Posts Tagged ‘brown bear’


This is Admiralty Island, which is not far from Juneau. It is known by the Tlingit as Xootsnoowú, which translates as “Fortress of the Bears.”

It is home to 1,600 brown bears, which I didn’t see while whale watching. This island has one the highest densities of brown bears anywhere in the world, and it is the highest for North America.

These aren’t just normal brown bears, however.  This is where things get really interesting.

About ten years ago, it turned out that many brown bears from Admiralty Island and the neighboring islands of Baranof and Chichagof had mitochondrial DNA that is similar to the polar bear.  This caused quite a bit of a sensation, because if these brown bears really were closely related to the polar bears, then we might have found the place where polar bears evolved from brown bears. This was also at the time when there was a growing body of evidence that polar bears evolved very rapidly and relatively recently from brown bears.

A later nuclear DNA study revealed that the similarities between these brown bears and polar bears were the result of ancient hybridization. The genomes of these brown bears is roughly 1 percent polar bear, but 6.5 percent of the X chromosomes come from polar bears.

These islands and Ireland are both places where polar and brown bears hybridized at the end of the last glacial maximum. Polar bears got stranded on islands, which became great brown bear habitat. Male brown bears mated with polar bear sows, and the offspring were fertile. However, they bred back into the brown bear population in such a way that they are almost entirely brown bear in ancestry.

As the arctic is warming, polar bears are finding themselves stranded on land for longer periods during the mating season, and brown bears (mostly grizzlies) are wandering north. Several hybrids have been killed in recent years, including one from this year.

Polar bears could very likely become extinct as a result of climate change, but their genes could still live on in the brown and grizzly bears that manage to hybridize with them during this transition period.

I wish I had been able to see one of those bears on Admiralty Island,  but I am just glad I got a photo of the island itself.

Whales were calling. Not bears.




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One dead moose sure can feed a lot of creatures!

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polar bear and cub

Right now there is a lot of talk about whether polar bears will go extinct as the climate changes.

The animal has become very much a symbol of demise of ice in the Arctic Ocean, where the bears prey on seals that that whelp on the ice.

The theory goes that if polar bears, they are automatically doomed to extinction.

I have always found this to be a very simplistic (and somewhat alarmist) proposition.

Please note that I do believe climate change is a major problem, and yes, we must do what we can to reduce greenhouse gases in the atmosphere.

What I don’t accept is that polar bears are automatically doomed by climate change.

There are two major reasons why:

The first is that polar bears are not stupid animals. They can learn to utilize new food sources fairly easily, and I don’t think for a minute that they are doomed because they can no longer hunt ice seals. The seals themselves might be doomed, because if they try to whelp on shore, they are going to be easy pickings for just about every predator. Climate change is happening too fast for these seals to evolve new reproductive strategies.

But polar bears themselves can learn to hunt other things. I see a future in which polar bears become the ultimate scavengers, competing with wolf packs that have brought down moose. Wolves will have a very hard time protecting their kills from such behemoth scavengers, and this certainly will put a new selection pressure on wolves in northern Canada and Alaska, who have had to worry only about about more omnivorous and generally smaller brown bear subspecies scavenging their kills.

Also, for those of you who are not aware, the short arctic summer brings about some of the most productive avifaunal events in the world. There are hundreds of birds that fly north to the arctic each spring to lay their eggs.

Why do they do this?

Well, during the summer, the sun is beating down almost 24 hours a day. That’s very good for plants, and it’s also good for insects that eat the plants, which are very good for certain birds to eat.

So if you’re a small insectivorous bird, and you want to raise your chicks in a productive environment, you go to the arctic to raise your young. There are hundreds of species that have evolved to do just that.

And then there are other birds that fly up there to hunt those little birds, and there are others, such as snow geese,  that fly up there to raise their offspring in vast green meadows that erupt each summer.

There is already evidence that polar bears are taking advantage of the arctic’s annual avifaunal glut.

Polar bears are eating now eating snow goose eggs, which are quite high in fat.  The geese produce enough eggs every year to sustain a healthy population of polar bears, and if polar bears began to capitalize on birds, they would be able to survive a warming climate, where ice seals are either extinct or whelping elsewhere.

The other thing is that polar bears have survived warming periods before.

And how do we know this?

Well, it turns out that brown and polar bears are very close relatives. The two species can interbreed and produce fertile offspring, which has caused quite a bit of confusion about the age of the polar bear species.

