Rainfall alters network structure, while fragmentation results in the breakdown of a mixed-species group of birds.

Understanding the influence of species interactions on community structure and biodiversity is a long-standing goal in ecology. While species interactions are predicted to be vulnerable to environmental change, how the environment influences species interactions is not well understood. We used a network analysis approach to examine how network structure and dissimilarity of one type of mixed-species animal group, army ant-following birds, varied along rainfall and habitat suitability (i.e., fragmentation) gradients in Panama. Network structure varied across both gradients and there was high interaction dissimilarity across networks, owing to both species turnover and rewiring. These results highlight the role of the environment in structuring species interactions. Importantly, there was total dissolution of ant-following groups at sites with lower habitat suitability. In drier sites, networks were more speciose, cohesive, and well-connected compared to wetter forests, potentially because of the increased benefits of attending swarms in drier sites. The high cohesion and connections found suggest that ant-following birds may be particularly vulnerable to the loss of important species and environmental change. These ant swarms are an important, shared food resource that draws together a diverse and tightly connected group of birds. Understanding the relationships between the environment and species interactions contributes to our ability to predict how species interactions will change in the future, with cascading effects on community structure and biodiversity.