Data from: Is bee-avoidance by bird-pollinated flowers driven by nectar robbing in Erica?

Nectar robbing (consuming nectar from a perforated flower without pollinating) generally negatively affects plant fecundity, and plants exhibit multiple mechanisms in defence. The colour of bird-pollinated flowers that are prone to robbing by bees may consequently be explained by the bee-avoidance hypothesis, proposing that bird-pollinated flowers are less visible to bees than bee-pollinated flowers. This visual avoidance mechanism may co-occur with mechanical avoidance mechanisms; however, flower conspicuousness has not yet been related to nectar robbing rates across multiple species using a combination of comparative methods and field observations. To test the bee-avoidance hypothesis, we quantified conspicuousness and flower visitor rates in multiple congeneric ornithophilous and entomophilous Erica species from South Africa. Visual modelling and Phylogenetic Generalised Least Squares analyses of spectral reflectance of 33 ornithophilous and 31 entomophilous species revealed that bird-pollinated flowers were less conspicuous (relative to their leaf background) to honeybees than insect-pollinated flowers, but equally conspicuous to birds, supporting the bee-avoidance hypothesis. However, natural nectar robbing rates in 27 populations of bird-pollinated species were unrelated to conspicuousness to bees, and pollination rates were unrelated to conspicuousness to birds. Finally, the conspicuousness of bird-pollinated flowers to bees and birds was unrelated to mechanical traits associated with nectar robbing (variation in corolla length, corolla aperture diameter, sepal size, or corolla stickiness). These results suggest that nectar-robbing bees may have influenced the evolution of flower colour of sunbird-pollinated species, although the maintenance of this trait appears decoupled from current robbing pressure.