Large floral displays increase self-pollination but do not affect visitation rates in Clarkia concinna

Optimal floral display (the number of simultaneously open flowers) is
frequently viewed as a balance between pollinator attraction and avoidance
of pollinator-mediated interfloral selfing (geitonogamy). However, the
most beneficial display size may be affected by pollinator abundance,
pollinator identity, and other environmental variables. We determined the
effects of individual floral display and patch size on pollination
outcomes in natural populations of a mixed-mating annual plant, Clarkia
concinna. We predicted that individual plants with larger floral displays
would have both greater pollinator visitation and more geitonogamy.
Additionally, we tested whether the effects of floral display would be
greater in smaller patches of plants. Larger individual floral displays
increased total geitonogamy, but the effect of display on geitonogamy
differed among pollinator taxa. Visitation rates were lower in small
patches for some pollinators. However, individual display size did not
affect per flower visitation rate in small or large patches. Therefore, if
we only consider the expected tradeoff between pollinator attraction and
geitonogamy, the number of simultaneously open flowers appears excessive.
In this species, large floral display size requires explanations beyond
increased pollinator attraction, such as temporal constraints on flowering
imposed by a limited growing season and the benefits of additional
low-quality offspring.