734 Molecular and spatial analyses reveal links between colony-specific foraging distance and landscape-level resource availability in two bumblebee species Claire Carvell, William C. Jordan, Andrew F. G. Bourke, Robert Pickles, John W. Redhead and Matthew S. Heard C. Carvell, J. W. Redhead and M. S. Heard (mshe@ceh.ac.uk), NERC Centre for Ecology and Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BB, UK. – W. C. Jordan and R. Pickles, Inst. of Zoology, Zoological Society of London, Regent’s Park, London, NW1 4RY, UK. – A. F. G. Bourke, School of Biological Sciences, Univ. of East Anglia, Norwich, NR4 7TJ, UK. Foraging distance is a key determinant of colony survival and pollination potential in bumblebees Bombus spp. However this aspect of bumblebee ecology is poorly understood because of the difculty in locating colonies of these central place foragers. Here, we used a combination of molecular microsatellite analyses, remote sensing and spatial analyses using ker- nel density estimates to estimate nest location and foraging distances for a large number of wild colonies of two species, and related these to the distribution of foraging habitats across an experimentally manipulated landscape. Mean foraging distances were 755 m for Bombus lapidarius and 775 m for B. pascuorum (using our most conservative estimation method). Colony-specifc foraging distances of both species varied with landscape structure, decreasing as the proportion of foraging habitats increased. Tis is the frst time that foraging distance in wild bumblebees has been shown to vary with resource availability. Our method ofers a means of estimating foraging distances in social insects, and informs the scale of manage- ment required to conserve bumblebee populations and enhance their pollination services across diferent landscapes. Bumblebees are important insect pollinators, contributing to a key ecosystem service that is vital to the maintenance of both wild plant communities (Aguilar et al. 2006) and agricultural productivity (Klein et al. 2007). However there is mounting evidence that bumblebees have declined across Europe and North America (Biesmeijer et al. 2006, Grixti et al. 2009, Williams and Osborne 2009), along with the plant species they rely on as foraging resources (Carvell et al. 2006). Habitat loss and fragmentation are considered to be the most important drivers of these declines (Winfree et al. 2009, Potts et al. 2010) hence there is growing interest in developing mitigation options such as agri-environment schemes to restore the value of agricultural landscapes for pollinators (Carvell et al. 2007, Heard et al. 2007). Te spatial and temporal distribution of resources is particularly important for central place foragers such as bumblebees (Dukas and Edelstein-Keshet 1998), since their colonies occupy single nest sites from which foragers access a restricted area. Te distance over which workers from a col- ony are able to locate and forage on foral resources is a key determinant of colony survival, especially where resources are widely dispersed (Schmid-Hempel and Schmid-Hempel 1998). It is also critical for pollination because it determines how far and how often pollen is transported across landscapes (Schulke and Waser 2001). According to optimal foraging theory, foragers will maximise their net rate of energy intake by foraging close to the colony, given a relatively homo- geneous distribution of forage patches (Heinrich 1979a). Variation in foraging range with resource distribution has been demonstrated for honeybees by decoding the ‘waggle dance’ of foraging workers (Beekman and Ratnieks 2000). However, predicting or estimating foraging distances and worker distributions for bumblebees (Cresswell et al. 2000) are difcult due to the challenges of fnding and studying colonies in the feld (Suzuki et al. 2009). Tis is further complicated by the fact that, unlike honeybees, bumblebees are thought not to communicate foraging locations to their nest mates (Stefan-Dewenter and Kuhn 2003, Dornhaus and Chittka 2004). In order to manage landscapes at the appropriate scale to conserve bumblebees and enhance their pollination services, it is important to understand how far individuals are capable of foraging, how nests are likely to be distributed across landscapes and how their location might infuence the observed foraging distances of bees from those colonies. Estimates of the fight distances and space use of bumble- bees have previously been obtained by one of three general approaches: 1) observation of foragers from known wild or experimentally positioned colonies using mark–recapture approaches (Dramstad 1996, Walther-Hellwig and Frankl 2000, Osborne et al. 2008), radar tracking (Osborne et al. 1999) or timed observations of trip duration (Westphal et al. Oikos 121: 734–742, 2012 doi: 10.1111/j.1600-0706.2011.19832.x © 2011 Te Authors. Oikos © 2011 Nordic Society Oikos Subject Editor: Koos Biesmierer. Accepted 25 July 2011