Biology Reference
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(i.e., consecutive visits to different flowers of the same plant, resulting in self-
fertilization) by bumblebees. Indeed, preliminary observations using a similar
experimental design showed that bumble bees perform a higher percentage of
geitonogamous visits than do syrphids (I. Dajoz, unpublished data). Finally, the
mean number of seeds per fruit in the plant communities tended to increase with
functional diversity of pollination treatments (contrast [A + B] versus C; Figure
2D).
Effects on Natural Recruitment
We analysed the long-term effects of our pollination treatments on the natural
recruitment of our experimental plant treatments after the first and second
pollination seasons. The results are presented in Table 2. There was a signifi-
cant effect of year on recruitment richness with a higher richness after the
second pollination season (mean ± SE: 1.916 ± 0.075 in 2004, and 2.291 ±
0.0856 in 2005). Among the possible causes was a severe drought in 2003
[27], which likely affected both plant and insect populations. Such a drought
did not occur in 2004. This difference in climate between years may account
for a large part of the year effect.
Table 2.
Analysis of Plant Recruitment Richness and Density.
Recruitment richness was significantly different among plant treatments, with
fewer species recruiting in tubular communities (Figure 3). This is very likely due
to two perennial species (whereas all species are annuals in the other group) which
may have different reproductive traits and create differences in competitive inten-
sity among the plant treatments. There was a significant effect of pollination treat-
ment, with a higher recruitment richness when both groups of pollinators were
present (means ± SE: syrphid 1.854 ± 0.973, bumble bee 2.052 ± 0.826, and both
