Associations between spatial position, stress and anxiety in forest baboons Papio anubis

Spatial position within a group affects the value of group-living benefits such as reduced predation risk and improved foraging. The threat of predation, poor nutrition or increased competition from conspecifics can all cause stress. In many species, central positions are known to be more beneficial than peripheral positions in terms of reduced predation, vigilance and foraging. In this study, we examine whether spatial position within a group is associated with stress and anxiety in a troop of olive baboons (Papio anubis). We predicted that the benefits of occupying central positions would be reflected by a reduction in stress and anxiety for animals who spent the most time in the centre of the group. The study subjects appeared to compete actively for the centre of the group. Physiological stress measures (faecal glucocorticoid concentrations) were positively correlated with time spent in central positions. Time spent in central positions was positively correlated with proximity but negatively correlated with vigilance behaviours (alarm barks). Vigilance rates were positively correlated with measures of anxiety (self-scratch frequency). It is suggested that individuals experience chronic stress due to proximity to conspecifics in central positions, whilst perceived predation risk causes anxiety, with perceived predation risk experienced more by individuals on the periphery.