BIODIVERSITY RESEARCH Consequences of warming up a hotspot: species range shifts within a centre of bee diversity Michael Kuhlmann 1 *, Danni Guo 2 , Ruan Veldtman 3,4 and John Donaldson 3 INTRODUCTION About 25,000 bee species globally (Michener, 2007) are the major pollinators of flowering plants and of more than half of the 3000 crop species (Klein et al., 2007). As such, they are essential ecological keystone species contributing to the integrity of most terrestrial ecosystems. Numerous studies have demonstrated their economic value to agricultural (Klein et al., 2007; Allsopp et al., 2008) and to natural ecosystems (Kearns et al., 1998). Aizen et al. (2009) show that pollination shortage will intensify demand for agricultural land, a trend that will be more pronounced in the developing world potentially leading to decreased food security and increasing pressure on supply of agricultural land. South Africa and especially the Cape Floristic Region (CFR) is known as a centre of bee (Kuhlmann, 2009) and plant 1 Department of Entomology, The Natural History Museum, Cromwell Road, London, UK SW7 5BD, 2 Climate Change and Bio- Adaptation Division and 3 Applied Biodiversity Research, South African National Biodiversity Institute, Private Bag X7, Claremont 7735, South Africa, 4 Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch, Private Bag X1, Matieland 7602, South Africa *Correspondence: Michael Kuhlmann, Department of Entomology, The Natural History Museum, London, UK. E-mail: m.kuhlmann@nhm.ac.uk ABSTRACT Aim Bees are the most important pollinators of flowering plants and essential ecological keystone species contributing to the integrity of most terrestrial ecosystems. Here, we examine the potential impact of climate change on bees’ geographic range in a global biodiversity hotspot. Location South Africa with a focus on the Cape Floristic Region (CFR) diversity hotspot. Methods Geographic ranges of 12 South African bee species representing dominant distribution types were studied, and the climate change impacts upon bees were examined with A2 and B2 climate scenarios of HadCM3 model, using MaxEnt for species distribution modelling. Results The predicted levels of climate change-induced impacts on species ranges varied from little shifts and range expansion of 5–50% for two species to substantial range contractions between 32% and 99% in another six species. Four species show considerable range shifts. Bees of the winter rainfall area in the west of South Africa generally have smaller range sizes than in the summer rainfall area and generally show eastward range contractions toward the dry interior. Bee species prevalent in summer rainfall regions show a tendency for a south-easterly shift in geographic range. Main conclusions The bee fauna of the CFR is identified as the most vulnerable to climate change due to the high level of endemism, the small range sizes and the island-like isolation of the Mediterranean-type climate region at the SW tip of Africa. For monitoring climate change impact on bees, we suggest to establish observatories in the coastal plains of the west coast that are predicted to be worst affected and areas where persistence of populations is most likely. Likely impacts of climate change on life history traits of bees (phenology, sociality, bee-host plant synchronization) are discussed but require further investigation. Keywords Bees, climate sensitivity, future climate scenario, geographic range shift, pollination, South Africa. Diversity and Distributions, (Diversity Distrib.) (2012) 1–13 DOI: 10.1111/j.1472-4642.2011.00877.x ª 2012 Blackwell Publishing Ltd http://wileyonlinelibrary.com/journal/ddi 1 A Journal of Conservation Biogeography Diversity and Distributions