Variation in the pollinator community visiting invasive Cytisus scoparius L. Link (Fabaceae) along an elevation gradient

Abstract

Invasive plants are a novel resource for the resident pollinator community, but may not be able to successfully attract pollinators if they have a specialized pollination system or restrictive floral morphology. Pollinator limitation may limit invasion success, but a plant able to attract many pollinators in different conditions will be a successful invasive species. In this study, we measured the pollinator community by capturing pollinators at several timepoints during the flowering season. Captures were made at six field sites along an elevation gradient. Measurements were specific to an invasive shrub with very low self-compatibility and a restrictive floral morphology, Cytisus scoparius (Scotch broom). We found that the pollinator community varies along an elevation gradient, having more Apis mellifera at low elevation sites and more Bombus spp., especially Bombus sitkensis at higher elevations. We saw different higher pollination rates, but lower seed set at higher elevation sites. Although C. scoparius has been able to attract a variety of pollinators, pollen robbing by one species may result in decreased plant fitness.