Patterns of phylogenetic beta diversity in China's grasslands in relation to geographical and environmental distance

Abstract

Patterns and determinants of beta (β-) diversity can be used to explore the underlying mechanisms regulating community assembly. Despite being the most commonly used measure of β-diversity, species turnover does not consider the evolutionary differences among species, treating all species equally. Incorporating information on phylogenetic non-independence or relatedness among species in the calculation of β-diversity may substantially advance our understanding of the ecological and evolutionary mechanisms structuring communities. Here, we investigate the relative influence of geographical distance and differences in environmental conditions (environmental distance) on the phylogenetic β-diversity between grassland communities expanding 4000km across the Tibetan Plateau, the Inner Mongolia Plateau and the Xinjiang Autonomous Region in China. Both observed and standardized effect size of phylogenetic β-diversity were significantly correlated with geographical and environmental distance across all regions. However, the effect of geographical distance on the standardized effect size of phylogenetic β-diversity disappeared when environmental distance was controlled. We also found that within different regions, the effect of environmental distance on both observed and standardized effect size of phylogenetic β-diversity was more significant than geographical distance. Among environmental variables, climate played a more important role in shaping observed phylogenetic β-diversity across and within regions, and standardized effect size of phylogenetic β-diversity across regions. Soil properties played a more important role in shaping standardized effect size of phylogenetic β-diversity within regions. The phylogenetic β-diversity of species from dicot and monocot clades exhibited similar patterns along environmental and geographical distance. The results suggest that at the study scale, phylogeny of grassland communities in China is predominantly structured by environmental filtering, and the dominant environmental factors may be scale-dependent.