Western University Scholarship@Western Electronic Thesis and Dissertation Repository 1-28-2013 12:00 AM Small mammal foraging and population responses to northern conifer mast Nikhil Lobo The University of Western Ontario Supervisor Dr. John S. Millar The University of Western Ontario Graduate Program in Biology A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Nikhil Lobo 2013 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Ecology and Evolutionary Biology Commons Recommended Citation Lobo, Nikhil, "Small mammal foraging and population responses to northern conifer mast" (2013). Electronic Thesis and Dissertation Repository. 1107. https://ir.lib.uwo.ca/etd/1107 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. SMALL MAMMAL FORAGING AND POPULATION RESPONSES TO NORTHERN CONIFER MAST (Spine title: Interactions between conifer seeds and small mammals) (Thesis format: Integrated Article) by Nikhil Lobo Graduate Program in Biology, Collaborative Program in Environment & Sustainability A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy The School of Graduate and Postdoctoral Studies The University of Western Ontario London, Ontario, Canada © Nikhil Lobo 2013 THE UNIVERSITY OF WESTERN ONTARIO School of Graduate and Postdoctoral Studies CERTIFICATE OF EXAMINATION Supervisor Examiners ______________________________ ______________________________ Dr. John S. Millar Dr. David Sherry Supervisory Committee ______________________________ Dr. Hugh Henry ______________________________ Dr. Liana Zanette ______________________________ Dr. Ian Colquhoun ______________________________ Dr. David Sherry ______________________________ Dr. Hannu Ylönen The thesis by Nikhil Lobo entitled: Small mammal foraging and population responses to northern conifer mast is accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy ______________________ _______________________________ Date Chair of the Thesis Examination Board ii Abstract Conifer seeds are a component of the diet of many rodents, and post-dispersal seed predation by rodents is often implicated as a critical constraint on the regeneration of coniferous forests. However, little is known about the effects of conifer seed availability on individual rodents and their populations. The over-arching goal of this dissertation was to investigate the effects and implications of conifer seed production on the foraging and population dynamics of northern small mammals. The predominant conifer study species were white spruce (Picea glauca) and subalpine fir (Abies lasiocarpa), and the main rodents examined were the deer mouse (Peromyscus maniculatus) and southern red-backed vole (Myodes gapperi). Nutritional analysis and laboratory experiments showed that spruce seeds are a high quality food source to rodents. Mice were able to maintain body condition on diets restricted to these seeds, and voles were able to use spruce seeds as a sole food source in the short-term. In the field, caching rates of spruce seeds varied with seed abundance, but rodents readily consumed these seeds within experimental patches regardless of abundance. Conversely, fir seeds were avoided by rodents in experiments, as was expected based on their low nutritional value and high concentration of plant secondary compounds. Mice increased food intake and retention of digesta in the caecum to maintain body mass on diets restricted to fir seeds. However, voles did not compensate for this low quality seed-diet, and their body condition deteriorated rapidly. In the field, rodents disregarded fir seeds as a valuable resource for current or future use, even at exaggeratedly abundant seed densities. iii Given these individual-level interactions, the rodent population responses to conifer mast seeding that I observed were unexpected. Summer mouse densities and breeding varied with previous fir seed production, although this may have been mediated by population responses of invertebrate post-dispersal seed predators to fir seed availability. In contrast, mouse demography was not affected by spruce mast seeding, but likely due to interspecific competition with the North American red squirrel (Tamiasciurus hudsonicus), a dominant pre-dispersal spruce seed predator. These results reveal direct and indirect consumer-resource pulse dynamics that require further examination. Keywords Rodent, northern coniferous forest, nutritional ecology, population dynamics, foraging behaviour, seed production, seed predation, mast seeding, resource pulses, food quality, plant secondary compounds, consumer-resource dynamics, deer mouse, southern