Hymenopteran Parasitoid Diversity & Tri-Trophic Interactions: The Effects of Habitat Fragmentation in Wellington, New Zealand Franz-Rudolf Schnitzler A thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology and Biodiversity Victoria University of Wellington Te Whare Wānanga o te Ūpoko o te Ika Māui 2008 Cleora scriptaria larva on Macropiper excelsum With all those in mind that are close to me All denen gewidmet, die mir nahe stehen Abstract Habitat fragmentation and the resulting decline in biodiversity through the loss of habitat are thought to be the main threat to insect extinctions. According to the trophic level hypothesis, habitat fragmentation affects parasitoids more severely than their herbivorous hosts. Parasitoids also may be correlated with plant species richness, because plants host a variety of phytophagous insects acting as hosts for parasitoids, or plants provide food or act as shelter for parasitoids. In this study, the effects of the forest fragment properties; area, isolation, percentage of residential area surrounding focal fragments and plant richness on parasitic wasps and their interactions were examined. These fragmentation effects were examined in 10 urban native bush remnants in the Wellington and Hutt Valley region of the lower North Island, New Zealand. Fragmentation effects on species abundance, richness and diversity and on community assemblages were examined for the wasp families Ichneumonidae, Pompilidae and Proctotrupidae. Correlations between beta diversity of the plant community and the parasitoid community were analysed and the study investigated whether individual parasitoid occurrences can be predicted by the range of their host‟s host plants. This study focused on interactions between the kawakawa moth larva Cleora scriptaria, its primary host plant Macropiper excelsum and the parasitism rates by two parasitoids Aleiodes declanae (an endemic species) and Meteorus pulchricornis (an exotic species) and the herbivory caused by C. scriptaria larvae. In addition to interaction responses to forest fragmentation properties, interaction responses were also examined with respect to the properties of the plot and individual plant. i Individual species showed different trends in response to the fragmentation properties, making interpretation of a general community response difficult. The abundance, richness and diversity of small-bodied parasitoids were inversely related to increasing area and plant species richness. Parasitoid community composition changed with fragment isolation and plant species richness. Ichneumonidae strongly responded to isolation in one year, whereas the Pompilidae responded to plant species richness. The Proctotrupidae community structure showed no response to any of the fragmentation properties. Correlations between plant and parasitoid community structures were not significant and individual parasitoid-plant associations were weak and inconclusive. Parasitism rates for A. declanae were significantly higher in more isolated fragments with smaller trees, and were negatively affected by overall parasitism rates, more so in isolated fragments. Parasitism rates by M. pulchricornis responded positively to larval densities and declined with increasing plant richness. Herbivory was positively related to the abundance of M. excelsum, tree size and larval density. The current study provides evidence that the forest fragment properties examined are, on their own, not always sufficient predictors of community structure and interactions for parasitoids. Aspects of the results from this thesis conflict with the trophic-level hypothesis with species responding in a negative or positive way, or not responding at all to forest fragmentation effects. The findings of this thesis support to conserving species diversity by maintaining and enhancing all types of existing forest fragments to prevent species extinctions. ii Acknowledgements Foremost I would like to thank my supervisors Phil Lester and Stephen Hartley. Without their help and support this thesis would never have happened. I surely must have tested Phil‟s patience to its limits and I am very grateful for his thought-provoking comments and ideas from the very start until the very end. Many thanks also go to Stephen who joined my project as second supervisor and has spent much time with me sorting out those bloody statistics. Many thanks go to Shirley Pledger and Clare Salmond whose statistical knowledge has been invaluable. Eleven years ago, prompted by my partner Jutta Humpfer, I started my university studies and enrolled for a Bachelor of Social Sciences. At that time I did not envisage that I would end my studies by writing this thesis. Jutta‟s support through all those