Bears of the Pleistocene

[brotherbear]

https://www.allgrizzly.org/pleistocene-holocene-diet 
 
I suspect that the amount of meat in local diets of Pleistocene grizzlies varied widely, primarily as a function of the competition they faced from other carnivores. However, I also suspect that the meat in grizzly bear diets increased substantially during the late Pleistocene-Holocene transitions as most of their competitors (and predators) went extinct, and despite the demise of most species of large herbivores as well.
 
Why do I think this? As I describe in the page devoted to Early Prehistory, there were a lot of large carnivores around during the Pleistocene, including lions, short-faced bears, dire wolves, and saber-tooth and scimitar-tooth cats. Grizzlies would not have fared well trying to either protect a kill or contest a found carcass when confronting such competitors. In fact, they probably sometimes ended up as prey of the largest of these predators, as seems to have been the case for cave bears in Pleistocene Europe and as continues to be the case for brown bears in areas occupied by Siberian tigers. On the other hand, in the absence of such competitors brown and grizzly bears can be quite carnivorous, as is the case for contemporary populations in meat-rich environments. 
 
But getting back to the Pleistocene. I suspect that competition with and predation by other large carnivores could have been intense enough to limit most grizzlies to marginal areas such as the swath of tundra along the continental icesheet margins (see above). But given such limits, grizzlies were probably locally adaptive in response to variations in competition and the meat resource. Herve Bocherens describes precisely such a situation in Pleistocene Eurasia, where brown bears coexisting with the largely herbivorous cave bears in Europe seem to have been quite carnivorous, while grizzlies hanging around meat-eating giant short-faced bears in Beringia were much more herbivorous. 
 
What might this mean for Pleistocene grizzlies? First, there was probably a lot of meat around in the form of carrion in most areas of the West. Even though the competition for this resource was probably intense, a fast-moving lucky grizzly might have still been able to scavenge of lot. Second, smaller-bodied camels and horses might have been an especially important resource given that competing for meat from a fallen giant such as an elephant was probably particularly hazardous for a grizzly. And, third, the concentration of elephant remains along recently-melted margins of the ice sheet would have likely increasingly contributed to the sustenance of grizzlies in these dynamic rapidly revegetating environments of the East. This would fit my speculations about the distribution of early Holocene grizzly remains in this region, the extent to which grizzlies seemed to track recently melted environments, and the apparent absence of eastern grizzlies after about 9k years ago. Reply