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Dupont, Y. L., C. Damgaard, et al. (2011). "Quantitative historical
change in bumblebee (<i>Bombus</i> spp.) assemblages of red clover
fields." <u>PLoS ONE</u> <b>6</b>(9): e25172.<br><br>
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<dd>Background - Flower visiting insects provide a vitally important
pollination service for many crops and wild plants. Recent decline of
pollinating insects due to anthropogenic modification of habitats and
climate, in particular from 1950's onwards, is a major and widespread
concern. However, few studies document the extent of declines in species
diversity, and no studies have previously quantified local abundance
declines. We here make a quantitative assessment of recent historical
changes in bumblebee assemblages by comparing contemporary and historical
survey data.<br>
<dd>Methodology/Principal Findings - We take advantage of detailed,
quantitative historical survey data from the 1930's on bumblebee
(<i>Bombus</i> spp.) abundances and species composition in red clover
(<i>Trifolium pratense</i>) fields, an important floral resource and an
attractant of all bumblebee species. We used the historical survey data
as a pre-industrialization baseline, and repeated the same sampling
protocol at nearly the same localities at present, hence setting up a
historical experiment. We detected historical changes in abundances
(bees/m2) of both workers (the units and queens (effective population
size), in addition to species composition. In particular, long-tongued
bumblebee species showed consistent and dramatic declines in species
richness and abundances throughout the flowering season of red clover,
while short-tongued species were largely unaffected. Of 12 <i>Bombus</i>
species observed in the 1930's, five species were not observed at
present. The latter were all long-tongued, late-emerging species.<br>
<dd>Conclusions/Significance - Because bumblebees are important
pollinators, historical changes in local bumblebee assemblages are
expected to severely affect plant reproduction, in particular long-tubed
species, which are pollinated by long-tongued bumblebees.<br><br>
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