Meeting Abstract
Aggregation is a common life-history trait in many species. Qualitative understanding of how aggregation by prey influences their encounter rates with predators is critical for understanding predator-prey interactions and trophic webs. We extend a recently-developed theory on visibility to predict the consequences of grouping in terms of increased visual detection of groups by predators. Our model suggests that enhanced visibility is relatively modest, with maximum detection distance typically only doubling for a 100-fold increase in the number of prey in a group. This result suggests that although larger groups are more easily detected, this cost to aggregation will in many cases be dominated by benefits, especially through risk dilution in situations where predators cannot consume all members of a discovered group. This in turn helps to explain the ubiquity of grouping across a great variety of taxa. We also find that the visibility cost of grouping increases rapidly as illumination levels drop, with this increase occurring at greater light levels in aerial versus aquatic organisms. In the case of aerial organisms, the cost increases rapidly during twilight, suggesting that this is a less advantageous time to aggregate.
