THE BALANCING ACT OF FORAGING: MAMMALIAN HERBIVORES TRADE-OFF MULTIPLE RISKS WHEN SELECTING FOOD PATCHES By MEGHAN JOAN CAMP A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE UNIVERSITY School of the Environment MAY 2017 Copyright by MEGHAN JOAN CAMP, 2017 All Rights Reserved Copyright by MEGHAN JOAN CAMP, 2017 All Rights Reserved To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of MEGHAN JOAN CAMP find it satisfactory and recommend that it be accepted. ______________________________________________ Lisa A. Shipley, Ph.D., Chair ______________________________________________ Jennifer Sorenson Forbey, Ph.D. ______________________________________________ Timothy R. Johnson, Ph.D. ______________________________________________ Rodney D. Sayler, Ph.D. ______________________________________________ Daniel H. Thornton, Ph.D. ii ACKNOWLEDGMENTS First, I want to thank my advisor, Lisa Shipley, for being a mentor, advocate, friend, and inspiring example, both professionally and personally. Lisa has provided support and guidance during every step of my project and career. I would like to thank Tim Johnson for providing valuable assistance on the quantitative aspects of my project. Thank you to Jennifer Forbey for insight on the physiology aspects of this project, and for her professional mentorship, guidance, and friendship. Thank you to Dan Thornton for his collaboration and guidance on the spatial and remote sensing components of this project and to Rod Sayler for his general ecological knowledge, support, and valuable feedback on my dissertation. All members of my committee have been generous with their time and knowledge, and their suggestions have greatly improved my dissertation. I would also like to thank Janet Rachlow, for her continued support, guidance, feedback, and mentorship. I am grateful for the volunteers and students who helped me care for rabbits. Specifically, thank you to Nicole Pupich and Miranda Crowell for their invaluable help at the Small Mammal Research Facility. I want to thank several fellow graduate students, Jon Heale, Charlotte Milling, Stephanie Berry, Iver Hull, Miranda Crowell, and Amy Ulappa for helping with a variety of tasks, including metabolic and feeding trials, teaching classes, rabbit care, and keeping me sane. I would like to thank John Fluegel for providing valuable assistance in building experimental patches, arenas, temperature controlled boxes, and rooms. I am also grateful for John’s general assistance at the Small Mammal Research Facility. Among other things, he has replaced sinks, fixed heaters, replaced fluorescent light bulbs, and installed electricity to our remote rabbit pens. iii Thank you to my family. I appreciate the support of my parents, Andy and Marie Leiper, and my Aunt Joan, in my decision to be a student for a very long time and as my inspiration to work hard and never give up. Thank you to my husband and best friend, Reid, for the emotional and logistical support during my Ph.D. I could not have done this without him. Finally, I want to thank the pygmy rabbits and mountain cottontail rabbits at the Small Mammal Research Facility. They participated in thousands of trials and this project would not have been possible without them. They are ambassadors for their species and it was a privilege to work with them. This dissertation was funded by the National Science Foundation (NSF; DEB-1146368, L.A. Shipley; DEB-1146166, J.L. Rachlow; DEB-1146194, J.S. Forbey), and USDA National Institute of Food and Agriculture (NIFA; Hatch Project 1005876, L.A. Shipley). iv THE BALANCING ACT OF FORAGING: MAMMALIAN HERBIVORES TRADE-OFF MULTIPLE RISKS WHEN SELECTING FOOD PATCHES Abstract by Meghan Joan Camp, Ph.D. Washington State University May 2017 Chair: Lisa A. Shipley Animals face multiple risks while foraging such as the risk of acquiring inadequate energy from food, the risk of predation, and the risk of thermal stress. My first objective was to predict the overall perceived risk in foraging patches with multiple types of risks using a novel modeling approach that quantifies tradeoffs among competing risks by foraging animals. I evaluated how two sympatric rabbits (pygmy rabbits, Brachylagus idahoensis, and mountain cottontail rabbits, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush-steppe of western North America respond to different levels of perceived risks, including fiber and toxins (1, 8 cineole) in food, exposure to predation (inverse of concealment cover), and distance from a burrow refuge. Exposure to predation risk and distance from a burrow refuge were riskier for pygmy rabbits than cottontails, but the dietary toxin was riskier for cottontails than for pygmy rabbits. Pygmy rabbits consumed lower quality food, containing higher fiber or toxins, to avoid feeding in exposed patches or traveling far from their burrow to forage. In contrast, cottontails fed in exposed patches and traveled farther from the burrow to obtain higher quality food with lower fiber and toxins. My second objective was to evaluate how the interactions between ambient temperature and food quality influence selection of food patches and diets by pygmy rabbits and cottontails. I v examined preferences for temperature in food patches, and the effect of temperature on diet selection, intake, digestion, passage rate, and metabolism in both species of rabbits. Both species generally chose to feed in patches that were relatively colder, and this effect was greater for the larger cottontails. Both species also chose to eat more total food and a greater proportion of high fiber food when the ambient temperature was colder, passing food more quickly through their digestive system. Temperature did not affect how much 1,8 cineole they consumed nor how thoroughly they digested food. Food quality affected dry matter digestibility, but not resting metabolic rate of the rabbits. vi TABLE OF CONTENTS Page ACKNOWLEDGMENTS ....................................................................................................................................... iii Abstract ..................................................................................................................................................................... v LIST OF TABLES.................................................................................................................................................... ix LIST OF FIGURES .................................................................................................................................................. xi CHAPTER ONE ........................................................................................................................................................ 1 INTRODUCTION .................................................................................................................................................................. 1 METHODS .............................................................................................................................................................................. 6 Capture and maintenance of study animals ....................................................................................................... 6 Preference trials ............................................................................................................................................................ 7 Equivalence point trials .............................................................................................................................................. 8 Relative risk model ....................................................................................................................................................... 9 RESULTS............................................................................................................................................................................... 11 Preference trials .......................................................................................................................................................... 11 Equivalence point trials ............................................................................................................................................ 11 Relative risk model ..................................................................................................................................................... 12 DISCUSSION ........................................................................................................................................................................ 13 ACKNOWLEDGMENTS ................................................................................................................................................... 20 REFERENCES ...................................................................................................................................................................... 21 CHAPTER TWO ................................................................................................................................................... 35 INTRODUCTION ................................................................................................................................................................ 35 METHODS ...........................................................................................................................................................................