A new study published in the journal Marine Ecology has found that a change in climate is the most likely cause of the mysterious disappearance of ancient brown bears and lions from North America about a millennium before the last Ice Age.
By sequencing DNA from fossils of cave lions and bears from North American and Eurasia, a research team from the University of Adelaide discovered that the timing of these ancient animals’ extinction from parts of North America (especially the Yukon Territory and Alaska) coincided with widespread vegetation change in these regions.
According to the scientists, the warm temperatures before the last Ice Age might have caused significant changes in the abundance of different kind of plants, which initially led to the extinction of several species of herbivores and then also of their predators, including lions and bears. A few centuries later, the colder temperatures that led up to the Ice Age might have reversed the changes and made these regions once more hospitable for both the herbivores and their predators.
These findings suggest that past ecosystems have been extremely changeable and that the abundance of various species has always been highly sensitive to changes in climate.
“There’s a common perception that outside of mass extinctions or direct human interference, ecosystems tend to remain stable over thousands or even millions of years,” said study co-author Dr. Kieren Mitchell, an evolutionary biologist and expert in Bioinformatics at the University of Otago, New Zealand.
“As illustrated by our study of the fossil record, that’s not necessarily the case. Previous research has shown that brown bears (or grizzly bears) disappeared from some parts of North America for thousands of years prior to the last Ice Age. They later reappeared, walking from Russia to Alaska across the Bering Land Bridge – possibly at the same time as people moved across the Bridge into North America too.”
“While many might think that species arrive in a region and stay put, we show that the past was much more dynamic, involving multiple waves of dispersal and local extinctions in this case,” Dr. Mitchell concluded.