Polar bears are widely considered a keystone species in the Arctic, though the label comes with some nuance. Their most measurable ecological impact isn’t through controlling prey populations, as you might expect from a top predator. Instead, it’s through the massive amount of food they leave behind for other Arctic wildlife. That scavenging network, combined with their role as the Arctic’s dominant predator and their cultural importance to Indigenous and non-Indigenous communities, is what earns them keystone status.
What Makes a Species “Keystone”
A keystone species has a disproportionately large effect on its ecosystem relative to its population size. Remove it, and the ecosystem changes dramatically. The classic example is a predator that keeps herbivore populations in check, preventing overgrazing. But keystone status can also come from other roles: creating habitat, cycling nutrients, or supporting food webs in ways no other species can replace.
Polar bears fit this definition, but not in the textbook predator-prey way most people assume. Their influence on the Arctic food web operates through a less obvious channel.
How Polar Bears Feed the Arctic Food Web
A single polar bear kills roughly 2,200 pounds of marine mammals each year, mostly ringed and bearded seals. But polar bears are fatty-tissue specialists. They eat the blubber and often leave about 30% of each kill behind. Across the global population of approximately 26,000 polar bears, that adds up to nearly 17 million pounds of carrion made available annually to other Arctic species.
At least 11, and possibly up to 18, other wildlife species depend on these leftovers. Arctic foxes are among the most reliant. While they primarily hunt rodents during warmer months, carrion can fill up to two-thirds of their diet during winter, when other food is scarce. Glaucous gulls, ravens, and wolverines also scavenge polar bear kills regularly. Without polar bears generating this supply of nutrient-rich marine mammal remains, these species would lose a critical food source, particularly during the harshest months of the year.
Researchers at the San Diego Zoo Wildlife Alliance estimated that documented declines in just two of the 20 global polar bear subpopulations resulted in a loss of about 661,000 pounds of carrion from the food web. That’s a measurable hit to the entire scavenger community in those regions, and it illustrates exactly why polar bears qualify as keystone: their absence ripples outward.
Their Predatory Impact on Seals
Surprisingly, polar bears don’t appear to strongly regulate ringed seal populations the way wolves regulate elk or sea otters regulate sea urchins. Ringed seals are their primary prey, and the two species’ population sizes are closely linked across their overlapping ranges. But research in the eastern Beaufort Sea found that polar bear predation has a negligible effect on ringed seal population growth.
Polar bears do show interesting hunting flexibility. In years when seal pup numbers are high, they overwhelmingly target pups, which are easier to catch and energy-rich. In low-productivity years when fewer pups are born, they shift to hunting adult seals instead. This prey switching actually benefits the seal population slightly: by easing predation pressure on the few pups available in bad years, it allows more of that small cohort to survive. But the overall effect on seal population dynamics is small either way.
Polar bears also prey on bearded seals, and they may lean more heavily on this alternative when ringed seal numbers dip. Still, the evidence doesn’t support the idea that polar bears are preventing seal overpopulation or protecting Arctic fish stocks through top-down control. Their keystone role is better understood through the carrion pathway than through predator-prey regulation.
Flagship and Cultural Keystone Roles
Polar bears also function as what ecologists call a flagship species, a high-profile animal that draws public attention and funding to broader conservation efforts. When people donate to protect polar bears, the habitat protections that follow benefit countless other Arctic species, from seals to seabirds to the microscopic organisms in sea ice.
There’s a less well-known designation that also applies: cultural keystone species. In Churchill, Manitoba, polar bears are central to a mixed Indigenous and non-Indigenous community where the local economy depends heavily on polar bear tourism. The species shapes livelihoods, cultural identity, and community structure in ways that go beyond ecology. Researchers have noted that both polar bears and grizzly bears serve as cultural keystone species even in communities that don’t hunt them, because their influence on human communities is mediated through economic and cultural connections rather than extractive use.
What Happens if Polar Bear Numbers Drop
The Arctic is already providing a real-time test of what declining polar bear populations mean for the ecosystem. As sea ice shrinks, some polar bear subpopulations are spending less time hunting on the ice and killing fewer seals. The direct consequence is less carrion entering the food web. The estimated loss of 661,000 pounds of carrion from just two declining subpopulations gives a sense of scale, and there are 20 subpopulations total.
For species like Arctic foxes that depend on scavenging polar bear kills to survive winter, fewer polar bears could mean population declines, changes in distribution, or shifts to less nutritious food sources. Those changes would then cascade further, affecting the rodent and bird populations that foxes prey on and compete with. This is the hallmark of a keystone species: pull it out, and the web starts to unravel in directions that aren’t immediately obvious.
Polar bears occupy a unique position in the Arctic. They’re the only marine mammal predator that hunts on the ice surface, and no other species can replicate the nutrient transfer they create by dragging seal carcasses onto the ice and leaving substantial portions behind. That irreplaceability is ultimately what makes them keystone.