Data from: Pollinator-mediated mechanisms for increased reproductive success in early flowering plants

Mating activities change within a season in many animal and plant
populations. In plants, selection towards early flowering is commonly
observed. Pollinator-mediated selection is hypothesized to be a pervasive
evolutionary force acting directionally on flowering time. However,
pollinator-mediated mechanisms have rarely been tested in realistic field
conditions, especially in perennial plants visited by a diversity of
generalist insect pollinators. We examined pollinator visitation in eight
Echinacea angustifolia populations in western Minnesota, USA, to gauge the
potential for pollinator-mediated selection. Echinacea is a common prairie
perennial that persists in isolated remnant populations. Echinacea is
self-incompatible and is pollinated by a diversity of generalist solitary
bees. A previous study found that early flowering Echinacea plants have
higher seed set and their reproduction is less pollen-limited than late
flowering plants. Twelve times throughout a flowering season, we
quantified pollinator visitation rates and pollinator community
composition. In three sites, we also estimated the quality of pollinator
visits by examining the composition of pollinators’ pollen loads brought
to Echinacea plants. We found that three aspects of pollination
dramatically decreased over the course of the flowering season. (1)
Pollinators visited early flowering plants more frequently than late
flowering plants. (2) The pollinator community was also less diverse late
in the flowering season and became dominated by a single species of small
bee, Augochlorella aurata. (3) Pollinators visiting Echinacea late in the
season carried proportionally less conspecific pollen compared to
pollinators visiting Echinacea early in the flowering season.
Understanding within-season dynamics of pollination helps predict the
prevalence of inbreeding, phenological assortative mating, and
reproductive failure, especially in fragmented plant populations.