Size-based dominance relationships in female forest elephants, Loxodonta cyclotis

Abstract

The ecological model of female social relationships predicts variation in female social behaviour based on variation in environmental factors. When resources are abundant, females should exhibit poorly defined affiliative and dominance relationships. If resources are clumped, female-bonded societies should emerge with despotic age–size-based or nepotistic dominance relationships. African elephants (Loxodonta sp.) contradict socioecological theory. Despite feeding primarily on abundant herbaceous vegetation, female savannah elephants, Loxodonta africana, exhibit age–size-based despotic dominance relationships, while female forest elephants, Loxodonta cyclotis, rely heavily on clumped resources and form weak social bonds as females disperse from their natal groups to forage in small groups. Here we provide first insights into dominance relationships among female forest elephants based on displacement interactions over access to small monopolizable mineral pits at the Dzanga Bai forest clearing in Dzanga-Ndoki National Park, Central African Republic. We found that body size, but not relatedness, determined the outcome of displacement interactions and resulting dominance rank relationships. Tall females were more likely to initiate displacements and had higher ranks compared to short females. Relatedness had no influence on a female’s ability to displace another, and related females were not more similar in rank compared to nonrelated females. Our results suggest that female forest elephants exhibit size-based despotic dominance relationships, similar to savannah elephants, despite the two species relying on vastly different resources. The discrepancy with the socioecological model suggests it may not be entirely applicable to elephants. As proposed for various well-armoured herbivore species, including savannah elephants, despotic dominance relationships may emerge in forest elephants to reduce the risk of injury during low-gain competitive interactions. Further studies are needed to disentangle the effects of resource distribution and the risk of injury on dominance relationships in the genus Loxodonta.