title: Positive relationships between association strength and phenotypic similarity characterize the assembly of mixed-species bird flocks worldwide.
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.
authors.affiliation: Centre for Ecological Sciences, Indian Institute of Science, Bangalore, India.
authors.forename: Hari
authors.initials: H
authors.lastname: Sridhar
authors.forename: Umesh
authors.initials: U
authors.lastname: Srinivasan
authors.forename: Robert A
authors.initials: RA
authors.lastname: Askins
authors.forename: Julio Cesar
authors.initials: JC
authors.lastname: Canales-Delgadillo
authors.forename: Chao-Chieh
authors.initials: CC
authors.lastname: Chen
authors.forename: David N
authors.initials: DN
authors.lastname: Ewert
authors.forename: George A
authors.initials: GA
authors.lastname: Gale
authors.forename: Eben
authors.initials: E
authors.lastname: Goodale
authors.forename: Wendy K
authors.initials: WK
authors.lastname: Gram
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Hart
authors.forename: Keith A
authors.initials: KA
authors.lastname: Hobson
authors.forename: Richard L
authors.initials: RL
authors.lastname: Hutto
authors.forename: Sarath W
authors.initials: SW
authors.lastname: Kotagama
authors.forename: Jessie L
authors.initials: JL
authors.lastname: Knowlton
authors.forename: Tien Ming
authors.initials: TM
authors.lastname: Lee
authors.forename: Charles A
authors.initials: CA
authors.lastname: Munn
authors.forename: Somchai
authors.initials: S
authors.lastname: Nimnuan
authors.forename: B Z
authors.initials: BZ
authors.lastname: Nizam
authors.forename: Guillaume
authors.initials: G
authors.lastname: Péron
authors.forename: V V
authors.initials: VV
authors.lastname: Robin
authors.forename: Amanda D
authors.initials: AD
authors.lastname: Rodewald
authors.forename: Paul G
authors.initials: PG
authors.lastname: Rodewald
authors.forename: Robert L
authors.initials: RL
authors.lastname: Thomson
authors.forename: Pranav
authors.initials: P
authors.lastname: Trivedi
authors.forename: Steven L
authors.initials: SL
authors.lastname: Van Wilgenburg
authors.forename: Kartik
authors.initials: K
authors.lastname: Shanker
mesh_terms: D000818:Animals; D001717:Birds / Q000033:anatomy & histology* / Q000502:physiology*; D049628:Body Size; D003163:Competitive Behavior; D017753:Ecosystem; D005247:Feeding Behavior; D008954:Models, Biological; D012919:Social Behavior