O. Totland et al., VARIATION IN POLLEN LIMITATION AMONG PLANTS AND PHENOTYPIC SELECTION ON FLORAL TRAITS IN AN EARLY-SPRING FLOWERING HERB, Oikos, 82(3), 1998, pp. 491-501
Female reproductive success in animal pollinated plants may be limited
by the amount of suitable pollen that reaches stigmas, but little kno
wledge exists on how the extent of pollen limitation varies among plan
ts of the same population. Here we ask; (1) if there is pollen limitat
ion at the whole population level in a Norwegian population of an earl
y spring blooming herb, Crocus vernus, (2) if so, if a variation in po
llen limitation exists among plants, (3) over which plant traits this
variation occurs, and (4) if there is phenotypic selection on plant tr
aits caused by pollen limitation. Pollen limitation on seed number and
seed:ovule ratio occurred at the whole population level. By measuring
flowering time, plant size, and various aspects of floral display on
both supplementary hand-pollinated plants and control plants, we found
a significant relationship between reproductive success and petal siz
e in the control plants, but not in plants that received additional po
llen. Reproductive success of plants with white stigmas were more poll
en limited than that in orange-stigma plants. It is likely that plants
with small petals and white stigmas have lower chances of being recog
nised by pollinators (Apis mellifera), and that this causes the pollen
limitation on reproductive success in such plants. Multivariate selec
tion analyses showed significant linear selection on petal size in con
trol plants, but not in extra-pollinated plants, suggesting pollinator
mediated selection on petal size.