MULTIYEAR STUDY OF POLLEN LIMITATION AND COST OF REPRODUCTION IN THE ITEROPAROUS SILENE VIRGINICA

E-ISSN： 1939-9170|78|2|484-493

ISSN： 0012-9658

Source： Ecology, Vol.78, Iss.2, 1997-03, pp. : 484-493

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Abstract

We investigated whether pollen deposited onto stigmas limited female reproductive success in the hummingbird‐pollinated, short‐lived, iteroparous, Silene virginica (Caryophyllaceae). The study was conducted over a 4‐yr span in a population occurring in a woodland area and over a 3‐yr span in a second population occurring in a nearby open meadow. We contrasted average fruit set, seed set per fruit, and total annual seed production (in only the woodland site) between open‐pollinated control plants and hand‐pollinated experimental plants. We also followed surviving individuals in subsequent years and repeated the same treatments on plants when they flowered. All plants were monitored annually for survival and reproduction at both sites; growth was monitored at only the woodland site because of extensive herbivory in the meadow population.Lack of pollen deposited onto stigmas significantly limited reproductive potential at the level of percentage fruit set throughout the study for both sites. In contrast, pollen deposition onto stigmas exhibited considerable site and year heterogeneity in its effect on seed production per fruit. In the cumulative test of pollen limitation, however, we detected no difference between total annual seed production between our open‐pollinated control and hand‐pollinated experimental plants in the woodland site during the 4‐yr study. A weak negative trend was detected between fruit set per plant and average seed set per fruit among all plants in the woodland site, suggesting a limited role for an intraplant compensation mechanism. No significant trade‐off was detected in probability of survival and flowering between the control and hand‐pollinated experimental treatment groups at either site. In addition, no cost was detected in future growth and reproduction in the woodland population. Similar total seed production among individuals in the two treatment groups explains in part, why no difference was observed in future survival, growth, and reproduction between the control and hand‐pollinated treatment groups.