Newly discovered information into the inflexible diet of one group of prehistoric bears has scientists rethinking how the creatures lived and what caused the large mammals’ extinction some 25,000 years ago.
Working with scientists in Japan, Belgium and Germany, Western biologist Keith Hobson used an isotopic composition found in the collagen of the cave bears’ bones to show the large mammals subsisted on a purely vegan diet. In the study, recently published in the Journal of Quaternary Science, the international team proposed this inflexible diet killed off the bears.
“It’s almost a paradigm shift to what we were always thinking,” Hobson said. “Now, we have to rethink how they existed on the landscape and, more importantly, why they went extinct. Did they have the wrong strategy all along? Being herbivores were they therefore particularly prone to any kind of climate change? If the weather turned cold, they would not do well, whereas omnivores and carnivores would look for other sources of food.
“Because their niche was so specialized, they were vulnerable to such changes. Any animals that feed on only one thing are very vulnerable. That makes sense ecologically.”
The Cave Bears of Belgium lived in Europe during the most recent glacial period, approximately 400,000 years ago. With a length of 3.5 metres and a height of 1.7 metres at the shoulder, these bears were noticeably larger than their modern-day relatives. Despite their name, they did not live in caves but only used them for hibernation.
Researchers analyzed amino acid in the bone collagen of 10 cave bears skeletons (eight adults, two cubs), five brown bears from Goyet Cave in Belgium and three modern grizzly bears from Alberta. All the cave bears, as well as some brown bears, had the feeding habits of herbivores (plant eaters).
Today’s brown bears are omnivores (feeding on both plants and animals) and, depending on the time of year, will devour plants, mushrooms, berries, smaller to larger mammals, fish and insects. Cave bears were a different story.
“Similar to today’s giant panda, the cave bears were extremely inflexible in regard to their food,” he said. “We assume that this unbalanced diet, in combination with the reduced supply of plants during the last ice age, ultimately led to the cave bear’s extinction.”
Because they were vegan, researchers believe the creatures were slower and less aggressive than one would expect of a large bear. That may have made them more vulnerable to hunters.
“This adds a whole new dimension to the discussion,” said Hobson, who worked with Hervé Bocherens, a former Western postdoctoral scholar, now a professor in the Department of Geosciences at the University of Tübingen in Germany.
“The reliance on a purely vegan diet was a crucial reason for the cave bear’s extinction,” Bocherens said. “We now intend to examine additional cave bear bones from various European locations with this new method, as well as conduct controlled feeding experiments with modern bears, in order to further solidify our proposition.”
This new interpretation around the extinction of the cave bear has added to a body of evidence as to why some species continue to thrive, while others remain on the brink of extinction.
“There are many existing bear species – some more vulnerable than others, such as the polar bear – who have a very specialized diet,” Hobson said. “Understanding what happened to their ancestors in the past, where they may have gone down the wrong way, can help you with modern-day conservation issues, especially now with such a flux in environmental changes.
“Are there factors today that could put species at risk for the very same reasons? A specialized diet? Not being able to get out of that niche they are in? What do we do about those ones? So this research does have a modern day equivalent.”