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Land-use Change and the Decline of the Western Bumble Bee Open Access

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Recent studies have documented a drastic decline in managed honey bee colonies (termed Colony Collapse Disorder), and in an attempt to catalog the current status of native pollinator communities, successive research has inadvertently revealed a parallel decline. Of interest for the present study, researchers reported in 2010 that populations of North American bumble bees, Bombus spp., are in steep decline. While many unique North American bumble bee species exist, all share similar natural history traits and significantly contribute to the maintenance of local biodiversity through their pollination services. The present study focuses on the decline of B. occidentalis, a bumble bee with an historic range throughout the western United States. Maxent, a presence-only species distribution modeling (SDM) program, was used to measure the impact of land-use change from 1992 to 2006 on the recent decline of B. occidentalis in the state of Oregon. Analysis and measurement of the projections revealed that land-use change has not been a driver of the decline in B. occidentalis populations; conversely, land-use change, theoretically, should have allowed for the geographical expansion of B. occidentalis populations, thereby suggesting that other factors, such as agricultural intensification, use of neonicotinoids, and fungal parasites, are responsible. The present study concludes that the suitability of a given location for B. occidentalis can be significantly predicted via proximity to natural habitat and floral resources. Optimally, the distances to nesting habitat and floral resources should be no greater than 5 km and 1 km, respectively.

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