Eared Sliders in Singapore
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THE ECOLOGY OF NON-NATIVE RED-EARED SLIDERS AND THEIR POTENTIAL IMPACTS ON THE NATIVE FAUNA OF SINGAPORE NG PEK KAYE ABIGAYLE (B.Sc. (Hons), NUS) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF BIOLOGICAL SCIENCES NATIONAL UNIVERSITY OF SINGAPORE 2009 “Slow but steady wins the race”, said the turtle as he crossed the finish line. - Aesop’s fables 1 Acknowledgements I would like to thank my supervisors Dr. Ruth Ramsay (O’Riordan) and Professor Chou Loke Ming for their continued guidance and support throughout my candidature. I owe my deepest gratitude to Dr. Neil Ramsay and Dr. Ruth Ramsay for their hospitality, generosity and patience. I am also deeply indebted to Professor John Davenport and his lovely wife, Julia for taking an interest in my project and for being extremely generous with their time and advice. Also, I would like to thank Prof. Peter Ng, Prof. Li Daiqin, Prof. Navjot Sodhi and Prof. Diong Cheong Hoong for their advice and support. I want to thank National University of Singapore for funding this project (Grant number R-154-000- 214-112) and the staff of the Department of Biological Sciences at NUS, especially Lat, Tommy, Poh Moi, Reena, Joan, Mrs. Chan, Ann Nee, Wei Fong, Sor Fun, Mr. Soong and Miss Lua for their administrative and logistical support and encouragement. I deeply appreciate the help and support rendered from the National Parks Board (research permit NP/RP409), especially Chew Ping Ting, Jeffrey Low, Derek Liew, Benjamin Lee and Lena Chan from the National Parks Board for assistance and permits to conduct my field studies. I also want to acknowledge Lye Fong Keng, Lou Ek Hee and Leow Su Hua from Agri-food and Veterinary Authority of Singapore, and Chong Poh Choo from the Society for the Prevention of Cruelty to Animals for their correspondence and advice on my project. I also thank the Public Utilities Board and the Ministry of Defence for allowing me entry into the areas under their purview during the course of my research. I also want to thank the NUS Institutional Animal Care and Use Committee (IACUC) for approval to carry out my research. I would also like to thank my lab mates at the Marine Biology Lab, Zeehan, Yujie, Wai, Michelle, Jani, Danwei, Angie, Karenne, Pete, Christina, Esther, Kok Ben, Li Ling and James; and friends from the Biodiversity cluster, Joelle, Duc, E-wen, Reuben, Norman, Mingko, Kelvin, Heok and Siva, as well as November for their words of encouragement and assistance in many ways. I also appreciate the help of Guillaume Juhel and Mark Jessopp from the ZEPS at University of Cork for their help and advice. I also want to thank the following people for their enjoyable company and hard labour during lab and fieldwork - Angeline, Bing, Cheng Puay, Cheryl, Danwei, Dionne, Edina, Eugene, Gillian, Huiling, Jani, Jing En, Joelle, Lynn, Meishan, Mingkang, Reuben, Ruth and Neil, Sean, Sher Vin, Teck Min, Tse-Lynn, Victor, Wai, Wan, Weisong, Yijun, Yuanting, Yvonne, Zeehan and Zhigang. I would like to express my heartfelt appreciation to my parents and relatives for their unconditional love and support; and friends: Zeehan, Joelle, Jani, Dionne, Gillian, Lynn, Huiling, Beverly, Sher Le, Tse-Lynn, Reuben, Angeline, Mingkang, Jeffrey, Jhin Hurng, Ann, Wai and Ria for their love, support and friendship that has kept me sane throughout the past five and a half years. Last but not least, I thank God for the providence of love, joy and strength which has seen me through the years. And also, TGIF (Thank God I Finished)! 2 SUMMARY ............................................................................................................ V LIST OF TABLES.................................................................................................VI LIST OF FIGURES............................................................................................VIII CHAPTER 1: INTRODUCTION ........................................................................... 1 1.1 Introduction to the Order Testudines............................................................ 1 1.2 The red-eared slider ..................................................................................... 4 1.2.1 Taxonomy and natural ranges.................................................................................................... 4 1.2.2 Ecology and Biology ................................................................................................................... 7 1.2.3 Current distribution of red-eared sliders................................................................................... 7 1.3 Past and present studies on red-eared sliders ................................................ 9 1.4 Environment of Singapore ......................................................................... 12 1.5 Status of freshwater turtles in Singapore .................................................... 18 1.6 Overview of this study............................................................................... 22 1.6.1 Objectives of this dissertation...................................................................................................22 1.6.2 Brief overview of chapters ........................................................................................................22 CHAPTER 2: THE DISTRIBUTION, ABUNDANCE AND DEMOGRAPHY OF FRESHWATER TURTLES IN SINGAPORE .............................................. 25 2.1 Introduction ................................................................................................ 25 2.1.1 Turtles in Singapore..................................................................................................................25 2.1.2 The red-eared slider in Singapore............................................................................................27 2.1.3 Red-eared slider populations and demography.......................................................................32 2.1.4 Objectives of this study..............................................................................................................33 2.2 Materials and methods ............................................................................... 34 2.2.1 Testing trap efficiency...............................................................................................................34 2.2.2 Visual census .............................................................................................................................36 2.2.3 Mark and recapture using traps ...............................................................................................37 2.3 Results....................................................................................................... 43 2.3.1 Trapping efficiency....................................................................................................................43 2.3.2 Visual census .............................................................................................................................44 2.3.3 Population size ..........................................................................................................................44 2.3.4 Sex Ratio at five sites.................................................................................................................46 2.3.5 Terrapin sizes at five sites.........................................................................................................47 2.3.6 Home range and homing behaviour of sliders ........................................................................50 2.3.7 Injured and deformed sliders....................................................................................................51 2.3.8 Other species of turtles..............................................................................................................53 2.4 Discussion ................................................................................................. 54 2.4.1 Visual survey technique ............................................................................................................54 2.4.2 Trapping methods......................................................................................................................56 i 2.4.3 Slider populations size ..............................................................................................................57 2.4.4 Population structure..................................................................................................................60 2.4.5 Home range and homing behaviour.........................................................................................62 2.4.6 Other turtle species ...................................................................................................................63 2.5 Conclusion..................................................................................................... 65 CHAPTER 3: THE REPRODUCTIVE BIOLOGY OF RED-EARED SLIDERS IN SINGAPORE.................................................................................................... 66 3.1 Introduction ............................................................................................... 66 3.1.1 Reproduction of turtles..............................................................................................................67 3.1.2 Reproduction of the red-eared slider in Singapore.................................................................69 3.1.3 Objectives...................................................................................................................................70