Positive relationships between association strength and phenotypic similarity characterize the assembly of mixed-species bird flocks worldwide

Hari Sridhar, Umesh Srinivasan, Robert A. Askins, Julio Cesar Canales-Delgadillo, Chao Chieh Chen, David N. Ewert, George A. Gale, Eben Goodale, Wendy K. Gram, Patrick J. Hart, Keith A. Hobson, Richard L. Hutto, Sarath W. Kotagama, Jessie L. Knowlton, Tien Ming Lee, Charles A. Munn, Somchai Nimnuan, B. Z. Nizam, Guillaume Péron, V. V. RobinAmanda D. Rodewald, Paul G. Rodewald, Robert L. Thomson, Pranav Trivedi, Steven L. van Wilgenburg, Kartik Shanker*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

84 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)777-790
Number of pages14
JournalAmerican Naturalist
Volume180
Issue number6
DOIs
Publication statusPublished - Dec 2012
Externally publishedYes

Keywords

  • Community assembly
  • Interspecific competition
  • Metaanalysis
  • Mixed-species flocks
  • Null models
  • Positive interactions

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