DECOUPLING of NEOTROPICAL SEASONALLY DRY TROPICAL FOREST PLANT-POLLINATOR INTERACTIONS in the MIDST of CLIMATE CHANGE a Thesis S
Total Page：16
File Type：pdf, Size：1020Kb
DECOUPLING OF NEOTROPICAL SEASONALLY DRY TROPICAL FOREST PLANT-POLLINATOR INTERACTIONS IN THE MIDST OF CLIMATE CHANGE A thesis submitted to Kent State University in partial fulfillment of the requirements for the degree of Master of Science by Theresa N. Wolanin August 2021 Copyright All rights reserved Except for previously published materials Thesis written by Theresa Wolanin B.S., Kent State University, 2014 M.S., Kent State University, 2021 Approved by Oscar J. Rocha, Ph.D. , Advisor Laura G. Leff, Ph.D. , Chair, Department of Biological Sciences Mandy Munro-Stasiuk, Ph.D. , Interim Dean, College of Arts and Sciences TABLE OF CONTENTS TABLE OF CONTENTS .............................................................................................................. iii LIST OF FIGURES ...................................................................................................................... v LIST OF TABLES ........................................................................................................................ vi ACKNOWLEDGMENTS ..................................................................................................…..... vii I. INTRODUCTION ................................................................................................. 1 II. CHANGES IN ABUNDANCE AND COMPOSITION IN THE SEASONALLY DRY TROPICAL FOREST POLLINATOR BEE COMMUNITY: A COMPARISON BETWEEN HISTORICAL AND CURRENT COMMUNITIES..........................................................................................…...... 7 ABSTRACT............................................................................................................ 7 INTRODUCTION.................................................................................................. 8 MATERIALS AND METHODS.......................................................................... 12 RESULTS............................................................................................................. 16 DISCUSSION...................................................................................................... 19 III. LONG-TERM VARIATION IN PRECIPITATION PATTERNS AFFECT PLANT- POLLINATOR RELATIONSHIPS OF SEASONALLY DRY TROPICAL FORESTS TREES ............................................................................................... 35 ABSTRACT.......................................................................................................... 35 INTRODUCTION ............................................................................................... 36 MATERIALS AND METHODS ......................................................................... 39 RESULTS ............................................................................................................ 45 iii DISCUSSION .................................................................................................... 48 IV. CONCLUSION ...................................................................................................... 57 REFERENCES............................................................................................................................. 63 APPENDICES A. Rarefied observations of genera in each dry season collection........................................ 79 B. Wet season precipitation data compiled from IMN and PVNP meteorological stations . 80 iv LIST OF FIGURES Figure 1. Dissecting differences in bee community structure across sample seasons…………28 Figure 2. Population dynamics in three common SDTF solitary bee genera…………………..29 Figure 3. Non-Metric Dimensional Scaling model for bee communities from thirteen dry seasons………………………………………………………………………………....………..30 Figure 4. Boxplots mapping the variance in bee community structure during the dry season between decades……………………………………………………………………………..…...30 Figure 5. Comparison between historical bee community structure of 1971-1972 and 2016-2018 in the SDTF of Guanacaste, Costa Rica………….……………………............…………..…….31 Figure 6. Taxa turnover of the dominant SDTF pollinator genera……………………………..32 Figure 7. Decomposed additive time series analysis of wet season precipitation patterns in regions of SDTF in Guanacaste, Costa Rica……………………………………………………54 Figure 8. A bimodal plant-pollinator network comparing the pollinator networks for five SDTF plants……………………………………………………………………………………………55 v LIST OF TABLES Table 1. Presence/absence table of genera found in thirteen sampled dry seasons in Guanacaste, Costa Rica………………………………………………………………………………………33 Table 2. Measures of diversity calculated on rarefied dataset (s = 96) of thirteen dry seasons that were representative in terms of sample duration and size……………………………………...34 Table 3. Results from seven Mantel Peason’s product-moment correlation tests…………..