Investigating the Effects of Fire on Spiders at the Individual and Community Level
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The fire ecology of spiders: investigating the effects of fire on spiders at the individual and community level. Jessica Marsh BSc Hons, MSc School of Biological Sciences, Faculty of Science and Engineering, Flinders University, Adelaide, South Australia Thesis submitted for the degree of Doctor of Philosophy July 2017 Table of Contents Thesis Abstract .......................................................................................................................... iv Declaration ............................................................................................................................... vi Acknowledgements .................................................................................................................. vii Contextual Statement ............................................................................................................. viii CHAPTER ONE ............................................................................................................................ 9 Introduction to Thesis ................................................................................................................ 9 Review of literature 9 Background 12 Thesis overview 14 References 17 CHAPTER TWO ......................................................................................................................... 25 The effect of experimental burning on the composition and diversity of spider communities in nationally threatened remnant vegetation communities .......................................................... 25 Abstract 25 Introduction 26 Methods 34 Study sites 34 Surveys 37 Statistical Analyses 43 Results 45 Question One: Burn treatment, burn temperature and time since burn on community composition and diversity 47 Question Two: Vegetation and litter depth on spider community composition and diversity 60 Question Three: ‘Fire specialist’ species and burning 69 Discussion 72 References 80 i CHAPTER THREE ....................................................................................................................... 90 A novel morphological trait-based system for categorising the spider community into guilds and measuring community response to burning. ............................................................................. 90 Abstract 90 Introduction 91 Methods 100 Experimental sites 100 Functional guild classification 101 Trait scoring 102 Statistical analysis 106 Results 108 Fire effects on spider guild composition 108 Diversity and richness 111 How does trait distribution affect species’ responses to environmental variables? 112 References 119 CHAPTER FOUR ...................................................................................................................... 125 How to define a spider community? Comparing the use and limitations of common methods for categorising spider communities in ecological studies. ............................................................ 125 Abstract 125 Methods 133 Spider identification and trait classification 134 Statistical analyses 134 Results 136 Patterns of response of morphospecies, family, RGS and MGS guild assemblages 136 Exclusion of immature specimens 147 Discussion 150 References 155 ii CHAPTER FIVE ........................................................................................................................ 160 Smoking spiders: Investigating the response of spiders to exposure to smoke. ....................... 160 Abstract 160 Introduction 161 Methods 166 Results 169 Discussion 175 References 179 CHAPTER SIX .......................................................................................................................... 185 Thesis Conclusion ................................................................................................................... 185 References 192 Appendix ............................................................................................................................... 194 iii Thesis Abstract Fire is a major disturbance event that can have profound effects on ecosystems and on the biota within. The increasing use of anthropogenic fire in Australia, as a means to control fuel loads and provide asset protection, coupled with predictions for larger and more frequent wildfires has meant that the need to understand, and make predictions about how these events affect ecosystems, and the biota within them, is high. This need is especially potent where burning is being conducted in areas of high conservation status or environmental concern, such as the Eucalyptus cneorifolia vegetation communities on Kangaroo Island, which are listed as Critically Endangered under the Environment Protection and Biodiversity Conservation Act 1999. The chapters of this thesis are dedicated to increasing the understanding of how fire affects spiders, both at an individual and community level, and is focussed on spiders occupying fragmented patches of threatened E. cneorifolia vegetation communities. The first empirical chapter of this thesis used a controlled and replicated experimental design to show how burning small fragments of native vegetation affected the composition and diversity of spider communities within. We found burn temperature, burn treatment and vegetation structure to significantly affect the composition and diversity of spider communities. The second chapter expanded on these findings by analysing a functional response of spiders to fire, utilising two novel guild systems. In support of the findings from the analysis of a taxonomic response in Chapter One, we found burning to significantly affect the diversity and composition of functional guilds. In order to accurately record and analyse patterns of spider community change following burning it is crucial to understand the implications of the method used to categorise the data and the effect it has on patterns of community response to environmental variables. We investigated this in the third empirical chapter. In order to do so we used multivariate techniques to analyse changes in the community composition and diversity of family, morphospecies and guild assemblages in response to environmental variables associated with burning. Ordinations revealed significant differences in the response of these three assemblages to burning. The fourth chapter used a novel approach and experimental design to investigate the responses of individual spiders to exposure to smoke. We detected significant increases in the rate of movement following exposure to a smoke stimulus. These findings are novel and suggest a potential mechanism for emigration of spiders away from fire, however they require further iv testing. This thesis covers diverse elements of spider fire ecology that link together, building on the findings of previous studies and adding new and novel insights. In it we cover aspects of spider community fire ecology with recommendations for management techniques, methodological suggestions for improving the use of spider data in ecological research and experimental analyses of behavioural responses by spiders to fire related stimuli. v Declaration I certify that this thesis does not incorporate without acknowledgment any material previously submitted for a degree or diploma in any university; and that to the best of my knowledge and belief it does not contain any material previously published or written by another person except where due reference is made in the text. Signed…………………………………………………………….. Date…………………16/12/2016………………………….. vi Acknowledgements I would like to thank my supervisors, Duncan Mackay, Molly Whalen and Richard Glatz for all their help, support, advice, comments and encouragement. I am especially thankful to them for keeping me in the loop and stopping me from feeling too isolated here on Kangaroo Island. Thank you to Dave Taylor for getting me started on this road, for the encouragement and support along the way and for being my fellow PhD buddy. Big thank you to Danny Male, Ivy Male and Belle Male for helping with field work, for being my go- to for computer tech. advice (the last bit not so much from Ivy and Belle) and for being understanding when I have needed to work late. I honestly couldn’t have done it without your support. Thank you to the private land holders on Kangaroo Island, who let me their land be burnt and the let me chase spiders about on their property. Thank you to Department of Environment and Natural Resources, Kangaroo Island, for lending me a microscope and for letting me have access to all the specimens that had been collected in pre-burn trials. This research was supported by funds from the Australian Arachnological Society, the Nature Foundation, SA, and the Holsworth Wildlife Research Endowment. vii Contextual Statement This thesis is divided up in to six chapters. Chapters One and Six form the Introduction to the thesis, comprising a review and discussion of the literature, and the Thesis Discussion. Chapters Two to Six present original research. These are in the format of scientific papers. For this reason, each chapter has a separate reference list, and the tables and figures are presented in the text. viii 1 CHAPTER ONE 2 Introduction to Thesis 3 Review of literature 4 Fire is a part of Australia’s natural history. Humans have long been manipulating fire to manage 5 the natural environment (Bowman, 1998); however, in recent years alterations to the natural fire 6 regime have increased at a rate not seen before. Following recent large-scale wildfire events,