Whew! Climate change not likely to cause 'grolar bears'

From the University of Washington comes this sigh of relief.

Risk of interbreeding due to climate change lower than expected

grolar-bearOne of the questions raised by climate change has been whether it could cause more species of animals to interbreed. Two species of flying squirrel have already produced mixed offspring because of climate change, and there have been reports of a hybrid polar bear and grizzly bear cub (known as a grolar bear, or a pizzly).

“Climate change is causing species’ ranges to shift, and that could bring a lot of closely related species into contact,” said Meade Krosby, a research scientist in the University of Washington’s Climate Impacts Group.

She is the lead author of a study published July 6 in Nature Climate Change that tallies the potential number of such pairings. Looking across North and South America, it finds that only about 6 percent of closely related species whose ranges do not currently overlap are likely to come into contact by the end of this century.

“People have been concerned that climate change would be bringing all these species into contact, and that this could unleash a wave of interbreeding,” Krosby said. “What we found is, not so much.”

A 2010 editorial in the journal Nature suggested that northern species may begin to interbreed and create a so-called “Arctic melting pot,” and even prompted one artist’s rendition of what those new offspring would look like.

The idea also worried land managers looking at how to prepare for climate change. At a workshop, land managers told Krosby they worked with very closely related species separated by small distances. What if managers linked the two areas with a wildlife corridor, and as the climate changed the species started to mix?

This study is an attempt to see how much that should be a concern. It looked at 9,577 pairs of closely related species of birds, mammals and amphibians in North and South America. For the 4,796 pairs whose ranges currently do not overlap, computer models show that only 6.4 percent of them will come into contact due to climate change by the year 2100.

The most overlap among species occurred in the tropics, and among birds, likely because more species live in the tropics and birds cover wider ranges, Krosby said.

While the study suggests that climate change is unlikely to result in widespread interbreeding, wildlife biologists still need to consider their particular region and animals of interest to best protect specific populations.

“Managers still need to look case-by-case at species at a local scale, but at a global scale, the big picture is that it’s probably not going to be a huge problem,” Krosby said.

The study likely overestimates how many species could be at risk of interbreeding because it assumes that all species will be able to access new habitats that become available due to climate change. In fact, natural barriers prevent animals from reaching all potential new habitats, and humans have created new barriers such as highways, farms, and cities that can block migrations to more hospitable places.

“The number one strategy for helping biodiversity respond to climate change is to increase connectivity, to link up habitats that have been fragmented by human activity, so species can move, and track climate as it shifts to stay comfortable,” Krosby said.

“If people are worried that wildlife corridors and other ways to increase connectivity could bring these species into contact, we’re saying: That’s probably not going to happen, and allowing species to move is far more important.”

Krosby did her doctoral work looking at how historic climate changes affected species in the past, including how the end of the last ice age led to interbreeding among West Coast songbirds. Now she focuses on contemporary climate change, to see how species are responding and how land managers can best protect biodiversity under faster, human-driven changes to Earth’s climate.


Co-authors include Joshua Lawler, an associate professor in the UW’s School of Environmental and Forest Sciences; Joshua Tewksbury, a UW professor of biology; postdoctoral researchers Theresa Nogeire and Julie Heinrichs in the School of Environmental and Forest Sciences; and former UW researchers Chad Wilsey, now at the National Audubon Society; Jennifer Duggan, now at California State University Monterey Bay; and Jenny McGuire, now at the Georgia Institute of Technology. The research was funded by the Wilburforce Foundation, the Doris Duke Foundation and the David and Lucile Packard Foundation.

112 thoughts on “Whew! Climate change not likely to cause 'grolar bears'

  1. Um, they already interbreed, albeit at low levels. Polar bears are a subspecies of brown (grizzly) bears.

      • There needs to be a certain level of genetic similarity for species to be able to successfully breed , hence way you do not get any catdogs. So although Polar Bears may not be a subspecies of brown bears they are certainly related at the level that really matters.

