Territorial aggression and coexistence in hybridizing Campylorhynchus: disentangling the roles of climate, resource availability, and species interactions in western Ecuador

Abstract

Interspecific territoriality is a prevalent form of interference competition among animals across environments. However, the connections between interspecific territorial aggression and other related aspects such as hybridization and climate remain unexplored. We investigated territorial aggression in two Neotropical wren species, Campylorhynchus zonatus brevirostris and C. fasciatus pallescens, along a precipitation gradient in western Ecuador using playback experiments. Campylorhynchus f. pallescens exhibits geographic variation: northern populations (C. f. pallescens north) are hybrids of C. z. brevirostris and C. f. fasciatus, while southern populations (C. f. pallescens south) show primary genetic admixture with C. f. fasciatus (from northeastern Peru). We pursued three objectives: 1) to compare intra- and inter-territorial aggression of C. z. brevirostris and the admixed C. f. pallescens north and south; 2) to assess territorial aggression across these three genetic clusters; and 3) to examine direct and indirect (via primary productivity) associations between climate and territorial aggression. We simulated territory intrusion using playback experiments and quantified aggressive responses using principal component analysis (PCA) to integrate three behavioral measurements: minimum approach distance to the stimulus, latency to reach this distance, and the number of aggressive displays (fixed action patterns). Admixed C. f. pallescens north displayed no significant differences in aggression across treatments, supporting the established trend of high interspecific territoriality in hybrids. Campylorhynchus f. pallescens south was the only genetic cluster that showed significant differences among treatments, exhibiting more pronounced aggressive responses to intraspecific stimuli and higher aggression than C. z. brevirostris and C. f. pallescens north. This pattern of dominance in territorial aggression contrasts with the previously reported direction of genetic introgression from C. z. brevirostris towards C. f. pallescens. Precipitation is related to aggression, potentially through resource availability. We emphasize the importance of understanding the interactions among hybridization, territoriality, and environmental stressors in tropical birds.