When polar bears and grizzlies mate: Climate change brings together species that previously lived separately from each other. This creates bizarre new hybrids that may even have a future
It was an icy day when a 66-year-old man trudged through the snowy landscape of the Canadian Arctic island of Banks Island. Jim Martell, the name of the owner of a telephone company from Idaho, was wrapped up in a white winter jacket, ski mask and ski goggles to keep out the cold. Now he got a sign from his guide: A polar bear was in sight, close enough to start an attempt: Martell had put $ 50,000 for the license that allowed him to shoot a polar bear; a practice that outraged conservationists. Martell didn’t care. He raised his rifle, saw the creamy white fur, and pulled the trigger. The bear slumped.
When the marksman leaned over the animal on April 16, 2006, he realized that it was quite small for a polar bear and had a hump and long brown claws. He saw the dingy-looking fur and the dark spots around the eyes and muzzle. Was it a grizzly he’d shot after all? In this case, Martell faced up to a year in prison because Canada had placed the subspecies of the brown bear under protection.
A comparison of the DNA showed that it was neither a polar bear nor a grizzly bear – but a mixture of both: a hybrid that was descended from a polar bear mother and a grizzly father. From then on, it traded in the press as “Pizzly” (Polar Bear and Grizzly), “Grolar” (Grizzly and Polar Bear) or as “Cappuccino Bear”. Scientists initially considered it a rare exception, some an evolutionary accident.
But in the years that followed, more hybrid bears appeared, all of them sired by female polar bears and male grizzlies. One of the hybrid bears later turned out to be a descendant of another pizzly in a genetic analysis. It was known that polar bears and grizzlies can mate, because both are closely related and their common evolutionary line only split between 500,000 and 600,000 years ago. However, they had mostly avoided each other in the past, which is why the discovery of several hybrid bears amazed biologists, embarrassed taxonomists and posed challenges for conservationists.
Climate change provides an explanation for the phenomenon. Through it, the habitats of Ursus maritimus and Ursus arctos continue to overlap, which opens up more opportunities for unusual associations. While male grizzly bears head for the far north of America because they are less hunted there and, thanks to global warming, can spread to areas whose climate was previously too inhospitable for them, the polar bear’s habitat is shrinking because the sea ice is retreating from the out he hunts for seals. In the summer of 2020, the Arctic sea ice only spread over half the area of decades ago and only reached half its former thickness, reported a few days ago researchers of the so-called “Mosaic” expedition of the research vessel Polarstern led by Markus Rex from the Alfred- Wegener Institute (AWI), which ended eight months ago. If nothing but the free ocean opens up for the polar bear, he has to take refuge on land in order not to starve. But there he not only meets people, but also grizzlies.
Grizzlies and polar bears represent a mass phenomenon that is currently taking place in the Arctic: When trees and bushes spread north and the ice melts, the conditions for the boreal forest animals from the south improve. They are flowing en masse into the Arctic, as they can now assert themselves there thanks to climate change. Mountain hares, white-tailed deer, moose and beavers – they are all among the winners of climate change.
Losers are the long-established species: musk ox, caribou, arctic fox and polar bears. You are at a dead end and cannot escape climate change. At the same time, they are challenged by the species from the south.
For the Arctic people, it is a tragic turn in their fate. Normally now is the time for her. Because after the intermezzo of the Holocene, a warm period that lasted ten thousand years and offered man a stable climate in which he could develop from hunter-gatherer to farmer, the earth was long on the way to the next ice age.
If this had happened, Arctic Fox & Co. would have been able to occupy ever larger areas of Central Europe with the spread of the cold, as they did in the past Ice Age. 6500 years ago, the earth had aligned itself in such a way that the radiation of the summer sun in the northern latitudes was approaching its lowest level – actually a sure sign of the beginning of a cold period. If it wasn’t for the carbon dioxide that was beginning to build up in the atmosphere; why is still controversial among climate researchers today. While some blame changes in ocean currents, others see the cause in our ancestors, who burned forests to grow crops and graze cattle.
With industrialization at the latest, the pendulum has definitely turned, and the world is warming up again – the predicted warming is likely to be as strong as it has been for two million years. By mid-century at the latest, the Arctic Ocean could be completely free of ice in summer. The ice age, it’s canceled.
At the rate of current climate change, most Arctic species have no chance of evolutionarily adapting. For many there is no other means than emigration to the far north. The British naturalist Charles Darwin already described this process in his 1959 work “The Origin of Species”: “When it got warmer again, the arctic forms retreated to the north, and the inhabitants of the more temperate regions immediately followed them.
Arctic foxes, musk oxen and caribou still remain huge areas in which they can live. However, with every degree of latitude that they retreat to the north, the geophysics of the earth outsmarted them: the closer they get to the North Pole, the more their catchment area shrinks. Because the earth is an ellipsoid; it is like a medicine ball that someone is sitting on. If we imagine that a ring was located around the equator and migrated north, then it would contract further and further. The animals and plants therefore have ever smaller areas at their disposal. Scientists speak of the “polar constriction” (English: “polar squeeze”). Some species like seals and polar bears will literally end up at the end of the world at some point.
At first glance, it is a paradox: the biodiversity in the Arctic is growing – thanks to immigrants from the south. At the same time, however, the Arctic’s contribution to biodiversity around the world will decrease, as polar species will become extinct if they fail to find a way to survive in times of climate change.
Some Arctic researchers assume that sooner or later the grizzly bears will take over the High Arctic, while the polar bears will gradually disappear. Because while their hunting grounds collapse on ice, they reach their physical limits on land: with their relatively small molars and elongated heads, they are well adapted to hunting seals and their bacon, but poorly suited to the varied and bony food on land. “Polar bears are morphologically specialized and have biomechanical limitations that can limit their ability to consume mechanically demanding food, with changes in diet only occurring under the most extreme scenarios,” wrote a group of biologists, anthropologists and archaeologists recently in the journal Global Change Biology. “Overall, the highly specialized diet and skull morphology of polar bears can severely limit their ability to adapt to a warming Arctic.”
It is true that polar bears also manage to capture sea birds or caribou on land; however, they have to spend more energy and receive fewer calories than on the sea ice. Their populations are projected to halve by the middle of the century. At some point they will only have retreats in the high Arctic in Canada and in northern Greenland. If they die out completely, their genes will at least live on in the grizzly bears. Similar to that of the Neanderthals to a small extent in modern humans.
And the hybrid bears? It is difficult to say today what role these will play in the future. However, some biologists assume that they may have a better chance of survival on land than their maternal relatives, the polar bears. The physical characteristics of the grizzly in the hybrid bears could potentially give them a distinct advantage. The paleontologist and biologist and co-author of the study Larisa DeSantis from Vanderbilt University in Tennessee calls the cappuccino bears a “sad but necessary compromise in view of the current warming trend”. These could possibly take over part of the polar bear’s niche and thus also play an important role in the ecosystem.
Such bizarre gatherings are likely to be more common in the future, given the mass migration that climate change has sent species around the world; when the areas of distribution of the species continue to mix due to climate change and this opens up new ways of connecting. The cappuccino bear is just the beginning.
