The field of animal personality seeks to understand the potential adaptive value of temporally consistent inter-individual differences in behavior. Over the past several decades, this personality framework has helped behavioral ecologists better understand how social groups structure themselves behaviorally, and how intra-colony variation in personality can shape the emergent collective behavior of groups. While studies investigating how collective personalities interact with their environments and influence group survival are becoming more prevalent, research on this topic is still relatively scant. One important aspect of collective personality yet to be given attention is how group personality composition may influence a group’s response to invasion by a predator, or how the mere threat of predation can alter the collective behavioral phenotypes of groups. Given the near ubiquity of predation as a selective force in nature, it is important to incorporate both the direct and indirect effects of predators on collective behavior. This will lead to a better understanding about the environmental factors that shape the expression of group personality.

This dissertation approaches these questions using three experiments. The first investigates how the behavioral distribution of colony constituents influences collective behavior in the context of colony defense. This study found that colonies of mixed personality composition exhibited twice as much defensive behavior as other compositions, and that bold compositions were displayed high degrees of behavioral flexibility relative to mixed and shy compositions. The second study observed how prolonged exposure to predators feeds back to determine the collective behavior of groups, and showed that colonies exposed to predators decreased overall collective aggressiveness by half, and eliminated the relationship between personality composition and aggressiveness. The last study investigated how groups prioritize information regarding predator presence when that information is possessed by the majority, or singleton immigrants that vary in leadership traits. This experiment found that groups operate under a “better-safe-than-sorry” strategy, and exhibit cautious collective behavior when any member of their group had been previously exposed to predators. Together, these experiments demonstrate that collective personality is a highly plastic and complex trait, that is determined by a combination if internal (group behavioral composition) and external (environmental risk) factors. Finally, I conclude this dissertation with a comprehensive review on the current state of collective personality research in insects and arachnids.