Wolves

Pack structure, and what happens to a system without them.

The gray wolf (Canis lupus) is the largest wild canid and the ancestor of the domestic dog. It once ranged across most of the northern hemisphere.

Pack structure

A pack is usually a family: a breeding pair and their offspring from several years. The older “alpha” framing came from studies of unrelated captive animals and describes a situation wild wolves rarely encounter. In the wild the breeding pair leads because they are the parents.

Communication

Howling coordinates a dispersed pack and advertises territory. Scent marking sets boundaries, and posture and facial expression handle close-range signalling.

Trophic cascade

Wolf removal in North America was followed by elk and deer increases and heavy browsing of streamside willow and aspen. Reintroduction to Yellowstone in 1995 was followed by changes in elk numbers and behaviour and by recovery in some browsed areas. The scale of the effect is still debated, since climate, other predators and drought moved at the same time — but the direction of change is not.