years meant a lot to me and it was also she who encouraged me to enrol in Biology alongside Psychology. I will never forget the day when I sought permission from the Biology Department at Waikato University to double major. I remember appearing forlorn in the Biology Department‟s corridors asking someone where the office was so I could have my enrolment signed. This person happened to be Peter Molan, who proudly announced „I am Biology‟ and signed my life away for the next 11 years. From then on it became all too clear. After my very first assignment about compost toilets for the New Start course offered by Waikato University, to changing my degree to a Bachelor of Science, the discovery of my real passion, entomology, to the very end of this thesis, I would like to thank all of you who have contributed and supported me along iii the way in whatever form. Without this support I would not be here and I would not have written this thesis. Other people have contributed their time and expertise, for which I am greatly thankful: John Brightwell, Travis Chellman, Adrian Pike, Nick Rawlence, Megan Sarty and Lloyd Stringer for the assistance in the lab and sorting of insects with special thanks to Megan for her help looking after the live larvae whilst I was in the field. For help with some of the species identification I would like to thank Jo Berry, John Dugdale, Allen Heath, Phil Lester and Gregor Yeates. For the use of their Hymenoptera collections special thanks to Jo Berry (New Zealand Arthropod Collection), John Early (Auckland Museum) and Ricardo Palma and Phil Sirvid (Museum of New Zealand Te Papa Tongarewa). Many thanks go to Cleland Wallace for surveying the plant communities. I thank the New Zealand Department of Conservation for the loan of Malaise traps especially Ian Stringer and Mike Wakelin. The Department of Conservation also supplied me with Topo Vector Data for the Wellington region. Thanks also to the bug-club of the School of Biological Sciences at Victoria University of Wellington for valuable comments on my thesis during the research, analysis and writing process. Special thanks go to Kirsti Abbot, Vaughn Bell, Catherine Duthie, Marc Hasenbank, Angela Moles and Adrian Pike. I would like to thank all my friends and coffee mates, especially James Mathew, Adele White, Bruce Norris, Sonja Miller and Phil James, who had to share an office with me and endure my ups and downs during all this time. It was especially handy to share an office with the ever charming Bruce. His PC and IT knowledge certainly made life and computer usage much easier and I learned a lot from him. iv I also would like to thank the Karori Wildlife Sanctuary (Raewyn Empson), the Otari Botanical Gardens, the Wellington City Council (Joanna Gillanders and Jane Wright), the Hutt City Council (Kelly Crandle), the Upper Hutt City Council (Brett Latimer), and the Wellington Regional Council (Philippa Crisp and Chris Wootton) for permission to establish traps in native bush fragments. A very big thank you goes to the School of Biological Sciences, with special thanks to Marry Murray, Delwyn Carter and Patricia Stein. I enjoyed my time and felt very much at home within the whole department and I am very grateful for the support and encouragement I have experienced from all staff and students alike. Many thanks also go to Paul Blackman for making the final professional proof reading of my thesis possible, which was carried out by Dick Ward from Write You Are. With so many people to thank I am bound to have unintentionally overlooked some and sincerely apologise for this. For funding I would like to thank the Victoria University of Wellington, for providing research funds, a PhD scholarship and a PhD finishing scholarship. This research was also funded by the 21st Anniversary Fund from the Entomological Society of NZ and the Claude McCarthy scholarship allowed me to present my work at an international entomology conference. v Table of Contents Abstract…………………………………………………………………………... i Acknowledgements……………………………………………………………… iii CHAPTER 1. Forest fragmentation and trophic levels: Introduction and overview 1.1 Introduction...................................................................................................... 1 1.1.1 Habitat fragmentation…………………………………...…….………… 5 1.1.2 Habitat fragmentation effects on arthropods………..……….….……… 7 1.1.3 Habitat fragmentation responses at higher trophic levels………………. 11 1.1.4 Conclusions…………………………………...………………………… 18 1.2 Study sites…………………………………………………………………… 21 1.3 Parasitoids…………………………………………………………………… 22 1.4 Thesis outline………………………………………………………………... 27 1.4.1 Chapter 2………………………………………………………………... 28 1.4.2 Chapter 3………………………………………………………………... 30 1.4.3 Chapter