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

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