Mammoths lost their steppe habitat due to climate change

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About 25,000 years ago, Earth’s largest terrestrial biome – the “mammoth steppe” – began to disappear. Throughout the last ice age, commonly referred to as the last ice age, the arctic was surrounded by a vast grassland that was home to as much animal and plant life as the African savannah today. The ecosystem was home to extinct megafauna like mammoths and woolly rhinos and, to a greater extent, stretched from the Iberian Peninsula to eastern Siberia and across the Bering Strait to Alaska and Canada.

Today, the gigantic steppe no longer exists. As the planet thawed, it vanished, but not without leaving traces.

Today, the gigantic steppe no longer exists. As the planet thawed, it vanished, but not without leaving traces.

Using ancient animal and plant environmental DNA (eDNA) extracted from sediments across the Arctic, scientists have reconstructed a 50,000-year history of this lost ecosystem and published their findings in Nature. Not only does the new data show mammoths may have lingered in small pockets of the mammoth steppe in Siberia for thousands of years longer than previously thought, the findings also implicate climate change – not excessive hunting by ancient humans – in the loss of the biome and in the extinctions of the Pleistocene megafauna.

“[Sediment eDNA] is a game changer, ”said the biogeoscientist Marc Macias-Fauria from the University of Oxford who was not involved in the new study. “It makes it possible to answer new questions or old questions differently. “

50,000 years of arctic ecosystem change preserved in DNA

Researchers analyzed ancient DNA from Arctic sediments, pictured here, to shed light on why the gigantic steppe, once Earth’s largest biome, disappeared after the last Ice Age. Credit: Yucheng Wang

To go back in time, researchers sequenced extracts of eDNA from hundreds of arctic sediment samples collected over more than 20 years. They then aligned these eDNA sequences across more than 1.4 million genomes, including those of arctic animals and plants, to determine which organisms the eDNA originally belonged to.

This effort was made possible by a massive new dataset of 1,541 new plant genomes, which allowed researchers to identify far more dDNA than they could before, the botanist said. Arctic and co-author of the study. Inger Greve Alsos from the Arctic University of Norway.

Along with this eDNA data, the researchers used a computer model of the climate of the past biome and the distribution of prehistoric humans in the Arctic. Together, the eDNA model and data revealed how animal and plant populations moved as humans moved north and the globe thawed before the holocene. Analysis showed that Arctic vegetation was shifting as the climate changed.

“When the climate warms in the Holocene, the vegetation in different regions starts to look different,” said paleoecologist Yucheng Wang from the University of Cambridge and the University of Copenhagen, the lead author of the study. “For example, in the North Atlantic… we see aquatic plants increase dramatically immediately after warming, while in Central Siberia, which is more continental, we see that the vegetation of the steppes has remained virtually unchanged.”

Climatic extinction or human overexploitation?

The eDNA from herbivores such as mammoths tended to be absent in samples containing more eDNA from woody and aquatic plants and samples that the climate model associated with higher and more intense seasonal precipitation. This finding could indicate that the wetter Holocene climate allowed swamps, lakes and forest to encroach on steppe vegetation, leaving large herbivores like mammoths without suitable habitat. This interpretation placed the new findings on the side of a long scientific debate about the nature of the mammoth steppe and the cause of megafauna extinctions.

New research has “definitely added very strong evidence to this debate to support that climate change was the driving force behind the last Quaternary extinction.”

An alternative theory is that the gigantic steppe disintegrated because humans over-hunted large herbivores, what researchers sometimes call the human overexploitation scenario. The new data, however, didn’t show much evidence of exaggeration. Unlike vegetation and precipitation, the presence of ancient humans was almost completely independent of the eDNA-based distribution of most herbivores, including mammoths, across the Arctic. Additionally, researchers found that mammoths survived in parts of Siberia until 4,000 years ago. Not only did this take longer than previously thought, but the discovery also suggested that humans have coexisted with megafauna for thousands of years without excessively hunting them.

While the debate over the fate of the mammoth steppe and the definitive cause of megafauna’s extinction is not over, this research “has definitely added very strong evidence to this debate to support that climate change has been the driving force. of the last Late Quaternary extinction, ”Wang mentioned.

—Elise Cutts (@elisecutts), science writer

Quote: Cutts, E. (2021), Mammoths lost their steppe habitat due to climate change, Éos, 102 years old, https://doi.org/10.1029/2021EO210622. Posted on November 19, 2021.
Text © 2021. The authors. CC BY-NC-ND 3.0
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