Treeline ecotones shape the distribution of avian species richness and functional diversity in south temperate mountains

Tomás A Altamirano,Devin R De Zwaan,Kathy Martin,Scott Wilson,José Tomás Ibarra

doi:10.1038/s41598-020-75470-2

Abstract

Mountains produce distinct environmental gradients that may constrain or facilitate both the presence of avian species and/or specific combinations of functional traits. We addressed species richness and functional diversity to understand the relative importance of habitat structure and elevation in shaping avian diversity patterns in the south temperate Andes, Chile. During 2010–2018, we conducted 2202 point-counts in four mountain habitats (successional montane forest, old-growth montane forest, subalpine, and alpine) from 211 to 1,768 m in elevation and assembled trait data associated with resource use for each species to estimate species richness and functional diversity and turnover. We detected 74 species. Alpine specialists included 16 species (22%) occurring only above treeline with a mean elevational range of 298 m, while bird communities below treeline (78%) occupied a mean elevational range of 1,081 m. Treeline was an inflection line, above which species composition changed by 91% and there was a greater turnover in functional traits (2–3 times greater than communities below treeline). Alpine birds were almost exclusively migratory, inhabiting a restricted elevational range, and breeding in rock cavities. We conclude that elevation and habitat heterogeneity structure avian trait distributions and community composition, with a diverse ecotonal sub-alpine and a distinct alpine community.

Highlights

Mountains produce distinct environmental gradients that may constrain or facilitate both the presence of avian species and/or specific combinations of functional traits
Species range limits may be dictated by constraints on total resource availability, and these limits can be visualized as the position of the species in a dynamic and multidimensional ecological niche space [2,9]
Fewer studies have focused on the influence of heterogeneity on diversity in temperate mountain ecosystems where high seasonality and low species richness should reduce the intensity of inter-specific competition relative to tropical mountains [13,16,17]

Summary

Introduction

Mountains produce distinct environmental gradients that may constrain or facilitate both the presence of avian species and/or specific combinations of functional traits. Habitats with greater heterogeneity should facilitate ecological niche divergence, allowing for a greater number of cooccurring species in a given space and structuring the distribution of avian communities across elevational gradients [10,11]. These effects are pronounced in tropical mountains where habitat specialization among species combined with heterogeneity in vegetation typically generates high diversity turnover (i.e. beta diversity) 12–15. Little is known about the relationship between habitat heterogeneity, elevation, and diversity in temperate mountain ecosystems, in the southern hemisphere [20,21]

Methods

Results

Discussion

Conclusion