Diagnostic indicators of wild pollinators for biodiversity monitoring in long-term conservation

For the conservation of wild pollinators, instead of surveying the whole community, one or more indicator species can be used as monitoring targets for long-term conservation. China, the richest country in terms of bumblebee species with 125 species, was selected here to investigate the indicator species of the different biogeographic regions of bumblebees. Four principal biogeographic regions of bumblebee species, i.e., South China, North-Northeast China (North China), the Mongolian Plateau and surrounding mountains (Mongolian Plateau) and the Tibetan Plateau and surrounding mountains (Tibetan Plateau), were revealed by Ward's agglomerative cluster analysis. The role of climatic factors in defining the biogeographic regions was found to be greater than those of topographical factors and their joint effects. We found that 14, 13, 12 and 12 species were associated with the regions of South China, North China, the Mongolian Plateau and the Tibetan Plateau, respectively. In addition, among these species, seven (Bombus atripes, B. bicoloratus, B. breviceps, B. eximius, B. flavescens, B. montivagus and B. trifasciatus), five (B. deuteronymus, B. patagiatus, B. pseudobaicalensis, B. tricornis and B. ussurensis), ten (B. armeniacus, B. confusus, B. cryptarum, B. cullumanus, B. hortorum, B. muscorum, B. ruderarius, B. soroeensis, B. subterraneus and B. terrestris) and four species (B. kashmirensis, B. personatus, B. rufofasciatus and B. waltoni) were identified as important indicator species for South China, North China, the Mongolian Plateau and the Tibetan Plateau, respectively. Furthermore, we identified specific areas for targeted bumblebee diversity monitoring in each region. This study highlights the bioregionalization and the identification of indicator species of bumblebee pollinators for long-term monitoring in conservation.