AN ABSTRACT OF THE THESIS OF Chiho Kimoto for the degree of Master of Science in Wildlife Science presented on December 3, 2010. Title: Effect of Livestock Grazing on Native Bees in a Pacific Northwest Bunchgrass Prairie. Abstract approved: Sandra J. DeBano Native bees play an important role as pollinators of natural vegetation and agricultural crops. Yet many pollinators, including some native bees, are declining in numbers. Some of the potential causes of these declines are habitat destruction and degradation by various human land uses, including urban development and sprawl, construction of roadways, and habitat conversion to agriculture such as crop production and livestock grazing. Livestock grazing is one of the most common land uses in western North America and it can impact floral and nesting resources that are important to native bees. These effects are likely manifested through grazing’s effect on vegetation and soil characteristics. However, few studies have investigated how livestock grazing impacts native bees in North America. As a result, the overall goal of this research was to determine how a gradient of livestock grazing intensities impacts native bee communities in a threatened and poorly studied grassland of western North America, the Pacific Northwest Bunchgrass Prairie. Because no studies have examined the bee fauna of this grassland habitat, our study had two objectives: 1) describe the native bee community in the Zumwalt Prairie in northeastern Oregon, which is one of the largest remaining remnants of this unique grassland type, and how it changes through time, and 2) investigate how livestock grazing affects that native bee fauna. To address these objectives, we sampled pollinators during the summer of 2007 and 2008 in 16 40-ha pastures on a plateau in the Zumwalt Prairie using blue vane traps. Each pasture was assigned one of four cattle stocking rates (high, medium low, and no cattle), and grazing intensity was quantified by measuring utilization. Grazing treatments were applied in the early summer for two years. We measured soil and vegetation characteristics that related to floral and nesting resources of bees as well as several metrics of the bee community, including diversity, richness, abundance, and community composition. We found 92 species and 119 morphospecies of native bees in 27 genera. This diverse community of native bees showed strong interseasonal and interannual variation that appears to be related to weather and plant phenology. We also found that even after exposure to just two years of grazing, some effects on vegetation and soils were evident. For example, increased grazing intensity significantly reduced vegetation structure, the abundance of certain blooming plants, surface soil stability, and the amount of soil surface covered by herbaceous litter. In addition, increased grazing intensity significantly increased soil compaction and the amount of bare ground. Native bee communities responded grazing intensity through changes in abundance, richness, diversity and community composition. Different bee taxa responded to grazing intensity differently and this response varied temporally. For example, bumble bees were sensitive to grazing intensity early in the season, showing reduced abundance, diversity, and/or richness with increased grazing intensity. In contrast, halictid bees did not respond to grazing intensity in any season. However, even within a genus or family, different species responded to grazing intensity in different manners, potentially because of variation in life histories. This research suggests that maintaining land with a mixture of livestock grazing intensities may be the best way to conserve this important and diverse pollinator group in the Pacific Northwest Bunchgrass Prairie. ©Copyright by Chiho Kimoto December 3, 2010. All Rights Reserved Effect of Livestock Grazing on Native Bees in a Pacific Northwest Bunchgrass Prairie by Chiho Kimoto A THESIS Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented December 3, 2010 Commencement June 2011 Master of Science thesis of Chiho Kimoto presented on December 3, 2010. APPROVED: Major Professor, representing Wildlife Science Head of the Department of Fisheries and Wildlife Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Chiho Kimoto, Author ACKNOWLEDGEMENTS I would like to thank my academic advisor and committee members. Dr. Sandra J. DeBano was always there for me whenever I needed her help to understand the various aspects of the research and encouraged me through my master student’s life. She introduced me to the beauty of terrestrial insects and always amazed me with not only her knowledge of science but also her knowledge of writing. I also would like to thank Dr. Andrew R. Moldenke who spent many hours identifying thousands of bees to species or morphospecies and