Abstract
Dominance hierarchies in groups of social animals can be based either on asymmetries that are important for agonistic interactions (such as body mass) or on more ‘conventional’ cues (such as age), which are respected despite having little relationship to the animal's fighting abilities. We investigated how social dominance is influenced by age and body mass in a herd of 29–39 beef cows over a 10-year period, focusing on all levels of the dominance hierarchy (individual, dyadic and group). The results demonstrate that age prevails over body mass in the structuring of the dominance network in beef cattle. At the individual level, path analysis confirmed that the dominance index of a cow was more strongly associated with her age than with her body mass. At the dyadic level, age superiority had a stronger influence on the direction of social dominance in pairs than body mass superiority. Older cows were dominant in 73.6% of those dyads studied, even when the younger cow was heavier. At the group level, the strong influence of age on dominance produced a hierarchy that was very stable and strongly transitive. Our findings show that beef cows, for the most part, do not use their physical strength to attain dominance over older, but lighter, herdmates. This results in a stable age-based hierarchy, which might serve a universally shared function that promotes the smooth functioning of the herd and/or the expression of experience by older cows. Among the theoretical models of conflict resolution, the system most closely resembles the partial bourgeois evolutionarily stable strategy.
Highlights
IntroductionDominance hierarchies in groups of social animals can be based either on asymmetries that are important for agonistic interactions (such as body mass) or on more ‘conventional’ cues (such as age), which are respected despite having little relationship to the animal’s fighting abilities
Dominance hierarchies in groups of social animals can be based either on asymmetries that are important for agonistic interactions or on more ‘conventional’ cues, which are respected despite having little relationship to the animal’s fighting abilities
We investigated how social dominance is influenced by age and body mass in a herd of 29e39 beef cows over a 10-year period, focusing on all levels of the dominance hierarchy
Summary
Dominance hierarchies in groups of social animals can be based either on asymmetries that are important for agonistic interactions (such as body mass) or on more ‘conventional’ cues (such as age), which are respected despite having little relationship to the animal’s fighting abilities. 2003), that is, those in possession of phenotypic traits that enable them to prevail in agonistic interactions (such as large body mass), should use these traits to acquire dominance over animals that are less able to oppose them (such as lighter opponents; Arnott & Elwood 2009) This does not always need to be accomplished by escalated physical fights, since the weaker opponent often quits the contest soon after having assessed its own and/or the opponent’s RHP in the initial phases (Rillich et al 2007; Hsu et al 2008; Arnott & Elwood 2009). (Cant et al 2006) of the intensively investigated conjecture that uncorrelated asymmetries in RHP (such as prior residence or ownership) decide contests over a resource (Hammerstein & Parker 1982; Grafen 1987; Kemp & Wiklund 2004; Eshel 2005; Kemp et al 2006; Kokko et al 2006; Kokko 2013)
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