They're a unique species in terms of our coexistance and tolerance and competition for resources. Grizzlies are probably our closest competitor in North America and their needs are very similar to the needs of early Americans. In fact, many of the most important bear foods have names that indicate their use by humans like Biscuitroot, which is the genus Lomatium and Eskimo Potato which is the genus Hedysarum. So, we probably competed for a lot of the same resources and we're still competing today.
Bears are omnivorous and feed on a wide variety of plants and animals.
Basically, anything that humans can eat, bears can eat, also. If you wanted to use an umbrella species in parts of Africa, something like Mountain Gorillas or Chimpanzees, which are really close, would be a good one to choose as far as allocating resources that humans might take from other species. Because of their broad ecological niche, bears can be viewed as an excellent umbrella species. If you're unfamiliar with this term, it's a species whose habitat encompasses the habitat needed by a large number of other species. So, if we maintain a population of Grizzly Bears, hopefully we will also be maintaining a large number of other animals, plants, and ecosystems and ecosystem functions.