Female gorillas compete for food and males

Abstract

As most organisms, humans and other apes compete for access to fitness-determining resources and competition is expected to increase with the competitor-to-resource ratio. We use 23 years of behavioural data on five wild groups from the two gorilla species which live in different socioecological environments, to test if female gorillas compete simultaneously for food, mates and/or protectors. Females were more aggressive to each other in medium-sized groups (∩ − shaped relationship) and when the groups contained more females but fewer males (lower sex ratio). Contrarily, female-female aggression was not influenced by the operational sex ratio and female mating activity. Hence, our results support the competition for food and protectors hypotheses but cast doubt on the competition for mates hypothesis. Yet, despite female western gorillas (Gorilla gorilla gorilla) experiencing higher monopolization potential of food and a lower abundance of food and males, they did not exhibit higher aggression rates than female mountain gorillas (Gorilla beringei beringei). Altogether, these results suggest that female competition for males outside the mating context is not unique to humans and might have common evolutionary origins in humans and other apes.