EFFECTS OF ABUNDANT SNOW AND ROSS’S GEESE ON ARCTIC ECOSYSTEM STRUCTURE: PLANTS, BIRDS, AND RODENTS A Thesis Submitted to the College of Graduate and Postdoctoral Studies In Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy In the Department of Biology University of Saskatchewan Saskatoon By Dana K. Kellett © Copyright Dana K. Kellett, April 2021. All rights reserved. Unless otherwise noted, copyright of the material in this thesis belongs to the author. PERMISSION TO USE In presenting this thesis/dissertation in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis/dissertation in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised my thesis/dissertation work or, in their absence, by the Head of the Department or the Dean of the College in which my thesis work was done. It is understood that any copying or publication or use of this thesis/dissertation or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis/dissertation. DISCLAIMER Reference in this thesis/dissertation to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favoring by the University of Saskatchewan. The views and opinions of the author expressed herein do not state or reflect those of the University of Saskatchewan, and shall not be used for advertising or product endorsement purposes. Requests for permission to copy or to make other use of material in this thesis in whole or in part should be addressed to: Head of the Department of Biology 112 Science Place University of Saskatchewan Saskatoon, Saskatchewan S7N 5E2 Canada OR Dean College of Graduate and Postdoctoral Studies Room 116, Thorvaldson Building 110 Science Place Saskatoon, Saskatchewan S7N 5C9 Canada i ABSTRACT Migratory animals link and often have profound impacts on geographically distant ecosystems through trophic interactions and transport of nutrients, energy, toxins, parasites and pathogens. Moreover, when seasonally linked ecosystems differ in carrying capacity of migrant species, detrimental effects to biodiversity through trophic cascades can occur in ecosystems with lower carrying capacity. Access to agricultural production has increased carrying capacity of lesser snow (Anser caerulescens caerulescens) and Ross’s geese (Anser rossii, collectively, ‘light geese’) in southern agricultural landscapes where these species winter and stage during migration to and from northern breeding regions. Rapid population growth in response to increased carrying capacity during fall, winter, and spring has caused trophic cascades in less productive subarctic and arctic ecosystems during summer. I investigated changes to plant community structure in direct response to foraging and nesting by abundant and highly concentrated light geese within the Queen Maud Gulf (Ahiak) Migratory Bird Sanctuary, Nunavut, Canada, with particular reference to Karrak Lake, one of the largest nesting goose colonies in the world. I further studied indirect impacts of vegetation change on aspects of sympatric vertebrate response, including resident brown lemmings and ptarmigan, and migratory shorebirds and passerines. Foraging by light geese created spatially heterogeneous landscapes composed of lightly and intensely foraged grazing lawns in the brood-rearing and molting region north of Karrak Lake, within the pre-existing mosaic created by variation in topography, moisture, and soil properties created by geomorphic processes. Although foraging light geese nearly depleted aboveground plant biomass in some areas in the Sanctuary, belowground biomass was largely intact and thus, plant communities have strong potential for aboveground regeneration. Nesting and foraging geese severely reduced aboveground plant biomass within the nesting colony at Karrak Lake. Colonizing plant species established on bare sediment or peat exposed by previous vegetation removal by geese, resulting in shifts in species composition of plant communities. High occupancy by nesting light geese resulted in transition of lowland communities dominated by grasses and sedges (collectively, ‘graminoids’), Sphagnum spp., and willows (Salix spp.) to those comprised of exposed peat, birch (Betula glandulosa), non-Sphagnum mosses, marsh ragwort (Tephroseris palustris), and mare’s tail (Hippuris vulgaris). Community changes were less apparent in upland regions that are naturally less vegetated even in the absence of geese, but ii fruticose lichens, crowberry (Empetrum nigrum) and white heather (Cassiope tetragona) dominated undisturbed plant communities whereas crustose lichens and bearberry (Arctostaphylos spp.) comprised disturbed communities. Reduction of plant biomass and community shifts from graminoid dominance to those with high proportions of exposed peat and birch had negative effects on abundance of brown lemmings and occupancy by graminoid-specialist shorebirds; however, some open-nesting and generalist cover-nesting avian species showed neutral or positive responses to establishment of birch in altered habitats. Intact graminoid communities are important to ecosystem structure and function and population health of many resident and migratory arctic vertebrates. However, light geese often nest in localized, dense aggregations, and thus negative impacts on sympatric species may be spatially limited and confined to large nesting colonies and severely altered brood- rearing and molting regions. Moreover, altered upland and lowland habitats remained largely vegetated in the Sanctuary, contrasting sharply with altered coastal marshes in subarctic regions. iii ACKNOWLEGEMENTS In June 2015 on a helicopter flight from Cambridge Bay to Karrak Lake, I had nearly dissuaded myself from pursuing PhD research. Upon my arrival, Jim Leafloor greeted me with “let’s talk about your PhD”, and continued with statements such as “we need to support good people”. Evidently Jim viewed me in such company, as he assured me “that graduate work would not be an issue [for me]” (there were some issues), and to “let him know what I need”. Like Ray, Jim is hard to disappoint, and armed with his confidence and that of others, I sought approval from our management team to pursue graduate work concurrently with employment responsibilities. Thus, I am indebted to the support and encouragement of Kevin Cash, Roxanne Comeau, Elsie Krebs, Janine Murray, and Patrice Simon, and many others within the Wildlife Research Division of Environment and Climate Change Canada, and at the Prairie and Northern Wildlife Research Centre. I owe most of my professional success from long association with, and encouragement and mentorship by Ray Alisauskas. Ray is a coauthor on all my publications to date, except one. Under his guidance as a graduate student and technician, I have learned analytical techniques and improved writing skills, as well as gained decades of practical and leadership experience with co-management of a remote research site. The greatest encouragement to pursue a PhD came from Ray, who simply repeated on a number of occasions “you’re going to do it [write the papers] anyway”. Like many of his former students, Ray, Penny, and their family have become my extended family. My earliest memories of the Alisauskas clan include their youngest child Andrea, a toddler in the mid-1990s, hanging off the underside of Drake, a black Labrador retriever. More recently, Ray and Penny are blessed grandparents, marking the passage of time. I am thankful to have been watched over by them all of these years. I thank Erica Nol for agreeing to serve as my external examiner. An engaged advisory committee comprised of Douglas Clark, Jill Johnstone, Philip McLoughlin, and Christy Morrissey has guided me; I thank them for their insights, questions, and suggestions, and look forward to an equally engaging final defense. I certainly wish this could occur in person, and I look forward to the future meeting of Erica beyond the confines of our computers. Research presented in this dissertation drew from data collected in all years that the Karrak Lake Research Station (established 1991) has been in existence, and historical data from iv John Ryder, Bob McLandress, Richard Kerbes, and others. Arctic Goose Joint Venture, Central and Mississippi Flyway Councils, Environment and Climate Change Canada, Natural Sciences and Engineering Research Council of Canada, Polar Continental Shelf Project, and University of Saskatchewan have most recently supported Alisauskas-led research within the Queen Maud Gulf (Ahiak) Migratory Bird Sanctuary. Historical supporting agencies have included California Waterfowl Association, Delta Waterfowl Foundation, Institute for Wetlands and Waterfowl Research, Sea Duck Joint Venture, Northern Ecosystems Initiative, Northern Scientific Training Program, and Nunavut Wildlife Management Board. The majority of this extensive data collection from 1991-present occurred at Karrak Lake, with efforts provided by over 200 field assistants to date (Appendix A). In the early days, I am thankful for