Evolution is not just for the long-term – natural selection also goes on over short time periods. In the case of polar bears, this adaptation is almost certainly critical for its long-term survival.
Not all polar bears are identical — that is the reality that allows natural selection to operate.
I will argue that early breakup years in Western Hudson Bay weed out individual polar bears that do not have the physiological or behavioral characteristics necessary to be useful members of the population – and that this is a good thing for the entire population.
Figure 1. Slide from presentation by Julienne Stroeve, “Arctic sea ice reduction: the evidence, models, and global impacts” 22 September 2014, courtesy Ed Hawkins via Twitter. Note values prior to 1979 are vague approximations, error bars not shown (see previous post here
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