What killed the woolly mammoths on St. Paul Island? Thirst. For the first time, scientists have pinpointed the date — 5,600 years ago — and a likely cause of extinction. They believe the environmental changes that killed the animals mirror today’s climate changes.
Six thousand years ago, St. Paul Island looked about the same except for one big difference: There were mammoths. And it’s not like they swam there. Penn State University’s Russell Graham says they walked on the Bering Land Bridge.
“As the glaciers melted, the water in the ocean started to rise,” said Graham. “In this process, a group of mammoths was isolated on the island.”
For a while, it was a good strategy for survival. Without predators, mammoths on St. Paul survived thousands of years longer than many other mammoths around the world. But eventually, they met their end. And Graham and a team of scientists wanted to know exactly when that happened.
“We were able to actually pinpoint when the mammoths actually went extinct,” he said. “It wasn’t like, ‘Well, we think it was this time.’ We actually know!”
Graham’s team analyzed a sediment core from a lake on the island. They examined ancient DNA and three species of fungal spores that grow on the dung of large animals.
All the evidence pointed to one culprit in the mammoths’ extinction: not enough fresh water. As the sea level rose, St. Paul shrunk. Some lakes were lost to the ocean and a more arid climate caused other freshwater sources to evaporate. As island dwellers, Graham says these mammoths were especially vulnerable.
“A change in the climate of the magnitude that caused this extinction on the mainland probably would have been insignificant,” he said. “But because the animals and plants are restricted to the island — and particularly smaller islands — this little change came together with a whole series of things to create a perfect storm that then caused the extinction.”
In the small world of paleoecology, the findings are a really big deal.
“What is especially powerful about this study is that you have completely independent lines of evidence that back up the same story,” said Jacquelyn Gill of the University of Maine.
As an Ice Age ecologist, she studies the past to put modern-day environmental problems — like climate change — in context. Since climate change and extinction have happened before, scientists can use what they know about various species responses to help protect today’s biodiversity.
Some might say 6,000 years ago is ancient history. But in geological time, it isn’t. While mammoths roamed St. Paul Island, Gill says ancient Egyptian civilization was well underway.
“When you tell someone, ‘You could have had a mammoth-drawn chariot if things had gone differently,’ I think it makes them think a little bit differently about Ice Age ecology and how relevant this work is to the environmental problems we’re facing right now,” said Gill.
The changing climate that claimed the mammoths of St. Paul has struck again. But this time, it’s human-driven. In June, a small Australian rodent became extinct, driving home Graham’s point that island populations are especially vulnerable.
And Graham says it’s not just the rising sea levels that should concern islands and coastal communities. Take a look at Florida.
“They may be waiting for the water to come up and inundate the peninsula,” Graham said. “But in reality, they maybe should be looking behind themselves because they’re probably going to face other issues — like fresh water availability — before that actually happens.”
The vulnerability of island populations is one lesson from the 72-foot-long sediment core. There could be more. Right now, scientists are hard at work analyzing the rest of it — all 18,000 years.