Biology Reference
In-Depth Information
be influenced by soil conditions (cf. also Shuel, 1952, 1955; Shuel & Shivas,
1953), which may alter nectar attractiveness, and therefore have important
implications at the plant-pollinator interface.
3.6
Ecological succession
Time is an important parameter in the framework of pollination ecology and
several nectar secretion attributes appear to depend on flowering time, at
least within a genetically related group of plants. Among all attributes
Petanidou et al. (2000) studied in the Lamiaceae, only nectar concentration
seemed to increase with flowering time, whereas the majority of attributes
were affected negatively—flower depth and corolla width, the size of the
nectary and its stomata, as well as the volume and sugar content of the nectar.
There is evidence that nectar secretion changes with time, not only in the
course of the flowering season, but also within ecological time. A very inter-
esting case is the change of nectar yield that some plants show in the course
of post-fire succession in Mediterranean habitats (Petanidou & Ellis, 1996;
Petanidou, 1999; Potts et al., 2003).
Firstly, this change may be a consequence of changes in the community
structure, with annuals being gradually replaced by perennials as the system
ages, combined with the fact that perennials bear more alluring flowers (i.e.,
more nectar-rewarding) than annuals (Petanidou & Smets, 1995; Petanidou,
1999). Potts et al. (2003) quantified some key parameters of both pollen and
nectar forage at the community level in different ages of post-fire communi-
ties and showed that changes in floral reward structure reflected the general
shift from annuals (generally low-reward open-access flowers) to perennials
(mostly high-reward and restricted access flowers) as post-fire regeneration
ensues. In particular, the authors found that nectar volume, water content,
concentration, and the diversity of nectar-foraging niches are all greatest in
the first post-fire stage of succession, i.e., immediately after fire, with a steady
decrease as regeneration proceeds (Table 3). This is slightly different to what
Petanidou and Ellis (1996) suggested—relatively low per-flower nectar
quantity in the first post fire years. A similar decline with ecosystem age af-
ter fire was found in energy availability in nectar and pollen, and the relative
importance of pollen to nectar energy (Potts et al., 2003).
Secondly, within the core of the main flowering season, perennials are
much more competitive than annuals, the latter offering about half the nectar
yield of the former (as per day sugar equivalent) (Petanidou & Smets, 1995;
Petanidou & Ellis, 1996).
