Likewise, if bears are the only predator, bears do not keep prey numbers low. This occurs where wolves and bears are at relatively high densities and are only lightly harvested. Wolves and bears keep moose in the predator pit by killing many moose, especially calves, that would otherwise live and reproduce. Caribou herds may also remain at very low numbers when preyed upon by both wolves and bears. Caribou differ from moose, because caribou can sometimes escape the effects of wolf and bear predation by migrating, by selecting calving areas with few predators, and by greatly outnumbering predators.
Predation has less effect on large caribou herds that it has on small herds.
A certain portion of any prey population must survive to reproduce and maintain the herd. The rest can be killed by wolves, bears, or people without causing a decline in numbers. The size of this excess portion will vary over time in different areas and can be affected by wildlife management. Naturally low prey numbers do not necessarily create a management problem. If people are satisfied with a small share of the prey, predator-prey relationships may not need to be adjusted to provide for increased human harvests.