Amphibians under stress: life history, density dependence, and differences in vulnerability by Sacha Melanie O’Regan B.Sc. (Hons. Biology), Western University, 2010 Thesis Submitted In Partial Fulfillment of the Requirements for the Degree of Master of Science in the Department of Biological Sciences Faculty of Science © Sacha Melanie O’Regan 2013 SIMON FRASER UNIVERSITY Spring 2013 Approval Name: Sacha Melanie O’Regan Degree: Master of Science Title of Thesis: Amphibians under stress: life history, density dependence, and differences in vulnerability Examining Committee: Chair: Tony Williams Professor Wendy J. Palen Senior Supervisor Assistant Professor Nicholas K. Dulvy Supervisor Professor Bernard D. Roitberg Supervisor Professor Purnima Govindarajulu External Examiner Small Mammal and Herpetofauna Specialist, Ministry of Environment Date Defended/Approved: January 24, 2013 ii Partial Copyright Licence iii Ethics Statement The author, whose name appears on the title page of this work, has obtained, for the research described in this work, either: a. human research ethics approval from the Simon Fraser University Office of Research Ethics, or b. advance approval of the animal care protocol from the University Animal Care Committee of Simon Fraser University; or has conducted the research c. as a co-investigator, collaborator or research assistant in a research project approved in advance, or d. as a member of a course approved in advance for minimal risk human research, by the Office of Research Ethics. A copy of the approval letter has been filed at the Theses Office of the University Library at the time of submission of this thesis or project. The original application for approval and letter of approval are filed with the relevant offices. Inquiries may be directed to those authorities. Simon Fraser University Library Burnaby, British Columbia, Canada update Spring 2010 Abstract Numerous anthropogenic stressors are known drivers of amphibian declines. Nonetheless, research has revealed few lessons for preventing declines in advance of their occurrence. This thesis presents a conceptual framework for identifying when spatial and temporal overlap of density-dependent bottlenecks, life-history traits, and stressors increase decline risk. I evaluated this framework using published empirical amphibian density-dependence data, and found that population dynamics and life-history theory could be useful in prioritizing vulnerability to stressors, though current data deficiencies limit evidence of correlations between these factors. In an experimental test with three frog species, I found that not all species share the same sensitivities to combined climate warming and habitat permanency scenarios. These results suggest larval life-history requirements can influence species’ responses to climate change. Integrating theoretical and empirical tests provides useful tools for estimating species vulnerability and helps identify gaps in our knowledge of the dynamics that govern amphibian responses to stressors. Keywords: climate warming; density dependence; intrinsic sensitivity; life history; phenotypic plasticity; risk correlates iv Acknowledgements There are many people whose support, patience, and commitment were central to the development of this thesis. I am first thankful to Wendy Palen for her support, enthusiasm, editing, and encouragement of collaboration over the course of this work. Thank you to my committee members, Nick Dulvy and Bernie Roitberg for your considered feedback and great discussion about my research. I owe thanks to many colleagues who provided equipment, advice, and breeding site information, and to field assistants and volunteers who were involved in setting up and conducting my mesocosm experiment. Their names are listed in the chapter acknowledgements. It was truly the BISC and Earth to Ocean grad students who made this experience fantastic. Thank you for your statistical advice, emergency tank-lifting assistance, and laughs along the way. I want to extend a special thanks to my original derby group members, Corey Phillis, Stephanie Green, and Jeanette Bruce, for having the gumption to see such a fun side-project to completion. That experience made me more excited about science than any in my thesis. I am so grateful to Sean Anderson. Thank you for being my go-to backup field assistant and photographer, my statistical and visualization guru, my sounding board, and my morale-booster. Your incredible attention to detail, your insistence on doing things ‘the better way’, and your guidance in finding and using the tools to do so, has in particular made me a better scientist. Finally, I am forever thankful to my family. To Guy and Léanne, for your support, sharp humour, and interest in my work. To Grammie and Mémère, who take unconditional pride in whatever I do. Most of all, to my brother and my parents who have provided constant love and support. My research was funded through a NSERC Alexander Graham Bell Canada Graduate Scholarship, a SFU Pacific Century Scholarship, and SFU Graduate Fellowships. In addition, financial support was provided through the NSERC Discovery Grant and Canada Research Chairs Programs to Wendy Palen. v Table of Contents Approval ............................................................................................................................. ii Partial Copyright Licence .................................................................................................. iii Abstract ............................................................................................................................. iv Acknowledgements ............................................................................................................ v Table of Contents .............................................................................................................. vi List of Tables ................................................................................................................... viii List of Figures ................................................................................................................... ix General Introduction ....................................................................................................... 1 References ........................................................................................................................ 3 1. A framework for prioritizing amphibian decline risk: linking density- dependent bottlenecks to stage-specific stressors ........................................... 6 1.1. Abstract .................................................................................................................... 6 1.2. Amphibian Declines ................................................................................................. 7 1.3. The Need for a Predictive Framework ..................................................................... 7 1.4. Lessons From Other Taxa ..................................................................................... 11 1.5. Tailoring a Priority-setting Framework for Amphibian Conservation ...................... 12 1.6. A First Evaluation ................................................................................................... 15 1.6.1. Literature search ........................................................................................ 15 1.6.2. Evaluating density dependence and life history correlations ..................... 17 1.7. Research priorities in life histories, demography, and density dependence .......... 20 1.8. Conclusions ........................................................................................................... 22 1.9. Acknowledgements ................................................................................................ 22 1.10. References ............................................................................................................. 22 1.11. Tables .................................................................................................................... 27 2. Climate warming mediates negative impacts of rapid pond drying for three amphibian species ..................................................................................... 29 2.1. Abstract .................................................................................................................. 29 2.2. Introduction ............................................................................................................ 30 2.3. Methods ................................................................................................................. 33 2.3.1. Species ....................................................................................................... 33 2.3.2. Experimental design ................................................................................... 33 2.3.3. Temperature, depth, chlorophyll-a measurements .................................... 34 2.3.4. Tadpole growth and metamorphosis .......................................................... 34 2.3.5. Statistical analysis ...................................................................................... 35 2.4. Results ................................................................................................................... 36 2.4.1. Temperature and pool depth ...................................................................... 36 2.4.2. Effects of pool warming .............................................................................