Lincoln University Digital Thesis Copyright Statement The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). This thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: you will use the copy only for the purposes of research or private study you will recognise the author's right to be identified as the author of the thesis and due acknowledgement will be made to the author where appropriate you will obtain the author's permission before publishing any material from the thesis. ` Apparent Competition Between Native and Exotic Plants Mediated by a Native Insect Herbivore A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University by Scot Michael Waring Lincoln University 2010 ` Abstract of a thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy. Abstract Apparent Competition Between Native and Exotic Plants Mediated by a Native Insect Herbivore by Scot Michael Waring Invasive species can significantly impact native food webs through indirect effects. Examples of apparent competition typically involve a non-native consumer disproportionately affecting one host population in the presence of another. My research finds evidence for apparent competition between two herbs, one invasive and one endemic, and mediated by an endemic insect herbivore. The European pasture herb Jacobaea vulgaris (formerly Senecio jacobaea), is an invasive weed in several parts of the world, including New Zealand. New Zealand is also home to 19 native species of Senecio – thirteen of which are endemic – that support an endemic insect fauna. Some of these insects have since expanded their host range to include the invasive J. vulgaris. I examined the relationships between one of those herbivores, the New Zealand magpie moth (Nyctemera annulata, Lepidoptera: Arctiidae), J. vulgaris and one endemic (S. wairauensis) and two native host plants (S. minimus and S. quadridentatus). In my laboratory assays, magpie moth larvae found J. vulgaris as attractive as native host plants and larvae fed only J. vulgaris developed at comparable rates to those fed only native hosts. My landscape surveys revealed a strong association between J. vulgaris infestations, magpie moth abundance and increased levels of herbivore damage of the endemic S. wairauensis. Likewise, S. wairauensis was more likely to be present in transects where J. vulgaris was rare. There is convincing anecdotal evidence that the native magpie moth became far more abundant because of an invasive weed and my study suggests that this detrimentally affects native plants through population spillback. Keywords: apparent competition, indirect effects, invasive, enemy release, Jacobaea vulgaris, Senecio, minimus, quadridentatus, wairauensis, rufiglandulosus, dunedinensis, Nyctemera annulata, magpie moth, New Zealand ii ` Acknowledgements While my name alone appears on this thesis, there were many others involved and without whom this project would not have been completed. First and foremost: my family. Thanks to my wife, Anna, who encouraged me to pursue a PhD and helped make it happen. She, along with my children, Sequoya, Anja, Ronin and Rigel, suffered with me through the tough times. I’m sorry and thank you. Many thanks to my parents, Lynn and Jayne, and brother, Shane, who helped support us in so many ways and during every step of this crazy adventure and who, along with my aunt and uncle, Russ & Sue, and Anna’s family, Marty, Stan, Alison and Ron, helped in overcoming some difficult aspects of this journey. I sincerely appreciate their collective and individual sacrifices. I have an enormous amount of gratitude for my PhD advisor, Jon Sullivan. Unfortunately for many graduate students, they will never experience a mentor with a relentless sense of optimism, a wealth of skills and knowledge, and a love of life & science like I have. I consider myself lucky to have had the experience of working and learning with him. Thank you also to my co-advisors, Simon Fowler and Roddy Hale, for their support, particularly at vital points along the journey. Thanks also to the ecology graduate students (too many to list here) all of whom taught me something and most of whom made the complicated process of a doctoral program much more enjoyable. Without the many field assistants that helped with data collection in the final season I would not be writing this now: Ronny Groenteman, Raviv Carasuk, Sam Abercrombie, Tim Forrest, Leyla Cardenas, Gordon Gundlach, Katrina Wisniewski, Sequoya Waring, Mo Correll, John Mulhouse, Fannie Demarque, Virginie Laberge, Heather Rickard, Maren Poitras, Hamish Maule and Myles McKintosh. Much appreciation also to Corbin Jones and Judge Rebecca Knight. I received support from several people at Lincoln University and Landcare Research – particularly Simon Fowler (again), Hugh Gourlay, Lynley Hayes, Lindsay Smith, Stella Belliss and Brad Case. Thanks also to Rob Dunn, Andrea Lucky and the Dunn Lab at NCSU for their edits and support. Great thanks to Landcare Research for funding my PhD programme and for supplying research resources that were unavailable through the university. I appreciate the use of collection data from various national herbaria and the individual custodians of National Vegetation Survey data (listed in Appendix A) for letting me use their data in my analyses. Thank you to Sabrina Leucht, the Department of Conservation and the West Coast and Canterbury Conservancies for facilitating my access to Crown Lands for this research. Thank you also to the people of New Zealand for the experience of a lifetime, your support and hospitality and for such a comprehensive education (sensu lato) in your beautiful country. iii ` Table of Contents Abstract ..................................................................................................................................... ii Acknowledgements .................................................................................................................. iii Table of Contents ..................................................................................................................... iv List of Tables ............................................................................................................................ vi List of Figures ........................................................................................................................ viii Chapter 1 Introduction ............................................................................................................ 1 1.1 Species Invasions .............................................................................................................. 1 1.2 Invasion Facilitation .......................................................................................................... 3 1.3 Apparent Competition ....................................................................................................... 5 1.4 Community Impacts .......................................................................................................... 8 1.5 Indirect Effects of Novel Plant-Herbivore Associations ................................................. 10 1.6 Thesis Structure ............................................................................................................... 14 Chapter 2 Invasion of New Zealand by Jacobaea vulgaris ................................................. 16 2.1 Introduction ..................................................................................................................... 16 2.2 New Zealand Senecio Specialists .................................................................................... 20 2.3 Magpie Moth (Nyctemera annulata) ............................................................................... 20 2.4 Jacobaea vulgaris invasion of New Zealand and the Response by Nyctemera annulata .......................................................................................................................... 23 2.5 Discussion ....................................................................................................................... 26 Chapter 3 Spatial and Temporal Associations Between Native New Zealand Senecio and a Closely-Related Invasive Weed ................................................................................... 30 3.1 Introduction ..................................................................................................................... 30 3.2 Methods ........................................................................................................................... 33 3.3 Results ............................................................................................................................. 39 3.4 Discussion ....................................................................................................................... 44 Chapter 4 Host Expansion in the New Zealand Magpie Moth, Nyctemera annulata ....... 53 4.1 Introduction ..................................................................................................................... 53 4.2 Methods ........................................................................................................................... 56 4.2.1 Magpie Moth ....................................................................................................... 56 4.2.2