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UCLA Electronic Theses and Dissertations UCLA UCLA Electronic Theses and Dissertations Title The population biology of dispersal and gene flow in the desert shrub Acacia (Senegalia) greggii A. Gray in the Mojave National Preserve Permalink https://escholarship.org/uc/item/4192z5zp Author Gaddis, Keith Donald Publication Date 2014 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA Los Angeles The population biology of dispersal and gene flow in the desert shrub Acacia (Senegalia) greggii A. Gray in the Mojave National Preserve A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Biology by Keith Donald Gaddis 2014 © Copyright by Keith Donald Gaddis 2014 ABSTRACT OF THE DISSERTATION The population biology of dispersal and gene flow in the desert shrub Acacia (Senegalia) greggii A. Gray in the Mojave National Preserve by Keith Donald Gaddis Doctor of Philosophy in Biology University of California, Los Angeles, 2014 Dean Victoria L. Sork, Committee Chair Desert ecosystems are increasingly affected by the human-driven environmental pressures currently changing global landscapes and climates. Plant species are especially susceptible to these changes due to their inability to move except through propagules and a frequent reproductive dependence on dispersing animal species that could themselves be displaced. To identify the limitations climate and landscape already exert on the movement and reproduction of plant species in desert zones, we examined the desert shrub Acacia (Senegalia) greggii A. Gray in the Mojave National Preserve. In chapter one, we give an overview of the ecosystem and study species. In chapter two, we present determinants of reproductive success in A. greggii shrubs. Limited water availability in deserts leads to annual and spatial variation in floral production. The impact of this variation on the reproductive success of a plant depends on the response of dispersal agents and seed predators to fluctuating food resources. We conducted observational surveys and experimental manipulations, and found that greater floral abundance attracted a greater number of pollinators, increased fruit-set, decreased the seed predation rate, ii and thus increased the pre-dispersal reproductive success of the shrub. In chapter three we present the historic and contemporary dispersal in A. greggii. We compared the genetic patterns of adults and pollen in a 4 km2 area, and found widespread gene flow indicating pollen flow may be more extensive than seed dispersal. Despite this extensive movement, both adult and pollen genetic patterns were explained by separation between dry-washes, suggesting a potential dispersal corridor for pollen and seeds. In chapter four, we present our comparison of alternative landscape pathways derived from both climatic and topographic variables to explain regional genetic structure. We examined movement across 2,700 km2 to determine if the fine-scale patterns observed in chapter three translate into regional connectivity. We again found widespread dispersal was best explained by gene flow along dry-washes. Our work documents a species with a well-adapted reproductive strategy and historically widespread dispersal. In spite of these results, the movement pattern of A. greggii is shaped by landscape features suggesting a potential impact of landscape change and development on future movement. iii The Dissertation of Keith Donald Gaddis is approved. Thomas W. Gillespie Stephen P. Hubbell Gregory S. Okin Dean Victoria L. Sork, Committee Chair University of California, Los Angeles 2014 iv To my mother for teaching me work ethic, my father for giving me an appreciation for the natural world, my Aunt Pat for pushing me into higher education, and to my wife for believing in me when I didn’t believe in myself. v TABLE OF CONTENTS LIST OF FIGURES .................................................................................................................... viii LIST OF TABLES ........................................................................................................................ ix ACKNOWLEDGMENTS ............................................................................................................. x VITA ........................................................................................................................................... xiii CHAPTER 1: Introduction to a desert study system Main Text ........................................................................................................................................2 Figures and Tables .......................................................................................................................... 9 References ..................................................................................................................................... 15 CHAPTER 2: Impact of floral display on fertilization success and seed predation in a common desert shrub Acacia (Senegalia) greggii A. Gray Abstract ......................................................................................................................................... 18 Introduction ................................................................................................................................... 19 Methods......................................................................................................................................... 25 Results ........................................................................................................................................... 30 Discussion ..................................................................................................................................... 32 Figures and Tables ........................................................................................................................ 38 References ..................................................................................................................................... 46 CHAPTER 3: Pollen movement facilitates extensive gene flow in the desert shrub, Acacia (Senegalia) greggii A. Gray Abstract ......................................................................................................................................... 55 Introduction ................................................................................................................................... 56 Methods......................................................................................................................................... 61 Results ........................................................................................................................................... 68 Discussion ..................................................................................................................................... 71 Figures and Tables ........................................................................................................................ 75 References ..................................................................................................................................... 82 vi CHAPTER 4: Impact of dry-wash pathways on gene flow and genetic diversity in the desert species Acacia (Senegalia) greggii A. Gray Abstract ......................................................................................................................................... 92 Introduction ................................................................................................................................... 93 Methods......................................................................................................................................... 98 Results ......................................................................................................................................... 104 Discussion ................................................................................................................................... 106 Figures and Tables ...................................................................................................................... 110 References ................................................................................................................................... 118 vii LIST OF FIGURES 1-1: Species accumulation curve of 42 bee and 57 wasp species collected across 23 sites in the Mojave National Preserve ............................................................................................................... 9 1-2: Relationship between peak flowering of A. greggii time and site elevation at 23 one-hectare sites in the Mojave National Preserve across three years ............................................................. 10 1-3: Map showing current and past distribution of Acacia (Senegalia) greggii in the Southwestern US ........................................................................................................................... 11 2-1: Hypothetical path diagram to explain fertilization success, seed predation, and final fruit abundance in A. greggii ................................................................................................................ 38 2-2: Map of 23 one-hectare sites in which phenology and pollinator abundance, fertilization success and seed predation of A. greggii were monitored over two years ................................... 39 2-3: Relationship
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