Here's a story that sounds like something out of our own not-too-distant future: Encroaching sea-levels caused by a warming climate triggered the downfall of a population living on a remote island in the Pacific, after they failed to adapt.
Scientists have been warning about this scenario playing out in the face of climate change. But in this case, we're talking about the distant past: the final stand of the woolly mammoths on St. Paul Island, Alaska, some 5,600 years ago. The island is famous as a refuge for these animals, which thrived there long after they'd been wiped out elsewhere. Now, a team of researchers from Pennsylvania State University and the University of Alberta has discovered why the iconic megafauna was wiped out, after they didn't adapt to a changing environment.
Given what's happening in the world today, there could be some valuable lessons here for us.
Changes that turn out to be catastrophic don't all happen at the same time
Rising oceans, caused by the thaw after the last Ice Age, were just one of their mounting problems. Fresh water was also disappearing as seawater replaced the mammoths' drinking sources. Scientists took core samples from the bottom of lakes on the island, and noticed changing salinity, as well as evidence of increasing 'turbidity.' In other words, more and more particles were dissolved in the lakes, which indicated a decline in the quality of available drinking water.
Researchers tracked spore and fungus traces that were commonly found in mammoth dung, and discovered a steady decrease between 9,000 to 5,650 years ago. In other words, less and less poop indicates a shrinking population.
These clues gave researchers the hints they needed to see that the end of the St. Paul's woolly mammoth was pretty much a foregone conclusion—especially because the population was already small and isolated. Very isolated.
"[There were] many, many hundreds of kilometers to the nearest place," Duane Froese, professor of earth and atmospheric sciences at the University of Alberta, told me over the phone. "And unlike some of the other mammoths that were stranded on islands, these one didn't adapt in becoming pygmy-sized. At some point, something was going to knock them out."
Humans don't share in the blame for this particular extinction. Froese and his team found no evidence that these mammoths were hunted by humans, as the first known settlement of the island was Russian whalers in 1787.
According to these researchers, the situation that the large animal had found itself in could be a natural example of what is known as extinction debt. As Motherboard has previously reported, seemingly small changes that turn out to be catastrophic don't all happen at the same time. All the factors that piled up to doom the St. Paul mammoth happened over generations, eventually creating an unavoidable outcome.
"These island populations are really precarious because they don't have a release valve"
"These island populations are really precarious because they don't have a release valve. They can't migrate out of an area when resources are scarce. These mammoths really were stuck," said Froese.
There are examples of successful adaptation: elsewhere, mammals shrunk in size. While not as small as the Channel Islands pygmy mammoths, the woolly mammoths of Wrangel Island, in the Arctic Ocean, also shrunk over generations and could have been the very last population of the species. That group lasted until 1650 BC. Their smaller stature caused them to require less from their environment.
That doesn't sound like a bad idea at all.
Larger mammoths on St. Paul Island didn't do themselves any favours. Since they were huge, they had a heavy impact on the very erodible soils of the once-volcanic island. They would have literally worn out the ground under their feet, explained Froese.
Parallels to humanity's struggle against a shifting climate are sobering when you consider cases like the plight of people living in the Marshall Islands. The sandy atolls in the South Pacific, where the US conducted nuclear bomb tests, are disappearing into the rising seas.
We have an advantage over St. Paul Island's stranded woolly mammoths: We can see these problems coming. The climate is changing rapidly, and I just hope we're not beyond being able to pay what is owed to our own extinction debt.