Human-induced changes in land use/cover and climate are affecting biodiversity patterns at different spatiotemporal scales. Since environmental heterogeneity has long been recognized as an important landscape characteristic relevant for species distribution, changes in the heterogeneity may have profound impacts on the variation in species composition among communities across space, i.e. beta diversity. To understand how environmental heterogeneity affects beta diversity across spatial scales, we examined the relationship between heterogeneity and beta diversity among ~200 breeding bird communities along an elevation gradient of ~4000 m, based on Taiwan Breeding Bird Survey data collected from 2009-2015. For each bird survey site, we calculated the Sørensen index as a measure of overall beta diversity at three spatial scales and split it into two components: turnover and nestedness. We then investigated the associations between the three measures of beta diversity and environmental heterogeneity in climate, resources, and land cover at the three scales using regression models. We also assessed the relative importance of the three types of environmental heterogeneity in determining beta diversity across scales.
Results/Conclusions
Results showed that, at all three spatial scales, the beta diversity of breeding birds in Taiwan was mostly contributed by turnover. However, considerable contributions of nestedness at each scale suggested another mechanism affecting breeding bird community dissimilarity. Heterogeneity in land cover and climate generally had positive effects on the beta diversity through changing turnover, while resource heterogeneity had negative effects through influencing nestedness. At the finest scale, land cover heterogeneity was most important among the three heterogeneity types in determining the beta diversity among the bird communities. With increasing spatial scales, the relative importance of climatic and resource heterogeneities increased. This study improves our understanding of the patterns and potential drivers of beta diversity across spatial scales. It also implies that continued intense changes in land cover and potential future changes in climates may lead to biotic homogenization of bird communities.