      • I read that polar bears are an evolutionary off shoot from brown bears. Theory being some browns were trapped on the ice, failing to migrate soon enough during a glaciation. True? False?

      • I did not say polar bears and grizzlies don’t interbreed occasionally (see my other comment further down), what I’m saying is that this phenomenon does not make polar bears a subspecies of grizzly.
        Species in different genera occasionally interbreed: a harp seal x hooded seal hybrid has been documented (in the wild), as has a false killer whale and a bottlenose dolphin (in captivity). Fin whale X blue whale hybrids (in the wild) are probably as common as polar bear x grizzly hybrids, or more so – they are well known back to whaling days.
        Polar bears and grizzlies are closely related but so are lots of other animals. Occasional hybridization and genetic similarity does negate their status as distinct species. Polar bears and grizzlies are distinct on many levels that are more important than genetics: life history, ecology, physiology, behaviour, morphology.
        Even geneticists agree: http://polarbearscience.com/2012/12/06/more-evidence-that-the-polar-bear-is-a-distinct-species/

      • Can you provide a definition of species? The concept seems very vague.
        We are in real trouble if polar bears interbreed with flying squirrels, especially if warming results in more trees in the arctic from which the new kind of bears can launch attacks!

      • and species shift due to climate change is an another nonsense alarmist chestnut. Since the 19th century , even earlier, species have adapted and moved thanks to the movement of mankind. Sometimes beneficial sometimes not.

      • Hello Susan
        I tend to think that if the only thing separating two taxa is geography, then they ain’t species. In the old-fashioned model of allopatric speciation, a taxon that becomes separated geographically then undergoes selection and/or drift. If now the ranges of the two taxa coalesce once more, then the test of good species is whether they interbreed and have successful offspring.
        Obviously there are morphological and behavioural differences here but perhaps the interesting point comes when the behaviour/morphology of the intermediates is investigated.

      • Note that the example I gave was a second generation polar-grizzly hybrid,in the wild,not in a zoo.
        The interbreeding is more common than most people believe,just talk to Inuit hunters,who see the hybrids regularly.
        It is possible,even likely that both species have a common ancestor,and the polar and grizzly evolved separately from that ancestor.
        Anyhow-they interbreed quite often,and it’s not something new,not related to changing climate.

      • “Polar bears are not a subspecies of brown bears – you saying so every time this issue arises does not make it so.” — Dr. Susan Crockford, zoologist
        I learned at university that there were “Lumpers and there were Splitters” and that the issue of categorizing species is very controversial. As a “lumper”, I don’t see polar bears as a different species from the brown bear. It is OK with me that splitters think they are different species — but they are wrong. 🙂
        As a side note; I do not see the white human of the far north as a different species from the black human of the equator regions either. I am consistent in a way that splitters can never be. 🙂

      • Dr. Crockford,
        Some folks get their shirts in a knot when different populations of the same species interbreed (never mind different species like lions and tigers). Hmm … With domestic animals, we celebrate hybrid vigor. For instance, many people would far rather have a mule than a horse.
        Do wildlife biologists, as a group, have an opinion on hybrid vigor?

      • Blueday
        “We are in real trouble if polar bears interbreed with flying squirrels, especially if warming results in more trees in the arctic from which the new kind of bears can launch attacks!”
        Have you ever visited the great West Island of New Zealand – traditionalists call it Southern Hemisphere Penal Colony #1, or – strangely – Orstralia.
        There, they have a voracious carnivore – the drop bear – Thylarctos plummetus.
        Puts your squirrel-bears to shame, even with the modelled sylvanian bonuses for the Far North.
        Vividly aware of the fauna of the continent of Fourecks in the Discworld novels . . . .

