Mammals Seek Higher Elevations as Climate Warms

Many species of mammals in Yosemite National Park have shifted their home ranges to higher elevations over the last hundred years. A research team led by Craig Moritz at the Museum of Vertebrate Zoology of the University of California, Berkeley, focused on the relationship between the change in elevation and global climate change. Moritz and his team utilized the information provided by naturalist J.P. Grinnell who had extensively mapped, surveyed and catalogued California’s wildlife at the beginning of the twentieth century.

Grinnell’s ninety-year-old maps, photographs and field notes provided a basis for locating his original survey sites along a transect that passed from the San Joaquin Valley through Yosemite to Mono Lake, and covered an elevation range from near sea level to more than 10,000 feet. Within the park, Moritz’s team returned to sites from the valley floor to the mountain crest and collected animals in many of the same locations as Grinnell. Moritz’s team relied on live-animal traps; whereas Grinnell’s original survey used lethal traps to collect animals. Mathematical checks showed that the different collection techniques were not a problem in successfully comparing the two sets of data.

Moritz’s team used the new survey results and Grinnell’s original data to compare the ranges of 28 species of mammals. On average, the mammals had moved their ranges upward about 500 meters at the same time that the temperature in the area increased 3 degrees Celsius. The species that were originally found at lower elevations tended to expand their ranges to higher elevations. Species originally at higher elevations tended to contract their ranges as their minimum elevations shifted even higher. This suggests that species are already trying to adapt to a warmer climate. It also suggests that species that have historically lived at higher elevations may not have anywhere to go in the future as mountain tops experience temperature changes. Further warming would lead to the extinction of many species that are adapted to cold, alpine conditions.

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