Effects of Shrub Encroachment in Grass-Dominated Biomes on Vertebrate Communities
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EFFECTS OF SHRUB ENCROACHMENT IN GRASS-DOMINATED BIOMES ON VERTEBRATE COMMUNITIES By RICHARD A. STANTON, JR. A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2017 © 2017 Richard A. Stanton, Jr. To my parents ACKNOWLEDGMENTS I thank my advisors, Rob Fletcher and Bob McCleery, as well as my committee members, Ara Monadjem, Tom Frazer, and Todd Palmer, for their invaluable guidance and support at every stage of my doctoral studies. I would not have been successful without it. I also thank Muzi Sibiya, who devoted many hours in the field with me collecting data, translating SisWati to English, and generally making it possible for me to work in Swazi communities. His cheerful demeanor, hard work, and outstanding talent as a naturalist were all essential to the success of this research, and I consider myself incredibly fortunate to have had his assistance. Joe Soto-Shoender, Wes Boone, and Niels Blaum also made critical contributions that made my dissertation possible by providing or collecting data and offering input on one or more of my chapters. Likewise, Julie Shapiro, Jessica Laskowski, and Sarah Duncan provided more feedback on chapters, grant applications, and proposal drafts than I can properly measure much less repay. Brian Reichert, Brad Udell, Dan Greene, and Rajeev Pillay were always willing to make time to discuss data analysis, coding, field methods, or logistics with me, and their unique knowledge was invaluable in helping me to make progress in my research. The School of Natural Resources and the Environment and the Center for African Studies provided essential fellowship and grant support, respectively, for which I am very grateful. I am also deeply appreciative that Drs. Fletcher and McCleery provided funding to offset my travel costs. I want to extend warm thanks to the staff at the Savanna Research Center in Swaziland, who provided lodging, vehicles, meals, and field assistance for a reasonable price, as well as protected area managers and staff at: Mbuluzi Game Reserve; Mlawula Nature Reserve; Mhlosinga Nature Reserve; Bar Circle Ranch; Mabuda Farm; and Nisela Safaris, who provided access, assistance, and in some, cases, complimentary or reduced-rate lodging. I thank the 4 management at Tongaat Hulett for permitting us to count birds on their sugar cane fields and the local chiefs that allowed us to do the same in Swazi homesteads and community pastures. Members of the Fletcher and McCleery Labs, the Natural Resource Management in Africa working group, the Florida Cooperative Fish and Wildlife Research Unit, and the Oli Lab all provided camaraderie and an invaluable social setting for research productivity that I truly appreciate. Finally, Hillary Carter and my family were an ongoing source of guidance and support in life that is beyond measure, and their assistance during my doctoral studies was no exception. 5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES ...........................................................................................................................9 LIST OF FIGURES .......................................................................................................................10 ABSTRACT ...................................................................................................................................12 CHAPTER 1 INTRODUCTION ..................................................................................................................14 2 SHRUB ENCROACHMENT AND VERTEBRATE DIVERSITY: A GLOBAL META-ANALYSIS ................................................................................................................22 Synopsis ..................................................................................................................................22 Background .............................................................................................................................23 Materials and Methods ...........................................................................................................26 Study Design ...................................................................................................................26 Literature Search .............................................................................................................26 Inclusion Criteria .............................................................................................................27 Data Collection ................................................................................................................27 Analysis ...........................................................................................................................29 Effect size calculations .............................................................................................29 Modeling approach ...................................................................................................30 Candidate models .....................................................................................................31 Model goodness-of-fit and possible publication bias ...............................................32 Results.....................................................................................................................................32 Literature Search .............................................................................................................32 Meta-analyses ..................................................................................................................33 Discussion ...............................................................................................................................35 Shrub Encroachment Effects Across Climatic Gradients and Taxa ................................35 Shrub Encroachment Effects Among Continents ............................................................36 Data Gaps and Limitations ..............................................................................................36 Implications for Ecology, Conservation, and Management ............................................37 3 SHRUB ENCROACHMENT AND LAND-USE INTENSIFICATION IN AN AFRICAN SAVANNA HAVE DIFFERENT EFFECTS ON BIRD ALPHA AND BETA DIVERSITY ................................................................................................................44 Synopsis ..................................................................................................................................44 Background .............................................................................................................................45 Materials and Methods ...........................................................................................................48 Study Area .......................................................................................................................48 6 Sampling Design .............................................................................................................49 Stratification by land use and shrub encroachment ..................................................49 Bird surveys ..............................................................................................................50 Patch vegetation structure ........................................................................................50 Analytical Methods .........................................................................................................50 Estimating species presence-absence and richness ..................................................50 Generalized dissimilarity modeling .........................................................................52 Visualizing community change across environmental gradients .............................53 Partitioning dissimilarity owing to turnover and nestedness....................................54 Results.....................................................................................................................................54 Discussion ...............................................................................................................................55 4 DIET AND BODY SIZE EXPLAIN SHRUB ENCROACHMENT AND LAND-USE EFFECTS ON BIRD OCCUPANCY IN AN AFRICAN SAVANNA ..................................63 Synopsis ..................................................................................................................................63 Background .............................................................................................................................64 Materials and Methods ...........................................................................................................68 Study Area .......................................................................................................................68 Sampling Design .............................................................................................................69 Stratification by land use and shrub-encroachment .................................................69 Bird surveys ..............................................................................................................70 Patch vegetation structure ........................................................................................70