A new paper on the evolutionary history of bears (Bears breed across species borders: Kumar et al. 2017) has concluded that hybridization is common and natural among all species of ursids. And while some media outlets (e.g. DailyMail) have framed this as surprisingly convincing proof that experts were wrong to claim that climate change is the cause of recent polar bear X grizzly hybrids, definitive evidence against that interpretation has been available for years to anyone who bothered to look: see my recent “Five facts that challenge hybridization nonsense.”
This genetic evidence is just a cherry on top of the rest but will help get the paper the media attention the authors crave.
Polar bear X grizzly hybrids were known long before climate change and sea ice decline became an issue. See also previous posts here, here, and here. In fact, as I’ve pointed out, “most polar bear hybrids said to exist have not been confirmed by DNA testing” (including virtually all of the bears specialist Andrew Derocher claimed were hybrids, including the latest one from 2016 that prompted such gems as “Love in the time of climate change”).
A polar bear X grizzly hybrid, see Kumar et al. 2017. Photo by A. Derocher.
In my opinion, the most important conclusion of this paper is that occasional but widespread hybridization among bears is why it has been so hard to say with confidence when polar bears arose (which I addressed years ago, in my Polar bear evolution series: Part 1, Part 2, and Part 3). You cannot use traditional methods of pinpointing the timing of speciation events from genetic data if one or more of the species have hybridized (traded genes). See the long, fuzzy “divergence times” for bears in the image below from the Kumar paper.
From Kumar et al. 2017, Fig. 5: “The scale bar shows divergence times in million years and 95% confidence intervals for divergence times [speciation events] are shown as shadings.”
Posted in Evolution, Hybridization
Tagged bears, climate change, evolution, global warming, grolar bear, hybridization, media hype, pizzly, species, ursids
A new paper that combines paleoclimatology data for the last 56 million years with molecular genetic evidence concludes there were no biological extinctions [of Arctic marine animals] over the last 1.5M years despite profound Arctic sea ice changes that included ice-free summers: polar bears, seals, walrus and other species successfully adapted to habitat changes that exceeded those predicted by USGS and US Fish and Wildlife polar bear biologists over the next 100 years.
Cronin, T. M. and Cronin, M.A. 2015. Biological response to climate change in the Arctic Ocean: the view from the past. Arktos 1:1-18 [Open access] http://link.springer.com/article/10.1007/s41063-015-0019-3
Thomas Cronin is a USGS paleoclimatologist at the Eastern Geology and Paleoclimate Science Center, and Matthew Cronin is a molecular geneticist at the University of Alaska Fairbanks (see previous posts here and here about Matt’s work on the genetics of polar bear evolution).
From the Abstract:
Arctic climatic extremes include 25°C hyperthermal periods during the Paleocene-Eocene (56–46 million years ago, Ma), Quaternary glacial periods when thick ice shelves and sea ice cover rendered the Arctic Ocean nearly uninhabitable, seasonally sea-ice-free interglacials and abrupt climate reversals.
The final discussion and two summary graphics from this paper (copied below) are especially useful:
Posted in Evolution, Sea ice habitat, Summary
Tagged adaptation, Arctic, arctic seals, biological responses, climate change, climate extremes, Cronin, evolution, facts, genetics, glacial, he, ice-free summer, information, interglacial, LGM, marine mammals, paleoclimate, polar bear, resilience, sea ice, USGS, walrus
The longest-ever-recorded underwater dive by a polar bear, stalking three bearded seals, shows in striking fashion how truly difficult it is for a polar bear to catch a seal from summer sea ice. After the long dive, the bear (see below screen capture) erupts from the water to try and take the seal resting on the ice but it escapes.
The paper reporting this dive, by Ian Stirling and photographer and Arctic expedition organizer Rinie van Meurs, has hit the news again in a big way, as it finally appeared in print. I wrote about it in June here, when it came out in press. The video was shot on 19 August 2014, at the height of the Arctic summer (July, August, September).
CBC Radio posted the video and interviewed van Meurs yesterday (“As It Happens” 4 August), in which he reportedly made this astonishing statement:
“…after 27 years working, I have seen clearly changes in the sea ice. I don’t need to see the NASA records and graphs and all that.”
Indeed, who needs science and all that? You just have to look out the window of your ship! Anecdotal reports are what count as evidence to people who are not scientists. Van Meurs, who is not a scientist, is who the media gets to interview. Where’s co-author Stirling, the scientist?
More stills from the van Meurs video below – too bad, so sad, the bear gets no seal. Why polar bears eat little in the summer even if they are out on the ice hunting, as I discussed here.
Posted in Life History, Sea ice habitat
Tagged anecdotal reports, bearded seal, dive, evolution, fast, habitat, polar bear, science, scientific evidence, sea ice, stalk, summer, underwater
Recently, several polar bear biologists have teamed up with photographers to get pictures of starving bears into the scientific literature – and picked up by the media, with mixed results.
For the second time in five years, polar bear biologist Ian Stirling has teamed up with a photographer to give unwarranted scientific credence to an anecdotal account of polar bear behaviour. It included a picture of a pitifully thin animal (classic animal tragedy porn) and was framed to increase alarm over predicted effects of global warming. It got little media attention.
His Norwegian colleagues Jon Aars and Magnus Andersen have just done the same with a bear caught eating a white-beaked dolphin (photo above) – but this time the media took the bait.
Update 13 June 2015 – Information added on white-beaked dolphin distribution, sea ice conditions in 2014 and a correction. See below.
Posted in Advocacy, Life History, Sea ice habitat
Tagged Aars, AMO, Andersen, aquatic stalk, Arctic, Barents Sea, bearded seal, behavior, behaviour, caching, dive, evolution, global warming, Lagenorhynchus albirostris, polar bear, Polar Bears International, polarbearscience, sea ice, starving, Stirling, Svalbard, swim, thin, thin ice, tragedy porn, trapped, underwater, White-beaked dolphin
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.
Hudson Bay female with cub Wapusk National Park, Thorsten Milse, Government of Canada
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.
Posted in Evolution, Population, Sea ice habitat
Tagged adaptation, declining sea ice, early breakup, evolution, historical sea ice record, indivdual variation, late freeze-up, natural selection, NSIDC, polar bear, resilience, sea ice minimum, sea ice variability, Stirling, Stroeve, survival, western hudson bay
What with polar bear populations higher than they were 50 years ago and with many bears onshore during the ice-free season, a few polar bear attacks are to be expected – but how does the behaviour that drives those attacks compare with their closest evolutionary cousin, the grizzly?
I’ve done some summer reading on this topic, which I’ve summarized below. The results may surprise you.