Bumblebees, climate and glaciers across the Tibetan plateau (Apidae: Bombus Latreille)
The Tibetan plateau and its immediately surrounding mountains include the greatest hotspot of diversity worldwide for bumblebees, which are among the most important pollinators in temperate ecosystems. We make the first quantitative description of variation in the species composition of alpine social bumblebee faunas across the Tibetan plateau, for 44 species in 124 of the 307 one-degree grid cells. Data were compiled from field surveys, published sources and museum collections. Sampling effort could not be standardized across the region so our inferences have to be provisional. Faunal variation is described using detrended correspondence analysis (DCA); the faunal variation explained by climate variation is described using canonical correlation analysis (CCA); and the contribution of the climate data to the explanation is assessed using Procrustes analysis. Results show: (1) a particularly distinct group of endemic Himalayan faunas in the south; (2) a group of Tibetan interior faunas, with connections to faunas in the north-west in the Hindu Kush, Pamir and Tian Shan; and (3) a group of faunas in north-eastern Qinghai and Gansu, with connections to faunas to the north-east in Mongolia. The eastern and southern faunas in wetter habitats appear to be closer to equilibrium with climate factors, whereas some western faunas in more arid habitats appear further from equilibrium with the measured climate factors. One possibility is that these western faunas may depend on highly localized factors for mitigating the low precipitation over much of this region, and particularly on continuous summer streams with meltwater from distant permanent glaciers or high-ridge precipitation. Consequently, conservation threats to Tibetan bumblebees now include climate change causing loss of permanent streams in the west as well as the over-grazing documented in the east, threats that have not been major concerns for bumblebee conservation elsewhere.