AN ABSTRACT OF THE DISSERTATION OF Lauren Ashley Smith DiCarlo for the degree of Doctor of Philosophy in Wildlife Science on June 1, 2018 Title: Native Bee and Spider Community Responses to Grassland Restoration and Wildfire Abstract approved: ______________________________________________________ Sandra J. DeBano Up to 99.9% of native North American grasslands have been degraded since European settlement, primarily due to agricultural conversion. Today, grasslands are a top priority for restoration as they provide essential habitat for many rare and endangered species; however, the majority of studies in grasslands have focused on vegetation or vertebrate responses to restoration while largely neglecting invertebrates. Grassland invertebrates are highly diverse and provide important ecosystem services such as pollination, nutrient cycling, food for vertebrates, and pest control. This dissertation seeks to understand the structure of spider and native bee communities within arid bunchgrass prairies and determine how grassland restoration and wildfire impact these beneficial invertebrates. In Chapter 2, I focus on spider communities in a low-elevation, arid Pacific Northwest bunchgrass prairie and compare degraded, native, and restored sites to examine how spider communities and habitat respond to arid grassland restoration. Spider communities responded strongly to invasive annual grass, litter, and biological soil crust cover. Native sites differed from those in restored and degraded sites by community composition and abundance, with fewer spiders found in native sites than degraded and restored sites. However, native and restored sites had more species than degraded sites. I also examine how responses varied with the age of the restoration project. Chronosequence data showed trends for lower abundance, higher species richness, and changing community composition as restoration projects mature. Chapter 3 describes the unique bee community found within the same bunchgrass prairie, identifies environmental variables associated with variation in bee abundance, richness, diversity, and community structure, and assesses the effect of grassland restoration on bee communities. I identify temporal trends within the bee and floral resource community that span over several seasons and years. As with the spider community, the bee community composition at native sites differed from both the degraded and restored communities, which did not differ from each other. However, there was no statistically significant difference in bee abundance, richness, and diversity among degraded, restored, and native sites. Bee abundance was most closely associated with litter cover, bee richness was associated with maximum vegetation height and floral abundance, and bee diversity was associated with floral abundance. Chapter 4 examines spider community response to restoration at the regional scale. I compared degraded and restored communities at three separate grassland locations in eastern Oregon to determine what impact landscape context has on restoration and identify the environmental variables that underlie spider community patterns at this larger scale. Spider communities did not respond similarly to restoration among locations, indicating that landscape context may play a larger role in responses than restoration treatments. Regionally, spider abundance responded largely to changes in invasive grass and litter cover, while richness and diversity responded to changes in maximum vegetation height and forb cover. Wildfire frequency has increased across the western United States, yet it is unclear how these fires affect beneficial invertebrates in arid grasslands. In Chapter 5, I examine bee, spider, and vegetative communities one year before and one year after wildfire. Both native bee and spider community composition were significantly altered one year after the fire. The fire did not affect bee or spider abundance, or spider diversity or richness but significantly increased native bee diversity and richness. Habitat variables such as invasive annual grass and biological soil crust declined significantly, while forb abundance increased after the burn. Taken together, the findings show that invertebrate responses to grassland restoration and wildfire in inland Pacific Northwest grasslands are complex. Spider communities appear to largely respond to changes in vegetative structure (grass cover and height) and litter, while bee communities appear to be sensitive to changes in potential nesting sites (grass and litter cover) and floral resources (floral abundance). Depending on the degree that these environmental factors are influenced by future grassland restoration or wildfire, managers may expect to see strong effects on spider and bee communities. ©Copyright by Lauren Ashley Smith DiCarlo June 1, 2018 All Rights Reserved Native Bee and Spider Community Responses to Grassland Restoration and Wildfire by Lauren Ashley Smith DiCarlo A DISSERTATION submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented June 1, 2018 Commencement June 2018 Doctor of Philosophy dissertation of Lauren Ashley Smith DiCarlo presented on June 1, 2018. APPROVED: Major Professor, representing Wildlife Science Head of the Department of Fisheries and Wildlife Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. Lauren Ashley Smith DiCarlo, Author ACKNOWLEDGEMENTS I would like to thank my advisor, Sandy DeBano, for her incredible advice, encouragement and unwavering support throughout this process. Not every advisor provides free rein over research design and spends hundreds of hours with their students in the field and for this I simply cannot express my immense gratitude. My other committee members, Andy Hulting, John Lambrinos, Taal Levi, David Pyke, and the late Don Horneck, each helped make this dissertation better and offered exceptionally helpful comments and suggestions, not only to the text, but also to the project design. This work would not have been possible without the people at the Hermiston Agricultural Research and Extension Center including the NIFA faculty, administration, and field crew. Thank you for providing me with a fantastic opportunity by bringing me on as a PhD student at Oregon State, providing every type of assistance at all hours of the day, and fixing many flat tires. I’ve learned an unbelievable amount from all of them. Also, the other NIFA students and Fisheries and Wildlife Graduate students have been a great source of support, I’m happy to call them both friends and colleagues. In addition, thank you to all of the field and lab assistants, many of which spent their summers working long strenuous hours in 100+ degrees or bent over a lab bench separating spiders or pinning bees. The list of remarkable women include: Lauren J. Smith, Samantha Roof, Estany Campbell, Keelie Kirby, Lexie McDaniel, Mamo Waianuhea, and Briana Price. Lastly, I would like to thank my family for their encouragement. The difficult decisions were made much easier through their support and help driving across the country (many times) and moving lots of furniture. My grandparents, in particular, have always been my biggest cheerleaders and my spirit was greatly uplifted by my grandmother’s handwritten letters each week, of which I will forever cherish. Above all, I would like to thank my husband, Michael, who has given up so much to support me. Thank you for commuting every other week to various locations around Oregon, the delicious dinners, and taking care of our two amazing dogs, Pearl and Louie. And most importantly, thank you for making my dreams into a reality. CONTRIBUTION OF AUTHORS Dr. Sandra DeBano contributed to all aspects of this dissertation including study design, analysis, and writing. Skyler Burrows of the USDA Bee Lab in Logan, Utah identified all bees and helped with editing of Chapters 3 and 5. TABLE OF CONTENTS Page CHAPTER 1. GENERAL INTRODUCTION ..............................................................1 Objectives ................................................................................................................3 Literature Cited ........................................................................................................4 CHAPTER 2. Citation Information ...............................................................................8 CHAPTER 2. SPIDER COMMUNITY RESPONSES TO GRASSLAND RESTORATION: BALANCING TRADEOFFS BETWEEN ABUNDANCE AND DIVERSITY ..................................................................................................................9 Abstract ....................................................................................................................9 Introduction ..............................................................................................................9 Methods..................................................................................................................12 Study Site .........................................................................................................12 Site Selection ...................................................................................................12 Spider Sampling ...............................................................................................13 Habitat