Final answer:
Adult muskox forming a circle to protect their calves is an example of predator avoidance benefits, a type of altruistic behavior that helps ensure the survival of the young in a cooperative social structure.
Step-by-step explanation:
The behavior of a group of adult muskox forming a circle to protect calves located at the center illustrates predator avoidance benefits. This strategy enhances the survival chances for individual muskoxen, particularly the more vulnerable calves. By living in groups, these mammals exhibit altruistic behavior where the adults may risk themselves for the safety of the young. Such social behaviors are an adaptive trait that has evolved to increase the chances of offspring survival.
Additionally, ungulates like muskox exhibit cooperative behaviors where each member takes on a specific role. Herd members surrounding and protecting the young in such a clumped population distribution is one of the most effective forms of predator defense, and it's a clear example of cooperation within a society of animals. These key elements of social living can also be seen in other species, such as lions and zebras, where the social structure benefits all members of the group.