Copyright by Megan O’Connell 2021 The Dissertation Committee for Megan O’Connell certifies that this is the approved version of the following Dissertation: PLANT-POLLINATOR INTERACTIONS IN THE FACE OF GLOBAL CHANGE Committee: Shalene Jha, Supervisor Stanley Roux Lawrence Gilbert Alexander Wild Thomas Juenger PLANT-POLLINATOR INTERACTIONS IN THE FACE OF GLOBAL CHANGE by Megan O’Connell Dissertation Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy The University of Texas at Austin May 2021 Dedication I dedicate this dissertation to anyone who is curious about pursuing the sciences but does not believe they can. To anyone who thinks they are not smart enough or feels they do not have the resources and support to pursue field work, research, and graduate studies. To anyone who does not see their likeness reflected in the images of scientists they see in the media, text books, and names of authors listed on publications. With training, we all can be scientists, we all can earn PhD’s, we all can pursue our curiosities about the world, measure its patterns, and marvel at its wonders. I dedicate my dissertation to anyone who dreams of being a scientist but is too intimidated to pursue their dream. On your behalf, I promise to actively work make my field a more welcoming, diverse, and inclusive community in all my future endeavors. iv Acknowledgements This dissertation would not have been possible without the tremendously generous support of so many people, but above all my graduate mentor, Dr. Shalene Jha. Without your open-mindedness and visionary imagination, I would not have felt seen and accepted in the sciences. You helped me carve a niche in the fields of ecology and conservation that feel true to who I am, and I have you to thank for so much of my personal and professional growth. I would also like to thank the many researchers and professionals who helped me get to where I am today: Dr. Andy Jones and Dr. Eric Manzane, you introduced me to one of my greatest loves: researching tropical forests; Dr. Antonio Castilla, you have always believed in me and kindly encouraged me through my self-doubts, I would not have a dissertation if it were not for the massive research efforts you undertook in Panama; Dr. Alex Wild, you gave me a chance to incorporate my inner artist and journalist into my career; Trevor Hance, you graciously continue to give me avenues through which I can bring my research to my community and make real, lasting impacts. I also give immense thanks to all the kind and generous members and friends of the Jha lab: Dr. Kim Ballare, Dr. Sarah Cusser, Dr. Nate Pope, Rebecca Ruppel, Dr. Nathan LeClear, Nick Ivers, Camila Cortina, Laurel Treviño, Dr. Hollis Woodard, Dr. Daniel Katz, Dr. Elinor Lichtenberg, Dr. Gabriella Pardee, Dr. Sean Griffin, Dr. Hannah Gray, Dr. Felicity Muth, Dr. Rodolfo Jaffe, Dr. Jay Banner; you all made me feel safe to ask questions and to be vulnerable with my ideas. I could not have completed my research without the incredibly hard work of my undergraduate and high school student researchers: Pragati Kore, Apoorva Magadi, Leticia Lee, Yadira Rodriguez, DJ Ojeda, Katie Pennartz, Amy Wrobleski, and Jen Schlauch. Immense, heartfelt thanks to my friends and team in Panama who were patient with my rudimentary Spanish and helped me achieve what felt like the impossible: Dr. Angie Estrada, Hilario Espinosa, Nelson Jaen, Maikol Guevara, Valeria Franco, Tyler Macy, Peter v Marting, Dr. William Wcislo, Leonardo Simmons, Debbie Rivera, and Dr. Alonso Santos- Murgas. Thank you to my committee members who have given me crucial feedback throughout my dissertation: Dr. Stanley Roux, Dr. Alexander Wild, Dr. Lawrence Gilbert, Dr. Thomas Juenger; as well as the UT IB support staff for all the help over the years: Tamra Rogers, Sylvia Moore, Frances Lemear, Sean Schaffer, and Theresa Kelly. Additional thanks to my dear friends and family who have always believed in me through this wild journey: Dr. Jade Florence, Dr. Amanda Vaughn, Dr. Rose Stafford, Olivia Haun, Ash Dionne, Iffy Roma, David McKay, Gabe Patterson, Clayton Noyes, Ross Woods, Walker Pickens, Gabe Miller, Jerod and Lauri Walz, Denise, Neil, Patrick, Sean and Kacy O’Connell. Lastly, thanks to my grandma and grandpa Fern and Larry O’Connell who are no longer with us: you forged this path into the sciences for me, you showed me what a strong independent woman looks like, you laid the groundwork that allowed me to be the first PhD in our family – we did it grandpa! vi PLANT-POLLINATOR INTERACTIONS IN THE FACE OF GLOBAL CHANGE Megan O’Connell, PhD The University of Texas at Austin, 2021 Supervisor: Shalene Jha More than 80% of terrestrial plant species are dependent on animal