Spatial organization of mantled howler monkeys in relation to dog disturbance.

Predation risk fundamentally shapes primate social structure by influencing cooperation, competition, and spatial organization within groups. Although domestic dogs (Canis lupus familiaris) represent one of the world's most impactful invasive species affecting wildlife, their influence on primate social structure remains largely understudied. We examined how dog presence and barks influence interindividual proximity among group members in mantled howler monkeys (Alouatta palliata). We studied two habituated groups (10 and 8 adults, respectively) in Veracruz, Mexico, combining 242 h of observational data with experimental playbacks of dog barks at different intensities (40 and 80 dB). We calculated proximity indices from instantaneous sampling of interindividual proximity. Howler monkeys were closer immediately following exposure to dogs, partially supporting our hypothesis that interindividual proximity would change in response to dogs. Contrary to predictions, individuals were farther from each other as bark intensity increased and as proximity to dog stimuli decreased. During longer timeframes, individuals were closer when exposed to low-intensity barks compared to periods without dog stimuli. These findings demonstrate that dogs influence howler monkey spatial organization through context-dependent effects that vary with stimulus characteristics and temporal scale. Despite the short-term nature of this study, the consistency between observational and experimental results suggests these patterns are reliable. Therefore, these results contribute to our understanding of how invasive predators affect primate social structure and highlight the importance of managing free-ranging dogs in areas where they overlap with wildlife populations.