Phylogenetic clustering and overdispersion for alpine plants along elevational gradient in the Hengduan Mountains Region,southwest China

To better understand the elevational pattern of phylogenetic structure shown by alpine taxa and the underlying causes, we analyzed the phylogenetic structure of each elevational belt of alpine plants in the Hengduan Mountains Region, measured by net related index (NRI) and net nearest taxon index (NTI). We found both the indices of phylogenetic diversity indicated that alpine plants tended to show phylogenetic overdispersion at low elevational belts, implying that the distribution of alpine plants in these belts was mainly determined by interspecific competition. Alpine plants at higher elevational belts tended to phylogenetic clustering indicated by NRI, and NTIrevealed phylogenetic clustering at the belts between 4300 m and 5500 m, which presumably suggested environment filtering and rapid speciation. Above 5500 m,NTI indicated that the phylogenetic structure became random again, perhaps due to the low intensity of filtering and the large distances between plants at the top of the scree slopes. We concluded that phylogenetic structure was, indeed, influenced by the environmental filter, interspecies interaction, rapid speciation during the uplift of the Qinghai–Tibet Plateau, and distance between plants.