Bad Blood in the Pecking Order: Phylogenetic Relatedness and Body Size Correlate with Aggressive Interaction Structure in a Hummingbird Assemblage 

Interspecific aggression plays a central role in hummingbird community structure, as individuals seek to maintain access to high-value resources. However, patterns of how aggressive behaviors manifest across a hummingbird assemblage remain unclear. We examined whether differences in body mass and phylogenetic distance predict dissimilarity in target selection of aggressive behavior among co-occurring hummingbird species in the Ecuadorian cloud forest. Behavioral observations conducted at feeders in the Santa Lucía Reserve were used to record interspecific aggression counts. Using difference-based analyses, we quantified the association between phylogenetic distance, size difference, and dissimilarity in aggression preference. Both body mass difference and phylogenetic distance between each aggressor-aggressor pair were significantly correlated with dissimilarity in aggression preference. Of the two factors, phylogenetic distance represented a slightly stronger association with aggression structure than body mass. Effects of both variables persisted independently when we controlled for each opposing factor. Therefore, both body size difference and genetic divergence shape the distribution of preference target species between aggressors, clarifying the factors contributing to competitive structuring in montane hummingbird communities. Understanding the drivers of aggression aids in improving understanding of cloud forest community structure and informs conservation knowledge on nectarivore dynamics in high-elevation tropical ecosystems.