Blera Fallax (Linnaeus) (Diptera, Syrphidae) and the Dispersal Ability of the Similarly Endangered Aspen Hoverfly, Hammerschmidtia Ferruginea (Fallén)
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The ecology and conservation of endangered saproxylic hoverflies (Diptera, Syrphidae) in Scotland Ellen L. Rotheray July 2012 A thesis submitted for the degree of Doctor of Philosophy Biological and Environmental Sciences School of Natural Sciences The University of Stirling Summary Hoverflies are important for their roles in ecological and environmental services, and are also charismatic species of conservation interest in their own right. Almost half of all hoverflies are saprophages, which are organisms that feed on dead or decaying organic matter, and these include saproxylic species that depend on deadwood. Deadwood and its associated community are a rich source of forest biodiversity and are fundamental to forest function, but due to poor management, many saproxylics are threatened or endangered, and techniques for conserving saproxylic species are poorly developed. In this thesis I study the ecology and conservation management of an endangered UK saproxylic fly, the Pine hoverfly, Blera fallax (Linnaeus) (Diptera, Syrphidae) and the dispersal ability of the similarly endangered Aspen hoverfly, Hammerschmidtia ferruginea (Fallén) (Diptera, Syrphidae). My main goals were to clarify methods to support their recovery in active programmes of species conservation in Scotland, UK. For B. fallax, this included experimenting with habitat creation techniques, investigating the best conditions for larval growth and assessing competition effects. In addition, I evaluated the genetic variability of the remaining population in Scotland by comparing it with one in Europe to determine whether genetic constraints may limit recovery. For H. ferruginea, I determined dispersal ability with field experiments involving mark and recapture techniques. By cutting holes at the surface of stumps of Pinus sylvestris, breeding habitat was created artificially for B. fallax at the remaining known locality for this species in the UK. Over 4 years, 81 % of holes were colonized by B. fallax, and by up to six 2 other saproxylic syrphid species. The most successful holes were those cut into the heartwood, seeded with pine chips and sawdust and partially covered, as indicated by a combination of field occupancy monitoring and lab growth experiments. Observations of larval morphology and behaviour within rot holes revealed specializations that largely segregate the species in both time and space, and may mitigate interspecific competition between B. fallax and three more common syrphid species. I further demonstrated that B. fallax has a life history that features facultative semivoltine development, which may be a bet-hedging strategy to cope with fluctuating levels of larval food. Fifty B. fallax larvae were successfully reared and bred in captivity and from these, 430 descendent laboratory reared larvae and adults were released across three relocation sites. After initial success at the first re- location site when a new generation of larvae appeared in holes in 2010, a population crash at all sites occurred in the following year, possibly caused by adverse weather conditions. This disappointing result highlights the vulnerability of small populations to stochastic events, and means that survival of B. fallax may now depend on those larvae that are semivoltine, supplemented by animals currently being reared in captivity. My genetic analyses revealed similarly troubling information that highlights the precarious existence of B. fallax in Scotland: compared with a population in Sweden, Scottish B. fallax had significant less neutral genetic variation, and showed signs of a recent and severe bottleneck that reduced the effective population size to just 12 (CI: 0 - 266) individuals at some point in the last 200 years. Mindful of these challenges, I exploit my new data on the ecology and life history of B. fallax and combine it with techniques for captive rearing and for monitoring the genetic health of B. fallax into specific protocols and general prescriptions for the on-going recovery and management of this species. 3 In order to assess the dispersal ability of H. ferruginea (and therefore its potential for recolonizing newly created habitat), in May to July over two years, adults were marked and released from a central point and subsequently monitored at the breeding site, decaying aspen wood Populus tremula, where adults tend to assemble for mating and oviposition. Adults were resighted visiting logs of decaying aspen set out at 1 km intervals along transects up to 7 km away. Up to 10 % of released individuals were resighted up to 5 km from the central release point. Most dispersing individuals (68 %) were resighted at 1 km, which I propose as the optimal distance for managing aspen for this species. Both of these hoverflies are case studies of techniques for recovering endangered saproxylic flies. Overall, my findings greatly increase fundamental knowledge of the ecology and natural history of these flies, and clarify some of the practical approaches that will be required in their conservation. 