Biology Reference
In-Depth Information
Figure 1.
Viscosity of sucrose solutions plotted against temperature and concentration, using
equation from Mathlouthi and Génotelle (1995).
flower handling. They also questioned the applicability of models to the low
nectar volumes generally available in hummingbird flowers.
Viscosity relationships in nectar may not be as simple as in pure solu-
tions. Sucrose solutions are more viscous than hexose solutions containing
the same weight of sugar, and the difference increases with concentration
(Weast, 1980). Values for mixtures are likely to be intermediate between
those for the pure sugars (Heyneman, 1983). Using capillary descent times,
Heyneman (1983) measured viscosities of various hummingbird nectars, ob-
taining higher values than for equivalent sugar solutions, and she attributed
the discrepancy to the presence of non-sugar solutes. These effects are not
easily predicted and empirical data are not available. It is possible that varia-
tions in nectar composition, including the presence of oligosaccharides, may
lead to unexpected viscosities. Occasionally, high molecular weight poly-
mers result in a jelly-like consistency in the nectar of vertebrate-pollinated
flowers (Johnson et al., 2001; Sazima et al., 2001).
