The ecological and evolutionary stability of interspecific territoriality

Interspecific territoriality may play an important role in structuring ecological communities, but the causes of this widespread form of interference competition remain poorly understood. Here, we investigate the phenotypic, ecological and phylogenetic correlates of interspecific territoriality in wood warblers (Parulidae). Interspecifically territorial species have more recent common ancestors and are more similar phenotypically, and are more likely to hybridise, than sympatric, non-interspecifically territorial species. After phylogenetic corrections, however, similarity in plumage and territorial song are the only significant predictors of interspecific territoriality besides syntopy (fine-scale geographic overlap). Our results do not support the long-standing hypothesis that interspecific territoriality occurs only under circumstances in which niche divergence is restricted, which combined with the high incidence of interspecific territoriality in wood warblers (39% of species), suggests that this interspecific interaction is more stable, ecologically and evolutionarily, than commonly assumed.