Habitat alteration modifies the structure and function of mixed-species flocks in an Andean landscape

Understanding the responses of species interactions to land-use change is a key challenge in ecology and conservation. In the tropical Andes, a large proportion of birds interact with other bird species and create networks of mixed-species flocks; however, the widespread effects of land-use change in the region raise concerns about the alteration of these interactions. Here we explored how structural (i.e., species richness and size) and functional (i.e., network connectivity indices) parameters of mixed flocks change along a gradient from open vegetation to native forest habitats. This study was conducted in the southern Andes of Ecuador, where we sampled mixed-species flocks in 12 areas for five consecutive months, and applied network analysis tools to characterize structural parameters (observed richness, flock size, flock encounter rate, composition) and functional parameters (degree, weighted degree, cluster, and skewness) of flocks. We found that the network indices, degree and weighted degree of species, were positively associated with areas of dense vegetation and native trees. These two network indices indicated that mixed flocks occupying native forest have higher connectivity, a factor that can promote the stability of flocks. The structural parameters of flocks, species richness, and abundance, were not associated with the vegetation structure. Overall, our results show that functional parameters of flocks can be more sensitive than structural parameters to the effects of land-use change in our study area. We demonstrate the importance of combining the analysis of structure and functionality of flocks to reveal the effects of land-use change. Lastly, our results highlight the importance of mature native forest for the conservation of species and the maintenance of non-trophic interactions. in Spanish is available with online material.