The vast majority of flowering plants rely on pollinators for outcrossed reproduction. Unfortunately, many species of pollinators are in decline. Pollinators face a number of challenges, including shifting land use, climate change and pesticides. In addition, pollinator habitat may be altered or eliminated through urbanization. Fragmented urban landscapes may lengthen the distances among foraging patches, limit resources in a given patch, and reduce the availability of pollinator nesting sites. Here, I examine the effects of urbanization on pollination services by addressing the following questions: (1) Does bee species richness and/or abundance change along an urbanization gradient?; (2) Does the pollen limitation of a focal species vary along the same gradient?; (3) Do plants with a mixed mating system produce more selfed seeds in more urban environments? Using the percentage of impervious land cover in the space immediately surrounding the site as a proxy for site urbanization, 15 study sites were set up across the city of Ottawa to span a range from minimal percent impervious surface (mostly green space) to mostly impervious surface (little green space) at a range of spatial scales. At each site I set up an array of 20 potted Impatiens capensis plants as well as six pan traps in order to collect data on pollen limitation, seed production, and the number of selfed progeny, in addition to information about local pollinator species richness and abundance. Plants in the arrays were randomly assigned to either a hand or open pollination treatment in order to assess the level of pollen limitation. Surprisingly, pollinator species richness and abundance were not correlated with urbanization. Pollen limitation declined with urbanization, however, so did overall seed set, making it difficult to detangle the effects of resource limitation and hand pollination treatments. The number of selfed seeds produced by a plant was also significantly correlated with site urbanization. Further investigation is required to better understand the dynamics of pollination services in urban environments. I recommend that future studies explore how the presence of individual bee species in rural and urban habitats could be influencing pollen limitation and selfing in I. capensis.

While pollinators and leaf herbivores have been a focus of research for decades, floral antagonists have been studied significantly less. Since floral antagonists can be as common as leaf herbivores and have strong impacts on plant reproduction, it is important to understand the role of floral antagonists in the ecology and evolution of flowers. I conducted four experiments to better understand the relationship between plants, floral traits, floral antagonists, and other plant-insect interactions. First, I manipulated resources (light and soil nutrients) that are known to have impacts on plants and floral traits to test how they affect floral antagonists and other plant-insect interactions. Plentiful resources increased the proportion of floral antagonists to visit flowers, but also increase tolerance of floral antagonists. Second, I manipulated flower bud gallers, a species-specific floral herbivore that destroys flowers, to test how it affected other plant-insect interactions, floral traits, and plant reproduction. Plants with flower bud gallers tended to have more pollinator visits, but this effect is due to a shared preference by gallers and pollinators for similar plants. Third, I manipulated florivory to examine how it affects subsequent plant-arthropod interactions, floral traits, and plant reproduction. Florivory had systemic effects on other plant-insect interactions, including leaf herbivores, and shifted the plant mating system towards more selfing. Additionally, I tested how several floral antagonists respond to floral attractive and defense traits to understand which floral traits are important in mediating antagonisms. Finally, I manipulated florivory, pollination, and nectar robbing to test for effects of multiple floral interactions on subsequent plant-insect interactions, floral traits, and plant reproduction. There were significant many-way interactions between the three treatments on subsequent plant-insect interactions and reproduction, indicating that the effect of one interaction depends on what other interactions are present. Understanding the role that floral antagonists play in plant ecology can help scientists determine which interactions are most important, and may help determine why some floral traits exist in their current state. Together, this work represents some of the most comprehensive research on the community consequences of floral antagonists, as well as the interplay between floral traits and floral interactions.