Posts Tagged ‘Mammuthus primigenius’

The Late Extinction of the Pribiloff Island Mammoths

September 15, 2013

The Pribiloff Islands are located above the Arctic Circle between Russia and Alaska.  Some are owned by the former and a few are American owned.  Russia owns Wrangel Island, the largest of the Pribiloffs, encompassing 2900 square miles of dry land.

Map of Pribiloff Islands located between Siberia and Alaska above the Arctic Circle.

Despite its location above the Arctic Circle, Wrangel Island is home to a diverse flora and fauna.  Most of the Pleistocene fossils were found in the rivers.

During the last Ice Age a landbridge known as Beringia connected Asia with North America.  Sea level rose following the end of the Ice Age, isolating the Pribiloff Islands from the rest of the mainlands.  Although the growing season averages 25 days, Wrangel Island hosts a remarkable diversity of plant species and communities.  There are 449 species of vascular plants, 330 species of moss, and over 300 species of lichen.  This is roughly double the number of species found on the mainland of Alaska.  Many of these unique species are found nowhere else in the world.  The high number of endemic species is evidence Wrangel Island was never glaciated.  Glaciers wipe out all plant species from any location they expand over.  Steppe grasses, dwarf willows, and low growing saxifragas cover much of the island.  Common plant communities include meadow grass-low shrub, sedge and rush marshes, steppe sedges similar to those found in Mongolia, willow shrub and xeric herb, and rocky saxifragas zones.  Amazingly, several species of endemic poppy flowers grow in the low meadow communities.

Arthropod diversity is also higher on the island than the nearby mainlands.  There are 31 species of spiders, 58 species of beetles, and 42 species of butterflies; again roughly double to what’s found on mainland Alaska.    But unlike in Alaska (and the Apure River–the subject of last week’s blog entry) there is not a single species of mosquito.

Wrangel Island has been a protected nature reserve since 1976.  Over 80,000 walruses live on this island–the largest population of walruses in the world.  Ringed seals and bearded seals also live on the island and gray whales feed offshore.  The concentration of pinnipeds and the occasional whale carcass attract hundreds of polar bears.  Caribou and musk-oxen have been re-introduced,  and wolves and wolverines roam the island.  Arctic foxes and snowy owls prey on lemmings.

Polar bears on Wrangel Island.

Arctic foxes and snowy owls control lemming numbers.  Thousands of empty and half-full fuel barrels litter Wrangel island from failed attempts at human settlement.  Some naturalists want these barrels removed, but I think there is a beauty in forlorn evidence of  abandoned human habitation.

Snow geese are year round residents while Brant geese nest on the island during summer.  Hundreds of thousands of sea birds, including thick-billed guillemots, kittiwakes, several species of sea gulls, and gray plovers nest on the island.  Arctic and peregrine falcons prey on the sea birds.  Lapland longspurs and arctic willow warblers are common inland birds.

Wrangel Island is famous for being the last known place on earth where woolly mammoths (Mammuthus primigenius) lived.  S.L Vartanyan shocked the scientific community in 1995 when his radio-carbon dates on mammoth tusks found in the Neozhydomaya River were found to be just 4000 calender years old.  This is 9,000 years later than the most recent woolly mammoth fossil found on the mainland, though recent studies of mammoth DNA in permafrost suggest mammoths still occurred in Alaska until about 10,500 years ago.  Wrangel island has been isolated from the mainland by sea level rise for approximately 10,000 years.  Apparently, this isolation protected the mammoths from human hunters for 6,000 years until Inuit hunters discovered the island and shortly thereafter rubbed out the world’s last mammoths along with the woolly rhinos (easternmost known occurrence), bison, musk-oxen, horses, and caribou that also lived on the island then.  All the large land herbivores disappeared from the island about 4000 years ago.  Not coincidentally, archaeological evidence of man has been found on the island dating to 3700 BP–roughly the same time all the large ungulates vanish from the fossil record.  No direct evidence of human hunting megafauna on Wrangel Island has been found, but I believe it can be safely assumed.

It didn’t take long for Inuit Indians to wipe out all the large land ungulates on Wrangel Island.

The late extinction of the woolly mammoth on Wrangel Island blows a big gaping hole in climate change models of  Pleistocene extinctions.  No discernible change in climate and plant composition occurred 4000 years ago.  However, man does show up in the archaeological record here at this time.  Proponents of climate change models of extinction in boreal regions believe the increase in precipitation at the end of the Ice Age changed the environment in this part of the world from dry grassy steppe to spruce forest and wet tundra.  Supposedly, these environments were unsuitable for grass-eating species such as woolly mammoths, woolly rhinos, bison, and horses.  However, these species survived the Sangamonian Interglacial which was an even warmer and wetter phase of climate than the one that allegedly caused the extinction of the above-mentioned species.  I doubt these species all of a sudden lost their ability to adapt to fluctuating climate. 

A recent study of woolly mammoth DNA determined that mammoth populations fluctuated with climate fluctuations, and the authors of the study concluded climate change caused the extinction of woolly mammoths.  This conclusion is an overreach–fluctuating populations does not equal extinction.  I’m sure there were refuges for grass-eating megafauna in boreal regions–none of the plants they ate ever became rare.  There seems to be a compromise consensus among many scientists who believe it was a combination of climate change and human hunting that caused the extinction of Pleistocene megafauna.  While it’s true that climate change may have affected the geographical distributions and populations of Pleistocene megafauna in a way that made them more vulnerable to human hunting, if man could have been theoretically removed from this equation, most, if not all, of these species would still exist on earth.  Therefore, man, not climate change, is the single cause of most end Pleistocene extinctions.

There is a misconception that the Wrangel Island mammoth was a dwarf species, but a Russian study determined they were full-sized woolly mammoths.  I don’t think this study has ever been translated into English, perhaps explaining the persistence of this misconception.  Scientists estimate Wrangel Island was big enough to host a population of 500-1000 mammoths.  Dwarf elephants are known to have occurred on Malta Island in the Mediterranean, and dwarf Columbian mammoths (Mammuthus colombi) lived on the Channel Islands off the coast of California.  There were dwarf woolly mammoths living on another Pribiloff Island.  St. Paul’s Island, property of the U.S., was also home to a late population of woolly mammoths,  They survived until 7500 BP.  However, sea level rise rather than human hunting doomed this population.  Sea level rise shrank the island to just 34 square miles which was not large enough to sustain a viable breeding population of mammoths.  The last mammoths on St. Paul showed evidence of starvation and were forced to eat lots of sea weed, a food that would normally have been just an occasional dietary supplement.