      • Wikipedia; “A species is often defined as the largest group of organisms where two hybrids are capable of reproducing fertile offspring, typically using sexual reproduction. While in many cases this definition is adequate, the difficulty of defining species is known as the species problem. Differing measures are often used, such as similarity of DNA, morphology, or ecological niche. Presence of specific locally adapted traits may further subdivide species into “infraspecific taxa” such as subspecies (and in botany other taxa are used, such as varieties, subvarieties, and formae).”
        This is the definition I learned. The species problem was then and still is now. Dr. Crockford’s distinctions: “life history, ecology, physiology, behaviour, morphology. ” If two species can’t produce fertile offspring(donkey, horses) they can’t propagate. If the offspring are fertile but less competitive in their environment they’re unlikely they are unlikely to succeed and maintain a breeding population. There are many examples of “species” which have different history, ecology, physiology, behavior, sexual selection, and morphology that are simply due to physical or environmental separation but can successfully interbreed and maintain a population resulting in polymorphic species(or subspecies).
        It’s an old argument that won’t be settled here or probably ever. But from what I’ve read polar bears are definitely more aggressive and dangerous to humans.

      • Polar bears are not a subspecies of brown bears
        Brown bears and Polar bears are no different that human “subspecies”. White, black, brown, yellow, we all can interbreed successfully, with viable offspring, which makes us all the same species.
        The same cannot be said for politicians, which are with very few exceptions the result of interbreeding lawyers with jackasses.

      • Ferd,
        I’m with Susan on this issue.
        Polar v grizzly bears are a case far different from human populations. They have not just geographic but important anatomical and behavioral differences for which there is no comparable human analogue. Brown and polar bears have been diverging for a lot longer than the human “races” (which they aren’t) and under greater selective pressure differences than even the most extremely separated human groups.

      • Polar bears are a cadist’s nightmare. Cladistics might be useful for higher level taxons but at the species level, that utility fades.

  2. How did the Polar Bears ever survive to today without humans to worry about their numbers? How did they ever survive previous hot eras? “Illogical! Does not compute! Please explain!” (Norman – “I Mudd” Star Trek TOS”

    • Polar bear populations appear to have rebounded successfully once aggressive hunting of them was controlled. They still live in a very tough environment so it likely the population will still be highly variable for many reasons. Dr. Crockford has done a fine job separating truth from fiction in this.

  3. Uh-oh, this means the risk of non-interbreeding is higher than expected, due to “climate change”. See, you just have to put the right spin on it.

  4. Now she focuses on contemporary climate change, to see how species are responding and how land managers can best protect biodiversity under faster, human-driven changes to Earth’s climate.
    Sounds so Earth Mother friendly; “land manager.” Nice benign term for EPA types that slap fines on people when they don’t respect a large puddle on their property as the vernal pool biodiversity micro-ecosystem it truly is.

  5. Are they saying that the polar bear I shot was probably just trying to eat me?…………… not trying to have her wicked way with me?

  6. Inter-breeding between different, but closely related, wild species is a problem why?
    Do they believe that all the species that exist currently have always existed, in their current forms? I suspect that bear do, and have always done, a lot more than just defecate in the woods. If differing species inter-breed successfully, rather than killing each other, I suspect it’s because that’s how nature made them.

  7. This articles seems to pre-suppose the the creation of “grolar” bears would be a bad thing.
    What exactly is the problem with species inter-breeding anyway? You can’t on the one hand complain about species extinction (and loss of bio-diversity) and then at the same time complain about the creation of new species.
    Surely this is nature’s way of adapting to climate change or any other change – mixing and mutation of genes to create a new species or sub-species that is better adpated to circumstances – or natural selection.

  8. Hybridization was never a global warming/sea ice issue with polar bears: mating with grizzlies happens in spring when sea ice coverage is at its maximum. It is known as far back as the late 1800s and occurs when the odd male grizzly wandering into polar bear country meets an receptive polar bear female.
    It occurs occasionally now because grizzly population numbers are increasing due greater hunting restrictions. It has nothing to do with Arctic warming or sea ice changes.
    Those who suggest otherwise are misleading the public.
    Dr. Susan Crockford, zoologist

    • It occurs occasionally now because grizzly population numbers are increasing
      or it could be because the bears are horny. any port in a storm.

