The Great Unknown: The Floating Stage as a Neglected Aspect of Social Systems

In the last few decades, important advances have been made in the knowledge on the behavioral ecology of pair-living primates such as owl monkeys (Aotus spp.). With the growing understanding, researchers have become increasingly aware that populations do consist not only of established family groups but also of solitary “floaters”: dispersing individuals who travel (mostly) solitarily after leaving their natal (or previous breeding) group and before obtaining a breeding position. Floaters may have a profound impact on local operational sex ratios and, thus, population dynamics, with the subsequent potential to change natural and sexual selection pressures on pair-living and sexually monogamous taxa. Unfortunately, floaters are notoriously difficult to study, so assessments of their role on social organization and mating systems remain challenging. Floaters of different taxa experience different selection pressures and employ varying strategies. In owl monkeys, a combination of limits to group size and habitat saturation forces all maturing individuals to become floaters as subadults or young adults, such that floating is essentially a life stage in the species. The dispersal process is accompanied by increased tensions between adults and pre-dispersing individuals, probably due to various aspects of food and mate competition. Owl monkey floaters balance the need for prospecting with avoidance behavior toward groups, with whom they can engage in highly aggressive and potentially lethal interactions, by adapting their ranging behavior to spatial avoidance while seeking proximity at a temporal scale. Some fundamental aspects of floater biology on owl monkey societies (e.g., mortality rates, impact on population dynamics) are still poorly understood. We strongly suggest that floaters in all taxa where they occur are taken more consistently into consideration and efforts are undertaken to improve understanding of their impact on group and population dynamics, and of sexual selection.