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

## TL;DR

Changes in rainfall and habitat fragmentation affect how bird species interact, with drier and more fragmented areas showing tighter but more vulnerable bird networks.

## Contribution

This study shows how environmental factors like rainfall and habitat fragmentation directly alter species interaction networks in bird communities.

## Key findings

- Network structure and interaction dissimilarity in bird groups vary with rainfall and habitat fragmentation.
- Ant-following bird groups completely dissolve in areas with low habitat suitability.
- Drier sites have more cohesive and connected bird networks, possibly due to greater reliance on shared food resources.

## Abstract

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.

The online version contains supplementary material available at 10.1007/s00442-026-05869-7.