Tag Archives: ice age

Early Holocene polar bear skeleton from Norway vs. other ancient remains

A press release issued yesterday (23 January 2018) by the University of Stavanger tells the story of decades of work on the most complete ancient polar bear skeleton in the world, found in 1976 in southern Norway, that culminated in an articulated museum display. This specimen was described in my research paper, Annotated Map of Ancient Polar Bear Remains of the World (Crockford 2012), which shows how many very early Holocene remains have been found outside current polar bear range.

Finn the ice age polar bear skeleton_U Stavanger_photo 2

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Genetic similarity of polar bears does not make them vulnerable to global warming

A new genetics paper suggests that global warming will “fragment” polar bear habitat to such an extent that it will further reduce the already-low genetic variability documented in the bears, with disastrous effects on survival.

Beaufort Sea male polar bear USGS_2005 Amstrup photo

However, that argument only works if you disregard a rather large body of literature on other mammals as well as the history of polar bears themselves. I’ve addressed this issue before (“Low genetic diversity will not make polar bears more vulnerable to extinction”) and what I said then needs to be repeated now:

“…there is lots of evidence to support my contention that polar bears are not more vulnerable to extinction just because they have low genetic diversity.

I continued:

Many populations that were reduced to very low numbers (i.e., gone through a ‘bottleneck’ ), ending up with low genetic variation, have subsequently recovered dramatically without adverse affects.

In other words, they not only recouped their population size after a population bottleneck but did so while dealing with subsequent environmental fluctuations and other natural threats to their survival (Lehman 1998:R723-724).

In some cases, genetic diversity increased after a population bottleneck, via mechanisms biologists are only just beginning to understand.

In fact, there is good evidence to suggest that ice age cooling is what previously fragmented polar bear populations: past warm interglacial periods brought bears closer together, confined more or less to the area within the Arctic Circle – even in winter.

Go back and read the entire genetic diversity post. I concluded it by recounting several examples of abundant and successful mammal populations with low genetic diversity (with references), including Northern elephant seals, Guadalupe fur seal, Sand Nicolas Island fox, Mouflon sheep, and North Atlantic right whale. The details are worth reviewing. If you can’t access a paper you want to read, contact me via the contact page above and I’ll send it along.

Regarding this new paper (Kutschera et al. 2016), what I said before needs repeating:

“To suggest that polar bears cannot endure a bit of Arctic warming in the future (whether natural or due to human influences on climate, or a bit of both) is absurd: climatic extremes have defined the evolutionary history of polar bears, which means that climatic extremes have fine-tuned their biological adaptability.”

In fact, the paleoclimate/genetics paper by Cronin and Cronin (2015) which I summarized a few days ago, documents those climatic extremes. See below for details on the polar bear genetic diversity paper.
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Polar bears barely survived the sea ice habitat changes of the last Ice Age, evidence suggests

While the polar bear is an Ice Age species, genetic and fossil evidence suggests it barely survived the profound sea ice changes associated with the Last Glacial Maximum, one of the most severe glacial periods of the Pleistocene.

polar_bear_usfws_no date_sm

A map of sea ice extent at the climax of the Last Glacial Maximum (both perennial and seasonal ice), prepared with the help of a colleague, makes it possible to discuss what genetic and fossil evidence can tell us about the probable effects of glacial conditions on polar bears and ringed seals.

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Polar bear spin reaches new heights as geneticists promote their work

A new paper out in the journal PLoS Genetics proposes that a hybridization event between female polar bears and male brown bears (aka grizzlies) occurred in Southeast Alaska at the end of the last ice age. I’ll get to a discussion of the paper itself (coming in a day or two) but first I have a few things to say about the global warming hyperbole generated by the people promoting the paper. I found it simply mind-boggling.

While the paper itself (Cahill et al. 2013: “Genomic Evidence for Island Population Conversion Resolves Conflicting Theories of Polar Bear Evolution”) contains only one short phrase that could possibly be interpreted as linking the results to future scenarios of catastrophic global warming, some of the co-authors have made statements (for the press release and in media interviews) that spin the global warming mantra right over the top. Continue reading

How long have polar bears lived in Hudson Bay?

The unique geographical position and oceanographic properties of Hudson Bay make it very different from other Arctic regions that polar bears inhabit.

Hudson Bay is a large shallow basin that freezes over every winter – somewhat like an enormous salt-water lake. This ice cover melts completely every summer, in part because it is well south of other truly “arctic” regions. As a consequence, while Hudson Bay offers excellent seal-hunting conditions for polar bears from winter through early summer, the long ice-free period with no or few feeding opportunities presents a unique challenge that polar bears elsewhere do not routinely encounter (see previous posts here, here and here).

Modern polar bears on the sea ice of Hudson Bay (Wikipedia photo and map).

But Hudson Bay also has a unique geological history. Since the end of the last ice age Hudson Bay has been available as polar bear habitat about half as long as other Arctic regions. This phenomenon is rarely discussed in the polar bear literature (although Andrew Derocher, in his new book [reviewed here] does mention it). In this post, I’ll summarize the geological history of Hudson Bay over the last 30 thousand years, as it pertains to polar bear habitat.

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