21 April ABSTRACT Our knowledge about the pollination ecology of plants globally, and especially in the tropics, is sadly lacking at a time when both plants and pollinators are experiencing sharp declines. Quantifying the pollination ecology of generalist plants in vulnerable tropical ecosystems should be a key goal of ecology. In order to do so, we must describe the pollination ecology of more systems and study how multipartite interactions with other species, for example nectar robbing, can impact plant-pollinator mutualisms. I investigated the pollination ecology of the Andean tree Oreocallis grandiflora (family: Proteaceae) at the northern and southern ends of its geographic range in Ecuador and Peru. Specifically, I quantified floral morphology, nectar properties and secretion rates, and pollinator visitation rates and community. I found that the two populations differed significantly in terms of floral morphology and nectar properties, and propose that the variation between them may be driven by differences in nocturnal pollinator community rather than by drift or isolation by distance. At both sites I observed nectar robbing by Diglossa flowerpiercers (family: Thraupidae) in O. grandiflora. I then investigated how trait-mediated indirect effects (TMIEs) of nectar robbing by Diglossa impacted nectar secretion, pollination, and reproduction in O.grandiflora in Peru using simulated nectar robbing treatments. I found that simulated nectar robbing significantly reduced the standing crop of O. grandiflora and led to chronically high nectar sucrose concentrations. I also found that robbed flowers experienced fewer visits from pollinators over all, especially by the dominant pollinator, the territorial hummingbird species Aglaeactis cupripennis. However, robbed flowers were visited by a more diverse and even community of hummingbirds. I predicted that any changes in pollinator community or visitation would have an impact on plant reproduction but there was no net effect of nectar robbing on plant reproduction in terms of seed set or mass. Notably, the trees that received no outcrossed pollen suffered a significant decrease in seed mass as compared to the treatments that were open to pollinators, suggesting that there are reproductive benefits to outcrossing for O. grandiflora. I tentatively conclude that nectar-robbing may simultaneously cause pollen limitation (through decreased visitation rates) and outcrossing benefits (through decreased monopolization by a territorial, short-range hummingbird species) in this system. These simultaneous but opposing TMIEs may cancel each other out, leading to a neutral net effect on the maternal reproduction of O. grandiflora. I then investigated how nectar robbing impacted the spatial foraging behavior of A. cupripennis. I used simulated nectar robbing treatments in a before-and-after-control impact (BACI) experimental design to study the response of A. cupripennis individuals to simulated nectar robbing in terms of territory area, distance flown, activity budget, and diet. Based on observed avoidance of robbed O. grandiflora by A. cupripennis, the principals of optimal foraging theory, and documented responses of different animals to resource depletion in the literature, I made predictions. I hypothesized that A. cupripennis would either expand their territory areas or increase their diet breadth to include more non-Oreocallis food sources, and would alter their activity budgets in either scenario to accommodate their new resource context, but I did not expect to see territory abandonment given the theoretically high costs of relocation. I found that individuals which received the nectar robbing treatment showed a significant increase in territory area in terms of both the minimum convex polygon (MCP) and the 95% home range, flew significantly farther after the robbing treatment, and shifted their diet away from O. grandiflora to incorporate other plant species as well as small-bodied flying insects. However, I found no impact of simulated robbing on the activity budget of A. cupripennis in terms of time spent foraging, perching, or territory defense. There was also generally no territory abandonment in response to simulated nectar robbing. I concluded that it is likely that nectar robbing is having a negative net effect on the daily net energy gain of A. cupripennis due to the direct costs of increased flight distances and the indirect costs of a lower quality diet that included insects and flowers with very low nectar production. This study has greatly elucidated how the plant-pollinator mutualism is part of bigger-picture multipartite species interactions. We found that nectar robbers can have significant ecological impacts within these interactions, and may therefore play a role in the evolution of pollinator behavior as well as plant floral properties. 21 April ACKNOWLEDGEMENTS I first thank my dissertation advisor Jordan Karubian, who has supported my ideas no matter how ambitious while still offering a practical perspective, and who has always made himself available for valuable support and feedback on the progress of my research. My other committee members, Thomas Sherry, Sunshine Van Bael, and Rebecca Irwin were each of critical importance to developing my dissertation and improving it with constructive critiques and advice, each bringing their own unique expertise to bear on the subject matter pursued in this dissertation. To the Karubian Lab members who have patiently watched and read drafts of various parts of this thesis for lab meetings until they grew tired of hearing about floral larceny, I thank you for all the time and help. To all of my field assistants over the years, with whom I shared more good memories and exciting discoveries than I have space here to describe, I thank you from the bottom of my heart. You helped to make me a better leader, scientist, and person. I am also grateful to Vanessa Luna, Boris Tinoco, Gustavo Londoño and Jill Jankowski for all the logistical and moral support, and sometimes even the lending of important equipment like laptops, food, and sometimes even Aglaeactis cupripennis. I would also like to thank the Castro family for their hospitality and friendship during my field season in Ecuador, this research would not have been possible without the constant stream of conversation, cuy, and cañaso that you brought to our hut every night. Samantha Lantz, ii Nicole Michel, Deborah Visco, Steven Darwin, and Michelle Jones all helped me with statistical analyses and in editing the later stages of my dissertation. Funding from the Louisiana Board of Regents Graduate Fellowship, multiple grants from the Stone Center for Latin American Studies, the National Geographic Society, the Animal Behaviour Society, and a Doctoral Dissertation Improvement Grant from the National Science Foundation (#1501862) made this research possible. Without the support for my career of my loved ones, especially my “casi-novio” Benjamin Brenner, my parents Gail and Dale, my “casi-in laws” and intrepid field assistants Wendy and Howard, and my wonderful NOLA friend troupe including Aliya, Susie, and Debbie, I would almost certainly have died from scurvy or an R-induced coma while writing my thesis. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS ...............................................................................................ii LIST OF TABLES ..............................................................................................................v LIST OF FIGURES ...........................................................................................................vi Chapter 1. The pollination ecology of Oreocallis grandiflora (Proteaceae) at the northern and southern ends of its geographic range………………………………………...1 Abstract........................................................................................................1 Introduction..................................................................................................2 Methods .......................................................................................................5 Results .......................................................................................................14 Discussion .................................................................................................24 Conclusions ...............................................................................................30 Acknowledgements ...................................................................................31 Appendix ...................................................................................................33 2. Nectar robbing impacts pollinator behavior but not plant reproduction……………………………………………………………………...34 Abstract......................................................................................................34 Introduction................................................................................................35 Methods .....................................................................................................40 Results .......................................................................................................48 Discussion .................................................................................................54 Conclusions ...............................................................................................58 Acknowledgements ...................................................................................58 3. Nectar