Structure and survival in animal groups

Abstract

Social grouping has repeatedly evolved in animals as a way of responding to and controlling their external environment. These groups are often greater than the sum of their parts: simple local interactions between individuals can give rise to complex group-level behaviors not possible at the individual level. The structure of the group - the spatial positions, orientations, and sensory neighborhoods of group members - is both a product and modulator of these local interactions, playing a critical role in how groups interact with their environments. Despite this importance, much of our understanding of the relationships between local interactions, group structure, and emergent behaviors has remained restricted to theoretical models due to the difficulty of obtaining reliable individual-level data in mobile animal groups. Recent advances in computer vision, however, now grant us the ability to observe within-group dynamics at a resolution detailed enough to finally test theories on how local interactions give rise to emergent group-level properties - as well as the intermediary role of group structure. In this thesis, I collected high-resolution data on schooling fish, known for their dynamic group structure, to examine local interactions, group structure, and the resulting consequences on survival. In Chapter 2, I quantify the distribution of visual information in fish schools and show that vision can be a useful metric for labeling the interior versus exterior of groups. In Chapter 3, I demonstrate that changes in information transfer due to perception of predation risk can be entirely attributed to group structure, with negligible changes in local interactions. Finally, in Chapter 4, I use live predator-prey interactions to empirically link group structure to survival, highlighting the importance of density and vision. Overall, this thesis adds to a growing movement of validating and improving upon our models of collective movement, cognition, and antipredator behavior.