Abstract
In social species, conspecific outsiders present various threats to groups and their members. These out-group threats are predicted to affect subsequent within-group interactions (e.g., affiliation and aggression) and individual behavior (e.g., foraging and vigilance decisions). However, experimental investigations of such consequences are rare, especially in natural conditions. We used field-based call playbacks and fecal presentations on habituated wild dwarf mongooses (Helogale parvula)—a cooperatively breeding, territorial species—to examine postinteraction responses to the simulated threat of a rival group. Dwarf mongooses invested more in grooming of groupmates, foraged closer together, and more regularly acted as sentinels (a raised guard) after encountering indicators of rival-group presence compared to control conditions. These behavioral changes likely arise from greater anxiety and, in the case of increased vigilance, the need to seek additional information about the threat. The influence of an out-group threat lasted at least 1 h but individuals of different dominance status and sex responded similarly, potentially because all group members suffer costs if a contest with rivals is lost. Our results provide field-based experimental evidence from wild animals that out-group threats can influence within-group behavior and decision making, and suggest the need for greater consideration of the lasting impacts of social conflict.
Highlights
Groups and their members face a variety of threats from conspecific outsiders but relatively little is known about the consequences of these so-called out-group threats
The behavioral changes following rival-group playbacks and fecal presentations cf. control treatments could be a response to any mongoose stimulus
We are confident that our results represent a response to rival-group stimuli rather than mongoose stimuli per se, and that our study provides rare experimental evidence from a wild population that out-group threats influence within-group behavior
Summary
Groups and their members face a variety of threats from conspecific outsiders but relatively little is known about the consequences of these so-called out-group threats. Individuals form stable permanent groups which often defend collective resources (Radford 2003; Kitchen and Beehner 2007; Batchelor and Briffa 2011; Christensen and Radford 2018). Out-group threats range from individuals seeking reproductive opportunities (Mares et al 2011; Bruintjes et al 2016), to single-sex groups looking to usurp dominant individuals (Ridley 2012), to whole groups attempting to acquire access to limited resources, such as food, mates, and sleeping sites (Wilson and Wrangham 2003; Kitchen and Beehner 2007; Golabek et al 2012).
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