Factors Limiting Fecundity and Germination in Small Populations of Silene regia (Caryophyllaceae), a Rare Hummingbird-pollinated Prairie Forb

Abstract

-The prairie forb Silene regia is restricted to small isolated populations in the eastern part of its range. I examined factors that limit fecundity and germination in these small populations. Although S. regia flowers rarely self due to dichogamy, geitonogamous crosses demonstrated self-compatibility. Substantial fruit production required pollination by ruby-throated hummingbirds (Archilochus colubris). Exclusion of hummingbirds (but not most insects) sharply reduced fruit production and seed numbers. Resource competition within individual inflorescences limited percent fruit set in some populations in certain years. Clipping of neighboring vegetation and watering S. regia did not increase reproductive output significantly. Silene regia seedings emerged at low rates (<5%) in field experiments, but field emergence increased twoto three-fold with soil disturbance and burning. Natural recruitment of seedlings occurred only in burned sites. Of all factors examined, burning had the greatest positive effects on reproductive output. In addition, controlling for the effects of burning, reproductive output was greater for plants in larger than smaller populations. By increasing fecundity and recruitment, prescribed burning can be used to expand population sizes of Silene regia.