Alpha, Beta, and Gamma Males
KeywordsDominance Hierarchy Social Hierarchy Alpha Male Alternative Reproductive Tactic Alternative Mating Strategy
The ranked order of males within a group.
The terms alpha, beta, and gamma male are typically used to describe an individual’s position within a social hierarchy. In linear hierarchies, alpha males are the highest-ranking males within a group, followed by beta, and then gamma males. While this section is focused on male social status, it should be noted that females can also form strong social hierarchies. Dominance hierarchies can commonly be found in taxa exhibiting group living, where frequent conflict among individuals can occur. Individual rank can be used to predict the outcome of agonistic interactions between males and thus be used to deter some of these aggressive encounters. This section will discuss some examples of how these terms are used across a variety of taxa.
Much of the research on dominance hierarchies comes from studies on nonhuman primates. In these groups, a male’s rank is based on a combination of age, health, competitive ability, and even maternal status. As such, males achieving alpha status are usually in their prime. While these hierarchies can be relatively stable, a male’s ranking is not permanent. One’s status can change as other males enter or leave groups or through rank changes within a group (Hamilton and Bulger 1990). Since challenges to alpha males can result in severe injury, males will often remain in their natal group until they reach their physical peak. The tenure of any alpha male can vary greatly among species but can be very short-lived, in some cases shorter than 6 months (Hamilton and Bulger 1990).
The position of an alpha male can incur significant costs to the individual. Higher-ranking males participate more in activities related to policing group conflicts and are often under threat of takeover by other males. However, one primary advantage of maintaining alpha status is obtaining higher reproductive fitness compared to other males in the group. Alpha males have priority access to ovulating females and fertilize a significantly higher proportion of offspring during their tenure compared to males in subordinate positions (Jack and Fedigan 2006). In multi-male groups, the reproductive skew between alphas and other males can be striking, but there is large variation among primates (Hagar 2003). Some of this variation in reproductive skew is likely driven by social interactions between alphas and other males. Males of varying status will form alliances, which can either reinforce current male rankings or overthrow an established alpha. In return for their help in these endeavors, alphas may “exchange” breeding opportunities with these subordinates (Snyder-Mackler et al. 2012), leading to higher reproductive success of beta or gamma males.
The term alpha male is often used in association with canines to designate the highest-ranking male within a pack. Much of the early work on social hierarchies in canines came from studies of captive wolf populations. In these populations, multi-male and female groups can consist of nonrelated individuals, which form structured social hierarchies in both sexes (Rabb et al. 1967). The alpha male and female are the main breeding pair and can behaviorally restrict the courtship of other adults in the pack (Rabb et al. 1967). While relatively stable, changes in social status can occur if an alpha is removed or becomes injured. Also, alphas can form alliances with other males to protect and shield one another during attacks (Rabb et al. 1967). However, it is possible that if the status of the alpha male declines, so does the status of his associated males.
The packs of wild populations are very different than those of captive populations. In the wild, packs tend to consist of familial groups that include parents and their offspring (Mech 1999). Although multifamily packs can exist, this is rare. The alpha male and female are the primary breeders of the pack. Once offspring reach a certain age, they will leave the natal pack to form their own in a different territory (Mech 1999). Alpha males are also responsible for scent marking their specific territories (Peterson and Page 1988), which can be maintained over multiple years. When conflicts arise between packs, it is the alpha individuals that primarily participate in these aggressive interactions (Peterson and Page 1988).
Like wild wolves, African wild dogs (Lycaon pictus) form familial packs consisting of an alpha breeding pair, their offspring, and sometimes the siblings of one of the alphas. The siblings are subdominant to the alpha pair but will cooperatively participate in hunting and protecting the offspring (Malcolm and Marten 1982). While there are some instances of subdominants mating with one of the alpha pair, the proportion of offspring subdominant males successfully fertilize is currently unclear.
Dominance hierarchies are often associated with group living; however, alpha/beta relationships can occur in non-group-living species. In the lance-tailed manakin (Chiroxiphia lanceolata), males form long-term cooperative breeding groups, with one male being dominant to one or more unrelated males. This species has a lekking mating system where males and females congregate and compete for mates during the breeding period. Alpha and beta males cooperate in performing elaborate mating displays to attract females. The energetic investment that beta males make in the partnership can be costly. They can engage in excess of three million duet calls and spend more than 1000 h performing displays during their time with an alpha male (McDonald and Potts 1994). However, alpha males obtain the majority of the reproductive success from these parings, and beta males rarely mate. Beta males do eventually benefit by the fact that they are more likely to become an alpha male if they have participated in these cooperative groups (McDonald and Potts 1994). Succession in this group is hierarchical with beta males moving into the alpha position once it is vacant.
While the terms alpha, beta, and gamma are usually related to male rank within social hierarchies, it should be noted that this is not always the case. In the marine isopod (Paracerceis sculpta), these terms are used to describe three different male reproductive morphs (Shuster and Wade 1991). The morphs are genetically determined by a single autosomal locus and represent alternative mating strategies. Alpha males are the largest morph and defend females within the central cavity of intertidal sponges (spongocoels). Beta males are intermediate in size and resemble females. These males mimic female behavior to enter spongocoels occupied by alpha males and females. Gamma males are much smaller than the other two morphs and effectively sneak into occupied spongocoels. The reproductive success of each morph is dependent upon the relative density of males and females within the spongocoel. When only one female is present, the alpha male fertilizes the majority of the offspring (Shuster and Wade 1991). As the number of females increases, the reproductive success of beta and gamma males increases and can surpass the alpha male. Across natural populations, the average reproductive fitness of each morph is relatively equal (Shuster and Wade 1991).
Social hierarchies can dictate how individuals interact with one another within a group. In group-living species, male ranking is typically correlated with male reproductive success, with alpha males receiving most of the mating opportunities. Beta and gamma males will contribute to the group and may form alliances with an alpha, sometimes in exchange for mating opportunities. Beta males may also cooperate to increase their likelihood of obtaining the alpha position once it becomes vacant. While these ranked terms often indicate male social status, it should be noted that they can also be used to describe different male alternative reproductive tactics in many taxa.
- Hagar, R. (2003). Models of reproductive skew applied to primates. In C. B. Jones (Ed.), Sexual selection and reproductive competition in primates: New perspectives and directions (pp. 65–101). Norman: American Society of Primatologists.Google Scholar
- Jack, K. M., & Fedigan, L. M. (2006). Why be alpha male? Dominance and reproductive success in wild white-faced capuchins (Cebus capucinus). In A. Estrada, P. Garber, M. Pavelka, & L. Luecke (Eds.), New perspectives in the study of Mesoamerican primates (pp. 367–386). New York: Springer.CrossRefGoogle Scholar