The Ecology Of Tadpoles In A Temporary Pond In The Western Cape With Comparisons To Other Habitats Samantha Hopkins Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in the Department of Biodiversity and Conservation Biology, University of the Western Cape. Supervisor: Prof. A. Channing March 2006 ABSTRACT This work centres on the tadpoles in a temporary pond in the middle of Kenilworth racecourse, Cape Town, South Africa. Trapping was carried out over two wet seasons and five species were found, Cacosternum platys, Microbatrachella capensis, Strongylopus grayii, Tomopterna delalandii and Xenopus laevis. Three of these species were trapped and their position in the pond was related to environmental variables. Water depth, water temperature, oxygen concentration, and substrate type were all found to correlate to the position of the tadpoles in the pond. Over a 24 hour period, sampling every three hours, tadpole species divided the pond spatially and were trapped in different numbers in different. Previous work has shown that some tadpole species can adjust their time to metamorphosis. When S. grayii and C. platys tadpoles were tested, there was no significant difference between the drying and control water treatments for either species. The food items the tadpoles were eating in the Kenilworth ponds was studied using gut contents analysis. Tadpoles were taken from the pond once a week and their gut contents were compared to the contents of the water column and differences were looked for between the species. These results suggest that the tadpoles do not select for certain food items and do not partition their environment, between species, using food. A similar study was then carried out in a tropical environment in North Luangwa National Park, Zambia. Here, 12 genera were collected and still the tadpoles’ guts contained the same quantities of food items as was found in the water column. The final part of this work is concerned with the tadpoles’ thermal tolerance. S. grayii was selected as a study species and 15 sites were visited across its distribution. These sites included the northern and southern ends of the distribution in the winter rainfall area as well as three sites with a different rainfall regime and six sites that were on the same latitude but at different altitudes. The results showed that the tadpoles of S. grayii are probably able to produce heat shock proteins that will last up to two weeks, however, the critical thermal maxima (CTM) of the tadpoles did not show a trend with latitude or altitude. The largest difference was seen between the tadpoles from the summer and winter rainfall regions. ii The summer rainfall tadpoles had a much higher CTM than the tadpoles from the winter rainfall regions before and after acclimation. This study is a very broad insight into tadpole ecology in the Western Cape. It has highlighted the fact that little work has been carried out here recently and more needs to be done to establish what environmental changes are occurring, and if these will affect the ability of these tadpoles to develop to metamorphosis under these new conditions. iii DECLARATION I. ___________________, declare that “The ecology of tadpoles in a temporary pond in the Western Cape with comparisons to other habitats” is my own work and that all the sources I have used or quoted have been indicated and acknowledged by means of complete references. iv ACKNOWLEDGEMENTS I would like to thank a number of people for their help during the past three years. Firstly, I would like to thank; Atherton deVillers, Marius Burger, all of the people at the race track and Cape Nature Conservation for allowing me to work on their land and for help with the Kenilworth pond. Secondly, the people in Zambia, Elsabe and Hugo van der Westhuizen for help with collecting tadpoles. I would also like to thank Jacques Deere, Paul Emms, Lorraine Glennon, Sara Haveron, Kev Hopkins, Darren Houniet, Jen Jackson, Pete le Roux, Sandi Willows-Monroe and all of the third year group for help with fieldwork and my Mum and Dad for always being on the end of the phone. I am grateful to Alan Channing for his guidance and support in my project and to all the people in the UWC Biodiversity and Conservation Biology department who have helped me out, particularly Martin Hendricks