Ahrné Karin, Bengtsson Jan, Elmqvist Thomas
Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
PLoS One. 2009;4(5):e5574. doi: 10.1371/journal.pone.0005574. Epub 2009 May 15.
Bumble bees and other wild bees are important pollinators of wild flowers and several cultivated crop plants, and have declined in diversity and abundance during the last decades. The main cause of the decline is believed to be habitat destruction and fragmentation associated with urbanization and agricultural intensification. Urbanization is a process that involves dramatic and persistent changes of the landscape, increasing the amount of built-up areas while decreasing the amount of green areas. However, urban green areas can also provide suitable alternative habitats for wild bees.
METHODOLOGY/PRINCIPAL FINDINGS: We studied bumble bees in allotment gardens, i.e. intensively managed flower rich green areas, along a gradient of urbanization from the inner city of Stockholm towards more rural (periurban) areas. Keeping habitat quality similar along the urbanization gradient allowed us to separate the effect of landscape change (e.g. proportion impervious surface) from variation in habitat quality. Bumble bee diversity (after rarefaction to 25 individuals) decreased with increasing urbanization, from around eight species on sites in more rural areas to between five and six species in urban allotment gardens. Bumble bee abundance and species composition were most affected by qualities related to the management of the allotment areas, such as local flower abundance. The variability in bumble bee visits between allotment gardens was higher in an urban than in a periurban context, particularly among small and long-tongued bumble bee species.
CONCLUSIONS/SIGNIFICANCE: Our results suggest that allotment gardens and other urban green areas can serve as important alternatives to natural habitats for many bumble bee species, but that the surrounding urban landscape influences how many species that will be present. The higher variability in abundance of certain species in the most urban areas may indicate a weaker reliability of the ecosystem service pollination in areas strongly influenced by human activity.
大黄蜂和其他野生蜜蜂是野花及多种栽培作物的重要传粉者，在过去几十年中其多样性和数量都有所下降。人们认为数量下降的主要原因是与城市化和农业集约化相关的栖息地破坏和碎片化。城市化是一个涉及景观剧烈且持续变化的过程，建成区面积增加而绿地面积减少。然而，城市绿地也可为野生蜜蜂提供合适的替代栖息地。
方法/主要发现：我们沿着从斯德哥尔摩市中心到更乡村（城郊）地区的城市化梯度，研究了分配花园（即集约管理的、花卉丰富的绿地）中的大黄蜂。在城市化梯度上保持栖息地质量相似，使我们能够将景观变化（如不透水表面比例）的影响与栖息地质量变化区分开来。大黄蜂多样性（在稀疏至25个个体后）随着城市化程度的增加而降低，从更乡村地区的约8种减少到城市分配花园中的5至6种。大黄蜂的数量和物种组成受分配区域管理相关质量的影响最大，如当地花卉数量。城市分配花园之间大黄蜂访花的变异性高于城郊环境，尤其是在小型和长舌大黄蜂物种之间。
结论/意义：我们的结果表明，分配花园和其他城市绿地可以作为许多大黄蜂物种自然栖息地的重要替代，但周围的城市景观会影响出现的物种数量。在受人类活动强烈影响的地区，某些物种在最城市化地区数量的更高变异性可能表明生态系统传粉服务的可靠性较低。
