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Foraging animals must often balance the conflicting demands of finding food and avoiding predators. Temporal variation in predation risk is expected to influence how animals allocate time to these behaviours. Counterintuitively, the proportion of time spent foraging during both high- and low-risk periods should increase with increasing time exposed to high risk. We tested this prediction using intertidal marine snails (Littorina spp.) that were exposed to temporal variation in perceived predation risk from crabs (Cancer productus and Cancer magister). Our results were consistent with those predicted for high-risk, but not low-risk, periods. During high-risk periods, a greater number of snails foraged (versus those that left the water or remained in their shells) as time at high perceived risk increased. For low-risk periods, there was no relationship between the number of snails foraging and time at high risk. This might be due to snails in all treatments foraging maximally in the low-risk periods. As a consequence, the difference in the number of snails foraging between high- and low-risk periods decreased with increasing time subject to high risk. These results indicate that the commonly used protocol of exposing foragers to a single pulse of heightened risk might tend to overestimate their typical investment in anti-predator behaviour.

Large brain size in mammals has been related to the number and complexity of social relationships, particularly social alliances within groups. The largest within-group male alliance known outside of humans is found in a social network (> 400) of Indian Ocean bottlenose dolphins (Tursiops aduncus) in Shark Bay Western Australia. Members of this dolphin 'super-alliance' cooperate against other alliances over access to females. Males within the super-alliance form temporary trios and occasionally pairs in order to consort with individual females. The frequent switching of alliance partners suggests that social relationships among males within the super-alliance might be relatively simple and based on an equivalence rule', thereby allowing dolphins to form large alliances without taxing their 'social intelligence'. The equivalence model predicts that the 14 males in the super-alliance should not exhibit differences in alliance stability or partner preferences. However, data from 100 consortships do not support the equivalence hypothesis. The 14 males exhibited striking differences in alliance stability and partner preferences suggesting that the super-alliance has a complex internal structure. Further, within the super-alliance, alliance stability correlates with consortship rate, suggesting that differentiated relationships within the super-alliance are based on competition for access to females.