Constance O'Connor, Adam Reddon, Isaac Ligocki, Jennifer Hellmann, Kelly Garvy, Susan Marsh-Rollo, Ian Hamilton, and Sigal Balshine (2015)
Motivation but not body size influences territorial contest dynamics in a wild cichlid fish
Animal Behaviour, 107:19-29.
Contests over resources are a key facet of social behaviour, and have received extensive theoretical attention. However, the assumptions and predictions of the theoretical models have rarely been tested experimentally in wild free-living vertebrates. Here, we look at resource contests in wild Neolamprologus pulcher, cooperatively breeding cichlid fish that live in permanent territories in Lake Tanganyika, Africa. To elicit a contest, we removed a dominant breeding male from his territory, and held him for either a short (4.5 hr) or long (20 hr) period. The original resident male was then returned to his territory, which typically resulted in an aggressive contest with a usurping male that had taken over in the original resident's absence. We found that contests were shorter than those previously observed in a laboratory setting, with more physically aggressive attacks. Contrary to our predictions, the relative size difference between the males had no effect on contest dynamics or outcome, likely because all of the males involved in these contests were similar in body size. Instead, motivational factors influenced contest dynamics. Longer original resident removal times increased usurper male aggression, as well as the duration and intensity of the contests. Original residents, contesting over their sole territory, were more aggressive than original residents that were contesting over one of multiple territories. Usurpers won more contests overall, and more aggressive fish were more likely to win contests. To our knowledge, this is the first study to examine resource contests in wild free- swimming cichlids, and reveals that subjective resource value is a primary driver of the dynamics and outcome of territorial conflicts among dominant N. pulcher males. Our results further suggest that ownership respect may reduce conflict in N. pulcher, and play an important role in governing colony structure.