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Abstract

Positive interactions between species have long been predicted to play a role in the evolution and maintenance of biodiversity. Despite their importance in understanding large-scale ecological processes, they have received less attention compared to negative species interactions like competition and predation. In this thesis, I used mixed-species flocks as a system to improve our understanding of how the positive interactions occurring in flocks contribute to the dynamics and organization of tropical avian communities. First, I demonstrated that mixed-species flocks comprised a distinct subset of the overall communities in which they occur, with constraints on the range of ecological and functional attributes observed among mixed-flocking species. This implies the existence of a set of ecological criteria that a species must satisfy to engage in this grouping behavior. Next, I delved into the adaptive value of flocking to explore whether participation in mixed-species flocks was associated with higher parasitism. I found that species foraging in mixed-species flocks did not exhibit significant differences in parasitism compared to non-mixed-flocking species, except for highly connected individuals. These findings suggest that reduced parasitism could be an important factor driving the evolution and persistence of mixed-species groups by mitigating the parasite burden typically associated with group living. Finally, I integrated information on life-history traits and mixed-species flocking behavior to ask whether the social environment (e.g., group living) is associated with unique life history attributes in tropical birds. I found that parental investment and development did not differ between mixed-flocking species and non-mixed-flocking species. This work creates a foundation for future studies to address the interplay of life-history traits and social behavior and the life-history adaptations of flocking species that allow them to maintain cohesive flocks during the breeding season. My dissertation examines the role of mixed-species flocking behavior as an interspecific positive interaction with implications for community organization, parasite transmission, and reproductive life history traits. This work underscores the underappreciated role of mixed-species flocks as a system for advancing our understanding of the interactions that shape avian communities and contribute to the evolution and maintenance of avian diversity.