[Pollinator] ARTICLE: Pollinator-mediated mechanisms for increased reproductive success in early flowering plants [Echinacea] (Oikos 2018)

[De Angelis, Patricia]

NOTE: ECHINACEA ANGUSTIFOLIA is an early flowering species native to the
tallgrass prairie and North American Great Plains, which is among the most
endangered habitats in the world [NSF 2014
<https://nsf.gov/discoveries/disc_summ.jsp?cntn_id=130338>]. This species
was chosen as the focal species for this research because 1) information
about its pollination and flowering biology exists; and 2) its reproduction
is known to decrease with habitat fragmentation. Considered to be one of
the best perennial flowers for bees, Over 26 pollinator species visit this
plant and yet isolated plants are consistently pollinator limited. This
research explores how three aspects of "pollinator services" change over
the season: which pollinator species are visiting? how many visits each
taxon makes? and how much pollen is transferred within the same plant
species?

POLLINATOR-MEDIATED MECHANISMS FOR INCREASED REPRODUCTIVE SUCCESS IN EARLY
FLOWERING PLANTS
By: Jennifer L. Ison, Leah J. Prescott, Scott W. Nordstrom, Amy Waananen
and Stuart Wagenius
Oikos 00: 1–13, 2018

ABSTRACT
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 (hereafter Echinacea) 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.
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