4 Declaration I hereby declare that this thesis has been composed by myself and that it embodies the results of my own research. Where appropriate, I have acknowledged the nature and extent of work carried out in collaboration with others. …………………………………………………………………… Ellen Louise Rotheray 5 Acknowledgements The completion of this project owes much to a large number of people and organisations to which I would like to express my sincere gratitude. Most importantly, I would like to thank Dr Luc Bussière and Professor Dave Goulson for their supportive and unfaltering supervision, expertise and guidance. Both seem to have had faith in me from start to finish, they have complimented each other well (in that they are completely different), and have never let me down. I also need to thank Iain MacGowan at Scottish Natural Heritage (SNH) for his supervision. Iain has been hugely supportive and encouraging throughout. I am grateful for the management, advice and encouragement from the Malloch Society, which includes Geoff Hancock, Steve Hewitt, Dave Horsfield, David Robertson, Richard Lyszkowski and Kenn Watt. Many thanks also to the RSPB for their support, especially staff at Insh Marshes reserve including Carl Mitchell and Karen Sutcliffe; and Abernethy reserve including Ross Watson and Jeremy Roberts. I am particular grateful to Pete Moore at Insh for his time, effort and care over the years. I would also like to thank the Hoverfly Steering Group members: Jane Sears, Anne Elliot, John Parrott, Andy Amphlett and Ern Emmet. Thanks to Kenny Kortland and Colin Leslie at Forestry Commission Scotland for their assistance and advice. Thanks to private landowners on Alvie and Dunachton Estate, John Grant at Rothiemurchus Estate, Angus Macpherson at Craig Dhu, and Henry J. Beker at Curr Wood, for their permission to work on or use their land as part of the project. 6 There were a number of enthusiasts and experts that helped and supported the work some of which could not have been achieved without their assistance including Stewart Taylor, Stuart Blackhall, Pete Moore (SNH), Hans D. Bartsch, Francis Gilbert and Tom Prescott. Thank you to my research assistants Claire Watson, Sarah Hoy, Vicky Nall and Linnea Bergstrom, as well as volunteers Kate Williamson, Debbie Leigh, Morten Bucheister and Andrew Ford. I was continually surprised and delighted at their enthusiasm for log watching! A great number of colleagues at Stirling have helped in various ways from analysis to advice and support including Kirsty Park, Olivier Lepais, Mario Vallejo-Marin, Matt Tinsley, Lynn Macgregor and Scott Jackson. I am, as are the remaining population of the pine hoverfly, indebted to James Weir who ensured the safekeeping of the flies in the University’s climate controlled facilities. I must thank my colleagues and friends at Universität Zürich: Michael Krützen, Alex Nater, Maja Greminger, Corinne Ackermann and Anna Kopps who collectively introduced me to the beautiful Swiss people and way of life, and molecular genetics, and have inspired me to love both. I want to thank Jenny Owen, Elisa Fuentes-Montemayor, Krista Gilliland, Caroline Griffin, and Anne Winther, in my office who have been considerate and empathetic 7 over the past four years. I’d also like to thank Jeroen Minderman, Steph O’Connor, Danielle MacKenzie, Lucy Woodall, Tom Houslay and Penelope Whitehorn (Brown), colleagues and friends who have supported and encouraged me in various ways not least of which in providing light relief when it has been most needed. My closest and dearest friends and family who have supported me throughout deserve mentioning, in particular Ruth Muir, Richard Siller and Gillian Bracher, Pope Beeb, and especially Joanne Rotheray. A special thank you is reserved for Geoffrey Wilkinson who not only stayed up with me for 24 hours on maggot-watch, which turned out to be a rather tedious pass time, but has willingly volunteered to assist in various activities throughout the four years from creating hoverfly habitat to log watching and counting maggots. He has kept me entertained and balanced, but also dropped to my level of absurdity just to keep me company. He has helped keep my head above the water for which I am sincerely grateful. I would also like to thank Andre Gilburn and John Allen for taking the time to read my thesis, give valuable advice, comments and encouragement. Finally I would like to thank my father, Graham E. Rotheray, who is an inspiration; I accidentally managed to get tangled up in his