CLIMATIC AND HABITAT DRIVERS OF AMERICAN PIKA (OCHOTONA PRINCEPS) OCCUPANCY AND POPULATION DENSITY DYNAMICS IN THE SOUTHERN ROCKY MOUNTAIN REGION by LIESL PETERSON ERB B.A., Colorado College, 2004 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Ecology and Evolutionary Biology 2013 This thesis entitled: Climatic and habitat drivers of American pika (Ochotona princeps) occupancy and population density dynamics in the Southern Rocky Mountain Region written by Liesl Peterson Erb has been approved for the Department of Ecology and Evolutionary Biology Dr. Robert Guralnick Dr. Chris Ray Dr. Christy McCain Dr. Daniel Doak Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. iii Erb, Liesl Peterson (Ph.D., Ecology and Evolutionary Biology) Climatic and habitat drivers of American pika (Ochotona princeps) occupancy and population density dynamics in the Southern Rocky Mountain Region Thesis directed by Associate Professor Robert P. Guralnick and Research Associate Chris Ray ABSTRACT Climate change is affecting ecosystems worldwide. Among those ecological communities most affected are those inhabiting alpine habitats. These communities have evolved key adaptations to thrive in cold, wet environments. As temperatures warm and precipitation patterns become more variable due to global climate change, many alpine species are expected to be impacted. This dissertation research focuses on the American pika, a small lagomorph inhabiting broken rock slopes in the mountains and high plateaus of western North America. Population declines in the Great Basin region at the end of the 20th Century caused concern for populations elsewhere in the species range. The goal of this dissertation work was to document pika occupancy and density throughout the Southern Rocky Mountain region. Occupancy and density trends were modeled using potential climate- and habitat-based predictors known to impact pikas elsewhere in the species’ range. Survey sites were selected from among hundreds of locations known to be occupied by pikas prior to 1980. In 2008, modeling of the resurvey results from 69 of these sites indicated that mean annual precipitation plays an important role in maintaining pika populations in this region. Further surveys of 19 of these sites in 2009-2011 showed a shift toward mean summer temperature and forage quality as the top predictors of occupancy, though sites lacking pikas also remained drier than those with pikas throughout this survey period. Pika occupancy in this region was relatively high, with Southern Rockies occupancy rates ranging from 74% to 94%. Among the extant populations, variability in population densities were best explained by patch area and vegetation quality: the highest density populations were reported in regions with small patches of talus, high forb diversity, and low graminoid to forb ratios. These results suggest that intraspecific competition for food resources strongly influences pika density. iv As climate change continues, vegetation quality is expected to decline in pika habitats. Given this species’ reliance on cool, wet climates with high forb content, continued changes toward drier, hotter, and more graminoid-dominant habitats are likely to lead to declines in both pika densities and occupancy throughout the Southern Rockies and the western United States. v DEDICATION This dissertation is dedicated to my grandmother, Jean “Tommy” Peterson. vi ACKNOWLEDGEMENTS This dissertation would not have been possible without the wise and patient guidance of my co-advisors, Robert Guralnick and Chris Ray. I am also grateful for the guidance and advice of my dissertation committee, Christy McCain, Andrew Martin, and Dan Doak. I would like to thank Erik Beever, Andrew Smith, and other anonymous reviewers for their constructive comments on the manuscripts that compose this document. The research presented here would not have been possible without the hard work and positive attitudes of my amazing teams of undergraduate field assistants, including Justine Smith, Lizzy Studer, Gavin Dean, Nate Kleist, Aaron Stecker, and Kira Powell, whose tireless efforts and attention to detail were invaluable. Many thanks also to my collaborators at Colorado Parks and Wildlife, including Amy Seglund and the many dedicated research biologists in offices throughout the state. Thank you also to the staff of the parks, reserves, and wild places in which I conducted research, including Jennie Reithel, Bob Parmenter, Craig Allen, Judy Visty, Jeff Connor, Ralph Swain, Melanie Woolever, Wyoma Hansen, Missy Dressen, and many other hard working employees at public agencies across the Southern