There are currently eight different species of bears living here with us on planet Earth, but it's a bit more complicated than that. Take, for instance, the brown bear (Ursus arctos), whose range extends from the United States, through Canada and far into China, Russia and Scandinavia. There are many subspecies of the brown bear that hang out in very specific nooks and crannies: the Gobi desert, for instance, or the Russian peninsula of Kamchatka.
But the largest of the brown bear subspecies is the Kodiak bear (Ursus arctos middendorffi), which lives only on the Kodiak Archipelago off the southern coast of Alaska.
Kodiak bears and the rest of the species Ursus arctos are believed to have first evolved in Asia and spread into Europe around 250,000 years ago. Around 100,000 years ago, they likely moved into North America through Alaska, but didn't move farther south into the lower 48 until closer to between 13,000 and 15,000 years ago.
"It's hard to say exactly how brown bears ended up in Kodiak, but the most agreed upon theory is they likely crossed over from mainland Alaska via an ice bridge during the last ice age," says Shannon Finnegan, a Ph.D. candidate at the State University of New York (ESF), and a Kodiak bear researcher at the Alaska Department of Fish and Game, Kodiak, in an email. "It is believed that some of southern Kodiak may have been unglaciated at this point, and the first Kodiak brown bear population may have taken hold here. As the glacier retreated the bear population likely expanded to occur all across the archipelago taking advantage of the rich food supplies."
The Kodiak Subspecies
The Kodiak Archipelago is a string of islands cut off from mainland Alaska, which is the perfect condition for a subspecies of anything to evolve. However, distinguishing between similar animal species can be difficult, but defining subspecies is even trickier. In fact, biologists don't even completely agree about whether different groups of brown bears should be classified as subspecies or not.
"Generally speaking, all brown bears found across the world belong to the same species," says Finnegan. "However, it is said that brown bears can be split into five clades [branches that include a single common ancestor and all of its descendants] based on some genetic and geographical differences. Within this clade system Kodiak bears (Ursus arctos middendorffi) fit into a clade with bears from mainland Alaska."
Since the Kodiak bear has been living the island life for at least 12,000 years, it has been cut off from others of its species for long enough to display some genetic differences. For instance, the Kodiak bear can grow to larger sizes than any other brown bear — weighing in at up to 1,500 pounds (680 kilograms), they rival the polar bear (Ursus maritimus) for the title of biggest bear in the world.
Another reason Kodiak bears grow so large compared to their mainland counterparts: Their archipelago is rich in food like Pacific salmon, and there is relatively little competition from other predators.
Bears might have a reputation for being aggressive, but according to Finnegan, Kodiak bears have harmoniously cohabitated with humans on their islands for a long time — there has not been a human fatality from a bear attack on Kodiak in over 90 years.
"They are extremely adaptable and curious animals, with very distinctive personalities," says Finnegan. "Some bears around the city of Kodiak have even learned how to open car doors and bear-proof dumpsters — which are very tricky — to try and access human foods."
Kodiak bears, like all brown bears, have the ability to delay implantation of a fertilized egg in the womb. They usually breed in June but won't become "pregnant" until later in the fall — their bodies have to wait to see whether they can build up enough fat reserves to sustain a pregnancy and provide milk for offspring in the den.
Kodiak bear populations seem to be relatively stable at around 3,500 individuals on the archipelago. However, this wasn't always the case.
"Historically Kodiak bears were heavily persecuted on parts of the archipelago when cattle ranching was a prominent industry," says Finnegan. "They were viewed as vermin and exterminated whenever possible. Hunting groups on Kodiak took issue against this and fought to have protections put in place for the Kodiak bear."
Thanks to the efforts of these sport hunters, huge swaths of land were set aside as protected refuge for the bear, and their population increased. Legal hunting of Kodiak bears exists today, however the population is closely managed.
Climate change may impact Kodiak bears in the future, particularly if warming waters alter or negatively impact the Pacific salmon they rely on for food.
Now That's Interesting
A female brown bear can give birth to a litter of cubs, all sired by different fathers.
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