The Causes and Consequences of Community Disassembly in Human Modified Tropical Forest: Scarabaeine Dung Beetles as a Model System Elizabeth Stevens Nichols Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences COLUMBIA UNIVERSITY 2012 © 2012 Elizabeth Stevens Nichols All Rights Reserved The Causes and Consequences of Community Disassembly in Human Modified Tropical Forest: Scarabaeine Dung Beetles as a Model System ABTRACT Elizabeth Stevens Nichols A central aim of conservation science is improving our understanding how different human activities influence the persistence of native biota and associated ecological and evolutionary processes. Meeting this applied biodiversity research challenge requires that we understand (i) patterns in biological responses to anthropogenic environmental change, (ii) what biological mechanisms influence that response, (iii) how the loss of biological diversity will impact important ecological processes, and (iv) how this information can be translated into effective and practical information useful for decision makers. Increasingly, this final translational step is met through the use of ecological indicator assemblages – suites of species whose presence and abundance in a given area provide a useful gauge for measuring and interpreting changing environmental conditions. This thesis aims to improve our understanding of the patterns, causes and consequences of community disassembly for tropical forest insect species. To do this, I have combined systematic literature reviews and empirical approaches to understand how two widespread anthropogenic drivers of environmental change in tropical forest (i.e. land-use change and degradation) influence the community disassembly of Scarabaeine dung beetles in tropical forest, at a variety of spatial scales. I outline the potential for tropical forest defaunation to negatively impact dung beetle communities, summarize the contributions of dung beetles to a range of key ecological processes, provide empirical data demonstrating how dung beetles can serve as a model system to understand terrestrial trophic cascades, discuss the ability of species traits to explain population trends in observed dung beetle community disassembly, and conclude by demonstrating how these various lines of evidence linking dung beetle species with environmental condition strengthen their potential utility as ecological indicator taxa in applied conservation science. TABLE OF CONTENTS List of Tables ................................................................................................................................. iv List of Figures ................................................................................................................................. v List of Appendices ......................................................................................................................... vi Acknowledgments ......................................................................................................................... vii ABTRACT ...................................................................................................................................... 3 INTRODUCTION .......................................................................................................................... 1 Thesis aims .................................................................................................................................. 2 Thesis focal taxa .......................................................................................................................... 3 Thesis structure ........................................................................................................................... 3 CHAPTER 1 - Co-declining mammals and dung beetles: an impending ecological cascade ........ 6 Citation: ....................................................................................................................................... 6 Abstract ....................................................................................................................................... 7 Introduction ................................................................................................................................. 8 Consequences of hunting on beetle community structure ......................................................... 10 Mechanisms of beetle community disassembly ........................................................................ 13 Consequences of hunting on beetle community function ......................................................... 16 Current capacity for prediction ................................................................................................. 17 Future challenges ....................................................................................................................... 19 Tables and figures ..................................................................................................................... 22 CHAPTER 2 - Ecological functions and ecosystem services provided by Scarabaeinae dung beetles ........................................................................................................................................... 23 Citation: ..................................................................................................................................... 23 Abstract ..................................................................................................................................... 24 Introduction ............................................................................................................................... 25 Ecological functions .................................................................................................................. 26 Nutrient cycling ..................................................................................................................... 26 Bioturbation ........................................................................................................................... 30 Plant growth enhancement ..................................................................................................... 31 i Secondary seed dispersal ....................................................................................................... 33 Parasite suppression ............................................................................................................... 38 Enteric parasites ..................................................................................................................... 38 Parasite dispersal ................................................................................................................... 40 Fly control .............................................................................................................................. 41 Trophic regulation and pollination ........................................................................................ 44 Ecosystem services .................................................................................................................... 46 Dung beetle response to anthropogenic threats ......................................................................... 49 Conclusion ................................................................................................................................. 50 CHAPTER 3 - Hunting-induced trophic cascades in tropical forest: landscape-level evidence for community-level cascades in the ‘brown world’. ......................................................................... 53 Introduction ............................................................................................................................... 56 Methods ..................................................................................................................................... 62 Study site ............................................................................................................................... 62 Data analyses ............................................................................................................................. 65 Results ....................................................................................................................................... 67 Discussion ................................................................................................................................. 74 Acknowledgements ................................................................................................................... 84 Figures and tables ...................................................................................................................... 85 CHAPTER 4 - Trait-dependent response of dung beetle populations to tropical forest conversion at local to global scales ................................................................................................................. 90 Introduction ............................................................................................................................... 92 Materials and Methods .............................................................................................................. 96 Results ....................................................................................................................................