The role of fire in the ecology of Leichhardt's grasshopper (Petasida ephippigera) and its food plants, Pityrodia spp. Piers Hugh Barrow B. Sc. (University of Queensland) Hons. (Northern Territory University) A thesis submitted to satisfy the requirements for the award of the degree of Doctor of Philosophy in the Institute of Advanced Studies, School for Environmental Research, Charles Darwin University, Darwin, Australia. March 2009 I hereby declare that the work herein, now submitted as a thesis for the degree of Doctor of Philosophy is the result of my own investigations, and all references to ideas and work of other researchers have been specifically acknowledged. I hereby certify that the work embodied in this thesis has not already been accepted in substance for any degree, and is not being currently submitted in candidature for any other degree. Piers Barrow March 2009 i Acknowledgements My partner Cate Lynch provided support and encouragement, field assistance, proof- reading and editing, and forewent much of what is expected in normal life for a such a long time through this project, and I am deeply grateful. My supervisors Peter Whitehead, Barry Brook, Jeremy Russell-Smith and Stephen Garnett provided valuable advice and discussion, and, despite typically huge workloads, never failed to make themselves available to help. I am particularly indebted to Peter Whitehead, who shouldered most of the work, way beyond expectations, and provided guidance and insight throughout, and to Jeremy Russell-Smith, who has encouraged and facilitated my interest in the ecology of the Top End in general, and of the sandstone country and fire in particular, for many years. I am very much indebted to the traditional owners who worked with me throughout the project, especially as most of the work was done at the very worst time of year to be in the sandstone. We walked and clambered long distances and worked long hours under extremely arduous conditions, and in oppressive heat and humidity. There was often no shade, no breeze, and much heat and glare reflected off the bare rocks, yet people worked cheerfully and willingly, and always anticipated the next trip. I thank all the traditional owners who participated in field work, but especially my long term companions Andrew Moore and Colin Liddy. I thank all the traditional owners who allowed me to work on their country across the Top End. I am especially grateful to Jeffrey Lee who has taken a keen interest in the project throughout and who took me to otherwise closed areas at Koongarra. He also saved us many hours of walking by allowing us to camp at Gubara. I am also particularly indebted to Yvonne Margarula and the Mirrar people in Kakadu and to Ryan Barruwei and the Jawoyn people of Nitmiluk. I thank all the rangers in the various national parks who provided field assistance, logistical support, accommodation, encouragement, interest, enthusiasm, and quad bikes. ii Many, many rangers helped, so I mention only the supervisors here, but I am grateful to them all: Sarah Kerin (Nitmiluk, Gregory and Keep River), Rob Muller, Ollie Scheibe, Lyndall MacLean and Patrick Shaughnessy (Kakadu) Craig Hempel provided access to the Nitmiluk Vegetation Database. Owen Price gave access to the database for firescar transects. Jeremy-Russell-Smith and Cameron Yates gave access to the NT Ecological Attributes database. Felicity Watt extracted the information on fire histories from satellite imagery held by the NT Bushfires Council. I am most grateful all for this assistance which has helped to fill many gaps in the overall picture. I would also like to extend my sincere thanks to all of the following groups and individuals. To all the many volunteers, both friends and strangers. Especially to an extraordinary group of Green Corps volunteers at Nitmiluk whose enthusiasm (on their day off) astonished me. To the staff at the Darwin Herbarium for plant identifications, advice and valuable discussion, especially Whispering Bob Harwood, who undertook field work with me at Keep River. To Colin Wilson from NRETA who carried out joint field work with me in Keep river, Gregory and Nitmiluk National parks, along with Bev Maxwell and Ben Bayliss. Discussions with Colin, an entomologist, have always insightful, valuable and highly entertaining. iii Contents Abstract ........................................................................................................... 1 Chapter 1: Introduction .................................................................................. 4 1.1 Background........................................................................................................... 4 1.2 Description and taxonomy of the species ........................................................... 5 1.3 Social significance ................................................................................................ 6 1.4 Historical records and current distribution ...................................................... 6 1.5 Broad biology and ecology .................................................................................. 9 1.5.1 Life cycle....................................................................................................... 9 1.5.3 Dispersal...................................................................................................... 12 1.5.2 Aposematism............................................................................................... 13 1.5.4 Host plants................................................................................................... 13 1.5.5 Habitat......................................................................................................... 14 1.5.6 Population structure .................................................................................... 15 1.6 Conservation status............................................................................................ 15 1.7 Fire.......................................................................................................................16 1.7.1 Fire and Petasida ........................................................................................ 16 1.7.2 Fire ecology of Pityrodia and the heath communities................................. 17 1.8 Population modelling ......................................................................................... 19 1.9 Broad aims .......................................................................................................... 20 Chapter 2: Fire regimes................................................................................ 21 2.1 Abstract............................................................................................................... 21 iv 2.2 Introduction........................................................................................................ 22 2.2.1 Aboriginal fire regimes ............................................................................... 25 2.2.2 Contemporary fire regimes ......................................................................... 28 2.2.2.1 Season ................................................................................................ 29 2.2.2.2 Frequency and fire intervals............................................................... 30 2.2.2.3 Intensity.............................................................................................. 31 2.2.2.4 Extent ................................................................................................. 31 2.2.2.5 Patchiness........................................................................................... 32 2.3 Methods............................................................................................................... 34 2.4 Results ................................................................................................................. 38 2.4 Discussion............................................................................................................ 50 Chapter 3: The habitat of Leichhardt’s grasshopper – floristic and environmental relations and distribution patterns of Pityrodia. ............ 54 3.1 Abstract............................................................................................................... 54 3.2 Introduction........................................................................................................ 55 3.3 Methods............................................................................................................... 58 3.3.1 Study sites ................................................................................................... 58 3.3.2 Distribution Patterns. .................................................................................. 66 3.3.2.1 Regional distribution patterns ............................................................ 66 3.3.2.2 Local distribution patterns ................................................................. 67 3.3.3 Habitat data collection................................................................................. 68 3.3.3.1 Nitmiluk Vegetation survey ............................................................... 68 3.3.3.2 The current study ............................................................................... 69 v 3.3.4 Habitat data analysis ................................................................................... 71 3.3.4.1 Environmental correlates ..................................................................