Abstract
Conflict between rival groups is rife in nature. While recent work has begun exploring the behavioural consequences of this intergroup conflict, studies have primarily considered just the 1–2 h immediately after single interactions with rivals or their cues. Using a habituated population of wild dwarf mongooses (Helogale parvula), we conducted week-long manipulations to investigate longer-term impacts of intergroup conflict. Compared to a single presentation of control herbivore faeces, one rival-group faecal presentation (simulating a territorial intrusion) resulted in more within-group grooming the following day, beyond the likely period of conflict-induced stress. Repeated presentations of outsider cues led to further changes in baseline behaviour by the end of the week: compared to control weeks, mongooses spent less time foraging and foraged closer to their groupmates, even when there had been no recent simulated intrusion. Moreover, there was more baseline territorial scent-marking and a higher likelihood of group fissioning in intrusion weeks. Consequently, individuals gained less body mass at the end of weeks with repeated simulated intrusions. Our experimental findings provide evidence for longer-term, extended and cumulative, effects of an elevated intergroup threat, which may lead to fitness consequences and underpin this powerful selective pressure.
Highlights
In many social species, from ants to humans, groups are in conflict with conspecific outsiders over access to limited resources [1,2,3]
Grooming behaviour was significantly affected by treatment the day after the first simulated intrusion: a greater proportion of time was spent grooming on Day 2 of Intrusion weeks compared to Control weeks, especially by males (GLMM, treatment × sex: χ2 = 4.030, p = 0.045, estimate ± s.e. = 0.653 ± 0.320; electronic supplementary material, table S1a)
We provide strong experimental evidence for extended and cumulative effects of intergroup conflict on within-group behaviour in dwarf mongooses
Summary
From ants to humans, groups are in conflict with conspecific outsiders over access to limited resources [1,2,3]. An extensive literature exists on how animals behave during outgroup interactions, considering the type of encounter, who contributes during contests and the factors that influence the outcome [7,8,9]. Exposure to outgroup threats has been shown to influence other behaviours, such as group movement patterns and individual decisions about foraging and vigilance [12,19,20]. The majority of this work has focused on short-term effects (over minutes or hours) in the immediate aftermath of single interactions with outsiders or cues of their presence [12,13,14,15,16,17,20] (but see [21,22,23]). To understand fully the effects of outgroup conflict, investigation is needed of extended effects from single interactions and cumulative effects from repeated interactions
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