North American modern and fossil bison have decreased their body size with global temperature rises

What is it about?

North American bison (Bison bison) could be shrinking in response to climate change. Over the last 40,000 years, bison became smaller as the global temperature rose. If temperatures rise by 4°C as projected by the end of the 21st century, the body size of bison will probably decline an additional 46%. Small body size will affect the ranching industry that is based on bison and may also affect the many ecological relationships between wild bison and their grasslands on the Great Plains.

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Why is it important?

The authors used a novel combination of datasets; 1) global temperature reconstructions from isotopes in ice cores from the Greenland Ice Sheet Project (GISP2) and 2) body size reconstructions from the leg bones of fossil bison from Mexico to Canada. The GISP2 data, providing average annual temperature estimated from δ18O values, was already existing in the literature, but the body size of bison was reconstructed based on measures of the heel bone from more than 800 specimens. Currently, the global average temperature is 14°C (57°F) and, on average, the last Ice Age was 6°C (11°F) cooler than today. Although changes in body size of Bison may be a result of migration, disease, or human harvest, those effects are likely to be local and short-term and not likely to persist over the long-time-scale of the fossil record.

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