This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Carvalheiro, Luisa Mafalda Gigante Title: Impact and management of invasive plant species : a food web approach General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. llDI IMPACT AND MANAGEMENT OF INVASIVE PLANT SPECIES: A FOOD WEB APPROACH Luisa Mafalda Gigante Carvalheiro A thesis submitted to the University of Bristol in accordancewith the requirementsof the degreeof Doctor of Philosophy in the Faculty of Science School of Biological Sciences December2007 Word Count: 32 381 ABSTRACT Invasive plants can significantly affect ecosystems. While their impacts on plant populations are widely reported, data on how higher trophic levels are affected by those changes are scarce. The work presented here aims to provide further insights for the study of impacts and management of invasive species, using food webs as a tool for assessing and predicting consequences of habitat disruptions. The first question I address in this thesis is how the removal of alien plant species from a UK site of conservation interest affects the pollination of a rare plant Trinia glauca (Apiaceae). A food web approach was used to identify the main pollinators of this rare plant species, and to understand how this rare plant interacts indirectly with the introduced species present in the study area via shared flower visitors. I simulated the likely consequences of removal of alien plants on T. glauca pollination, any effects being mediated by shared pollinators. This approach was used to reveal the potential negative impacts of habitat management (here alien plant removal) on the native plants. Secondly, I consider how the impact of an invasive weed of UK heathlands,Gaultheria shallop, propagates through food webs affecting plants, herbivores and parasitoids. Using a quantitative food web approach,I found that diet breadth influences the propagation of impacts, leading to changesin the food web structure. Specialist consumerswhich had all their resource species affected by G. shallon were the most affected by the invasive plant. I consider the implications of these results for conservationecology and highlight the importance of extending impact evaluation to higher trophic levels as well as considering trophic diversity within levels, for a full evaluation of the consequencesof disturbances. Finally, I evaluated the indirect non-target impacts of a management measure considered safe and environmentally friendly: the use of highly specific weed biocontrol agents. I used 17 replicate food-webs to demonstrate that natural enemies are shared between an abundant successfully established biocontrol agent, Mesoclanis polana, and seed herbivore species from native plants. I found that the agent abundance is associated with local insect biodiversity losses, apparent competition being the most likely explanation. Thus, my study suggeststhat food webs are a useful tool for assessingand predicting consequencesof plant invasion and their management. DEDICATION Se hä que dedicar a alguem sö pode mesmoser a voces: ao meu Pai, a minha Me ea ti Eduardo ACKNOWLEDGEMENTS Several people have contributed with their help to this thesis. First of all I want to thank my supervisor, Jane Memmott. I really appreciated the guidance, support and encouragement through all these years. I also thank to Yvonne Buckley, who advised on many aspects of this thesis, particularly on the work developed in University of Queensland, Australia. Thanks to Fundacäo para a Ciencia e Tecnologia (Portugal) that has provided the funding for my studentship. Discussing my doubts and ideas with people was always very helpful. I thank everybody on `C28' for making our work environment so nice and pleasantand for all the useful discussions. Michael Pocock and Paul Craze for their great patience discussing the statistical analyses during all the thesis; Mariano Devoto, Michael Pocock, Martha Lopezaraiza, Kate Henson, Sarina Pearce, Darren Evans, Ruben Heleno, Rachel Gibson and Jo Brooks, for comments and discussionson the chapters. Interacting with you all was very rewarding. The help of several people during field and lab work was essential for getting good results. Concerning the work presented in Chapter 2, I would like to thank L. Houston for help on selection of field sites; M. Leivers (Bristol City Council) for permission to work on Avon Gorge; A. Robertsonfor help identifying Sorbus speciesin Avon Gorge; R. Boada, K. Henson, A. Collings, N. Boase and D. Craven for help in data collection in the Avon Gorge; E. Barbosa for all the help during field work; G. Orledge and C. Collingwood for identification of ant species;J. Deeming, B. Levey and M. Pavott for insect identification; P. Quinn for help with plant identification; M. Pocock for help on statistics; M. Devoto and four anonymous referees for commentson the previous version of the manuscript. Concerning the work presentedin Chapter 3, I would like to thank to T. Branston for permission to work in the field sites and for help locating study areas;T. Branston and I. Cross for information on insect diversity in the study area; H. Kirk, E. Barbosa and R. Torres for field assistance;R. Gibson for help rearing insects; M. Bailey, J. Deeming, G. Broad and A. Polascek for insect identification and information on iii parasitoids host range; G. Broad and M. Shaw for information on previous host records; M. Pocock and P. Craze for help on statistics; Y. Buckley, S. Pearce, M. Devoto, M. Pocock and R. Heleno for comments on the manuscript. Concerning the work presented in Chapter 4, I thank D. Hofineyer, A. Fay and J. Thomas for information and help defining field sites; P. Edwards and R. Holtkamp for information; E. Barbosa for lab assistance; K. Harris, J. Deeming, G. Daniels, C. Burwell, A. Polascek and M. Buffington for insect identification; J. Dwyer, J. Thomas and Brisbane Botanical Gardens for plant identification; P. Craze and M. Pocock for help on statistics; A. Willis, D. Evans, J. Denslow, L. Hennemman, H. Rebelo, M. Devoto, M. Pocock, N. Jennings, 0. Lewis, P. Syrett, R. Morris and R. van Klinken for comments on a previous version of the manuscript. Also a special thanks to Bernard and Dolor for receiving me and helping so much throughout my time in Australia, and to Ilyas whose company in the lab made the long hours of lab work rearing and sorting insect specimens so much nicer. The friendship and support of many people throughout these years was very important. Thank you Ruben, Martha y Jose, Kate and Tim, Rachel, Hugo, Miriam, Roberto, Mariano y Natalia, Sarah, Iszy for all your friendship. Special thanks to Martha and Kate whose friendship during nice and not so nice times helped me so much and was particularly important during the first year of my PhD. Finally, my family, whose encouragementand guidance helped me through all the stagesof this long learning process.A special thanks to my father and mother: e para alem de tudo desculpaspor toda a minha ausenciaque nunca you poder recuperar;and to Eduardo, whose support, affection and patiencemade a big difference. Obrigado por tudo! Iv AUTHORS' DECLARATION I declare that the work presentedin this thesis was carried out in accordance with the Regulations of the University of Bristol. The work is original, except where indicated by special referencein the text and no part of the dissertation has been submitted for any other academicaward. Any views expressedin the dissertationare those of the author. -1 o\-CýL'A-0 Luisa M. G. Carvalheiro Bristol 21S` December 2007 V TABLE OF CONTENTS Abstract i ........................................................................................................................... Dedication ii ....................................................................................................................... Ackowledgements .......................................................................................................... iii Authors' declaration ...................................................................................................... v Table of contents ........................................................................................................... vi Chapter 1: INTRODUCTION 1 ...............................................................................................................