      • In relation to enviromentalist [sic] arguments against fish farming in British Columbia, I once heard the term “genetic pollution”. It seems to be a very dangerous path to follow.

    • Mules come to mind – offspring of mating of a horse and donkey.
      Infertile though.
      Mules are said to be big but tougher than a horse, though hypothetical variations are many.
      Of course humans arrange opportunities for breeding.

  9. Really? Sub species? How much you want to bet they can interbreed with Brown Bears just fine. That’s all that counts. And in point of fact, isn’t there INHERENT RACISM in this worry about “interbreeding”. Why, consider the problem. “Mulatto bears..” 1/2 WHITE and 1/2 BROWN. The K.K.K. would not approve (Klondike Kolective Kooperative)

  10. Interbreeding became more common with better forms of transportation, EG Camels in Austrailia, Zebra mussels in NA etc etc etc
    Left to themselves animals do move, but it takes time, and normally its to warmer areas, see where most of the world population is….

  11. In the kingdom you have four views on other animals , eat it , run away from it or shag it , or ignore it
    In the case of Polar Bears its a easer choice , eat or shag , that is it , hence why the biggest risk to Polar Bear cubs is adult male bears, there not one so they must be the other.

  12. The flying squirrels….uhm, how exactly did they determine the interbreeding to be due to CC? Extra lift due to the hot air?

    • @Mike Bromley (July 6, 2015 at 10:14 am)
      The same thing caught my eye. From the article:

      Two species of flying squirrel have already produced mixed offspring because of climate change, and there have been reports of a hybrid polar bear and grizzly bear cub (known as a grolar bear, or a pizzly).

      I’d like to see some replicated, ironclad proof of the flying squirrels producing mixed offspring due to climate change. Or perhaps I need to go back and have a closer look at the Pope’s Encyclical. Maybe that’s where they came up with that; papal dispensation instead of computer models.
      Then again maybe it’s simple as, “We were drunk, it was closing time, and well, things just got out of hand.”

      • Two species of flying squirrel have already produced mixed offspring because of climate change,” Has Bullwinkle been informed of this?

    • That one caught my eye as well, especially since there has BEEN NO global warming for twenty years.

    • interbreeding to be due to CC?
      every spring millions of college kids flock south for a change of climate. is anyone seriously suggesting that this is the cause of interbreeding?
      reminds me of the schoolmarm who wouldn’t stand for any fooling around. if there was any fooling around to be had she wanted it lying down.
      it may well be more pleasant to hump with your ass in the warm sand in Florida than a frozen lake in Minnesota, but anyone that thinks this is what causes humping has never been to spring break.

    • I don’t get it: I thought I was supposed to believe that the species we see today arose from genetic variability and differential selection; now, I am supposed to believe that evolution happens when two similar species interbreed?
      I appreciate the update.

      • You’re also supposed to believe that Lysenko was wrong. Yet here we have proof that his ideas persist to this day:
        “The population represented by the bones in the cave probably developed Neanderthal- like jaws and teeth from chewing and the heavy use of their front teeth and incisors for other tasks.” Of course, this is taken from The Guardian, so lower your scientific expectations to zero or even lower.

      • evolution happens when two similar species interbreed?
        absolutely. a species diverges into two separate branches and then merges. the hybrid results are all over the map as compared to the original branches, allowing some hybrids on occasion to jump into niches neither of the two parent branches could successfully compete in.

  13. I feel a ” Human sacrifice, dogs and cats living together… mass hysteria! ” type quote coming on.
    Hey, I gave you an hour/+20comments 🙂
    ht/Peter Venkman, Ph.D. (Parapsychology)

  14. I swear, a mosquito I killed the other day was the size of an eagle. Coincidence? I think not.

    • Hang on. Why is OK for you to kill a mosquito if all of God’s creations are perfect? You best let her bite you next time, it is the balance of nature after all. You are committing a sin against God by interfering in the perfect balance of Mother Earth.