….56 vi ACKNOWLEDGMENTS I dedicate this thesis to my fellow women in science, who inspired and supported me with their expertise, tenacity, and passion for their work, especially: Davinia Beneyto Garrigós, Claire Bennett, Colleen Cosgrove, Anna Droz, EmmaLeigh Given, Lilliam Morales Gutiérrez, AE Nash, and Carlyn Rocazella. Carlyn and Claire were instrumental in assisting me in the field studies for this research, and continue to make the world a better place through their work. A special thanks to Mahmood Sasa, the staff of the Palo Verde National Park Biological Research Station, and the park rangers of the Palo Verde National Park. Without their help, my field research would not have been possible. I also thank the gracious curators and collectors who allowed me to access and collect samples from museum specimens of bees. These include the staff at the Instituto Nacional de Biodiversidad, Paul Hanson at the Universidad de Costa Rica, Terry Griswold at the Bee Biology and Systematics Laboratory at Utah State University, and Noelle Jordan and Paul Heithaus at the Brown Family Education Center at Kenyon College. Additional thanks to Chris Blackwood, Andrea Case, Rollin Coville, Dan Janzen, Monika Springer, and Brad Vinson for entertaining my many questions. Lastly, I would like to thank my advisor and mentor, Oscar Rocha, for his guidance over the years. Without this opportunity, I would not be the person or the scientist I am today. This research was partially funded through the Graduate Student Research Award, provided by the KSU Graduate Student Senate; and the ECTS Graduate Fellowship Award, provided by the Organization for Tropical Studies via the Emily Foster Memorial Fellowship (fund 512) and the Henry Leigh Fellowship (fund 517). vii CHAPTER I. INTRODUCTION Plants are the foundation of tropical ecosystems, 94% of which are dependent on animal pollinators (Ollerton et al. 2011). My research focuses on how the plant-pollinator relationships in a water-limited tropical forest system are being disrupted by climate change. Which pollinator species are going to win or lose in the process is uncertain, so this project seeks to establish the changing status of bees in the ecosystem, and to investigate the mechanisms that are disrupting the pollinator community. Costa Rican seasonally dry tropical forests (SDTF) are characterized by trees and vines that are adapted to severely arid dry seasons (Opler et al. 1976, Borchert 1983). During the wet season, many of these trees will begin the development of flowers, which remain dormant until dry season. The timing of anthesis, or flower emergence, in these trees is signaled by the last rain of the wet season, or in some cases, a rain event following a period of dormancy during or after the dry season. During the dry season, many trees will drop their leaves and synchronously bloom in spectacular mass-flowering events. Such events have been argued to be a key visual cue and evolutionary advantage in attracting pollinators and in increasing the efficacy of pollination (Frankie and Coville 1979, Thorp 1979, Michener 2000). 1 The pollinator community of SDTFs is characteristically dominated by solitary bees (Kalacska et al. 2004). Most non-parasitic solitary bees individually gather all provisions for their offspring. As such, solitary bees capitalize on the wide availability of resources during dry season mass-flowering events to maximize reproductive capacity (Michener 2000). This characterizes them as seasonal specialists, and reflects a strong evolutionary relationship between flowering trees and these pollinators (Thorp 1979). Peak solitary bee activity and diversity observed during February and March (Heithaus 1974, 1979) coincides with peaks in the mass- flowering events of several species of trees (Frankie et al. 1974, 1976, Opler et al. 1976, 1980). This strong seasonal specialization has been linked to the abundance and diversity of floral resources required for nest-building and offspring provisions (Frankie et al. 1988, 2013, Michener 2000). Little formal investigation was conducted to establish the bee pollinator community prior to many of the effects of climate change. In 1979, Ray Heithaus published a comprehensive survey of three dry, lowland habitats within Guanacaste, Costa Rica, which included SDTF. According to this study, bee diversity in the SDTF from 1971 – 1972 was historically higher than any temperate forest bee community surveyed to that point. This is largely driven by the diversity of the flowering plant community (Heithaus 1974), and by the relationship between the solitary seasonal specialists and mass-flowering events during the dry season (Heithaus 1979). Consequently, solitary bees accounted for 88% of the diversity for the sampled