Social Stratification and Population Regulation amongst Wolves
"...Wolves live in small groups of 6 to 12 or more individuals called packs. The pack is an extended kin group consisting of a mated pair, one or more juveniles from the previous year who do not become sexually mature until the second year, and several nonbreeding related adults.
The pack has two social heirarchies, one headed by an alpha female and one headed by an alpha male, the leader of the pack to whom all other memebers defer. Below the alpha males is the beta male, closely related, often a full brother, who has to defend his position against pressures from other males below.
Mating within the pack is rigidly controlled. The alpha male (occasionally the beta male) mates with the alpha female. She prevents lower ranking females from mating with the alpha and other males, while the alpha male inhibits mating attempts by other males. Thus each pack has one reproducing pair and one litter of pups each year. These pups are reared cooperatively by all members of the pack. At low wolf densities, some packs may rear two litters of pups a year (Ballard et al. 1987).
The size of a wolf population in a region is governed by the size of the packs, which hold exclusive areas. Regulation of pack size is achieved by events within the pack that influence the amount of food available to each wolf. The food supply itself does not affect births and deaths, but the social structure that leads to an unequal distribution of food does. The reproducing pair, the aplha female and the alpha male, has priority for food; they, in effect, are independent of the food supply. The subdominant animals, male and female, with little reproductive potential, are affected most seriously. At high densities the alpha female will expel other females from the pack. Other individuals may leave voluntarily. Unless these animals have an opportunity to settle successfully in a new territory and form a new pack, they fail to survive.
The social pack, then, becomes important in population regulation. As the number of wolves increases, the size of the pack increases. Individuals are expelled or leave, and the birth rate relative to the population declines because most sexually mature females do not reproduce. Overall the percentage of reproducing females declines. When the population of wolves is low in a region, sexually mature females and males leave the pack, settle in an unoccupied habitat, and establish their own packs with one reproducing female. More rarely, the pack may produce two litters instead of one litter in a year (Ballard et al. 1987, Van Ballenberghe 1983). But at very low densities, females may have difficulty locating males to establish a pack and so fail to reproduce or even survive. (For details on social regulation of population size in wolves see Mech 1970, Zimen 1978, Fritts and Mech 1981, Ballard et al. 1987.)"
Robert L. Smith and Thomas M. Smith, Ecology & Field Biology (New York: Benjamin Cummings, 2001), p. 202.