| Bumblebees are important pollinators for many flowering plants,and they play a key role in agricultural and natural ecosystems.However,the diversity of bumblebees has been declining rapidly in many parts of the world,especially in Europe and North America,due to various stresses,an alarm for the sustainable lifestyle of people all over the world.China is the richest region in terms of wild bee diversity,with 125 bumblebee species reported so far,which account for 50 % of the world’s known bumblebee species.However,studies on distribution pattern of bumblebees across whole China and their facing threat are insufficient.In this dissertation,I estimated,for the first time,the distribution pattern of the Chinese bumblebees and their risks by the invasion of the European bumblebee species Bombus terrestris and future environmental changes.Based on the shocking findings of threats to local bumblebees,I have developed the strategies to conserve those important pollinators.To understand the spatial distribution pattern and to establish a long-term biodiversity monitoring strategy for the conservation of bumblebees,the distribution data of 125 bumblebee species which collected in the past two decades across China were used to investigate the bioregionalization and the identification of indicator species.All 125 bumblebee species were overlaid on 3° × 3° grid cells.Based on Simpson’s dissimilarity index value of each grid cell(3° × 3°),four principal biogeographic regions of bumblebee species of China were revealed by Ward’s agglomerative cluster analysis,which includes South China(I),North-Northeast China(II),the Mongolian Plateau and surrounding mountains(III)and the Tibetan Plateau and surrounding mountains(IV).The contributions of climatic factors in terms of defining the biogeographic regions were found to be greater than those of the topographical factors and their joint effects.We found that seven,five,ten and four were identified as important indicator species for regions I,II,III and IV,respectively.And the overlapped habitats of those 26 indicator species are the most suitable sites for long-term monitoring in conservation of bumblebees.For the assessment of threat by the alien species,I have examined the habitat suitability for B.terrestris invasion in East Asian countries and the risk of habitat overlap with 24 bumblebee species from different groups,including three major regional groups in China and two taxonomic groups.The results indicated that all East Asian countries were predicted to be susceptible to invasion of B.terrestris,with the highest habitat suitability occurring in China followed by Japan,North Korea,South Korea and Mongolia.Within China,three different regions,North-West,Central to South-East and North-East,were predicted as being highly suitable for invasion and the suitable area was 21% of the total area of China.In China,the group of species closely related to B.terrestris from the same subgenus Bombus s.str.showed higher sensitivity(89%)to habitat overlap with B.terrestris than did the group of non-closely related species from other subgenera bumblebees(73%).The risk of habitat overlapped by B.terrestris for the three major regional bumblebees within China decreased in the order of southern region,northern region and Tibetan Plateau region.For the assessment of threat by future environmental changes,we evaluated the distributional responses of the 29 bumblebee species endemic to East Asia to future(2050s and 2070s)climates and land cover changes.For the future climate change scenarios,the two scenarios,RCP2.6(RCP under minimum emissions)and RCP8.5(RCP under maximum emissions)were used here,represented two extremes for future climate change.The results showed that 17-27(59-93 %)of the species exhibited range contractions.A decrease in species richness from 25 to 19 in the highest species richness region of central China,were detected due to range shifts of 17 km to 574 km.Furthermore,one(3.44 %),three to five(10-17 %),and two to eight(7-28 %)of the 29 bumblebee species were predicted to become critically endangered,endangered and vulnerable in the future,respectively.In conclusion,there are four biogeographic regions of Chinese bumblebees had been divided in this study.Long-term monitoring of the 26 indicator species in the overlapped habitat ranges is critical for the conservation of the 125 bumblebee species of China.Chinese bumblebees are under the threat of the European bumblebee B.terrestris invasion.The use of the introduced B.terrestris for pollination services should be discouraged in China,especially in the two new overlapping habitats of Central to South-East and North-East.Instead,we should enhance studies on pollination using local bumblebee species.Chinese bumblebees are also under the threat of the future climate and landcover changes.We should protect the regions of high species richness,especially the mountain regions surrounding the Sichuan Basin of central China and the Changbaishan Mountains of northeast China.Together with this,the most dominant land covers(grasslands,mixed forests,croplands,and multiple dominant land cover)within the current range should also be protected to mitigate the threat of these environmental changes.This study highlights the bioregionalization,indicators identification and threats assessment of wild pollinators for long-term conservation,and will be helpful for developing conservation strategies for other taxa. |
