Biology Reference
In-Depth Information
Thirdly, and most surprising, is the fact that some perennial plants may
increase their nectar secretion during the mature phryganic stage whereas
annuals/biennials may experience reduced secretion in the course of succes-
sion in Mediterranean communities (e.g.,
Capparis spinosa
,
Phlomis
fruticosa
, and
Stachys cretica
versus
Lamium amplexicaule
and
Salvia ver-
benaca
; Petanidou, 1999). Comparing the nectar standing crop of
Satureja
thymbra
in burnt and unburnt areas in Israel, Potts et al. (2001) found similar
results, with nectar standing crops two times higher in unburnt than in burnt
habitats. As a result, in the course of ecosystem succession, perennials may
become more attractive to bees and to other pollinating insects than annuals
within the community, thus promoting their fitness through differential seed
set. The conclusion drawn from all the above studies is that floral communi-
ties and associated rewards not only shape pollinator community structure,
but also have significant implications for the process of succession.
4
MATCHING NECTARS AND FLOWER TYPES
High-volume nectars have generally been associated with deep and tubular
flowers because of their smaller surface:volume ratio, which diminishes wa-
ter loss through evaporation (Corbet et al., 1979; Plowright, 1987; Dafni,
1991). Freely exposed nectar in open flowers tends to equilibrate with ambi-
ent humidity (Corbet et al., 1979; Nicolson, 1998, 2002). Similarly, nectar
concentration is more constant in deep flowers compared to open ones,
which contain smaller volumes of nectar where concentration can fluctuate
rapidly (Corbet, 2003).
These principles apply equally to the Mediterranean
phrygana
, where
nectar volume is found to be positively correlated with flower depth (R =
0.312, P < 0.01), whereas nectar concentration shows a negative association
(R = -0.485, P < 0.000) (Petanidou & Smets, 1995; Petanidou, 2005). Both
floral depth and nectar volume are highly related to sucrose/hexose ratios in
nectar at the community level (R = 0.441, R = 0.426, respectively; P < 0.001;
Petanidou, 2005). One can conlude that the
phrygana
community is made up
of two major sets of flower types and nectars (although intermediate values
do exist): deep flowers with high, albeit dilute, volumes of sucrose-dominant
to sucrose-rich nectars (such flowers may act as “nectar reservoirs” by slow-
ing the rate of sucrose breakdown); and shallow or open flowers with less
volume but more concentrated, hexose-rich nectars (Petanidou, 2005).
Among all the
phrygana
plant families, the Lamiaceae have the highest
average nectar yield per flower and Asteraceae the lowest (Petanidou & Smets,
