Many plant species have floral morphologies that restrict access to floral resources, such as pollen or nectar, and only a subset of floral visitors can perform the handling behaviours required to extract restricted resources. Due to the time and energy required to extract resources from morphologically complex flowers, these plant species potentially compete for pollinators with co-flowering plants that have more easily accessible resources. A widespread floral mechanism restricting access to pollen is the presence of tubular anthers that open through small pores or slits (poricidal anthers). Some bees have evolved the capacity to remove pollen from poricidal anthers using vibrations, giving rise to the phenomenon of buzz-pollination. These bee vibrations that are produced for pollen extraction are presumably energetically costly, and to date, few studies have investigated whether buzz-pollinated flowers may be at a disadvantage when competing for pollinators’ attention with plant species that present unrestricted pollen resources. Here, we studied Cyanella hyacinthoides (Tecophilaeaceae), a geophyte with poricidal anthers in the hyperdiverse Cape Floristic Region of South Africa, to assess how the composition and relative abundance of flowers with easily accessible pollen affect bee visitation to a buzz-pollinated plant. We found that the number of pollinator species was not influenced by community composition. However, visitation rates to C. hyacinthoides were reduced when the relative abundances of flowers with more accessible resources were high. Visitation rates were strongly associated with petal colour, showing that flower colour is important in mediating these interactions. We conclude that buzz-pollinated plants might be at a competitive disadvantage when many easily accessible pollen sources are available, particularly when competitor species share its floral signals.

Buzz pollination interactions were studied in the Cederberg, South Africa. Pollinator observations were conducted in three sites in September and October 2019. Each site was sampled twice, and enough time was allowed between sampling sessions to cause changes in plant community composition. Plant-pollinator interactions were observed in 20-minute intervals. Multiple observation sessions were conducted at each site. Further, plant densities were recorded in multiple random 2x2m plots at each site.

The excel file contains two spreadsheets. The first sheet contains plant density data per site (measured as flowers per square meter) of all the plant species that offered pollen as reward. The second spreadsheet contains the plant-pollinator interactions between all bees and pollen-offering plant species for each site (units = 1000 visits per flower per 20-minutes).