Land-use change effects on interspecific competition in highly diverse hummingbird assemblages

Esteban A. Guevara, Biodiversity and Conservation Biology, Swiss Federal Research Institue WSL, Zurich, Switzerland, Carolina Bello, Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Zurich, Switzerland, Ian R. McFadden, Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland, Matthias Schleuning, Senckenberg Biodiversity and Climate Research Centre, Frankfurt, Germany, Loïc Pellisier, Department of Environmental Systems Science, Swiss Federal Institute of Technology Zurich ETHZ, Zurich, Switzerland, Cristian Poveda, Aves y Conservacion / BirdLife in Ecuador and Catherine H. Graham, Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland

Background/Question/Methods
The current pace of biodiversity lose, owing to on-going land-use change, is unprecedented. Land-use change not only filters species that cannot survive in disturbed landscapes, but could also modulate biotic interactions among species. How land-use change reshapes species interactions; however, remains an open question. We experimentally tested the indirect effect of land-use change (i.e. forest conversion) on resource competition in Andean hummingbirds using selectivity experiments with artificial feeders located along an elevation gradient in natural and converted forests. Selectivity was measured as the time invested by hummingbirds feeding at feeders with high sucrose concentration when feeders with low and high concentrations of sucrose were simultaneously offered and in the presence of other hummingbird species. We evaluated the indirect effect of forest conversion on hummingbird selectivity mediated by morphological similarity (body mass and bill length), and flower resource abundance using structural equation models.
Results/Conclusions
We found that morphological similarity was greater in converted as compared to natural forests across the elevation gradient. The influence of morphological similarity and resource availability on resource competition varied along the elevation gradient. In highland assemblages, competition was more influenced by the presence of similar morphological competitors than by resource abundance. In contrast, resource abundance was a more important predictor of competition in the low elevation. Taken together our results suggest that competition is influenced by forest conversion but the importance of different drivers varies across elevation, highlighting the importance of considering context-dependency when studying competition. Although context dependency can hamper our ability to generalize about the effect of land use on biotic interactions, our results suggest that by considering community structure we can develop and test expectations about how biotic interactions will respond to land use in a local context