Collective cognition has received much attention in recent years but most of the empirical work has focused on comparing individuals and groups within single populations, thereby not addressing evolutionary origins of collective cognition. Here we investigated collective cognition in multiple populations that are subject to different levels of predation. Guppies (Poecilia reticulata) were given a simultaneous choice between an edible and a non-edible stimulus. We found evidence for an improvement in decision accuracy when in groups but only in low-predation guppies. This performance increase was due to a combination of increased private sampling behaviour when in groups (compared to being alone) and social information use. In contrast, high-predation fish did not sample more when in groups, nor used social information; hence did not improve decision-accuracy when in groups. The improvement of groups in foraging accuracy in low but not in high predation sites, suggests that these populations differ in their trade-off between attention dedicated to food and predators. In high predation sites, investing time in predator detection is more crucial than in low predation sites, thereby possibly conflicting with food detection. Our results highlight the importance of considering the effects of ecological gradients on collective cognition.