was very generous in training me in the identification of some bee groups. I was always fascinated by his knowledge of bees. Whenever I had questions about scientific papers, he provided me with great insights; he also reviewed my manuscripts and gave me a great deal of detailed information. I also would like to thank Dr. Robert V. Taylor who provided me with great and useful input on my manuscripts and interesting scientific papers. In the field, I was always impressed by his knowledge of all aspect of plants and the Zumwalt Prairie. I would like to thank Dr. Robbin W. Thorp who identified all Bombus bees to species at the University of California, Davis. Thank you very much for spending so many hours identifying bees and your great generosity in training me how to identify bumble bees to species. I was very fascinated by his knowledge of bees and willingness to share it with me. I also would like to thank Drs. William P. Stephen and Sujaya Rao who provided bee training sessions and laboratory space during those bee sessions as I learned about bee morphology at Oregon State University. Thank you very much, Dr, ACKNOWLEDGEMENTS (Continued) Sujaya Rao, for reviewing my manuscripts and providing me great insights. I would like to say thank you very much to Dr. William P. Stephen for providing me with his fascinating knowledge about bees. I also appreciate very much his willingness to share his great knowledge about bees whenever I have questions about them. I also would like to thank Drs. Terry L. Griswold and Molly G. Gee, who identified Megachile and Osmia to species at the USDA-ARS Bee Biology and Systematics Laboratory, Utah State University, Logan. This detailed information improved my thesis very much. I appreciate The Nature Conservancy for letting us conduct this study on their land and providing facilities. I also would like to thank Dr. Christopher Marshall for providing me laboratory space at the Oregon State Arthropod Collection. It was a great experience for me to work in the museum so that I had opportunities to see so many beautiful terrestrial insects. I also offer my thanks to The Bohart Museum of Entomology at the University of California, Davis, for providing me with workspace while I was being trained in bumble bee identification by Dr. Robbin W. Thorp. I have many thanks for the hardest worker, Dr. Mahmut Doğramaci. Ms. Anne Madsen and Ms. Kimberly Tanner helped with field work during very hot times of the year. I am very thankful to Ms. Heidi Schmalz and Ms. Tonya Vowles for helping me to identify all the blooming plants to species. I also would like to thank Mr. Austin Gurwell and Ms. Merrie Richardson for putting identification tags on each bee ACKNOWLEDGEMENTS (Continued) specimen. Your quality of work was greatly appreciated. I also would like to thank Ms. Sam Colby and Ms. Ariadne DeMarco, who assisted me in the laboratory. I am grateful to Drs. David E. Wooster, Robert V. Taylor, Robbin W. Thorp, Andrew R. Moldenke, and Sujaya Rao for reviewing my manuscripts and providing me great insights for improving my thesis. Many thanks to Dr. Robert V. Taylor, Dr. Patricia Kennedy, Dr. Timothy DelCurto, Ms. Heidi Schmaltz, Dr. Tracy Johnson, and Mr. Sam Wyfells for being so successful with their research. I appreciated all The Nature Conservancy staff members, Dr. Robert V. Taylor, Ms. Liza Jane Nichols, Mr. Phil Shepherd, and Ms. Angie Freeman for providing me with housing facilities Thank you very much to the funding agencies that made this research possible. This project was supported by an Oren Pollak Research Grant from The Nature Conservancy, a USDA National Research Initiative grant (#2006-35101-16572), and a US EPA STAR grant (#RD83456601-0). Finally, I would like to thank my family, especially my father Osami Kimoto, my mother Yoriko Kimoto, my older brother Takatomi Kimoto, relatives, friends, and my fellow graduate students who supported me during my graduate career. They always believed in me, supported me and encouraged me while I was at school. Thank you very much all of you once again. All of your hard work and all of your support helped make this research successful. CONTRIBUTION OF AUTHORS Dr. Sandra J. DeBano helped design and conduct the research; collect, analyze, and interpret the data; and revise the manuscripts. Dr. Andrew R. Moldenke identified all bees, except bumble bees and Osmia, to species or morphospecies; trained me how to identify some of the groups to species or morphospecies; helped interpret the data; and reviewed my manuscripts. Dr. Robbin W. Thorp identified bumble bee specimens to species; trained me to identify bumble bee species; and reviewed my manuscripts. Drs. Molly G. Gee and Terry L. Griswold identified Osmia to species. Dr. Sujaya Rao gave me the idea to use blue vane traps, and loaned me traps during my first field season.