Biology Reference
In-Depth Information
in differences in nectar volume, concentration, chemistry, and time of secre-
tion, in addition to the constraints on availability to different pollinators
owing to flower structure. Strong correlations have been found between nec-
tar volume and floral biomass, because nectar production increases with
nectary size (Opler, 1983; Szabo, 1984; Galetto & Bernardello, 2004), al-
though photosynthetic input from other parts of the plant is also an important
factor in nectar production (Pacini & Nepi, 2007, Chapter 4 in this volume)
Similarly, daily sugar production per flower is correlated with the body size
and energetic requirements of pollinators (Brown et al., 1978). Flowers must
meet high energy demands if their pollinators are endothermic, and if they
forage expensively by hovering. Figure 1 gives an indication of the huge dif-
ferences in nectar volumes offered to different consumers, using the data
collected in Costa Rica by Opler (1983), but does not take into account dif-
ferences in concentration, which also determine energy rewards.
The energy that animals gain from nectar must exceed the cost of acquiring
it, which includes the time to handle flowers and the time to travel between
them. The relationship between the energy reward provided and the energy
requirements of the visitor determines the extent of movement between
flowers and plants (Heinrich, 1975). It is generally assumed that competition
Figure 1.
Maximum nectar production (µl) for various pollinator classes, roughly in order of
increasing body size. Values are means ± SE (
note log scales
).
Hatched bars
indicate endo-
thermic animals. No data for flies. (From Opler, 1983.)
