Biology Reference
In-Depth Information
In Medicago sativa , reabsorbed sugars can be found in roots and leaves
(Pedersen et al., 1958).
We do not know if soluble substances in nectar are reabsorbed simulta-
neously or at different times. The molecular weight and chemical nature of
the substances may influence the temporal pattern of reabsorption.
3.2
Nectar standing crop
Different environmental parameters, dynamics of nectar production and re-
absorption, animal foraging activity, and their interactions contribute to
nectar standing crop. This can be considered the recent and current interac-
tion between a population of flowers, a population of foragers and environ-
mental parameters such as temperature and relative humidity (RH) (Corbet,
2003).
Nectar standing crop is defined by Kearns and Inouye (1993) as the
“quantity and distribution of nectar determined by randomly sampling flow-
ers, that have not been protected from pollinators by bagging, at a given
moment”. From the ecological point of view this parameter is fundamental;
in fact, there is a reciprocal dependent relationship between the nectar stand-
ing crop and animal visits: the foraging behaviour of visiting animals is
affected by standing crop, which is in turn affected by animal activity. The
distribution of the standing crop within a plant or within a population may
show some spatial patterning (Kearns & Inouye, 1993 and references
therein; Corbet, 2003 and references therein). Nectar standing crop was
patchily distributed within individual plants of two boraginaceous species,
Anchusa strigosa (Shmida & Kadmon, 1991) and Echium vulgare (Leiss &
Klinkhamer, 2005a). This implies that nectar volumes of neighbouring flow-
ers were positively correlated with each other and that differences in volume
of nectar between pairs of neighbouring flowers were significantly higher
than differences between flowers of the same pair. Because there is evidence
that foragers may selectively visit the more rewarding flowers (Corbet et al.,
1984; Kadmon, 1992), the spatial patterning of the standing crop has a great
influence on pollinator foraging movements among flowers of a plant or
among plants of the same population (Kearns & Inouye, 1993; Corbet,
2003). Shmida and Kadmon (1991) discussed the effect of within-plant
patchiness in nectar standing crop on the foraging behaviour of pollinators.
They argued that if nectar is patchily distributed within plants, foragers en-
countering nectar-rich flowers will move to neighbouring flowers, while
foragers encountering nectar-poor flowers will move longer distances in or-
der to avoid visits to neighbouring flowers. Under such circumstances the
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