  15. A colleague of mine discovered that she was the owner of a group of very odd looking pups that resulted in a one-night stand between a hound and shih tzu. They were sold as shithounds.
    I am the owner of a borderjack https://www.dogbreedinfo.com/b/borderjack.htm named Porkchop. She looks just like her white with black markings Jack Russell dad but weighs 32 pounds. Stinkin fast. These dogs make excellent mid-weight agility trial sporting dogs. My other dog, Jake, is a cross between a Blue Healer and a Border Collie, known as a borderheeler https://www.dogbreedinfo.com/b/borderheeler.htm. Smartest dog I have ever known. His favorite thing to do is chase wads from shotgun blasts. He finds them and brings them back to me. I wish I could train him to pick up casings. But no. He is only interested in the gun powder.
    Given the odd mixing (and some seemingly impossible pairings) we get with dogs doing what dogs do, I have no doubt we have interbreeding going on in the wild. No doubt. And you could no more stop it than my friend could which resulted in shithounds.

  16. Some Scandinavian folk have very pale hair and pale eyes whereas Inuit folk (among others) have black hair and dark eyes … have they ever been known to interbreed?

    • looking forward to Global Warming/Climate Change increasing
      my personal “wildlife corridor”

      • B. Cow: I’ve read that occasionally a male moose wants to get friendly with a (female) cow. Is this what you’re looking forward to coming down your enhanced wildlife corridor?

    • I am a blond (now gray) blue eyed mostly Norwegian/Swedish with some Finnish. My material DNA, as well as many other Scandinavians, can be traced to tribes in the far north part of Western Russia. They are darker. Also, there are Scandinavians with black hair; not too many though.

      • My ex wife insists I’m living proof that Neanderthals interbred with modern humans.

  17. Perhaps the real question is, can global warming hysterics ever interbreed to produce something scientifically useful.

  18. Species are certainly shifting, moving, adapting and thriving in hot cities. That’s what they do.

    • And work in ‘Climate “Science”‘?
      Auto – asking because I would really like to know.

      • Ligers are huge – up to twice the size of its daddy lion or mama tiger. Tigons result from a daddy tiger and mama lion, but they are smaller, about the size of a female tiger.

  19. According to DNA studies modern humans interbred with archaic humans probably due to climate change. But I don’t know about the risk part.

  20. I know where I heard this before:
    Dr. Peter Venkman: This city is headed for a disaster of biblical proportions.
    Mayor: What do you mean, “biblical”?
    Dr Ray Stantz: What he means is Old Testament, Mr. Mayor, real wrath of God type stuff.
    Dr. Peter Venkman: Exactly.
    Dr Ray Stantz: Fire and brimstone coming down from the skies! Rivers and seas boiling!
    Dr. Egon Spengler: Forty years of darkness! Earthquakes, volcanoes…
    Winston Zeddemore: The dead rising from the grave!
    Dr. Peter Venkman: Human sacrifice, dogs and cats living together… mass hysteria!
    Mayor: All right, all right! I get the point!

  21. Meade Jones should be working at Starbucks… not making shit up about Climate Change as a PhD… claiming species are already on the move… oh sure Meade… yea… sure…

  22. “People have been concerned that climate change would be bringing all these species into contact, and that this could unleash a wave of interbreeding,” Krosby said. “What we found is, not so much.”
    People have also been concerned about pseudoscience conduced by the cult of global warming, and the damage that this could cause to the economy and the public’s perception of science. What we found is that the cultists are idiots.

