Resource partitioning by color in a tropical hummingbird

Abstract

Many nectar-feeding animals use cues (floral signals) to locate, identify, and discriminate between floral resources. Whether competing pollinators can use cues to partition resources, however, has received little attention despite examples of pollinators differing in resource use. We examined whether sexes of the purple-throated carib hummingbird, Anthracothorax jugularis, partition artificial nectar sources (feeders) by color (red or yellow) or position (left or right), and whether such partitioning changes in response to changes in nectar reward. At equal nectar concentrations, sexes partitioned resources by color, but when one of the colors was reduced in quality, dominant males visited the more rewarding color, although they did not completely displace subordinate females. The position of the feeder had no effect on resource partitioning, and in the absence of color cues, male and female hummingbirds did not partition feeders. Our results differ from earlier studies where hummingbirds responded more to position than to color. We suggest that this difference may result from defense of patches as opposed to choice of individual food items as well as from differences between temperate and tropical hummingbird-plant communities in floral colors. Hummingbird-pollinated plants in many temperate communities converge on red flowers, which may eliminate color as a cue for resource partitioning, whereas the availability of plant species differing in floral color and pattern may provide tropical nectarivores with cues for resource subdivision. Our results have major implications for the evolution of species diversity. Because plants and pollinators may reciprocally affect each other’s evolution, partitioning of floral resources by color may not only affect traits of pollinators but also may maintain and drive the diversification of floral colors and other floral traits.