Invertebrate monitoring as measure of ecosystem change Mélissa Jane Houghton B. Arts and Sciences M. Environmental Management A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2020 School of Biological Sciences Centre for Biodiversity and Conservation Science Abstract Islands and their biodiversity have high conservation value globally. Non-native species are largely responsible for island extinctions and island ecosystem disruption and are one of the major drivers of global biodiversity loss. Developing tools to effectively measure and understand island ecosystem change is therefore vital to future island conservation management, specifically island communities and the threatened species within them. One increasing utilised island conservation management tool is invasive mammal eradication. Such programs are increasing in number and success, with high biodiversity gains. Typically, it is assumed that the removal of target non-native species equates to management success and in some instances, recovery of a key threatened or charismatic species affected by the pest species are monitored. Yet to date, there are few published studies quantifying post- eradication ecosystem responses. Such monitoring helps to calculate return-on-investment, understand the conservation benefits of management and inform conservation decision- making associated with current and future restoration programs. Not only are there few studies providing empirical evidence of whole-of-ecosystem recovery following mammal eradications, but research that measures the responses of lower trophic organisms and communities is also scarce. In consequence, questions remain regarding how best to manage ecosystems following large-scale eradications. When should we intervene to actively restore habitats or species interactions? What biodiversity indicators do we use to measure and monitor ecosystem change? How do we compensate when data are scarce? And perhaps most importantly, how can we learn from previous management efforts to inform future conservation decisions? To investigate optimal monitoring strategies for changing ecosystems, it is vital to understand which sampling methods to use, which habitats to focus on, and which taxa to monitor that will reflect broader ecosystem change. Moreover, non- native plant and invertebrate species that are not targets of invasive mammal eradication, can persist in an ecosystem following an eradication. These organisms interact with native species, impact biodiversity and can even create novel ecosystems. To understand the implications of these changes and make informed decisions to act effectively, conservation managers require tools to efficiently measure ecosystem change. My research focuses on World Heritage islands of the sub-Antarctic and I concentrate on a commonly overlooked group – terrestrial invertebrates. My thesis aims to address some of the questions raised above; first by reviewing the state of knowledge around non-native species ii impacts on invertebrates on in the sub-Antarctic region (Chapter 2), developing methods for effective and meaningful monitoring of invertebrates in changing ecosystems (Chapter 3), quantifying the invertebrate response to sub-Antarctic island mammal eradications (Chapter 4), understanding drivers of invertebrate richness and abundance in order to interpret these responses and develop indicators for effective long-term monitoring (Chapter 5), and using a traits-based analysis to identify non-native invertebrate taxa of biosecurity concern and future threat to the region (Chapter 6). iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, financial support and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my higher degree by research candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis and have sought permission from co- authors for any jointly authored works included in the thesis. iv Publications included in this thesis Houghton, MJ., Terauds, A., Merritt, D. Driessen, M., and Shaw, JD. (2019) Journal Insect Conservation 23: 435. https://doi.org/10.1007/s10841-019-00147-9 Houghton, MJ., Terauds, A., and Shaw, JD. (2019) Methods for monitoring invertebrate response to vertebrate eradication. Island Invasives: scaling up to meet the challenge 62. IUCN, Gland, Switzerland, 381-388. Submitted manuscripts included in this thesis No manuscripts submitted for publication. Other publications during candidature Peer-reviewed publications: Phillips, L., Janion-Scheepers, C., Houghton, M., Terauds, A., Potapov, M. Chown, S. L., (2017) Polar Biology 40: 2137. https://doi.org/10.1007/s00300-017-2129-9 Bergstrom, D.M., Sharman, A., Shaw, J.D. Houghton, M., Janion-Scheepers, C., Achurch, H., Terauds, A., (2018) Biological Invasions 20: 293. https://doi.org/10.1007/s10530-017- 1551-9 Russell JC, Peace JE, Houghton MJ, Bury SJ, Bodey TW (2020) Systematic prey consumption by introduced mice exhausts the ecosystem on Antipodes Island. Biological Invasions. Conference abstracts: Houghton M, Terauds A, Merritt D, Dreissen M, Possingham H, and Shaw, JD (2019). Invertebrates as indicators of ecosystem change on sub-Antarctic islands. Island Arks Symposium, February 2019, Rottnest Island, Western Australia. Houghton M, Terauds A, Merritt D, Dreissen M, Possingham H, and Shaw, JD (2018). Invertebrates as indicators of ecosystem change on sub-Antarctic islands. Australasian Wildlife Management Society Conference, December 2018, Hobart, Tasmania. v Houghton M, Terauds A, Merritt D, Dreissen M, Possingham H, and Shaw, JD (2018). Invertebrates as indicators of ecosystem change on sub-Antarctic islands. Ecological Society of Australia, November 2018, Brisbane, Queensland. Houghton M, Terauds A, Merritt D, McQuillan P, Chown SL, and Shaw JD (2017). Invasion risk of non-native invertebrates to sub-Antarctic ecosystems: a traits based assessment. Australian Entomological Society 2017, Terrigal, NSW, Australia. Houghton M, Terauds A, Merritt D, McQuillan P, Chown SL, and Shaw JD (2017). Invasion risk of non-native invertebrates to sub-Antarctic ecosystems: a traits-based assessment. British Ecological Society, July 2017, Durham University, Durham, England, UK. Houghton M, Terauds A, Merritt D, Dreissen M, Possingham H, and Shaw, JD (2017). Post- eradication invertebrate monitoring on Macquarie Island. Island Invasives Conference (IUCN Invasive Species Specialist Group), July 2017, Dundee, Scotland, UK. Contributions by others to the thesis Justine Shaw - was responsible for conceiving, designing and developing the overarching project. Shaw also provided advice and feedback on the interpretation of research data and revision of drafts for all chapters. Aleks Terauds – contributed ideas for analysis and interpretation of research data for all chapters, and contributed revisions of drafts for all chapters. David Merritt – provided advice and feedback for drafts of Chapter 2, 4 and 6. Michael Driessen – was instrumental in the design of the Macquarie Island invertebrate trapping survey underpinning Chapter 3 and 4 and provided feedback and advice for Chapter 2, 3, 4 and 5. James C Russell – provided feedback, advice and reviewed drafts for Chapter 4. Steven L Chown – provided input into the analysis for Chapter 6. Peter McQuillan – assisted in the identification of the ‘detected’ invertebrates used in Chapter 6. vi Statement of parts of the thesis submitted to qualify for the award of another degree No works submitted towards another degree have been included in this thesis. Research Involving Human or Animal Subjects During field surveys as part of this work, invertebrate animals (insects, slugs, spiders etc.) were trapped and preserved in ethanol. Ethics approval was not required for invertebrate subjects. vii Acknowledgements In the waning days of this PhD journey, I reflect on how I came to be here, furiously typing and formatting on a tome so long that I am allowed to use the word tome for the first time in practice. This all began with a strong urge to witness Macquarie Island with my own eyes. Remarkably, this fantasy became reality. I was included in the first field team on the ground for the Macquarie