Rockies. I would also like to the financial supporters of this work: the CU Ecology and Evolutionary Biology Department and Museum of Natural History, Audubon Society of Greater Denver, Colorado Mountain Club, Mountain Studies Institute, National Geographic Society, and National Science Foundation. Outside of the research realm, many members of the CU-Boulder community made positive contributions to my educational experience in graduate school. These include: David Armstrong, Carol Wessman, Laura Border, Michael Breed, Bob Hermanson, John Basey, Alexander Cruz, Jeffry Mitton, Barbara Demmig-Adams, William Adams, Mindy Sclaro, Jill Skarstad, Julie Graf, Tammy Maldonado, and Kristin Swihart. In addition, my graduate student vii peers and their families were instrumental in my happiness and success in this venture. Some of the many key members of this support group are: Leigh Cooper, Sara Hellmuth Paull, Kelly Ramirez, Kallin Tea, Sarah Wagner, Brian, Audrey, and Cole Buma, Eve Gasarch, Loren Sackett, SeJin Song, Monica Madronich, Joanna Hubbard, Clint Francis, Marcus Cohen, Mari Elise Ewing, Preston Cumming, Natalie Robinson, Sarah Orlofske, Robert Jadin, Stower Beals, Abbey Paulson, Samantha Weintraub, Ashwin Ravikumar, Mike and Heather Robeson, and Sierra Love Stowell. Perhaps even more admirable was the support of friends and family outside of academia, where it can at times be hard to understand what is happening inside the ivory tower. I would like to thank Amy Belcastro, Jeremy Sueltenfuss, Autumn Rivera, Kayly and Matt Newland, and Jaemey and Bill Bush for their friendship, love, and support. My heartfelt thanks also go to my biggest cheerleaders: my family. A big thanks to the Ambrose Aunties for their love and hugs and the Peterson clan for the support and encouragement. Thank you also to my “extra” families, who I love so dearly: Pam Peterson and the Allenger and Allen crews for letting me join in your fun and loving family; and Bob and Marilyn Erb, leaders of the amazing Erb clan, for teaching me so much about life. While I’ve already named a long cheerleading squad, my head cheerleaders have always been Phil and Polly Peterson, who taught me to love nature, hold myself to high standards, and always fight for what is right. The most credit for my success in this venture goes to my rock, my best friend, and my husband: Peter Erb. His love and encouragement have carried me through my darkest days and lifted me to be the best version of myself. And last but not least, I would be remiss in not thanking the “person” who got me out of bed each morning and kept my priorities straight: Bridger Erb. viii CONTENTS CHAPTER 1 On the generality of a climate-mediated shift in the distribution of the American pika (Ochotona princeps) Abstract……………………………………………………………………………………1 Introduction………………………………………………………………………………..1 Methods……………………………………………………………………………………3 Results……………………………………………………………………………………..8 Discussion………………………………………………………………………………..13 2 Interactive effects of climate and vegetation on multi-year occupancy of the American pika (Ochotona princeps) Abstract…………………………………………………………………………………..18 Introduction………………………………………………………………………………19 Methods…………………………………………………………………………………..21 Results……………………………………………………………………………………27 Discussion………………………………………………………………………………..31 3 Determinants of pika population density versus occupancy in the Southern Rocky Mountains Abstract…………………………………………………………………………………..36 Introduction………………………………………………………………………………36 Methods…………………………………………………………………………………..38 Results……………………………………………………………………………………48 Discussion………………………………………………………………………………..50 ix 4 Conclusion……………………………………………………………………………….53 BIBLIOGRAPHY………………………………………………………………………………..57 APPENDICES: I Histograms of precipitation and summer temperature at pika study sites……………….65 II Boxplot of mean pika occupancy predictor coefficients…………………………………66 III Comparison of climatic predictors at 18 pika latrine density study sites………………..67 IV Pika latrine density at 18 sites in the Southern Rocky Mountains……………………….68 V Models predicting pika density with ΔAIC<2, along with the null model………………69 x TABLES Chapter 1: 1. 2008 historical resurvey alternative hypotheses and candidate model covariates……7 2. Results of 2008 historical resurvey logistic regression modeling…………………...11 Chapter 2: 1. Relative support for candidate predictors of mean pika occupancy, 2008-2011…….26 2. Top models of mean pika occupancy compared with the null model……………….29 Chapter 3: 1. Predictor descriptions, expected relationships to pika population density, weighted average coefficients, and Akaike weights……………………………………………45