An assessment of the potential for pollination facilitation of a rare plant by common plants: Symphyotrichum sericeum (Asteraceae) as a case study

Abstract

Pollination facilitation can occur when plant species share pollinators. Whether facilitation occurs depends on the flowering period overlap (synchrony), number of shared insect visitors (similarity), quantity and quality of insect visits, and the subsequent impact on seed production. Western Silvery Aster (Symphyotrichum sericeum (Vent.) G.L. Nesom) is a rare, self-incompatible plant visited by a wide range of generalist insect species. There are 22 common plant species that may facilitate insect visitation to the rare plant by supporting shared pollinators. Plant species with low synchrony and high similarity with S. sericeum are potential facilitators. In contrast, plant species with high synchrony and similarity likely act as competitors as the aggregative response to increasing plant density was saturating, suggesting that synchronously flowering species do not increase insect visitations. Hymenoptera responded more strongly than Diptera to increases in flowering stem density. These data suggest that facilitation of insect visitation between plant species via a numerical response that extends the flower season is possible but not likely via an aggregative response. Restoration of S. sericeum may therefore be more successful if potentially facilitating plants are grown with it; further testing of the impact of potential facilitators on seed production in S. sericeum is required.