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Bommarco, R., O. Lundin, et al. (2012). "Drastic historic shifts in
bumble-bee community composition in Sweden." <u>Proceedings of the
Royal Society B: Biological Sciences</u> <b>279</b>(1727): 309-315.<br>
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<dd><x-tab> </x-tab>The
species richness of flower-visiting insects has declined in past decades,
raising concerns that the ecosystem service they provide by pollinating
crops and wild plants is threatened. The relative commonness of different
species with shared ecological traits can play a pervasive role in
determining ecosystem functioning, but information on changes in
abundances of pollinators over time is lacking. We gathered data on
relative abundances of bumble-bee species in Swedish red clover fields
during three periods in the last 70 years (1940s, 1960s and present), and
on clover seed yields since 1921. We found drastic decreases in
bumble-bee community evenness, with potential consequences for level and
stability of red clover seed yield. The relative abundances of two
short-tongued bumble-bees have increased from 40 per cent in the 1940s to
entirely dominate present communities with 89 per cent. Average seed
yield declined in recent years and variation in yield doubled, suggesting
that the current dependence on few species for pollination has been
especially detrimental to stability in seed yield. Our results suggest a
need to develop management schemes that promote not only species-rich but
also more evenly composed communities of service-providing
organisms.<br><br>
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