From The Art and Popular Culture Encyclopedia
The size of the pack may change over time and is controlled by factors including habitat type, individual personalities, and food supply. Generally packs contain between two and six animals, although packs with more than 20 have been recorded. The hierarchy or rank order of the pack is relatively strict, with the alphas (one male, one female) on top and the omega at the bottom. The hierarchy affects all activity in the pack, from which wolf eats first to which is allowed to breed (generally only the alpha pair).
In the case of the domestic dog, thousands of years of breeding for docility has made certain that most dogs easily accept humans as the natural pack alpha; households having more than one resident dog quickly establish their own hierarchy within the social context of the household.