red backed-vole, white spruce, subalpine fir, lodgepole pine, gut morphology, giving-up density, food supplementation, multi-trophic interactions. iv Co-Authorship Statement A version of Chapter 2 was published in the Canadian Journal of Zoology with Michelle Duong and John Millar as co-authors. Ms. Duong collected the field-based seed preference data under my supervision. Dr. Millar contributed to the study design, provided equipment and funding, and contributed editorial comments to the manuscript. A version of Chapter 3 was published in Mammalian Biology with John Millar as a co- author. Dr. Millar contributed to the study design, provided equipment and funding, and contributed editorial comments to the manuscript. A version of Chapter 4 has been submitted for publication to the Journal of Mammalogy with Derek Green and John Millar as co-authors. Mr. Green collected the subalpine fir seed data under my supervision, and contributed editorial comments on the manuscript. Dr. Millar contributed to the study design, provided equipment and funding, and contributed editorial comments to the manuscript. A combined version of Chapters 5 and 6 has been accepted for publication in the Journal of Animal Ecology with John Millar as a co-author. Dr. Millar contributed to the study design, provided access to long-term datasets (pre-2007), provided equipment and funding, and contributed editorial comments to the manuscripts. v Acknowledgments First, I would like to thank Dr. Jack Millar for his guidance and support over the last five years. It was quite serendipitous that I ended up working with Jack, and I could not have asked for a better graduate school experience. He has been the ideal supervisor, pushing me when I needed it (“Well, have you got the answer yet?”), but leaving me to my own devices otherwise. While I was always interested in ecological research, it was Jack who inspired a real passion for natural history and the mountains in this “city kid”. I sincerely appreciate his open-door policy, lightning-fast turn-around of written drafts, and generosity when it came to purchasing research equipment. Above all, I have to thank Jack for encouraging me to transfer into the PhD program, and providing me with an incredible diversity of research, teaching, and travel opportunities; and of course, the bags of farm-fresh vegetables I would periodically find on my desk. He has built an impressive professional legacy over his career, and I am honoured to be his final graduate student. I would also like to thank the past and present members of my advisory committee, Drs. Robert Scott, David Sherry, and Liana Zanette, for their recommendations and assistance with project ideas, statistical analyses, manuscripts, and reference letters. Special thanks also goes to Dr. Robert Bailey, who taught me to embrace statistics as my friend. Dr. Mark Bernards and the members of his lab, especially Dimitre Ivanov and Pooja Sharma, were very patient and helpful when I had questions about analytical chemistry. Mark’s enthusiasm for the project was contagious, and kept me motivated through the numerous times we had to start over in the lab. Even though the plant secondary compound work did not end up in this dissertation, it was an invaluable research experience, and one that I will integrate into my future work. Thanks also to Natalie Westwood for assistance in the lab. vi I spent five incredible field seasons out in the Kananaskis Valley, but I certainly could not have completed a project of this scale without assistance, or without the friendships, cold beers, and random adventures with so many people – mousers, honorary mousers, and other field station/Calgary/Edmonton dwellers. I am grateful to all of you, especially my actual field assistants; I pushed them very hard, but hopefully also taught them a few things along the way. While there were occasional complaints about the early mornings, late evenings, and endless seed sorting, I was very fortunate to have a skilled, motivated, and “character”- filled group of coworkers every summer. Thanks to Tracy Flach, Dr. Yeen Ten Hwang, Kurt Illerbrun, Chey Peterson, Edith Pounden, Kari Richardson, Jennifer Smith, Crisia Tabacaru, Michelle Duong, Andrew Geary, Eddie Liu, Laura Barclay, Craig Harding, Chris Ibbotson, Rachel White, Amanda Doyle, Derek Green, Grant Hilts, Sarah McPike, Lindsey Valliant, Beate Zein, Ashlynn Gomes, Lila Karolak, and Liz Morrison. I also have to thank the staff at the Kananaskis Field Station/University of Calgary Biogeoscience Institute for their logistical support and friendship