Pollinator species distributions and interaction networks across local environmental gradients to continental scales

Insect pollinator species are critical for angiosperm reproduction and maintenance of human food crop populations. Insect pollination networks are complex webs of overlapping links, and mutualistic associations between these pollinators and their host plants are imperative for network stability and robustness in the face of ecosystem perturbation. Even slight changes in the structure of mutualistic associations can affect the underlying topological features of pollination systems. While pollinator and plant species richness, abundance, or overall composition of plant-pollinator interactions may shift organically over time (seasons, months) and space (environmental gradients), warming temperatures are already causing unanticipated changes in plant-pollinator communities on local scales. My dissertation focuses on the local pollination networks of the San Francisco Peaks in northern Arizona. In Chapter Two, I evaluate how species richness, abundance, and critical network properties change across three life zones (vegetation zones) of this unique elevational gradient. I also determine the critical generalist pollinator species responsible for community stability in the highest elevation life zone. In Chapter Three, I evaluate the impacts of short-term drought on the plant-pollinator communities of the San Francisco Peaks. Specifically, in the 2017-2018 winter and spring seasons, Flagstaff experienced especially dry conditions, with very minimal precipitation and a significant 43-day period in spring with no rainfall. This allowed for a unique opportunity to compare year-to-year differences in species richness, abundance, and timing of flowering/foraging periods across seasons. I also examine the potential shift in pollinator species generalization (diet breadth) in the dry year and how this may vary across life zones. However, to predict the impacts of global change on insect pollinator species diversity and distribution, studies must also be conducted at regional and global scales. In Chapter Four, I perform large-scale analyses of current USA bee data completeness using 1.923 million occurrence records for the contiguous United States. I determine clear sampling biases for certain taxa and geographic locations as well as identify undersampled areas that are likely hotspots for bee diversity. Additionally, I show that even if we were to digitize the remaining ~6 million collected-yet-undigitized bee specimens in institutions, this would not be sufficient to fill gaps, underscoring the need for more strategic sampling and monitoring programs. I conclude this dissertation by highlighting how understanding insect pollinator species distributions and their mutualistic associations is fundamental for pollinator conservation, and that this holds true across local, regional, and global scales