Early mitochondrial DNA studies have suggested that polar bears are a recent offshoot of the brown bear lineage. If this were true, it would mean that the polar bear rapidly evolved to fit its niche within the past 150,000 years, which would almost make them a subspecies of the brown bear. Later genome-wide analysis revealed that the polar bear actually an older species. It evolved some 600,000 years ago from the brown bear lineage. Even more extensive genome-wide analysis found that polar bears were more likely in the 4 to 5 million year old range.

This discovery highlighted the perils of constructing phylogeny and taxonomy using only mtDNA data.

But it actually showed that polar bears have survived warming periods before, and they very likely will survive this one. If polar bears were a very recent offshoot of brown bears that had become specialized to arctic sea ice, their chances of survival would be much lower than they are now, but it now turns out that they aren’t as specialized to sea ice as we may have originally believed.

The other way we know polar bears have survived warming periods is through the evidence of hybridization in brown bear populations.

We actually now have two very good examples of this hybridization.

The first of these was the discovery that extinct Irish brown bears had almost the same mitochondrial DNA as polar bears.

And back when we believed polar bears were fairly recent species, it was suggested that all polar bears evolved from those Irish brown bears.

There was also another population of brown bears that had similar mtDNA to polar bears. The brown bears of Alaska’s Admiralty, Baranof, and Chichagof  (“ABC” ) Islands, also share an mtDNA sequence that is similar to that of polar bears. For a very long time, it was believed that polar bears evolved from these brown bears.

But the separation was even more recent– only 14,000 years ago.  If this were true, then polar bears would be a species younger than the domestic dog.

Of course, that notion was destroyed through the genomic analysis. Mitochondrial DNA is only a tiny piece of the genome, and it is inherited only via the female ancestors. Studies that use only this data simply do not get the full picture, and there are many, many revisions in the literature that have come from errors in mtDNA analysis.

So I was quite pleased to see a recent study on the ABC Islands’ brown bear population. It was a genomic study, and it found that these bears are actually derived from polar bears, not the other way around.

The researchers conclude that at some point during a warming period, a population of polar got stranded on these islands. They remained on those islands, feeding on a wide variety of food sources for male brown bears to reach them.

This study also suggested that initial finding that polar bears were derived from Irish brown bears was also in error. Instead, something similar had happened. Female polar bears became stranded in Ireland and then mated with native Irish brown bears. Over time, the main mtDNA lineage of Irish brown bears was replace by that of those bears that were derived from those polar bears– perhaps the polar bear blood infusion was a bit of genetic rescue or provided some other competitive advantage.

These genetic studies show that polar bears are not bound to the sea ice.

As intelligent, opportunistic predators, they have been able to survive warming periods, and they have been able to survive through hybridization with their closest relative.

If I were going to bet on the future of the polar bear, I would have to bet that it will survive the current warming period.

I’m not so sure about the ice seals, and I think they are a more appropriate icon for the movement to reduce greenhouse gas emissions.

When it comes to adapting to change, one would not be wise to bet against any species of bear, unless we’re talking the giant panda.

The panda is pretty much screwed.

No arguments there.

But I think the future for the polar bear in this warming world is much better than many people are forecasting.

This isn’t an overly specialized animal in the same way a giant panda is.

It can adapt. It can learn.

It’s not as bound to the ice as people think.

It’s evolutionary history clearly reveals this fact.


Now, before commenting on this post. Please read it in its entirety.

I am not denying climate change. Nowhere in that post do you see the words “Global warming is a hoax.” (except right here!)







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These are rainforest wolves from the Great Bear Rainforest in British Columbia.

Both bears and wolves eat salmon on their yearly runs.

And it’s also in this area where you can find “white” black bears.

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Remember when I said that polar bears should be considered a subspecies of brown bear?

I was wrong.

There was a study of ancient brown bear, modern brown/grizzly bear, and polar bear mtDNA that found that all polar bears have brown bear mtDNA that can be trace to a single female brown bear that lived in Ireland 20,000 to 30,000 years ago.

I then broke my own rule about believing mtDNA studies and accepted these findings.

I did not report, as some places did, that polar bears evolved in Ireland.

The fossil record shows that polar bears have been around for at least 110,000 to 130,000 years.

What happened was that a male polar bear mated with a female Irish brown bear, and it turned out that all living polar bears descend from that coupling.  The crossbred bears bread back into polar bears, and the only thing they have that is brown bear is that mtDNA.

