Emergent frequency-dependent social foraging: Individual variation in shoaling rules enhances social foraging success

Background/Question/Methods

For individuals in social species, the rate of return during foraging can depend heavily on the local social environment and the group’s overall foraging dynamics. Within a group, the relative costs and benefits vary depending on the spatial position an individual occupies within the group. Different types of individuals may occupy different positions within a group, and use public or private information differently. I examined the possibility that within-group cost/benefit heterogeneity can select for individual variation in social tendency and enhance overall group foraging efficiency using an agent-based model of social foraging. Agent-based models of shoaling have been successful in reproducing the types of movements typically seen in groups of foraging animals, but these models have rarely been used to model how individual variation in social behavior might affect the emergent social foraging outcomes. I built a model relying on very simple rules of responses to the positions of other individuals. I then included individual variation in social rules: social individuals pay more attention to the available social information than do asocial individuals. I then allowed groups with different densities and social compositions to forage on ephemeral, depletable resources.

Results/Conclusions

The model generated emergent negative frequency dependent selection on the shoaling rules, where different shoaling types took on different spatial positions, leading to differences in the emergent foraging roles. Asocial individuals move mostly independently of groups, and find more food patches than social individuals. However, they create public information by aggregating at food. Social individuals exploit this information. Thus, in a primarily social population, a single asocial can do well by finding food outside of the main group, thus avoiding competition, while in a primarily asocial population a single social individual increases its foraging rate by exploiting the public information generated by aggregated asocials. This is an emergent producer-scrounger game based on individual variation in movement rules. Asocials pay a movement cost to increase their rate of food discovery, but increase the amount of information available to socials. The evolutionarily stable mix of types in this system changes with density. As densities increase, the proportion of social individuals at the evolutionarily stable mix increases, suggesting they are better adapted to higher densities. At the stable mix, overall foraging efficiency is increased, increasing the carrying capacity. Thus, unlike in many frequency-dependent systems, evolution enhances overall group efficiency.