Fission-Fusion Group Dynamics and Cooperative Hunting Stabilise Social Carnivore Populations

Theory suggests that large social groups of carnivores should be unsustainable, due to reduced foraging efficiency because of overlapping perception radii. Using Serengeti lions as a case study, we apply behaviourally based foraging models to show that fragmentation of social groups into smaller subgroups or mutual cooperation during hunting are both plausible hypothetical mechanisms capable of sustaining larger lion prides. Data from the Serengeti ecosystem demonstrate that lion prides typically fragment into small hunting groups that are well approximated by an exponential distribution of group sizes typical of fission-fusion social systems. A model linking fission-fusion group dynamics with predator-prey interaction predicts both the surprising degree of population stability of the Serengeti lions as well as the long-term persistence of large prides. There is little evidence, however, that Serengeti lions cooperate during hunting except when they hunt Cape buffalo, so fission-fusion is apparently the dominant stabilising process in Serengeti.