Holocene Hybrids: “Prizzlies” May Be Here to Stay
By Abby Cariño, Environmental Studies ‘24
Image Credit: Stefan David – Bear Hybrid, a.k.a a “Grolar” or “Prizzly” sleeping.
Dramatic global temperature shifts are affecting Arctic bears in unanticipated ways. As food availability changes due to rising temperatures, the population distribution, size, and genetic makeup of bears in the Arctic have altered. Like all marine mammals, polar bears harvest food from the ocean, relying on a diet that consists primarily of seals as prey. Polar bears enter a feasting season in the spring when seal pups are born on ice. During the fall and winter, they hunt adult seals through breathing holes on the ice cover. Polar bears rarely feed on terrestrial species—meaning their window of opportunity to eat depends exclusively on whether there is sufficient ice to support their hunting activities. As sea ice coverage continues to decrease, there is diminishing territory for polar bears to meet their nutritional needs. Foraging targets are different for grizzly bears who obtain most of their caloric intake from eating berries, roots, caribou, and other land-based foods.
Image Credit: Christopher Michel – Polar bear exploring thin ice.
Polar and grizzly bears do not inherently compete for food sources: however, as warming in the Arctic increases, grizzlies in Alaska have begun to travel north in search of sustenance. As global warming extends terrestrial plant ranges further north, grizzly foods are encroaching on polar bear territory. The expansion of boreal forest biomes into tundras has created an overlap in the two species’ foraging and hunting zones. Thus, polar and grizzly bears have become unlikely neighbors during certain times of year. The outcome of these species cohabitating may be somewhat surprising.
Image Credit: Gregory “Slobirdr” Smith – Grizzly bear wandering across the tundra foraging greenery.
The bears are not fighting! Instead, their interactions can only be described as affectionate. Interbreeding between polar and grizzly bears has resulted in an ever-increasing number of “prizzlies”; bears with marbled white and brown fur. However, these hybrid offspring present many questions about their reproductive ability. Scientific studies suggest most of these prizzly offspring are predominantly grizzly in their genetic structure and are fertile. This contrasts the well known assumption that infertility arises from hybridization. Genetically, polar bears diverged from brown bears and the rest of the Ursus genus fairly recently – about 500,000 years ago. This means they are still genetically similar enough to other bears in the Ursidae family to produce fertile offspring. Geneticists estimate that in time, it is possible that the grizzly population may overrun the polar bear population.
Though the polar bear population may decline, an apex predator will still persist in the Arctic. The “prizzly” raises important questions about the global impacts of hybridization and how climate change may affect mammal populations worldwide. In our rapidly changing world, researchers will continue to explore the role of hybrids in the Arctic ecosystem, and elsewhere.