Multiple Interactions and Plant Reproduction: The Intersection of Herbivore, Pollinator, and Plant-Plant Interactions

Plants interact with a variety of organisms. Both positive and negative interactions exist between plants and other plant species as well as animals. Because these plants and animals exist in communities simultaneously, these interactions will in turn interact. In this dissertation, I examine both the costs and benefits of interactions between plants, herbivores, pollinators, and other plants and how these interactions impact plant reproduction. To start I synthesize the literature on herbivore-pollinator interactions, followed by updating a meta-analysis on the same topic. I then examine both direct and indirect interactions between shrubs and the surrounding desert annual plant community before testing how the same shrub benefactor can change the impact of pollination and herbivory on the reproductive output of one of its proteges. I found that plant reproductive output was dependent on all three types of interactions (pollination, herbivory, and plant-plant interactions) to varying degrees. I compared damage to different types of plant tissues in the literature as well as in the field using artificial damage. I found that damage to flowers and leaves generally decreased plant reproductive output in the literature, but that the relationship was more complex in the field, depending on the presence of other factors. While the interaction between both types of damage were not commonly studied in the literature, I found that applying both types of damage was required to consistently observe decreases in reproduction in response to damage. When testing the effects of shrubs on annuals, shrubs had a mixed effect on plant species density and floral density that depended on annual species identity. Indirect effects of shrubs through the plant community were more consistent between protege species. However, when examining individual plants (as opposed to populations or communities) of one species that was associated with the shrub species in an experimental setting, facilitation was only observed in the presence of damage. I show that herbivory is integral in driving the coevolution between plants and pollinators as well as facilitators and their proteges.