How does timing of flowering affect competition for pollinators, flower visitation and seed set in an early spring grassland plant?

Knowledge on how the timing of flowering is related to plant fitness and
species interactions is crucial to understand consequences of phenological
shifts as they occur under climate change. Early flowering plants may face
advantages of low competition for pollinators and disadvantages of low
pollinator abundances and unfavourable weather conditions. However, it is
unknown how this trade-off changes over the season and how the timing
affects reproductive success. On eight grasslands we recorded
intra-seasonal changes in pollinators, co-flowering plants, weather
conditions, flower visitation rates, floral longevity and seed set of
Pulsatilla vulgaris. Although bee abundances and the number of
pollinator-suitable hours were low at the beginning of the season, early
flowers of P. vulgaris received higher flower visitation rates and
estimated total number of bee visits than later flowers, which was
positively related to seed set. Flower visitation rates decreased over
time and with increasing number of co-flowering plants, which competed
with P. vulgaris for pollinators. Low interspecific competition for
pollinators seems to be a major driver for early flowering dates. Thus,
non-synchronous temporal shifts of co-flowering plants as they may occur
under climate warming can be expected to strongly affect plant-pollinator
interactions and the fitness of the involved plants.