  23. “People have been concerned that climate change would be bringing all these species into contact, and that this could unleash a wave of interbreeding,”
    I wonder who have been concerned about this, and exactly what they have been concerned about.
    To me it looks like a complete and embarrassing waste of the funds in the foundations.
    I was also about to ask who has taken that concern seriously – but I guess that question has been answered.
    Certainly many at this forum has had great laughs. 🙂

  24. For the record, I don’t give a flying fig about polar bears in the first place. They are nasty beasts. I certainly don’t give a rat’s rear who they get laid with. But this whole thing is stupid even if you do think it important to protect the purity of the polar bear’s DNA.
    Why is it stupid and even silly? Because it was about 2C warmer than now during this very interglacial. The polar bears surely are a species at least as old as the Holocene and so have seen warmer times. If they are not at least as old as the Holocene … then why should I care if some johnny-come-lately species is messing around with “the wrong sort”?
    This whole thing should have been an episode of All in the Family. (especially the silly assed argument about “sub species” or not)

    • Your “purity of polar bear’s DNA” somehow made me think of a movie. Perhaps the global warmists are channeling General Jack Ripper:
      “How does that coincide with your post-war Commie conspiracy, huh? It’s incredibly obvious, isn’t it? A foreign substance is introduced into our precious bodily fluids without the knowledge of the individual, and certainly without any choice. That’s the way your hard-core Commie works. I first became aware of it, Mandrake, during the physical act of love…Yes, a profound sense of fatigue, a feeling of emptiness followed. Luckily I-I was able to interpret these feelings correctly. Loss of essence. I can assure you it has not recurred, Mandrake. Women, er, women sense my power, and they seek the life essence. I do not avoid women, Mandrake…but I do deny them my essence.”
      It sort of fits.

  25. So, climate change will not cause as much debauchery and fornication in the animal kingdom as at first feared. What a relief!

  26. From the head article.
    Apparently from Nature Climate Change: –
    “In fact, natural barriers prevent animals from reaching all potential new habitats, and humans have created new barriers such as highways, farms, and cities that can block migrations to more hospitable places.”
    No mention of Wind farms – the fabled bird-choppers.
    Nor the solar concentration plants [absolutely not kamps, or champs] – the well-known bird carbonizers.
    I assume pure coincidence.
    Possibly others might not.

  27. “Now she focuses on contemporary climate change”: I don’t know what precisely ‘contemporary’ means in terms of years. However, climate change, as used by the IPCC (yes, I know they changed their definition, but they shoved Global Warming down our throats so they own it) implies Global Warming due to CO2 emissions from humans activity. So, my question – what is the prior period (vs contemporary? period) where CO2 emissions by human activity caused Global Warming.

  28. who cares?
    they’re “getting some” so let them enjoy it.
    been a long time so my memory may be wrong but wasn’t there an island in alaska area where the brown bears genetically were closer to polar bear than they were to other brown bears?
    my memory may be way off though.

    • Not too far off. Apparently the “stranded” polar bears on ABC islands engage in some hanky panky with wandering Grizzlies:

      At the end of the last ice age, a population of polar bears was stranded by the receding ice on a few islands in southeastern Alaska. Male brown bears swam across to the islands from the Alaskan mainland and mated with female polar bears, eventually transforming the polar bear population into brown bears.

      (my bold)
      DNA study clarifies relationship between polar bears and brown bears
      Here again we encounter the deadly receding ice, which apparently makes female Polar bears forget how to swim.

  29. For the 4,796 pairs whose ranges currently do not overlap, computer models show that only 6.4 percent of them will come into contact due to climate change by the year 2100.
    Good grief, do these people take their work seriously?

  30. It’s my understanding that polar bear diverged from brown bear about a million years ago. In that million years, they have survived far warmer climes than now.

    • Humans do that as well…like during the little ice age….or when your grocery shelves run dry. The weak perish…adapt or die.

      • You’re that hard, eh ?.
        Papa comes along and kills and eats your kids.
        Weak they were.

      • A, .308 just behind its right shoulder (don’t want the bullet to fragment on the bones), blows up both lungs and maybe its heart.

  31. Why are we even worried? The animals present on this planet evolved in response to environmental changes and interbreeding in the past, and gosh gee whiz – the process continues, despite mankinds belief that all animal life is static as of the 1850s! The worlds ecosystems are not static!

  32. I would have thought that “flying squirrels” were the result of inter-species breeding in the first place.

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