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Cameron, S. A., J. D. Lozier, et al. (2011). "Patterns of widespread
decline in North American bumble bees." <u>Proceedings of the
National Academy of Sciences</u>.<br>
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<dd><x-tab> </x-tab>Bumble
bees (Bombus) are vitally important pollinators of wild plants and
agricultural crops worldwide. Fragmentary observations, however, have
suggested population declines in several North American species. Despite
rising concern over these observations in the United States, highlighted
in a recent National Academy of Sciences report, a national assessment of
the geographic scope and possible causal factors of bumble bee decline is
lacking. Here, we report results of a 3-y interdisciplinary study of
changing distributions, population genetic structure, and levels of
pathogen infection in bumble bee populations across the United States. We
compare current and historical distributions of eight species, compiling
a database of >73,000 museum records for comparison with data from
intensive nationwide surveys of >16,000 specimens. We show that the
relative abundances of four species have declined by up to 96% and that
their surveyed geographic ranges have contracted by 23, some within the
last 20 y. We also show that declining populations have significantly
higher infection levels of the microsporidian pathogen Nosema bombi and
lower genetic diversity compared with co-occurring populations of the
stable (nondeclining) species. Higher pathogen prevalence and reduced
genetic diversity are, thus, realistic predictors of these alarming
patterns of decline in North America, although cause and effect remain
uncertain.<br><br>
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<a href="http://www.pnas.org/content/early/2011/01/03/1014743108.abstract" eudora="autourl">
http://www.pnas.org/content/early/2011/01/03/1014743108.abstract</a>
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