How competitive trade-offs limit elevation ranges for temperate-breeding hummingbirds
Abstract:One intriguing hypothesis about range limits of species along environmental gradients is that interspecific interference competition limits the activity of the better exploitation competitor. The hypothesis works if the costs of interference and (or) exploitation vary along the gradient. However, in some systems, species turnover happens over gradients that may be too short to induce changes in costs associated with competition. An example is breeding Black-chinned Hummingbirds (Archilochus alexandri (Bourcier and Mulsant, 1846)) and Broad-tailed Hummingbirds (Selasphorus platycercus (Swainson, 1827)) in western Colorado, USA, where turnover happens over ∼400 m. We recorded foraging and chasing activity of the two species at feeders and found that their foraging activity changed with elevation but interspecific competition did not. Because the foraging activity of the two species changed inversely with each other, it may be the presence of Black-chinned Hummingbirds rather than active interference that limits the activity of Broad-tailed Hummingbirds. Importantly, the relationship between foraging activity and elevation depended on the distance between the two feeders, which shows that relationships with elevation are contingent on other factors such as spatial distribution of resources. Our results suggest that interspecific differences in flight performance are not manifested over the short elevation gradient and do not account for changes in activity. Flight performance may indirectly affect patterns in breeding-season activity by influencing how species interact with other competitors during the nonbreeding season.
Keywords: Archilochus alexandri; Black-chinned Hummingbird; Broad-tailed Hummingbird; Selasphorus platycercus; alimentation; altitude; colibri à gorge noire; colibri à queue large; elevation; exploitation; foraging; interaction directe; interference; nectar
Document Type: Research Article
Affiliations: 1: Department of Biology, McGill University, 1205 Docteur Penfield, Montréal, QC H3A 1B1, Canada. 2: School of Biology and Ecology and Sustainable Solutions Initiative, University of Maine, Deering Hall, Room 202, Orono, ME 04469, USA.
Publication date: January 1, 2013
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