Abstract:

Flowering date along with interactions of other co-flowering species may be factors that determine pollination and reproductive success of a focal plant species. We investigated an alpine bumblebee-pollinated herb Pedicularis gruina to assess the effects of flowering date and co-flowering species on pollination, reproduction, and predation over a three year period (2003-2005). We analyzed pollen load of bumblebees to determine floral constancy, and calculated pollination rates of flowers, fruit set, seed production per capsule and the percentage of seed predation. We found that fruit sets did not differ significantly among years and between different flowering dates when there were no co-flowering species, with 34-38% of flowers producing fruits. However, the presence of co-flowering species could either increase or decrease the pollination and reproduction in P. gruina, which depends on pollinator type and flowering date of the co-flowering species P. densispica. Pedicularis densispica enhanced pollination and reproduction through increased floral resource diversity, whearas P. siphonantha enhanced pollination and reproduction through increased attractiveness with larger displays. Flowering date did not affect fruit set, but significantly affected seed production and seed predation. Seed production decreased significantly at later flowering dates given the same pollination condition(i.e., no co-flowering species, pollinator competition, or facilitative pollination). However, fruits produced in early flowering periods suffered more severe seed predation compared to those in later flowering periods.

Key words: facilitative pollination, flowering date, pollinator competition, Pedicularis gruina, reproductive success