Biology Reference
In-Depth Information
carefully monitored and protected. The loss of pollinator functional diversity is
likely to trigger plant population decline or extinctions [4], which in turn are
likely to affect the structure and composition of natural plant communities and
the productivity of many agroecosytems that rely on insect pollination [8]. Ul-
timately, higher trophic levels may be affected since the diversity and biomass of
consumers depend on primary production. Our results strongly suggest that the
functional diversity of complex interaction webs plays a crucial role in the sustain-
ability of ecosystems.
Materials and Methods
Experimental Plant Communities
At the beginning of spring 2003, plant communities were set up in a meadow that
remained almost undisturbed for 10 years at the Station Biologique de Foljuif,
France, 80 km southwest of Paris. Prior to the establishment of the communities,
soil was sterilized by injecting 120 °C steam (30 min) to destroy the seed bank
and soil pathogens. In each of the 36 4-m
2
plots, a total of 30 adult plants were
planted on a grid, spaced 25 cm from each other, to minimize competition and
homogenise spatial distribution. Thus, plant density was the same in all experi-
mental plots. We selected a moderate density to maintain within- and among-spe-
cies competition to a low level, and to allow enough space for future recruitment
in the plots. Each of these plant communities was enclosed in a 2-m-high nylon
mesh cage in order to eliminate natural pollinator visitation.
Pollination Rounds
During the flowering seasons (June-July 2003 and 2004), pollinators were cap-
tured around the study area and introduced into the cages. The relative abundance
of pollinator species in the various pollination treatments reflects their natural
abundances. From preliminary observations, we had noticed that, in order to
have no more than three insects active at the same moment in a 4-m
2
plot, it was
necessary to put about eight syrphid flies, or six bumble bees, or a mixture of six
syrphids and four bumble bees in each pollination cage. Each pollination round
in a given plot included 200 visits in the year 2003 and 300 in the year 2004. In
total, each plot received either four (in 2004) or five (in 2003) pollination rounds,
leading to a total of 1,000 visits per plot in 2003 and 1,200 in 2004.
Pollination Activity
Bumble bees needed approximately 30 min after introduction in the cages
to calm down and start to pollinate. In the pollination treatment with both
