Bones tell ecological ghost story

U. CHICAGO (US) — Animal bones scattered across the wilderness landscape are offering clues as to how species’ populations have changed due to decades of global warming, overharvesting, and habitat destruction.

“The skeletons of long-dead animals lying on landscapes provide critical insight into our understanding of ecosystem history, especially how populations have changed,” says Joshua Miller, a postdoctoral research fellow at Wright State University, who did his research for his doctoral dissertation at the University of Chicago.

“These changes result in population reductions and extinctions of some species, while others expand and invade new habitats and regions,” Miller explains. “Most ecosystems have not been studied over long time spans—many decades at least—which hampers the ability of wildlife managers and other scientists to properly document or mediate these dramatic ecological changes.”

The bones of Yellowstone

Miller surveyed bones from the skeletons of hoofed mammals (ungulates) in Yellowstone National Park ranging in age from newly dead to approximately 200 years old and then compared the numbers of specimens from each species documented in bones to surveys of the living populations.

All the native species in the living community were recovered and the order of species from most abundant to least abundant was similar for the bones and the living community. Species whose populations significantly diminished or expanded over the last 20 to 80 years were predictably over- or under-represented in the bones relative to the living community, Miller says.

The research is published in the journal PLoS One.

“Live elk were much more abundant in the 1990s than they are today and the bones of Yellowstone feature far more elk than one would predict based on the current Yellowstone community.”

Horses, which were replaced by cars as the dominant mode of transportation in Yellowstone in the early 1900s, also are readily found as skeletal remains. Radiocarbon dating confirmed that horse bones were generally remnants from when the cavalry controlled Yellowstone in the late 1800s to early 1900s.

In contrast to these ghosts of larger past populations, species that have recently increased in abundance (bison and the recently arrived mountain goat) are less common in the skeletal record than current living populations would predict.

Overall, the bones of Yellowstone correlate well with the area’s historical ecosystem and provide more detailed information about the historical community than can be acquired from only studying the ecosystem today.

“Bones provide a great tool for uncovering historical ecological data that allow us to put modern biodiversity in a broader temporal context,” Miller says. “The living populations of Yellowstone have been studied for a long time and provide a great opportunity to test how well bones record species’ histories.

“Now we can go the next step and use bone accumulations in regions we have only recently begun studying to obtain critical historical data and establish how ecosystems have changed over the last decades, century or even longer.”

Joshua Miller studies bone survey data sheets on Yellowstone National Park’s Northern Range. (Credit: Scott Rose)

The research suggests that the ecological information contained in the fossil record may provide more biological details on extinct ecosystems than previously thought.

“Josh has shown that the bones of Yellowstone accurately track recent and not-so-recent history of the large mammal populations in this famous North American ecosystem,” says Kay Behrensmeyer, curator of vertebrate paleontology of the Smithsonian Institution’s National Museum of Natural History.

“This should be a wake-up call for ecologists interested in the movements, increases and declines of large mammal populations anywhere—bones are a relatively untapped and valuable source of ecological data about animals when they were alive.”

Miller received funding from the National Science Foundation.

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