The showy invasive plant Ranunculus ficaria facilitates pollinator activity, pollen deposition, but not always seed production for two native spring ephemeral plants

Abstract

Showy invasive plants can reduce pollinator visitation to native plants, resulting in a reduction of seed-set in insect-pollinated species. Seed set in native plants may also be reduced due to the presence of foreign pollen. Alternatively, additional floral resources provided by invasive plants may increase pollinator activity, and facilitate pollination of native species. Ranunculus ficaria is a perennial herb invading deciduous forests of the eastern United States. It produces many showy flowers that may influence pollinator activity in heavily invaded habitats. We compared pollinator visitation rates, stigma pollen loads, and seed production of two sympatrically flowering, entomophilous native species (Claytonia virginica and Cardamine concatenata) between habitats invaded by R. ficaria and uninvaded habitats. We found significantly higher pollinator activity (visits to plots) in invaded plots. We also found significantly higher per flower visitation rates to C. virginica in invaded plots. Claytonia virginica stigmas from invaded habitats had more conspecific pollen resulting in more seeds per capsule in invaded areas. There was more conspecific pollen on C. concatenata stigmas in invaded compared to uninvaded habitats, but there were significantly more seeds per silique in uninvaded habitats. Our results indicated that this invasive species increases pollinator activity and conspecific pollen deposition on sympatrically flowering native ephemerals, but may have differential effects on native seed production. Management options should consider the facilitative effects of this species on pollination services, as well as the possible negative competitive effects.