Historical biogeography and current ecology influence Andean bird communities along an elevational gradient

Abstract Ecological and evolutionary characteristics need to be combined with the taxonomic identity of species to comprehensively characterize biodiversity, and to determine the relative importance of ecological and evolutionary mechanisms in shaping spatial patterns. We examined the elevational patterns of multiple dimensions of biodiversity in two suborders of passerines (oscines and suboscines), which differ in their biogeographic history, to gain insights into the complex interplay between ecological context and historical biogeography in shaping Andean bird assemblages. Specifically, we quantified and contrasted elevational gradients of species richness, phylogenetic dispersion, and functional dispersion of passerines, suboscines, and oscines along the extensive elevational gradient of Manu Biosphere Reserve in the Peruvian Andes. Furthermore, we determined if the empirical gradients of phylogenetic and functional dispersion were indicative of non-random mechanisms dominating community assembly. For all passerines and suboscines, species richness decreased in a saturating manner, phylogenetic dispersion declined linearly, and functional dispersion was stochastic with respect to elevation. For oscines, species richness and phylogenetic dispersion decreased linearly, and functional dispersion decreased in a saturating fashion. These differences in elevational gradients of oscines and suboscines likely result from a combination of adaptations arising from radiations that occurred elsewhere and an in-situ radiation in the Andes. Combined, our results suggest that biogeographic history, evolutionary contingencies, and potentially, climatic niche conservatism within each suborder might have contributed to the elevational biodiversity gradients at Manu. Our findings highlight the importance of explicitly considering historical biogeography across phylogenetic scales when examining whole-assemblage biodiversity gradients.