Within-Species Variation in Hawkmoth Foraging Behavior: Patterns, Causes, and Consequences

Abstract

Within-species variation is ubiquitous in nature and can have large consequences for both ecological and evolutionary processes. The major drivers of this variation, as well as their consequences, remain poorly understood for some interaction types. This is especially true in plant-pollinator mutualisms, where intraspecific variation in pollinator behavior has only been minimally studied. As many plants rely heavily on animal pollen vectors for their reproduction within-species variation has the potential to have large consequences for plant fitness. My dissertation focuses on intraspecific variation in the behavior of nectar-foraging hawkmoths, especially variation associated with sex. To examine this variation, I have used a variety of methods including literature reviews (Appendix A), long-term field observations (Appendices C and D), behavioral experiments (Appendices B and C) and experimental physiology (Appendix C). First, I show that sex is associated with large, discrete, and predictable variation in foraging behavior across all major pollinating taxa (Appendix A). In particular, female pollinators frequently gather more and different resources from flowers based on the requirements associated with offspring provisioning, while males frequently show more mobile and dispersive foraging patterns. These general patterns, however, emerge primarily from work on bees, and very rarely assess the consequences of these differences for visited plants. Second, I show that female hawkmoths show strong links between their nectaring and oviposition behavior (Appendix B). These links can have large consequences on their foraging choices, to the point that females may lay eggs on inferior larval hosts if those hosts offer nectar rewards. Third, I show that males and females of the hawkmoth Hyles lineata vary extensively and consistently in their foraging behavior in the field over five years, such that females carry larger and more species rich pollen loads than do males (Appendix C). This difference does not appear to be due to differences in floral fidelity, as wild-foraging males and females did not differ in their rate of switching between floral resources. Males do, however, invest more heavily into their flight apparatus and have higher flight endurance in the lab than females; males may therefore be bypassing resources in nature as they fly long distances looking for females. Finally, I show that individuals vary extensively in their diet breadths below the species level in several hawkmoth species (Appendix D). Across species, individuals carried pollen loads with similar species richness, but species evenness was lower for the specialist species than for the generalist. Together, these results demonstrate the importance and magnitude of variation below the species level in pollinator behavior, and highlight the need for further study across species to understand its impacts on plant-pollinator communities.