Phylogenetic and Morphological Relatedness of Bird Communities along Elevational Gradients in the Americas

Abstract

The composition of bird communities is thought to be largely shaped by the competing pressures of environmental filtration and competition. The differential effects of these two pressures can be understood in terms of the phylogenetic and morphological relatedness of different bird communities. Bird communities in elevational gradients across the globe have been found to have decreasing phylogenetic and morphological relatedness with increasing elevation. Further, many communities are phylogenetically and morphologically overdispersed, or less closely related than expected by chance, at low elevations and underdispersed at high elevations. While it is clear that these trends exist on a local level, global studies of these relationships are currently inconclusive. This paper further explores these relationships on the continental level using eBird data to examine bird communities along nine regional elevational gradients in the Americas. In contrast to previous studies, both phylogenetic and morphological relatedness on a continental scale are found to decrease with increasing elevation. Many low elevation communities are phylogenetically or morphologically overdispersed, and some high elevation communities are phylogenetically underdispersed. These patterns hold similarly for temperate and tropical regions and largely hold across dietary guilds. These results raise further causal questions regarding the structure of bird communities along elevational gradients globally.