Title: How collective foraging in social insects scales with colony size
Abstract: Colonies of cooperatively foraging social insects work together to efficiently find and exploit valuable food resources in a distributed fashion. Communication between individuals about the location of resources—e.g. in the form of waggle dances in honey bees, or pheromone trails in many ant species—is a key element in this process. In both ants and bees, it has been suggested that larger colonies benefit more from communication, particularly when resources are heterogeneously distributed. Yet the reasons for this are still unclear: do large colonies require communication in order to avoid or overcome inefficiencies, or do they benefit from communication in ways that smaller colonies do not? For example, large colonies might be able to search a wider area and select the best resources, or they might be able to quickly recruit more foragers to a high-quality resource before it is discovered by competitors. Using a differential equation model to explore how ant colonies select among food sources that vary in both quality and distance from the nest, we find that smaller colonies are more likely to focus on the closest resource while larger colonies are more likely to choose the one with the highest quality-to-distance ratio. This relationship is modulated by resource abundance and caused by the way that differences in recruitment rate scale with colony size. In this model, larger colonies are able to take advantage of farther away but more rewarding resources because foragers are recruited to such resources much more quickly, even though they are discovered later. This adds to a growing body of evidence that large colony size and communication are key features of a collective foraging strategy that work together to allow groups to gather food efficiently in patchy resource environments.