Now, based upon that evidence, I suggested that polar bears ought to be considered a specialized subspecies of brown bear.

Well, a nuclear DNA study came out yesterday that shot that possibility down.

This study revealed that polar and brown bears split about 600,000 years ago.  There was some cross-breeding between the two over that time period, but the two lineages have been distinct for a long time.

Instead of polar bears being a subspecies of brown bear, we have a species complex that exists between Ursus arctos and Ursus maritimus. 

The two species can and do interbreed when they wind up sharing territory, which isn’t often.

However, it is possible hybridization has affected the evolution of both species.

In addition to that finding about Irish brown bears, another mtDNA study found that brown bears living in Alaska’s Alexander Archipelago have mtDNA that is very similar to that of a polar bear.  It is possible that a female polar bear wound up on the islands. She mated with brown bears, and her offspring then bred back into the brown bear population.  For what ever reason– perhaps inbreeding– all the brown bears of that island descend from that female polar bear.

I know of know studies that have looked at these bears from this perspective.

Mitochondrial DNA studies don’t tell us everything.

We need to be careful when citing them as absolute fact.

They can really skew results.


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For a piece on specialization within the bear family, I could have gone with several options.   Sloth bears have evolved to live on termites, and most famously, giant pandas are almost entirely reliant upon bamboo.

But I decided to go a different route.

Sloth bears and giant pandas are just bizarre animals, and compared to the bear family as a whole,  they are pretty puny.

There is another species of bear that is hyper-specialized, though we usually don’t think of it in this manner.

After all, it shares the title of the largest terrestrial carnivoran with the Kodiak bear.

Of course, I’m talking about the polar bear.

Polar bears are often classified as marine mammals.

Now that should tell you something about them.

No other bear is so reliant upon the sea for its sustenance.

Of all the bears, they are the only ones that live almost exclusively on meat.

They can handle absolutely frigid conditions on the arctic sea ice, and they can swim in the most chilling waters of the Arctic Ocean– often swimming for as much as 60 miles at one stretch in order to access better hunting grounds and to return to the land.

You’d think such a large predatory animal would essentially be invulnerable.

But the truth is they are quite fragile.

Part of the reason why they are so fragile is that they are the youngest species of bear, if they are indeed a full species at all.

Indeed, one could make the case that they are nothing more than a modified but highly specialized brown bear.  The initial split between polar and brown bears may have happened 150,000 years ago. Of course, this was a mitochondrial DNA study, but because we don’t yet have the polar or brown bear genome sequenced, all we  have are these mtDNA studies. (The authors of that last study are working on it!)

150,000 years is a very short in terms of an evolutionary time frame.

And to make matters even more complicated, polar and brown bears have continued to exchange genes through the past 150,000 years.  The popular press likes to make a big deal about the killing of a confirmed polar/grizzly bear hybrid in Canada. (Grizzlies are just a subspecies of the Holarctic brown bear).

However, a more recent study of ancient and modern brown bear and polar bear mtDNA revealed that all modern polar bears descend from a liaison between a polar bear and a female brown bear living in Ireland 45,000 years ago.

American black bears never hybridize with brown or grizzly bears in the wild, but they can in captivity. However, polar and brown bears have done so in the wild, so one might be more willing to accept that the polar bear is nothing more (or less) than a modified brown brown bear.

And as a modified brown bear, it has evolved rapidly from a truly generalist ancestor.  Brown bears once range from all of Europe and most Asia. They also colonized a huge chunk of North America, including Mexico and even parts of the Eastern and Midwestern United States. (When Europeans came to the Americas, the brown bear was restricted to the Western half of the continent. It still lived in Mexico, but it was not found in the East.)

If count the polar bear as a brown bear, the brown bear species was also able to colonize the ice cover of the Arctic Sea.

But in order to do that, these modified brown bears had to give up many of their generalist adaptations.

Exactly what polar bears lost from the ancestral brown bear has only recently been revealed. These adaptations have only been extant in polar bears for about 20,000 years, which makes their specialization very recent.  The evolution of the main traits that separate a polar bear from a brown bear are actually more recent than the first signs of domestication in wolves, which appeared over 30,000 years ago.

Its head is proportionally smaller and flatter, which allows the polar bear to shove its head into seal dens and breathing holes.  The main prey of the polar bear on the ice are ringed and bearded seals– especially the pups of both species. Although these animals are relatively large, neither weighs as much as a fully grown male polar bear, and because the bears hunt mostly the pups of these species, they are essentially hunting little blobs of fat.

