Nectar is the most common floral reward produced by angiosperms, but little is known about the effect of nectar production rate on pollination success. This investigation will focus on this relationship for the hummingbird-pollinated monacarpic plant Ipomopsis aggregata. The primary question of the study involves the overall effect of nectar production rate on fitness: 1) Do plants with higher nectar production rates have greater pollination success? Preliminary field evidence indicates that this does occur (at least for male function pollination success), so study of the causal mechanisms of this effect will be profitable. This question will answered by: 2) How does NPR affect standing crop? 3) How does standing crop affect visitation behavior? 4) How does visitation behavior affect pollination success? The study will investigate these questions with a variety of mutually reinforcing approaches, including computer simulation, observation of the effects of natural variation in NPR, and manipulative experiments in the field and aviary. Estimates of the effect of each mechanism in isolation can be combined to produce an estimate of pollination success that can be compared with benchmark values from Question 1, testing the adequacy of the mechanisms proposed. The research will increase understanding, not only of the fitness consequences of variation in NPR, but the mechanisms through which such effects may be expressed.
