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  6. Fossil study shows impact of extinction of North American mammals on surviving mammal communities

Fossil study shows impact of extinction of North American mammals on surviving mammal communities

Lt. Emöke M. Tóth

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When the megafauna went extinct, many surviving mammals expanded their ranges, resulting in greater range overlap. In overlapping zones, segregations between species became stronger.

Ottawa, September 19, 2019 – Around 11,700 years ago, it was game over for about three-quarters of the large mammal species in North America. Gone were large carnivores and herbivores such as mammoths, sabre-toothed cats and ground sloths—potentially wiped out from human activity. Others such as deer, coyotes and bison survived in environments where the larger mammals were no longer around to shape the landscape or influence their populations.  

The implications of this type of loss to mammals living today is now reported in a paper published in the journal Science by an international team of 19 researchers in Australia, the United States, Europe and Canada (including Dr. Danielle Fraser with the Canadian Museum of Nature).

The study reports how the smaller surviving mammals changed their ecological interactions, causing upheaval across the continent. The results have implications for the conservation of today’s remaining large animals, increasingly under threat by human activities.

“Study after study shows that it’s the larger-bodied mammals that tend to be endangered or threatened. So by primarily examining the fossil record, we show that the ecological consequences are far ranging when larger animals are removed from an ecosystem,” says Dr. Fraser, palaeomammaologist with the Canadian Museum of Nature and member of the study team.

Lead author Dr. Aniko Toth at Australia’s Macquarie University worked with Fraser and other collaborators as part of an international scientific working group based at the Smithsonian Institution in Washington, D.C. The group’s goal has been to understand how communities of animals that have lived together have changed over time.

The scientists analysed reams of data for 93 species at hundreds of fossil sites to see how mammals were distributed across North America from the late Pleistocene (up to 11,700 years ago) to the Holocene (up to present day). It was a time when the continents were experiencing ecological transformation—the mammoth steppe disappeared, vegetation and fire regimes changed, functional groups of mammals were lost, and global biophysical feedback systems shifted.

The researchers analysed how often pairs of species that survived the extinction were found living in the same community or in different communities. They found that prior to the late-Pliocene extinction, co-occurrence of species was more common than after, when segregation of species pairs became more common. Also changed was the way in which species interacted. Surviving species increased their geographic ranges, with an increase in overlap among ranges.

Crucially, the study shows that the importance of interactions with other living things (called biotic associations) decreased after the end of the Pleistocene.   

“One of the key findings from this study is that biotic associations between surviving species break down,” explains Fraser. Some examples include associations between white-tailed deer and pronghorn, as well as coyotes and racoons.

So, what was happening when the larger, now extinct, mammals (megafauna) were present? Toth and the study team suggest that they may have mediated interactions among other species. Fraser explains that some of these interactions may have included mammals serving as “ecosystem engineers” (such as mammoths who grazed the steppe habitat) or those that were part of a predator-prey relationship.

“There is a prevailing opinion among scientists today that biotic interactions only operate on a local scale. We show that when megafauna were around, biotic interactions were structuring communities on a continental scale,” says Tóth. After the megafauna went extinct, the spatial outcome of biotic interactions changed.

“The legacy of these changes is that today’s mammals are living where they are in North America primarily because of environmental and climactic reasons, rather than because of relationships with other mammals,” says Dr. Fraser.

Information for media:

Dan Smythe
Media Relations
Canadian Museum of Nature
613.566.4781; 613.698.9253 (cell)
dsmythe@nature.ca

About the Canadian Museum of Nature
Saving the world through evidence, knowledge and inspiration! The Canadian Museum of Nature is Canada's national museum of natural history and natural sciences. The museum provides evidence-based insights, inspiring experiences and meaningful engagement with nature's past, present and future. It achieves this through scientific research, a national collection of 14.6-million-specimens, education programs, signature and travelling exhibitions, and a dynamic web site, nature.ca.