Avian ecology and community structure across elevation gradients: The importance of high latitude temperate mountain habitats for conserving biodiversity in the Americas

Abstract

Mountains are excellent systems for studying biodiversity as they promote rapid species turnover across relatively short elevational distances. Most research on biogeographic patterns in mountains has focused on tropical regions; far less is known about diversity across elevational gradients and their relative contribution to conservation in temperate mountains, particularly at high latitudes. To better understand the composition, ecology, and evolutionary history of high-latitude temperate mountain bird communities, we evaluated species richness, functional redundancy, and phylogenetic diversity across three elevation-specific habitats (upper montane, subalpine, alpine) in north temperate (9 mountains in British Columbia, Canada; 54°N) and south temperate (10 mountains in Chile; 39°S) regions representing distinct biogeographic origins. North temperate mountains had greater absolute species richness (77 versus 63 species), while south temperate mountains supported a greater proportion of the regional species pool (63% versus 44%). North temperate species richness increased with elevation to an ecotonal peak at treeline and then declined (subalpine = 58, alpine = 30 species), while the highest richness in south temperate mountains occurred at and above treeline (41 species). Similar species turnover patterns were observed in both systems with alpine habitats supporting the most distinct avifauna. Functional traits varied between regions with proportionally more migrants in the north, compared to more habitat specialists and cavity nesters in the south, particularly in the alpine. North temperate bird communities exhibited lower functional redundancy and higher total phylogenetic diversity, indicating a community susceptible to losing ecosystem functions and evolutionary potential. Southern communities contained greater functional redundancy and more evolutionarily isolated species, consistent with convergent evolution in challenging, high elevation habitats. Overall, in north temperate mountains, greater species richness and phylogenetic diversity, coupled with lower functional redundancy, particularly below treeline, highlights the importance of montane forests for biodiversity. In south temperate mountains, a distinct, speciose community at and above treeline, in combination with supporting a large proportion of the regional species pool, indicates a unique system with disproportionate conservation value. One-third of birds detected in north temperate mountains are considered of national or international conservation concern, compared to 9.5% of southern mountain birds. However, only 18% of the 63 species observed in the south temperate Andes (and only 5% of alpine species) have had a conservation status assessment. With increasing climate change and habitat loss pressures across elevations, temperate mountains in the Americas have significant conservation value and appear particularly important for maintaining regional biodiversity.