In most baboons, social interactions are shaped by dominance hierarchies. A dominance hierarchy is a linear ranking of individuals, i.e. a pecking order. Individual males almost always rank higher than individual females, but there is usually a separate hierarchy within each sex.
Dominance relationships are most obvious among males, who aggressively compete over the highest positions in the dominance hierarchy, engage in frequent aggressive competition over females, and use vocalizations to signal competitive ability (Hall 1962b; DeVore and Washburn 1963; Hall and DeVore 1965; Hausfater 1975a,b; Bernstein 1976; Kitchen et al 2003; Fischer et al 2004). In contrast to most baboons, hamadryas baboons (and possibly Guinea baboons as well) can be best characterized as having two social strata for males: those with females and those without (Boese 1973; Kummer 1968a, 1973; Abegglen 1984). In hamadryas, "leader males" of one-male units (OMUs) are dominant to follower and solitary males in the sense that the former have priority of access (in this case, near exclusive access) to females, but this relationship is maintained via ritualized "notifications" rather than traditional dominant-subordinate interactions.
In most baboons, females also maintain dominance relationships within linear, stable dominance hierarchies (Seyfarth 1976; Altmann 1980; Hausfater et al 1982; Smuts 1985; Byrne et al 1989; Bentley-Condit and Smith 1999) and higher-ranking individuals have greater access to food resources (Barton 1993; Barton et al 1996). Female dominance rank in baboons is inherited matrilineally, with each female generally ranking just below her mother and above her older sisters (called "younger daughter ascendancy"), and the process by which this rank is attained involves substantial maternal support (Cheney 1977; Altmann 1980; Walters 1980; Pereira 1986, 1988, 1989). In populations for which long-term data are available, female dominance hierarchies remain stable for many generations (Hausfater et al 1982; Samuels et al 1987; Silk et al 1999). In hamadryas baboons, by contrast, dominance relationships among females are either absent or extremely subtle in the wild. Hamadryas females do, however, develop and maintain dominance relationships in captivity (e.g., Vervaecke et al 1992; Leinfelder et al 2001), as do Guinea baboons (Boese 1973).
Dominance carries benefits for both sexes in terms of survival and reproduction. Among females, lower-ranking individuals suffer greater mortality via predation (Ron et al 1996); lower food intake via lower bite rates, shorter feeding bouts, or less-suitable feeding sites (Post et al 1980; Barton 1990, 1993; Barton and Whiten 1993); reduced fertility via lower nutritional status and/or body weight (Strum and Western 1982; Bercovitch 1985, 1987a; Barton 1990; Bercovitch and Strum 1993); and consequent reduced fitness (Altmann 1991, 1998). Higher-ranking females begin reproducing at an earlier age, reproduce at shorter intervals, and/or produce offspring that grow faster (and are weaned at earlier ages) compared to lower-ranking females (Altmann et al 1988; Smuts and Nicolson 1989; Packer et al 1995; Altmann and Alberts 2003b, 2005; Johnson 2003, 2006; Cheney et al 2004, 2006).
Among males, higher-ranking individuals are more successful at establishing and maintaining consortships, exclusive social and sexual associations between a male and a female when the female is in estrus (Altmann et al 1996, Hausfater 1975a; see section on Baboon Sexual Behavior, Reproduction, and Life History). Higher-ranking males also usually achieve higher mating success and/or reproductive success (Packer 1979b; Altmann et al 1996; Alberts et al 2003; Altmann and Alberts 2003b). In olive and yellow baboons, however, lower-ranking males can form coalitions and overturn consortships of higher-ranking males. Higher rank is also associated with lower stress hormone levels and more adaptive endocrinological profiles during periods of social stability (Sapolsky 1982, 1993; Bergman et al 2005), though social instability negates these rank-related advantages (Sapolsky 1992; Bergman et al 2005).
Content contributed by:
Dr Larissa Swedell
|Thanks to the following reviewers:
Dr Susan Alberts
Dr Cliff Jolly
photograph by Helga Peters
For a more scholarly version of the information on these pages, see:
Swedell, L (2011) African Papionins: Diversity of Social Organization and Ecological Flexibility. IN Primates in Perspective, Second Edition (Campbell CJ, Fuentes A, MacKinnon KC, Bearder SK, Stumpf, RM, eds). New York: Oxford University Press, pp. 241-277.
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