How can any mammal be endemic to an island in the North Pacific? That mammal did not evolve on that island, so it had to arrive on the island at some point. I guess the answer depends on your definition of endemic. Most biologists believe that if a species was present on an island when the island became separated from nearby land masses, and if that species continued to survive on the island, then the species is endemic or native to the island. In other words, the species was not transported to that island by man. Experts list six mammals they consider endemic to Kodiak Island. These are the Kodiak Bear, the red fox, the river otter, the short-tailed weasel, the tundra vole, and the little brown bat. Over the next few weeks, I will discuss each of these mammals. I have already written several posts on Kodiak Bears, so I will mention them briefly here, and then in subsequent posts, I will focus my attention on the other five mammals.
At the end of the Pleistocene epoch, 12,000 years ago, ice sheets covered the North Pacific, connecting Kodiak Island to the mainland. At this time, bears and other mammals could roam freely between the mainland and Kodiak, and we assume that this was when the six mammals we consider native to Kodiak Island arrived on the island. When the ice receded and water levels rose, these mammals were trapped on Kodiak Island, where they adapted, evolved, and thrived. Humans would not arrive for another 4500 years.
After the ice receded, vegetation was scarce, but conditions slowly improved. Vegetation grew and became the jungle-like growth we know on the island today, and salmon runs became established in the many rivers and streams here. More than 3500 bears presently inhabit the Kodiak Island Archipelago, the largest number to have ever lived here. The bears thrive on prolific berry crops and rich salmon runs. Many mammals have been introduced to Kodiak over the years, and while some have negatively impacted the vegetation here, none seem to have affected brown bear abundance and vigor.
Kodiak brown bears exist only on the islands of the Kodiak Archipelago. The archipelago is located in the western Gulf of Alaska, approximately 250 miles (408 km) southwest of Anchorage. The island group is 177 miles (283.2 km) long and 67 miles (107.2 km) wide at its widest point. Kodiak, the most prominent island in the group, has a land mass of 3,588 square miles (8,975 km²) and is the second largest island in the United States.
In 2005, the brown bear density on Kodiak Island was estimated at 0.7 bears/square mile (271.2 bears/1000 km²), making it one of the densest brown bear populations in the world. This density estimate is a bit misleading, however, since bears are not evenly distributed across the archipelago. In the spring, summer, and fall, the bear density is much greater along the coast and salmon streams, while there are fewer bears in alpine regions. During the past decade, the Kodiak bear population has been slowly increasing. Recent genetic research has shown that while Kodiak brown bears are closely related to Alaska Peninsula brown bears and brown bears in Kamchatka, Russia, Kodiak bears have been isolated since ice sheets receded at the end of the Pleistocene epoch 10,000 to 12,000 years ago.
Over the next few weeks, I’ll write posts about red foxes, river otters, short-tailed weasels, tundra voles, and little brown bats.
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