Biology Reference
In-Depth Information
5.5
Nectar secondary compounds and pollinators
The presence of secondary compounds in floral nectars may enhance plant
fitness both inside and outside the Mediterranean (see “Secondary com-
pounds” on page 348). This may be achieved through different methods:
•
Increasing pollinator visitation to plants defended against herbivore attack
(Adler, 2000a, 2000b)
•
Attracting more specialized pollinators (Masters, 1991)
•
Influencing the preferences of foragers (e.g., phenol and alkaloid com-
pounds; cf. Waller et al., 1972; Hagler & Buchmann, 1993)
•
Increasing floral constancy of legitimate pollinators and inhibiting nectar
thieves (Stephenson, 1981, 1982)
•
Increasing interflower and interplant movements to avoid ingesting exces-
sive levels of secondary compounds (London-Shafir et al., 2003).
5.6
Floral nectar, floral diversity, and bee diversity
Several studies have attempted to explain bee diversity using single quantita-
tive nectar parameters at a community level, and it has been shown that
changes in nectar levels influence bee visitation to flowers (see Proctor et al.,
1996; Potts et al., 2003, 2004 for reviews). The most commonly used attrib-
utes have been spatial and temporal patterns of nectar volume and
concentration. Although such parameters of nectar reward structure may de-
fine the suite of flower visiting, they fail to give a full picture of how the
community is organized on the basis of these single aspects of nectar reward.
In order to describe the nectar reward structure of Mediterranean communi-
ties, Potts et al. (2004) used a complex approach to quantify “nectar resource
diversity” which they defined as the variety of nectar volume and concentra-
tion combinations available in a community. They found that the variation in
bee species richness within a habitat is much better explained by such a pa-
rameter than by other nectar variables such as volume, concentration, energy
value, and water content, which have little predictive value per se. In fact,
the authors demonstrated that nectar resource diversity may be a fundamen-
tal factor organizing nectarivorous communities. Using a series of Mediterr-
anean habitats differing in successional stage and structure, they found that
nectar resource diversity is highly correlated with floral species richness and
particularly with the species richness of annuals. In addition, nectar resource
diversity is highly correlated with bee diversity, which illustrates the impor-
tance of this parameter in determining the flower-visitor web structure in
Mediterranean communities. This is a key finding in view of the manage-
ment of these communities, demonstrating the importance of mosaic structure
