive to adulthood, and dwindling populations."
It's enough, she added, to bring the polar bear into an extinction vortex in which small populations shrink as they become less capable of surviving long enough to mate.