and Kevin Christianson. v CONTENTS ABSTRACT ii DECLARATION iv ACKNOWLEDGEMENTS v CHAPTER 1: GENERAL INTRODUCTION 1 1.1 Amphibians 1 1.2 Tadpole Development 2 1.3 Predation on Tadpoles 3 1.4 Competition between Tadpoles 4 1.5 Amphibians on the Cape Flats 5 1.6 This Study 9 1.7 Key Research Questions 11 1.8 Species Descriptions 12 CHAPTER 2: ENTRY SEQUENCE AND TADPOLE NUMBERS IN THE KENILWORTH RACECOURSE POND 22 2.1 Introduction 22 2.1.1 Species assemblage 22 2.1.2 Sequence of tadpole entry 22 2.1.3 Competition 23 2.2 Methods 24 2.2.1 Marking techniques 24 2.2.2 Determining the presence of tadpoles at the pond 24 2.2.3 Mark and recapture 25 2.3 Results 26 2.3.1 Adult calling 26 2.3.2 Tadpole species presence 26 2.3.3 Tadpole species catch rate 27 2.3.4 Tadpole developmental stages in the pond 29 2.3.5 Mark and recapture 32 2.4 Discussion 33 2.4.1 The pond tadpole community 33 2.4.2 How many tadpoles occupy the pond? 34 2.4.3 Projections of tadpole numbers 35 CHAPTER 3: THE TADPOLE ENVIRONMENT 37 3.1 Introduction 37 3.1.1 Tadpole trapping 39 3.2 Methods 39 3.2.1 Study site 39 3.2.2 Tadpole trapping 44 3.2.3 Data analysis 47 3.2.4 Duration of study 48 3.3 Results 48 3.3.1 Species present in the pond 48 3.3.2 Pond temperatures 48 3.3.3 Oxygen concentration in the pond 51 3.3.4 Relationship between temperature and oxygen concentration 53 3.3.5 Pond depth through the season 53 3.3.6 Strongylopus grayii tadpoles 54 3.3.7 Cacosternum platys tadpoles 59 3.3.8 Xenopus laevis tadpoles 64 3.3.9 Tomopterna delalandii and Microbatrachella capensis tadpoles 66 3.3.10 Tadpole trapping vs. water temperature 66 3.3.11 Tadpole trapping vs. oxygen concentration 67 3.4 Discussion 68 3.4.1 Species present in the pond 68 3.4.2 Tadpole position 69 3.4.3 Tadpole trapping and water temperature 70 3.4.4 Tadpole trapping and oxygen concentration 70 3.4.5 Tadpole trapping and water clarity 71 3.4.6 Tadpole trapping and water column depth 72 3.4.7 Tadpole trapping and substrate 72 3.4.8 Success of the critically endangered micro frog 73 3.4.9 Real ponds are really complex 73 CHAPTER 4: TADPOLES IN A THREE-DIMENSIONAL HABITAT 74 4.1 Introduction 74 4.2 Methods 75 4.2.1 Surveys over 24 hours 75 4.2.2 Data analysis 77 4.3 Results 77 4.3.1 Temperature and oxygen over 24 hours 77 4.3.2 Tadpole captures over 24 hours 78 4.3.2.1 Strongylopus grayii 79 4.3.2.2 Cacosternum platys 82 4.3.2.3 Xenopus laevis 85 4.3.3 Environmental correlations 88 4.4 Discussion 92 4.4.1 Tadpole position 92 4.4.2 Environmental correlations 94 CHAPTER 5: THE THREAT OF DESICCATION: DO TADPOLES OF STRONGYLOPUS GRAYI AND CACOSTERNUM PLATYS METAMORPHOSE EARLIER UNDER DRYING CONDITIONS? 96 5.1 Introduction 96 5.2 Methods 98 5.3 Results 100 5.3.1 Strongylopus grayii 100 5.3.2 Cacosternum platys 101 5.4 Discussion 102 5.4.1 Cues used by tadpoles 102 5.4.2 Drying has no effect 103 5.4.3 Strongylopus grayii breeding strategy 103 5.4.4 Cacosternum platys breeding strategy 104 5.4.5 Implications for future climate change 105 CHAPTER 6: FOOD SELECTION AND COMPETITION IN A TEMPERATE POND 106 6.1 Introduction 106 6.2 Methods 108 6.3 Results 109 6.3.1 Availability of food in the water column 109 6.3.2 Tadpole diet 110 6.3.3 Competition between species and food resource partitioning 112 6.4 Discussion 114 6.4.1 Availability of food in the water column 114 6.4.2 Tadpole diet 114 CHAPTER 7: DO TADPOLES PARTITION FOOD IN A TROPICAL POND? NORTH LUANGWA NATIONAL PARK, ZAMBIA 117 7.1 Introduction 117 7.2 Methods 118 7.2.1 Study site 118 7.2.2 Tadpole morphology 120 7.2.3 Tadpole associations 121 7.2.4 Food items 121 7.3 Results 122 7.3.1 Study ponds 122 7.3.2 Tadpole morphology 124 7.3.3 Tadpole associations 125 7.3.4 Food items 128 7.4 Discussion 132 7.4.1 Study ponds 132 7.4.2 Tadpole morphology 132 7.4.3 Tadpole associations 134 7.4.4 Food items 134 7.4.5 Interplay of food and space 135 7.4.6 Comparison with the Kenilworth racecourse pond 136 CHAPTER 8: THE CRITICAL THERMAL MAXIMA OF STRONGYLOPUS GRAYII TADPOLES 137 8.1 Introduction 137 8.1.1 Global climate change 137 8.1.2 Effects of high temperature on ectotherms 138 8.1.3 Tadpoles 139 8.1.4 Thermal Tolerance 140 8.1.5 This study 142 8.2 Methods 143 8.3 Results 144 8.3.1 Collecting sites 144 8.3.2 Sites 1-3 (Southern) 150 8.3.3 Sites 10-12 (Northern) 152 8.3.4 Higher (sites 7-9) vs.