pollinators to facilitate their reproduction and survival via pollen dispersal and pollen-mediated gene flow. With anthropogenic habitat destruction, urbanization, and climate change intensifying, the alteration and loss of pollination services may be one of the greatest threats global biodiversity faces today. Plant-pollinator interactions meet a myriad of synergistic challenges, both spatial and temporal, that impact their frequency and efficacy, ultimately altering the movement of pollen-mediated genetic diversity across landscapes and rendering tangible consequences for plant reproduction. Therefore, the ability for ecosystems to support diverse and robust pollinator communities, that can facilitate sufficient pollination services in quickly changing landscapes, may largely determine the future genetic health and survival of plant communities. The spatial impacts of land-use change and urbanization alter both density- dependent dispersal patterns and pollinator foraging behavior, while climate change may exacerbate these issues by further altering floral resource availability and foraging behavior temporally. To explore these dynamics we conducted extensive field surveys (Chapters 1, 2, 3), molecular analyses (Chapters 1, 2), and pollen analyses (Chapters 2, 3) across two systems: the tropical lowland forests of the Panama Canal region (Chapters 1, 2) and a vii network of urban gardens along the central coast of California (Chapter 3). We explored the scales at which pollen dispersal and pollen-mediated gene flow can be influence by deforestation (Chapter 1), finding measurable fine-scale effects in a multipaternal tropical tree species. We then added a temporal aspect to our tropical study system to explore how density-dependence may interact with climate change to impact pollination services after a plant-pollinator network experienced a discrete phenological shift (Chapter 2), finding that the distribution of genetic diversity and the robustness of plant-pollinator networks may play important roles in buffering plants from the negative effects of climatic extremes. We also investigated how the most extreme form of habitat degradation, urbanization, impacts pollinator foraging preferences across a network of urban gardens (Chapter 3), finding clear patterns of how pollinators utilize resource patches within cities as a function of the surrounding urban matrix and the richness of plant communities in these patches. Lastly, I present a portfolio of professional science media products I produced and/or co-produced throughout the course of my dissertation studies (Chapter 4), illustrating the importance of science communication for the fields of ecology and conservation, and the potential ways researchers can participate in the creation of compelling science media products. viii Table of Contents List of Tables………………………………………………………………………………xi List of Figures…………………………………………………………………………….xii Chapter 1: Bee movement across heterogeneous tropical forests: multi-paternal analyses reveal the importance of neighborhood composition for pollen dispersal………………………………………………………………………….…...1 Abstract…………………………………………………………………….………...1 Introduction………………………………………………………………………......2 Methods………………………………………………………………………………8 Study System and Sample Collection…………………………………….....8 Genetic Analyses…………………………………………………………..11 Statistical Analyses………………………………………………………...13 Results……………………………………………………………………...14 Discussion………………………………………………………………….15 Chapter 2: Landscape genetic diversity and pollinator network specialization buffer plant reproduction and pollen-mediated gene flow from extreme climate events…………………………………………………………………….…29 Abstract……………………………………………………………………………..29 Introduction…………………………………………………………………………30 Results and Discussion………………………………………...……………………33 Methods……………………………………………………………………………..38 Study System and the 2015-2016 El Niño Southern Oscillation…………..38 Study Species, Neighborhood Traits, and Phenology……………………...39 Pollinator Observations and Community Composition, Pollen Load Analyses, and Netowrk Construction………………………………….41 Reproductive Success and Genetic Analyses……………………………...43 ix Statistical Analyses and Models…………………………………………...44 Chapter 3: Reap what you sow: local plant composition mediates bumblebee foraging patterns within urban garden landscapes………………………………….53 Abstract……………………………………………………………………………..53 Introduction…………………………………………………………………………54 Methods……………………………………………………………………………..59 Study Region and Garden Metrics…………………………………………59 Pollinator Survey…………………………………………………………..61 Bumble bee pollen loads…………………………………………………..62 Reference Collection………………………………………………………63 Impacts of local and landscape features on pollinator diversity…………..64 Within Garden