THE ROLE OF THE NOVEL WEAPONS AND ENEMY RELEASE HYPOTHESES ON THE INVASIVENESS OF KNAPWEEDS, CENTAUREA SPP., IN NORTH AMERICA, by David J. Carpenter, B.Sc. (Hons.) A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science. Department of Biology Carleton University Ottawa, Canada August 2007 © David Joseph Carpenter 2007 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 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ABSTRACT Knapweeds, Centaurea spp., are among the most successful grassland invaders in North America. Despite similar life histories, only certain members of this genus have become problem species, while others remain as benign, naturalized exotics. Two ideas which have been proposed to explain the success of exotic plants are the novel weapons (allelopathy) and enemy release hypotheses. In this study, both hypotheses were examined by comparing highly invasive knapweeds to their non- invasive kin. Leachates collected naturally from the soils of both highly invasive and non-invasive knapweeds had no noticeable allelopathic effects on indicator species. Though allelopathy has been reported in invasive knapweeds, it is likely the result of specific environmental factors. In terms of herbivory, non-invasives were fed on more by a generalist feeder, and incurred significantly more herbivory than invasives in a common garden. This indicates that invasive knapweeds may possess novel defenses which deter local herbivores. iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS I would like to thank my supervisor, Dr. Naomi Cappuccino, for her support, encouragement, and motivation throughout this project. Her guidance and friendship has helped me overcome many obstacles throughout the years, both educationally and personally, and to that I owe much gratitude. Much thanks to my committee members, Dr. Celine Boutin and Dr. Christiane Charest, for their advice and time throughout this process. I would also like to thank Ragan Callaway, Guy Kyser, and Andrew Kulmatiski for supplying the seeds of my study species. My thanks go out to my family for supporting me throughout this long process. To my sister Jennifer, for always being there for me and for putting up with me for so many years while we lived together. To my Aunt Louise and Uncle Frank, for their encouragement and motivation. To my cousin Melanie for being there when I really needed someone to talk to. And lastly, to my parents, Mary and Joe, for their unending support, love, and encouragement. Lastly, I would like to thank all of the grad students and staff at Carleton who have been by my side all these years. To Ed Bruggink for keeping my weeds alive in the greenhouse for the past three years. A special thanks to Tania Jogesh (lab mom) for her technical support and for helping me keep my sanity within our concrete prison in Nesbitt, even though she horded all the sheep. To Sunny Lee (unofficial lab mascot), Jethro Mercado (sensei), and Paul Sokoloff (lowly undergrad / Botanor), who helped me unwind with beer and trivia, sometimes on a daily basis. To Dave Ladd (self explanatory), Lisa Pirie-Chirrey (bird-girl), and Helen Pace (killer tennis coach!), for their friendship, encouragement, and overall awesomeness. iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT.......................................................................................................................iii ACKNOWLEDGEMENTS..............................................................................................iv TABLE OF CONTENTS...................................................................................................v LIST OF TABLES........................................................................................................... vii LIST OF FIGURES........................................................................................................viii CHAPTER ONE: GENERAL INTRODUCTION...........................................................1 Exotic Plant Invasions........................................................................................... 1 Life-History Traits of Invasive Plants...................................................... 2 Interactive Hypotheses of Invasion Success: Allelopathy, Enemy Release, andEICA................................................................................................................5 Natural History and Biology of Knapweeds (Centaurea spp.) ...........................9 CHAPTER TWO: ALLELOPATHY AND THE NOVEL WEAPONS HYPOTHESIS.................................................................................................................. 14 Introduction...........................................................................................................14 Allelopathy and the Novel Weapons Hypothesis ................................. 14 Allelopathy in Knapweeds ...................................................................... 17 Testing for Allelopathy ........................................................................... 19 Materials and Methods .........................................................................................21 Centaurea Species.................................................................................. 21 Activated Carbon - Juglone Verification..............................................21 Allelopathic Potential of Centaurea Soil Lechates ...............................23 Results..................................................................................................................26 Activated Carbon - Juglone Verification..............................................26 Centaurea Allelopathy ............................................................................27 Discussion.............................................................................................................28 v Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS CHAPTER THREE: HERBIVORY AND THE ENEMY RELEASE HYPOTHESIS..................................................................................................................38 Intoduction............................................................................................................38 Enemy Release Hypothesis .....................................................................38 Testing ERH: Comparisons of Herbivores in the Native and Introduced Ranges and Phylogenetic Comparisons in the Introduced Range............................................................................... 39 Materials and Methods .........................................................................................42 Centaurea Biology, Chemistry, and Herbivores .................................. 42 No-Choice Herbivory Trials ...................................................................44 Goldenrod Beetles (Trirhabda virgata) .................................... 44 Red-Legged Grasshoppers (Melanoplus femurrubrum) 45 Common Garden Field Experiment....................................................... 47 Results..................................................................................................................49 Trirhabda virgata..................................................................................