Montana State research maps out bison distribution over past 20,000 years
Though bison are often closely associated with the Great Plains, a new study by a Montana State University (MSU) doctoral student has found that bison actually occupied much of North America over the last 20,000 years.
John Wendt, a doctoral student in the Department of Earth Sciences in MSU’s College of Letters and Science, studies how the distribution and abundance of large herbivores, such as bison, changed over thousands of years.
His paper, “Large-scale Climatic Drivers of Bison Distribution and Abundance in North America Since the Last Glacial Maximum,” written with his MSU academic adviser David McWethy as well as Chris Widga from East Tennessee State University and Bryan Shuman from the University of Wyoming, was published online in the journal Quaternary Science Reviews in April.
The paper is the first to combine a large, interdisciplinary dataset to reconstruct how the distribution of bison herds shifted, expanding and contracting across North America over the last 20,000 years.
By mapping the occurrence of bison fossils over time, researchers determined that the animals occupied much of North America, not just the Great Plains region.
“This study brings a more holistic view of bison and how they responded to a varying climate,” Wendt said. “It also adds to our knowledge about how bison responded to past environments.”
The research paper includes a map that Wendt created to track bison distributions and how they changed since the Last Glacial Maximum, a time about 20,000 years ago when the ice sheets were at their greatest extent across North America.
From Alaska to the Gulf coast, the amount of change in both bison range and range size reinforces the idea that bison occupied a large part of North America at one time, he said.
McWethy, co-author on the paper and MSU associate professor in Earth sciences, said the paper corrects previous ideas about where bison lived in North America.
“Some scientists argued that bison were limited to small areas of the western United States. This data shows bison were found throughout much of North America and that they moved in response to changing conditions,” McWethy said.
Bison thrived across broad areas throughout North America and survived conditions – such as climate and environment changes, and hunting pressure from humans – that led other mammals, such as mammoths, to become extinct, Wendt said.
The research showed that during a climatic warming period, bison expanded where glaciers retreated, following the grasslands and rangelands across the continent.
“Bison adapted as the climate altered the availability and distribution of resources,” he said.
Between 1,000 and 4,000 years ago, the bison population expanded, according to Wendt: “We have this moment of time where there are written accounts of bison – the vast herds of the West. This paper shows that what those early explorers saw was the end point of this long trend of population growth."
The project collaborated across different research fields including the historical study of geography, climate and fossils.
“This paper really came out of John’s creativity and persistence,” McWethy said. “It involved a unique collaboration, and John came up with the idea to reconstruct the spatial distribution of bison across the continent since the Last Glacial period using a dataset that had not been fully explored.”
This approach provided a bigger picture of how bison herds moved in response to changing climate and ecosystems over time, Wendt said.
“It’s important to connect the dots between the past and today,” he said. “By integrating thousands of observations from the fossil record, we have gained a deeper understanding of bison and the evolution of North American ecosystems over the past 20,000 years. We think the results and maps from this research will be valuable resources for tribes, natural resource managers and communities who are working to conserve bison and restore rangeland ecosystems.”