Dominance rank relationships among wild female African elephants, Loxodonta africana

Socioecological models of the evolution of female-bonded societies predict a relation between resource distribution and the nature of female affiliative and dominance relationships. Species that mainly rely on abundant, widely distributed resources, like African savanna elephants, are predicted to have unresolved dominance hierarchies and poorly differentiated female social relationships. Contrary to this prediction, female elephants have well-differentiated social relationships; however, little is known about the nature of their dominance rank relationships. Here we present the first quantitative analysis of dominance relationships within ‘family’ groups of adult female elephants in two wild populations: one in Amboseli National Park, Kenya, and another in Tarangire National Park, Tanzania. We tested three possibilities, that female elephants: (1) are egalitarian, (2) have linear, nepotistic hierarchies, or (3) have linear age/size-ordered hierarchies. Our results best support the third outcome: dominance rank relationships were transitive within families and highly asymmetrical within dyads, such that older, larger females consistently dominated smaller, younger females. We discuss the implications of this result for understanding the evolution of female social relationships.