Effects of geographic distance and climatic dissimilarity on species turnover in alpine meadow communities across a broad spatial extent on the Tibetan Plateau

Understanding the underlying mechanisms that generate species turnover or beta diversity among biological communities is a central theme in ecology. Here, we distinguish the effects of geographic distance and climatic dissimilarity on species turnover of vascular plants in alpine meadow communities on the Tibetan Plateau in China. We calculated species turnover between each pair of 17 sites, using the Jaccard's and Simpson's indices. We selected six variables to quantify climate at each site, and subjected values of the climatic variables to a principal component analysis. We applied a variance partitioning approach to disentangle the effects of geographic distance and climatic dissimilarity on species turnover in alpine meadow communities. We also examined the effect of elevation variation on species turnover. Geographic distance and climate dissimilarity together explained 49.1 % of the variation in compositional difference between alpine meadow communities; the amount of the variation explained purely by geographic distance and purely by climatic dissimilarity was 6.8 % and 2.8 %, respectively. When geographic distance, climate dissimilarity, and elevation difference were included in an analysis, they together explained 55 % of the variation in compositional difference between alpine meadow communities; the pure effect of each of the three sets of explanatory variables was 4.8, 4.3, and 3.5 %, respectively. The fact that the vast majority of the variation explained by geographic distance and climatic dissimilarity cannot be independently attributed to either factor suggests that the two factors operate together in determining regional patterns of species composition in alpine meadows on the Tibetan Plateau.