Date of Award

Spring 1-1-2017

Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Michael D. Breed

Second Advisor

Samuel Flaxman

Third Advisor

Rebecca Safran

Fourth Advisor

Alexander Cruz

Fifth Advisor

Nikolaus Correll


Across scales, complexity emerges within groups of simple individuals. In many cases, groups succeed at tasks that are well beyond the capabilities of individuals; this is collective intelligence. Ants provide some of the best examples of collective intelligence, and groups of ants succeed at remarkable challenges. A highly conspicuous example of such behavior in ants is cooperative transport, which occurs when a group collectively moves a large, heavy food object. Cooperative transport groups must overcome two major challenges: 1) agreeing on a travel direction and 2) navigating around obstacles. The first challenge requires breaking deadlocks to reach a consensus decision. The second requires problem solving – groups must make a series of new decisions, each building on the previous. My goal was to discover the individual- and group-level mechanisms that allow some ant species to overcome these challenges, and spectacularly succeed at cooperative transport. At the individual level, I found that theoretically, even groups of individuals with simple behavioral rules can break deadlocks. Individuals only need to determine whether they are aligned with the majority. My theoretical work also indicates that individual persistence – reluctance to change direction – promotes group consensus. I tested this hypothesis empirically, and found that species with more persistent individuals form more coordinated groups, and artificially increasing persistence increases coordination. At the group level, I discovered that object size and mass affect group coordination time and speed, but not the maintenance of coordination. Finally, in a species of expert transporters, groups excel at maintaining consensus while navigating obstacles, and they add complexity to their navigation strategy only if simpler behavior fails. My dissertation contributes to our understanding of emergent group behavior by demonstrating simple behavioral rules and a trait – persistence – that promote consensus. I have identified object properties that influence transport in surprising ways, and found that groups use a flexible and robust problem solving strategy for obstacle navigation. This work elucidates important mechanisms that allow some species to excel at cooperative transport.