Interspecific Aggression Of Two Wrens Along An Environmental Gradient In Western Ecuador

Abstract

Interspecific territoriality is a prevalent form of interference competition among animals. However, the connections between hybridization, climate, and interspecies territorial aggression in tropical regions remain largely unexplored. Here, we investigated territorial aggression in two hybridizing tropical bird species, C. z. brevirostris and C. f. pallescens, in western Ecuador using playback experiments. We tested three hypotheses: 1) hybridizing species exhibit comparable intra- and inter-specific territorial aggression; 2) asymmetrical aggression driven by C. z. brevirostris dominance determines gene flow patterns; and 3) precipitation influences territorial aggression. Supporting hypothesis 1, the admixed C. f. pallescens North showed no difference in intra- vs inter-specific aggression. However, the non-admixed C. f. pallescens South exhibited greater inter-specific aggression, providing partial support for hypothesis 1. Contrary to hypothesis 2, C. f. pallescens South displayed significantly higher aggression than C. z. brevirostris and C. f. pallescens North. Furthermore, precipitation models outperformed null models, supporting hypothesis 3 that precipitation influences Campylorhynchus territorial aggression. Collectively, these findings suggest hybridization can stabilize coexistence via territoriality, and precipitation strongly affects aggression, potentially through resource availability. Unexpectedly, C. z. brevirostris dominance did not appear to drive asymmetric introgression between species, warranting further investigation into the underlying mechanisms. Complex factors shape territorial aggression in tropical birds, including genetic admixture, group size, latitude, and climate. This study highlights the need for additional research elucidating the relationships between hybridization, territoriality, and environmental stressors in tropical avian communities. We discuss possible mechanisms explaining the detected effects of precipitation on aggression and the lack of C. z. brevirostris dominance in determining introgression patterns.