POTENTIAL IMPACT OF INVASIVE ANURAN SPECIES IN WESTERN NEWFOUNDLAND by © Dion O. Kelly A thesis submitted to The School of Graduate Studies in partial fulfillment of the requirements for the degree of Master of Science Cognitive and Behavioural Ecology Programme Memorial University of Newfoundland March 2016 St. John’s Newfoundland and Labrador ABSTRACT Successful dispersal and establishment of invasive anurans (frogs and toads) may be influenced by competitive exclusion and/or niche differentiation with competing species. I investigated the dispersal of anurans in western Newfoundland using anuran calling surveys and pond-edge visual encounter surveys. The Mink Frog, Lithobates septentrionalis, had dispersed ~50 km northeast from the original (2001) discovery location and ~34 km southwest; displaying spatial separation from Green Frogs, Lithobates clamitans, at landscape and local scales. Visual encounter surveys did not reveal any correlation between adult Mink Frogs and odonate competitors. Additionally, I assessed the impact of varying tadpole densities on removal of epilithic periphyton by providing epilithon covered substrates for American Toad, Anaxyrus americanus, tadpoles raised in laboratory or field enclosures. Higher tadpole densities resulted in smaller tadpoles that removed more periphyton from substrates. As anuran population ranges expand, there may be effects on ecological resources for vertebrate and invertebrate competitors. ii ACKNOWLEDGEMENTS First and foremost, I thank Dr. Ian Warkentin for providing this opportunity to expand my knowledge in the field of ecology; his immeasurable support and guidance has been vital to the completion of this project. Thank you also to the members of my supervisory committee, Dr. Christine Campbell and Dr. Robert Scott, for their invaluable advice and assistance in the project design and analysis. I am particularly appreciative of the funding received from the Wildlife Division, Government of Newfoundland and Labrador and the Natural Sciences and Engineering Research Council of Canada in support of this research. To Jasmine Pinksen and Lindsay Batt, the research assistants, I am extremely grateful for your help in collecting the data. I also extend my gratitude to Wanda Ellsworth, Bobbie-Ann Parsons and Maria Howell, for the laboratory support. I sincerely thank Dr. Schneider, Dr. Erin Fraser and Chris Hammill for the advice provided in statistically analyzing data. The writing of my thesis was made easier by the comments, suggestions and support offered by Hayley Alloway, Nodgra Duhaney, Kathy Unger, and Lester Marshall; special thanks to you all for aiding in the completion of this study. To my parents and family, many thanks. I am immensely grateful to Stephanie Small-Kelly for her unwavering support, encouragement and suggestions in pursuing this Master’s degree. Without you, I would not have been able to complete my degree. Finally I offer a posthumous thank you to Peter Vogel, who started me on this road years ago and provided an initial inspiration. iii Table of Contents ABSTRACT ........................................................................................................................ ii ACKNOWLEDGEMENTS ............................................................................................... iii 1. Introduction and Overview ............................................................................................. 1 1.1. Invasive Species ...................................................................................................... 1 1.2. Anuran Ecological Effects ...................................................................................... 3 1.3. Invasive Anurans in Newfoundland ........................................................................ 5 1.4. Thesis Objectives and Outline ................................................................................ 8 1.5. Co-authorship Statement ....................................................................................... 10 1.6. References ............................................................................................................. 11 2. Initial Dispersal and Habitat Use of Newly Introduced Mink Frogs in Western Newfoundland, Canada ................................................................................................ 18 2.1. Abstract ................................................................................................................. 19 2.2. Introduction ........................................................................................................... 19 2.3. Materials and Methods .......................................................................................... 22 2.3.1. Study Species ............................................................................................... 22 2.3.2. Study Sites ................................................................................................... 23 2.3.3. Sampling Anuran Distribution ..................................................................... 24 2.3.4. Habitat Classification ................................................................................... 25 2.3.5. Statistical Analyses ...................................................................................... 26 2.4. Results ................................................................................................................... 27 2.5. Discussion ............................................................................................................. 31 2.6. Acknowledgements ............................................................................................... 35 2.7. Literature Cited ..................................................................................................... 35 3. Impact of Invasive Eastern American Toad Tadpole Populations on Pond Epilithon in Western Newfoundland ................................................................................................ 49 3.1. Abstract ................................................................................................................. 50 3.2. Introduction ........................................................................................................... 51 3.3. Methods ................................................................................................................. 54 iv 3.3.1. Study Sites and Experimental Setup ............................................................ 54 3.3.2. Growth Rate Assessment ............................................................................. 56 3.3.3. Periphyton Removal .................................................................................... 56 3.3.4. Statistical Analysis ....................................................................................... 57 3.4. Results ................................................................................................................... 58 3.4.1. Growth Rate Analysis .................................................................................. 58 3.4.2. Periphyton Removal .................................................................................... 60 3.5. Discussion ............................................................................................................. 61 3.5.1. Density-Dependent Effects on Tadpole Growth .......................................... 61 3.5.2. Periphyton Biomass Removal by American Toad Tadpoles ....................... 63 3.5.3. Conclusion ................................................................................................... 65 3.6. Acknowledgements ............................................................................................... 65 3.7. References ............................................................................................................. 65 4. Summary ...................................................................................................................... 77 4.1. Anuran Distribution and Ecological Impact ......................................................... 77 4.2. References ............................................................................................................. 82 5. Appendices ................................................................................................................... 88 5.1. Appendix I – Anuran-Odonate Surveys ................................................................ 89 5.1.1. Introduction .................................................................................................. 89 5.1.2. Methods ....................................................................................................... 90 5.1.3. Results.......................................................................................................... 91 5.1.4. Discussion .................................................................................................... 91 5.1.5. References .................................................................................................... 92 5.2. Appendix II - Tables ............................................................................................. 97 v List of Tables Table 2-1. Habitat Variables Recorded at Monitoring Sites ......................................... 47 Table 2-2. Water Quality Data – Manual Calling Surveys (2014).. ............................. 48 Table 3-1. Weekly Water Quality - pH, Dissolved Oxygen (mg/l), Conductivity (µS/cm)