Billy, Grizzly Bear Pet, Vancouver, British Columbia, Canada

Grizzlies directly regulate prey populations and also help prevent overgrazing in forests by controlling the populations of other species in the food chain. An experiment in Grand Teton National Park in Wyoming in the United States showed removal of wolves and grizzly bears caused populations of their herbivorous prey to increase. This, in turn, changed the structure and density of plants in the area, which decreased the population sizes of migratory birds. This provides evidence grizzly bears represent a keystone predator, having a major influence on the entire ecosystem they inhabit.
Conflicts with humans
Grizzlies are considered by some experts to be more aggressive than black bears when defending themselves and their offspring. Aggressive behavior in grizzly bears is favored by numerous selection variables. Unlike the smaller black bears, adult grizzlies are too large to escape danger by climbing trees, so they respond to danger by standing their ground and warding off their attackers. Increased aggressiveness also assists female grizzlies in better ensuring the survival of their young to reproductive age. Mothers defending their cubs are the most prone to attacking, being responsible for 70% of fatal injuries to humans. Historically, bears have competed with other large predators for food, which also favors increased aggression.