Abstract
BackgroundWe manipulated predation risk in a field experiment with the cooperatively breeding cichlid Neolamprologus pulcher by releasing no predator, a medium- or a large-sized fish predator inside underwater cages enclosing two to three natural groups. We assessed whether helpers changed their helping behaviour, and whether within-group conflict changed, depending on these treatments, testing three hypotheses: ‘pay-to-stay’ PS, ‘risk avoidance’ RA, or (future) reproductive benefits RB. We also assessed whether helper food intake was reduced under risk, because this might reduce investments in other behaviours to save energy.Methodology/Principal FindingsMedium and large helpers fed less under predation risk. Despite this effect helpers invested more in territory defence, but not territory maintenance, under the risk of predation (supporting PS). Experimentally covering only the breeding shelter with sand induced more helper digging under predation risk compared to the control treatment (supporting PS). Aggression towards the introduced predator did not differ between the two predator treatments and increased with group member size and group size (supporting PS and RA). Large helpers increased their help ratio (helping effort/breeder aggression received, ‘punishment’ by the dominant pair in the group) in the predation treatments compared to the control treatment, suggesting they were more willing to PS. Medium helpers did not show such effects. Large helpers also showed a higher submission ratio (submission/ breeder aggression received) in all treatments, compared to the medium helpers (supporting PS).Conclusions/SignificanceWe conclude that predation risk reduces helper food intake, but despite this effect, helpers were more willing to support the breeders, supporting PS. Effects of breeder punishment suggests that PS might be more important for large compared to the medium helpers. Evidence for RA was also detected. Finally, the results were inconsistent with RB.
Highlights
Avoidance of predators is thought to be an important benefit of group living
Note that corrected for distance, medium helpers (Fig. 2a) had a higher feeding rate per minute than large helpers (Fig. 2b, on average 5.1 more bites per minute 61.3 s.e., parameter estimate from Table S1 generalised estimating equations (GEE))
The total food intake was significantly lower for the medium compared to the larger helpers (Fig. 1b), because medium helpers were hiding more[11] and fed on average closer to protective shelter than the large helpers (Fig. 2, Table S1)
Summary
Avoidance of predators is thought to be an important benefit of group living (see reviews [1,2,3]). Predation risk has been proposed to increase the net benefits of remaining in their (natal) group for subordinates of cooperatively breeding species (‘ecological constraints hypothesis’, [11,15]). These benefits may be especially high in large groups due to e.g., being protected from predation by the larger group members or risk dilution effects (‘group augmentation hypothesis’, [11,16,17]). The purpose of the present paper is to test effects of experimentally varied risk of predation on helping behaviour and within-group conflict in the cichlid Neolamprologus pulcher. We assessed whether helper food intake was reduced under risk, because this might reduce investments in other behaviours to save energy
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