The effect of group membership on hiding behaviour in the northern rock barnacle, Semibalanus balanoides

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Publication Date

January 2001


Animals living in groups are thought to gain fitness through decreased predation risk, while often paying a cost in terms of increased competition in foraging. Thus, the balance struck between predator avoidance and foraging should be affected by group membership. For animals that avoid predation by withdrawing into a refuge (i.e. ‘hiding’), such as the northern rock barnacle, Semibalanus balanoides, that balance should be particularly important since predator avoidance excludes foraging altogether. We tested the hypothesis that barnacles living in groups should spend less time hiding when faced with a perceived threat than should solitary barnacles. We presented group-living and solitary barnacles with a simulated threat and measured hiding time with the prediction that barnacles in groups would return to foraging more quickly than solitary barnacles. Hiding time for group-living barnacles was significantly less than for solitary barnacles. We then manipulated barnacle group size with the prediction that an individual barnacle's behaviour would change based on group membership alone. We tested individual barnacles three times in an A–B–A design in which barnacles were tested in one of two sequences, solitary–group–solitary, or group–solitary–group. We found that group membership had a significant effect on barnacle foraging behaviour in that individuals emerged from hiding sooner when tested in a group than when tested alone. We conclude that, as predicted by optimality theory, group membership strongly affects foraging decisions by this refuge-using animal. We argue that the proximate mechanism for such behaviour may involve a simple binary reaction to living in a group.


Animal Behaviour





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