VARIATIONS IN NICHE BREADTH AND POSITION OF ALPINE BIRDS ALONG ELEVATION GRADIENTS IN THE EUROPEAN ALPS

Mountains support high biodiversity, often including endemic and vulnerable species, but they are also particularly sensitive to climate change. Whilst studies on mountain biodiversity at the species level are common, studies that consider whole assemblages are scarce. We assessed how an alpine bird assemblage varied in terms of ecological habitat niche by surveying birds and habitat at point count sites placed along elevational gradients (1,700-3,000m) in the Western Italian Alps. Niche breadth, as measured by habitat use, increased along the gradient, suggesting that being more generalist is an advantage in terms of survival at high elevation. Niche position also increased with elevation, which means that species occurring at higher elevations use habitats that are atypical with respect to the average species in the assemblage. Both niche breadth and position were negatively associated with habitat diversity, but these relationships were mainly driven by species occurring at elevations above 2,500m, suggesting that high alpine specialists show a different pattern from the other species of the assemblage. Our results therefore generally supported the idea that a wider niche breadth is useful in harsh environments, such as high mountains, enabling the exploitation of a wider range of resources. The broader niche of many high elevation species may therefore indicate some degree of resilience to environmental change, as long as key habitat types are maintained.