Plant Reproduction and Optimal Foraging: Experimental Nectar Manipulations in Delphinium Nelsonii

Abstract

Delphinium nelsonii Greene (Ranunculaceae) individuals which were watered produced significantly more nectar per flower than did control individuals. The watered plants also set significantly more seeds per flower than did the controls. Hand pollinations suggest that the seed set difference was due to the increased nectar volume rather than to watering directly. Bumblebee pollinators' responses to the increased standing crop of reward were consistent with predictions from optimal foraging theory and explain the increase in seed set. Pollinators both visited more flowers per inflorescence and spent more time in flowers on nectar-rich plants relative to controls. These results imply that D. nelsonii individuals could increase the female component (i.e. seed set) of plant fitness by increasing their nectar production rate. The results do not, however, allow an accurate assessment of the male component (i.e., pollen donation) of fitness.