Asymmetric interspecific aggression in New Guinean songbirds that replace one another along an elevational gradient. (13th June 2016)

• Record Type: Journal Article
• Authors: Freeman, Benjamin G.; Class Freeman, Alexandra M.; Hochachka, Wesley M.
• Is Part Of: Ibis. Volume 158:Number 4(2016:Oct.)
• Page Start: 726
• Page End: 737
• Publication Date: 2016-06-13
• Subjects: distributional limit -- elevational distribution -- interspecific aggression -- interspecific competition -- playback experiment -- range limit; Birds -- Periodicals; 598
• DOI: 10.1111/ibi.12384
• Languages: English
• ISSNs: 0019-1019

Abstract

Abstract : A common pattern in tropical avifaunas is for closely related species to inhabit largely parapatric elevational distributions such that they replace one another along the elevational gradient. A long‐standing hypothesis for this pattern is that parapatry is maintained by interspecific interference competition mediated by interspecific aggression. However, empirical tests of this hypothesis remain scarce. We used reciprocal playback experiments to measure interspecific aggression in five species‐pairs of New Guinean passerine elevational replacements. We found evidence of interspecific aggression in three species‐pairs. In these three cases, interspecific aggression was asymmetric, with the lower elevation species more aggressive towards the upper elevation species than vice versa. Two patterns suggest that this interspecific aggression is a learned response to the presence of a heterospecific competitor rather than misdirected intraspecific aggression or an evolved response to a competitor. First, when present, interspecific aggression was always strongest at the upper elevation range margin of the lower elevation species (i.e. in the elevational zone in which the two species were found in close proximity and thus interacted with each other), and diminished over very short distances away from this zone. Secondly, the two species‐pairs that did not exhibit interspecific aggression had narrow 'no man's land' gaps between their elevational distributions such that heterospecifics did not encounter one another, possibly explaining the lack of interspecific aggression in these examples. Our results support the hypothesis that interspecific aggression is one factor influencing elevational limits in species‐pairs of New Guinean elevational replacements.