Based on differences in sizes of bison across herds, Craine found that during the next 50 years, future generations of bison will be smaller in size and weigh less. Climate is likely to reduce the nutritional quality of grasses, causing the animals to grow more slowly.

　　“We know that temperatures are going to go up,” Craine said.

　　“We also know that warmer grasslands have grasses with less protein（蛋白质）, and we now know that warmer grasslands have smaller grazers. It all lines up to suggest that climate change will cause grasses to have less protein and cause grazers to gain less weight in the future.”

　　Craine said the results of climate change in coming decades can already be seen by comparing bison in cooler, wetter places with those in warmer, drier places. For example, the average 7-year-old male bison in South Dakota weighed 1, 900 pounds, while an average 7- year-old male bison in Oklahoma — a warmer place — weighed 1, 300 pounds.

　　“The difference in temperature between those two states is around 20 degrees Fahrenheit, which is about three times the projected increase in temperatures over the next 75 years,” Craine said. “It is a clear indicator that long-term warming will affect bison and is something that will happen across the U.S. over the next 50-75 years.”

　　24. In the next fifty years, researchers Say, bison will ________.

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