Is the climate crisis acting as cupid?

It’s no secret that the temperature of the world is slowly rising and it is impacting many species around the globe. But in one particular case, it is causing two species (who previously may never have been introduced) to cross paths. Global warming has meant that the Arctic temperatures are rising twice as fast as they are in other parts of the world- this is called Arctic amplification [1]. Hot temperatures in the ice caps have meant that sea ice is declining [1]. This sea ice plays an important role to our polar bears, who would usually use it to hunt for food, meaning they have to expand their hunting territories further south [1]. The slightly more comfortable Arctic climate has also meant that grizzly bears are expanding their territories further north [1]. The result is that these two species are now occupying similar ranges at certain points and coming into contact more. Both of these bears are opportunistic maters meaning they will seize any opportunity to pass on their genetics. When the two species come into contact, they have no problem mating with each other and making grizzly-polar hybrids, or as I like to call them, Pizzly bears.

A captive Pizzly bear-Photo by Corradox/CC 3.0

Now, what makes these awesome hybrid bears so interesting is that they can reproduce [2]. So, unlike other hybrid species, such as zedonks and ligers, which are sterile and cannot reproduce, these hybrid species can go on to have babies with other pizzlies, grizzlies or polar bears [2]. This means these species could (in theory) reproduce to outcompete the other bear species in the area. This could threaten biodiversity if these species replace other bear species in the area [1]. No one knows if these species are better adapted to the ever-changing climate that they live in, but there are examples of more vigorous hybrid species who are more able to adapt to their environment better [1]. However, in this case, each species they have come from are very specialised. Polar bears are very specialised in hunting seals but with global warming going on, these guys might have to be less picky and eat less-preferred foods to ensure that they don’t go into extinction [1]. Whereas Grizzly bears have adapted to eat more hard foods and scavenge carcasses when times are tough so may even outcompete the Polar bears that are coming into their region for food [1]. In my opinion, if these Pizzly bears can cope with the Arctic conditions even better than their Grizzly brothers, then they can travel even further North for harder food and potentially out-compete both Grizzlies and Polar bears.

Amstrup has suggested that this relationship is more beneficial to grizzlies than polar bears because the grizzlies are benefitting from the change in climate as it means that their territory is expanding, while for the polar bears it is having the opposite effect [3]. Amstrup even goes as far as to suggest that the grizzlies could dilute the polar bear population to extinction [3]. York states that the hybrid Pizzlies are also not providing any genetic diversity for the polar bears [3]. Derocher agrees with both and suggests that “from a genetic perspective, it’s quite likely the grizzly bears will eat polar bears up” [3]. This is because Polar bears need the ice, where the seals and walruses they prey on live and they are adapted to walk on the snow with their padded paws, so travelling south isn’t an ideal option for them [3]. However, for Grizzlies, travelling north would usually be a rare occurrence but now the Canadian Arctic is 75% grizzlies because of climate change [3]. Derocher agrees with my point above that grizzlies (and pizzlies) habitat will only get better as the north gets warmer as which means there’s a longer warming period and greater food potential [3]. But even Grizzly bears will face troubles when they get up north, even if it is warmer. This includes PCB’s (polychlorinated biphenyls) and other toxic pollution that affects the prey they eat and in turn, them, and causes their penis bones to break off making reproduction impossible [3]. So, while you can look at it and say, ah yes but the Grizzlies will thrive- they won’t. Not having ice is just one of the many issues that polar bears face and will impact both the grizzlies and pizzlies if they live up north. Some scientists say it won’t matter who ends up surviving this competition of the bears, if the issues up north aren’t solved then they are all doomed [3].

A polar bear struggling without sea ice

But back to the original point- is climate change solely responsible for these two species meeting and reproducing with each other or would it have happened on its own? Some ecologists believe that the melting sea ice and the warmer Arctic is what has pushed these two species to have overlapping territories [2] and combined with these species having flexible mate choice [3]. Some scientists also say that policies that have led to the protection of these species in the forms of banning culling and hunting of them have also meant that there’s more of them, meaning more competition and therefore increased range for food is needed to sustain the entire population [3].

So while it can be seen as good for the Grizzlies initially, if the root problems don’t get solved in the North then it’s not looking good for any of the bear species- I hope things do change as these species are so incredible and important species to many ecosystems.