Dioecious <Emphasis Type="Italic">Clusia nemorosa</Emphasis> achieves pollination by combining specialized and generalized floral rewards |
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Authors: | Blanka Vlasáková Stefan Jarau |
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Institution: | 1.Department of Mycorrhizal Symbioses,Academy of Sciences of the Czech Republic,Pr?honice,Czech Republic;2.Institute for Experimental Ecology,Ulm University,Ulm,Germany |
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Abstract: | Plants often combine multiple strategies to achieve pollen transfer. The dioecious Clusia nemorosa (Clusiaceae) produces floral resin, a specialized reward for resin-collecting bees. It also exhibits floral automimicry with
female flowers mimicking male flowers in order to attract pollen-collecting insects. We observed the hourly visitation frequency
and behaviour of bee visitors on two rock savanna sites in French Guiana. The major strategy in pollen transfer and the variation
in visitation rates among visitor species were examined. We hypothesized that the visitation rate will vary between the floral
sexes and degree of this variation will differ between the two-reward systems. We found no evidence for visits being exclusively
related to resin collection, which we expected to be the principal strategy in pollen transfer. Deceit pollination appeared
to have minor importance and seemed to be locally associated with the site, where demand for pollen was greater. Flower visits
that probably facilitated most pollen transfer, combined resin and pollen. The pollinators involved in this system collected
pollen from male flowers and resin from female flowers. The fruit set was not particularly low (44.19%) so offering different
rewards by different flower genders has not constrained reproductive success in this system. Pronounced variation in visitation
rates between sexes was not related to the pollination mechanisms but to the demand for the two rewards. Overall demand for
pollen was greater than demand for resin. Female flowers were visited much less frequently than male flowers. Peak pollen
collection occurred in the morning, i.e., as soon as the resource was available, while resin was collected throughout the
day. There was a local variability in demand for the two resources because both the visitation rate and the behaviour of foraging
bees varied between the two observation sites. |
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