Climate Fact: Mammal Diversity During Deglaciation
In Brief: Climate changes during the period from 15,000 to 12,000 years ago coincide with changes in small mammal communities in western North America.
Earth’s ecosystems changed rapidly 15,000 to 12,000 years ago and ecosystems in the western U.S. were no exception. The retreat of the region’s alpine glaciers during this period, which during glacial periods extended much farther into the valleys of the region’s mountain ranges than they do today, exposed new areas lands to plant colonization. In the Great Basin, a steady warming and drying trend evaporated the glacial age lakes that had dotted the landscape, leaving behind salt flats and the Great Salt Lake.
The forests that had grown beside these lakes were replaced by deserts. Other transitions from one type of plant community to another were experienced across the rest of the region as species shifted in response to relatively gradual multi-millennial warming, as well as more rapid but short-lived transitions in response to sudden changes in ocean circulation. Even catastrophic floods periodically swept across the Columbia River Basin, destroying everything in their path. This was also the time when the first humans arrived in North America. During this period, the Pleistocene Megafauna, a group of species that included wooly mammoths, giant ground sloths, American lions and mastodons, went extinct.
There has been much debate about whether these extinctions were caused by the arrival of humans with efficient hunting tactics or whether it was the climatic changes of the period that were chiefly responsible. An analysis of changes in small mammal populations, such as mice, gophers and shrews – species that would not have been actively hunted by humans – shows that more specialized species of small mammals were being out-competed and out-populated by more generalized species of mammals which were better adapted at adapting to rapidly changing landscapes. These small mammal population changes occurred before major declines in megafauna populations occurred. This suggests that while human hunting may have played a significant role in the extinctions of the Pleistocene Megafauna, shifts in populations that were already underway due to climate change was also an important factor.
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Source: Blois, JL et al. “Small mammal diversity loss in response to late-Pleistocene climatic change.” Nature 465 (2010): 771-774.
