The near-extinction of bison in North America in the 19th and 20th centuries was an ecological disaster, leaving major gaps in our understanding of how and where these animals lived prior to European colonisation.
Now, a groundbreaking new study of ancient lake sediment chemicals in Yellowstone National Park has revealed that large herbivores, such as bison and elk, have roamed the landscape for the past 2,300 years.
The discovery could prove "critical for understanding long-term dynamics of ecologically and culturally important herbivores,” says John Wendt, who led the study.
Herbivore history
Much of the information we have on past bison occurrence comes from fossilised vertebrate remains largely recovered from archaeological and paleontological sites. But these records are fractured, providing limited insights about past variations in habitat use and the dominance of different ungulate species within local ecosystems, explains Wendt.
The objective of the new study was to find a more continuous record of the large herbivores that once dominated the northern Yellowstone region by analysing steroids from animal dung preserved in lake sediments from 238 B.C. to the present day.
To achieve this, researchers identified the types of steroids that occur in the dung of several large herbivores believed to have lived in the region, including bison, elk, moose, mule deer and pronghorn.
They then tested samples from sediment layers retrieved from Buffalo Ford Lake in northern Yellowstone, which indicated that either bison, elk, or both have been the region's primary large herbivores for much of the past 2,300 years.
20th-century discoveries
The findings also highlight changes in the 20th century, when conservation policies altered the animals’ behaviours – with hunting bans, restricted winter migration, and a decline in natural predators, herbivore populations grew.
Based on plant pollen, microalgae and plankton present in sediment samples, the team think that these expanding populations consumed more local vegetation, such a willow and Idaho fescue, which in turn spurred on diatom (algae) growth in the lake.
The researchers also think that the provision of winter hay by park managers kept animals in the area for longer, resulting in further impacts to the ecosystem.
Why is this important?
Th study highlights the potential of using steroid biomarkers in lake sediments as a tool for understanding long-term shifts in herbivore communities and their ecological impacts, which can then be used as tools to help land managers and conservationists make informed decisions.
While the research illuminates historical shifts in a single watershed, the team anticipates that applying this method across multiple sites could yield essential insights into Yellowstone's grazing history – and beyond.
“We developed a 2,300-year record of wild herbivore activity in northern Yellowstone National Park with fossil biomarkers found in lake sediments," Wendt concludes. "This information is critical for understanding long-term dynamics of ecologically and culturally important herbivores such as bison and elk.”
Find out more about the study: A 2000-year record of fecal biomarkers reveals past herbivore presence and impacts in a catchment in northern Yellowstone National Park, USA
Main image: Lamar Valley, Yellowstone National Park/Getty
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