It’s hard to think of too many animals that could take out a grizzly bear.
At nearly 1,000 pounds and standing up to eight feet tall on its hind legs, the razor-toothed beast seems immune to all but the fiercest of contenders — and yet, one of the biggest threats to grizzlies is a tiny animal, hardly bigger than your fingernail.
Meet the mountain pine beetle.
This little insect looks harmless enough, and in fact it’s a native species in North America. But it’s been wiping out conifer forests all over the western United States — forests that grizzlies rely on for food. Helped along by rising temperatures and a drier climate, expressions of global climate change, the beetle is expanding its range and devastating forests throughout the western half of the country.
Here’s how they do it: Adult pine beetles burrow under the outer bark of conifer trees and lay their eggs. Later, these eggs hatch into hungry beetle larvae, which chow down on the tender inner bark, causing serious damage and often death to the tree.
This is bad news for the grizzly bear, which feeds on one of the beetle’s favourite targets: the whitebark pine. Whitebark seeds are a major source of calories for grizzly bears, particularly in the fall before they go into hibernation.
And with millions of these trees disappearing up and down the west coast, it’s looking like the bears may need to start exploring other options — and fast.
The pine beetle roams everywhere from New Mexico north to Canada, and it’s killed more than 70,000 square miles of trees in the last decade, alone. And scientists predict its reign of terror will only grow worse in the coming years.
While global climate change is a major threat to plants and animals all over the world, the mountain pine beetle is actually benefiting from rising temperatures.
Recent research, including a study published in the journal Ecology and a study published in Proceedings of the National Academy of Sciences, suggests that the beetles thrive in warmer temperatures and with less rainfall, two expected impacts of climate change in the western US. This is already apparent, as scientists have noticed the beetles reproducing earlier and spreading farther than ever before, leading to more frequent and severe infestations around the West.
As the climate continues to become warmer and drier, pine beetles will likely continue to multiply and expand their range, which is bad news for conifer forests and the vulnerable grizzlies. Although bears are good at adapting to food shortages and finding other things to eat, this ability often drives them close to human civilisation in search of snacks — but end up facing a hunter’s gun instead.
Defenders of Wildlife, a wildlife advocacy group, writes that a shortage of whitebark pine seeds can “lead [grizzlies] to seek out sources of food that can come from humans, like garbage, domestic fruit trees and livestock. Grizzly bears that choose to adapt to human-generated food resources often die as a result.”
Other studies suggest that mother grizzly bears who eat more whitebark seeds before hibernation have cubs that are healthier and more likely to survive, which is crucial to the future of grizzlies in North America. Fewer cubs that survive mean a smaller and smaller population of grizzlies.
Even more unfortunately, the pine beetle isn’t the only organism knocking out whitebark pines. An invasive fungus known as “white pine blister rust” is also killing off trees in the Western US.
Grizzly bears currently enjoy special protections as a “threatened” species under the Endangered Species Act. Out of the nearly 50,000 grizzlies that once roamed the United States, fewer than 2,000 are estimated to remain, according to the US Fish and Wildlife Service. In 2007, the Service moved to de-list the grizzly bear population in the Greater Yellowstone Ecosystem, arguing that the population was sufficiently recovering. But conservation groups sued the US government, and protections were restored, partly thanks to concerns over the declining whitebark pine, reports Nature.
Whether grizzly bears will keep their protected status in the long run remains up in the air. Conservationists remain serious about the threats to the whitebark pine, which — under the influence of beetles, fungus, and climate change — could be in for a long, rough road ahead.
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