Flower colour and visitation rates of Costus arabicus support the \"bee avoidance\" hypothesis for red-reflecting hummingbird-pollinated flowers

Floral colour mediates plant–pollinator interactions by often signalling floral resources. In this sense, hummingbird-pollinated flowers are frequently red-coloured, and there are two tentative hypotheses to explain this pattern: 1. hummingbirds are attracted to red due its easier detection and 2. bees are sensorially excluded from red flowers. The second hypothesis is based on bees’ red colour blindness, which lead them to be less frequent and less important than hummingbirds as pollinators of red-reflecting flowers. Here, we untangled the role of different flower traits mediating plant–pollinator interactions and empirically tested the above hypotheses. We chose Costus arabicus due to its synchronopatric white- and pink-flowered individuals and its bee and hummingbird pollination system. Although pink flowers are not totally achromatic as pure red ones, they show an achromaticity degree that could drive bee exclusion. Specifically, we tested whether differences on red reflectance work...