Increasing human environmental footprint does not lead to biotic homogenization of forest bird communities in northern USA

Studies have shown negative impacts of increased human pressures on biodiversity at local (alpha-diversity) and regional (gamma-diversity) scales. However, the diversity between local sites (beta-diversity) has received less attention. This is an important shortcoming since beta-diversity acts as a linkage between the local and regional scales. Decreased beta-diversity means that local sites lose their distinctiveness, becoming more similar to each other. This process is known as biotic homogenization. However, the mechanisms causing biotic homogenization have not been fully studied nor its impacts on different facets of biodiversity. We examined if land-use change due to human actions causes biotic homogenization of taxonomic, functional, and phylogenetic diversity in bird communities of forested habitats in the state of Minnesota, USA. We address if forest loss and increased human domination in a region were associated with decreased beta-diversity. Our results showed that elevated human pressure was not related to increased biotic homogenization in this study region. Effects of landscape change were incongruent among taxonomic, functional, and phylogenetic diversity. At all spatial scales, taxonomic diversity was unrelated to forest loss or human domination. Interestingly, increased human domination appeared to increase the functional beta-diversity of bird communities. This association was driven by a decrease in local diversity. Forest habitat loss was associated with decreasing functional and phylogenetic diversity in local communities (alpha-diversity) and in regional species pool (gamma-diversity), but not in beta-diversity. We highlight the importance of considering multiple facets of biodiversity as their responses to human land-use is varied. Conservation significance of beta-diversity hinges on local and regional diversity responses to human land-use intensification, and organization of biodiversity should therefore be analyzed at multiple spatial scales.