If your diet is little more than little blobs of fat, you aren’t going have the same selection pressures that maintain the robust skull of the generalist brown bear. Using finite element analysis, it was revealed that the polar bear’s skull has many more structural weaknesses than the brown bear.  A brown bear can kill a moose, but it is very hard for a polar bear to do the same.  Polar bears have roughly the same strength of bite as the brown bear, but it is much more potentially damaging to their skulls if they try to bite as hard. (Polar bears rarely attack walruses, despite what you’ve seen on TV.)

The polar bear is an ice seal hunting specialist.

It is a master at living on the sea ice and stalking and digging up seals.

However, as we all know, the sea ice in the arctic is staying in place for fewer and fewer weeks every year. Although some will argue about the exact cause, we are still experiencing a warming planet.*

And that’s causing polar bears to remain land bound for more weeks out of the year.

It’s also opening up land in the North for brown bears to colonize.

And that allows the two bears to meet once again.

Brown bears will thrive in a warming climate. Not only do they have more robust skulls.  They also have larger molar teeth for really chewing plant matter. Polar bear molars are relatively small.

Bears have to learn from their mothers what to eat, and if polar bear sow doesn’t teach her cubs how eat vegetation, they will likely starve if no meat is available.

Of course, they can learn to eat vegetation as adults, but they simply are physically less adept at this diet than grizzlies are.

And that means that the holarctic brown bear will outcompete the polar bear, and those that it doesn’t outcompete, it will absorb into its gene pool.

The brown bear’s generalist diet has served it well.

But it had to specialize to colonize the arctic ice..

And because it specialized so much, the form that evolved to do so cannot survive in a world without ice– at least in its current form.

However, I don’t think the polar bear will go extinct.

I think that hybridization will become very common between polar and Holarctic brown bears, and through that hybridization, brown bear traits will be introduced back into the polar bear population.

As we’ve seen with Eastern coyotes, hybridization with wolves has introduced several beneficial traits to allow them to specialize in hunting deer in the Eastern United States and Canada.

I don’t see why this hybridization wouldn’t be beneficial to polar bears in a changing climate.

However, I think that we are still operating under the assumption that polar and Holarctic brown bears are separate species, and thus, any time they crossbreed, it’s polluting the gene pool.

I think this is a very wrong way to think about polar and brown bears, for it is exactly that same sort of Victorian typological thinking that we are forced to deal within the dog fancy.

Nature doesn’t consider them separate species. If a polar bear is in estrus and brown bear is around, they will mate, and the offspring they will produce will be fertile.

Polar bears have always existed with occasional infusions of brown bear blood, just a domestic dogs existed for thousands of years with occasional additions of wild wolf blood– and still do in many locations.

A polar bear is a good example of what happens to a generalist species when it evolves a specialized form.

This is a bit of warning to all dog people. The Anglo-Saxon dog fancy has always celebrated the specialist dog and excoriated the notion of a generalist dog. Even some of the bad science about dogs adopts this framework.

However, we have seen time and again what happens to dog breeds that have become too specialized. Like the polar bear, they become masters at one particular thing, and when that thing disappears, the dog either adapts into becoming a fancy breed, develops a new set of talents, or becomes extinct. The baiting bulldog of England became a fancy breed once bull-baiting was banned– much to its detriment. The St. John’s water dog managed to survive on in the retrievers, which are very much multipurpose dogs, but the turnspit, the little short-legged dogs that ran giant “hamster wheels” to turn spits of meat over open fires are now extinct.

Specialization is fraught with perils– whether we’re talking domestic animals or wildlife.


*I really don’t want this post to lead to a discussion about the causes of climate change. The purpose of this post is to talk about perils of specialization, typological taxonomy, and the evolution of a specialize form of brown bear called the polar bear. I have my views on the issue, but you’re entitled to yours.  However, this is one argument that gets old very fast.


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Grizzly bears are a subspecies of the brown bear (Ursus arctos).

Polar bears are a modified and highly specialized brown bear, and their exact species status is a little bit questionable. They can produce fertile hybrids with brown bears, and these hybrids are becoming more and more common. At least one second generation hybrid has been recorded in the wild.

If the sea ice disappears from the arctic ocean, the only future for the polar bear is to be reabsorbed into the more generalist brown bear populations.

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