Positive Relationships between Association Strength and Phenotypic Similarity Characterize the Assembly of Mixed-Species Bird Flocks Worldwide

• Published in: The American naturalist 2012-12, Vol.180 (6), p.777-790
• Main Authors: Sridhar, Hari, Srinivasan, Umesh, Askins, Robert A., Canales-Delgadillo, Julio Cesar, Chen, Chao-Chieh, Ewert, David N., Gale, George A., Goodale, Eben, Gram, Wendy K., Hart, Patrick J., Hobson, Keith A., Hutto, Richard L., Kotagama, Sarath W., Knowlton, Jessie L., Lee, Tien Ming, Munn, Charles A., Nimnuan, Somchai, Nizam, B. Z., Péron, Guillaume, Robin, V. V., Rodewald, Amanda D., Rodewald, Paul G., Thomson, Robert L., Trivedi, Pranav, Van Wilgenburg, Steven L., Shanker, Kartik
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Aves; Biological and medical sciences; Birds; Birds - anatomy & histology; Birds - physiology; Body Size; Cloud forests; Competitive Behavior; Coniferous forests; Deciduous forests; Ecological competition; Ecosystem; Feeding Behavior; Flocks; Foraging; Foraging behavior; Forest reserves; Fundamental and applied biological sciences. Psychology; General aspects; Genotype & phenotype; Habitats; Meta-analysis; Mixed forests; Models, Biological; Size; Social Behavior; Species; Tropical rain forests; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0003-0147; 1537-5323
• DOI: 10.1086/668012

Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important subunits of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.