Environmental Engineering Reference
In-Depth Information
Bees, in particular, pollinate one or more cultivars of a majority of the
world's 1,500 crop species and thus are essential for an estimated 15 to 30
percent of world food production (Kremen et al. 2002). Farmers have re-
lied on such relationships for millennia and to foster efficiency have culti-
vated extensively the European honey bee ( Apis mellifera ) within crop fields
and orchards. This pollination function is now becoming compromised,
however, due to diseases and poisoning from insecticides (Kremen et al.
2002).This decline in beekeeping, combined with increasing demand for
the service is making cultivation of European honey bees expensive. One
solution is to look to natural, related species of pollinators to fill in their
ecosystem role.
Maintaining habitat for a diversity of native bees is important for crop
pollination because the abundances of individual species fluctuate from one
year to the next or they differ in abundance across a landscape. Indeed, up
to twenty species of native bees were necessary to ensure sufficient polli-
nation function in any one year (Kremen et al. 2002). Also, different bee
species are differentially effective as pollinators for different crops. In essence,
there is an element of both functional redundancy (bee species covering for
each other among years and in different locations) and functional diversity
or rivets (different groups of bee species effective on different plants) in this
pollinator community. Managing for bee diversity could therefore meet the
pollination requirements of a great number of crops and provide insurance
against shortages of domesticated honeybees and specific native pollinator
species (Kremen et al. 2002).
The pollination service offered by
native bees can, however, vary with
land management practices. To un-
derstand quantitatively just how land
use affected pollination function,
Kremen and colleagues undertook a
systematic study to document how
diversity in the native bee species
community affected the rate of crop
pollination on farms in the Central
Valley of California.They found that amount of crop pollination depended
on how close a farm was to natural bee habitat and on the type of farm it-
self (organic versus conventional). Native bees had the greatest effect on or-
ganic farms near natural habitat. All other farms (e.g., organic far from
Managing for bee diversity could
therefore meet the pollination re-
quirements of a great number of
crops and provide insurance
against shortages of domesticated
honeybees and specific native
pollinator species.
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