THE ROLE OF FIRE IN SHAPING POLLINATOR COMMUNITIES: A POST BURN ANALYSIS OF BEES IN SERPENTINE HABITAT HUMBOLDT STATE UNIVERSITY By Sheilah Lillie A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment Of the Requirements for the Degree Master of Arts In Biological Sciences May 2011 THE ROLE OF FIRE IN SHAPING POLLINATOR COMMUNITIES: A POST BURN ANALYSIS OF BEES IN SERPENTINE HABITAT By Sheilah Lillie “We certify that we have read this study and that it conforms to acceptable standards of scholarly presentation and is fully acceptable, in scope and quality, as a thesis for the degree of Master of Arts.” Approved by the Master’s Thesis Committee: ________________________________________________________________________ Erik S. Jules, Major Professor Date ________________________________________________________________________ Michael R. Mesler, Committee Member Date ________________________________________________________________________ Michael A. Camann, Committee Member Date ________________________________________________________________________ Gregory M. Crutsinger, Committee Member Date ________________________________________________________________________ Michael R. Mesler, Graduate Coordinator Date ________________________________________________________________________ Dr. Jená Burges, Vice Provost Date ABSTRACT THE ROLE OF FIRE IN SHAPING POLLINATOR COMMUNITIES: A POST BURN ANALYSIS OF BEES IN SERPENTINE HABITAT Sheilah Lillie Bees (Hymenoptera) represent one of the primary pollinators in most natural and managed ecosystems world-wide. Current concerns for a global decline in bee populations emphasize the need to better understand the factors that shape bee communities. Although habitat disturbance is believed to play an important role in bee community structure, little is known about how bees respond to fire, one of the most common disturbances in terrestrial ecosystems. I assessed the effects of a natural wildfire, the Biscuit Fire of 2002, on shaping bee communities in serpentine habitats of northwestern California and southwestern Oregon. In the summer of 2005 I surveyed bee communities in eight unburned and eight burned areas that each included a xeric, upland component and a wetland component (i.e., Darlingtonia fen). I also surveyed the vegetation at each site to determine if differences in floral diversity, abundance or composition could explain any differences in bee community structure between unburned and burned sites. Average bee species richness was 1.4× greater in unburned sites than in burned sites, although this difference was only marginally significant. Bee community composition differed between unburned and burned sites, however these differences were iii also weakly significant. In contrast, flowering plant communities did not differ in diversity, abundance or composition between unburned and burned sites and only two plant species differed in their abundance between sites. Since floral resources were comparable in unburned and burned sites, they do not explain the observed, albeit modest, differences in bee richness. Variation in the bee community is likely explained by changes in available nesting resources following the Biscuit Fire, however, I did not assess nesting resources directly in my study. My work supports a growing body of literature suggesting that serpentine plant communities are less affected by fire than plant communities found in other habitats, perhaps because open, low productivity habitats experience a relatively small release from aboveground competition that typically follows fire. Similarly, the effects on bee community structure I found are modest in comparison to some previous work assessing the effects of fire on bees in other habitats and are likely a reflection of the lack of significant post-fire changes in associated serpentine plant communities. iv ACKNOWLEDGEMENTS I would like to thank my major advisor, Dr. Erik Jules, for his guidance and incredible patience throughout this process. He not only introduced me to the amazing world of serpentine ecology but he enthusiastically encouraged my work to enhance our understanding of these wonderfully unique habitats. I would also like to extend my gratitude to my committee members, Dr. Michael Camann, Dr. Gregory Crutsinger and Dr. Michael Mesler. Additional thanks to Dr. Mesler who spent many hours by my side peering through a microscope to confirm the identity of my many bees. I would like to thank Priya Shahani for providing me with much of the field equipment needed to complete this study. Thank you to Jolynn Mahmoudi who assisted with processing and sorting specimens in the laboratory. I would like to thank Dr. William Bigg who assisted me in initial assessment of my data and Dave Franklin who provided me continuing assistance with both data analyses and sanity management. To my friends who have always supported me and who never lost faith in me, thank you. To my mom, who from a young age instilled in me the importance of education and hard work and never let me believe I was anything less than capable, thank you. To my big brother, who has always been my role model, thank you. And finally to John, who performed field assistant tasks free of charge, was my personal chef when I was too busy to cook, who provided technical support during every computer “crisis”, who endured unimaginable tantrums and acts of insanity over the last five years, and who still gave me unwavering encouragement and support, thank you. v TABLE OF CONTENTS ACKNOWLEDGEMENTS.................................................................................................v TABLE OF CONTENTS................................................................................................... vi LIST OF TABLES............................................................................................................ vii LIST OF FIGURES ......................................................................................................... viii LIST OF APPENDICES.................................................................................................... ix INTRODUCTION ...............................................................................................................1 MATERIALS AND METHODS.........................................................................................7 Study System ...........................................................................................................7 Study Design............................................................................................................8 Bee Community Sampling.....................................................................................12 Specimen Processing and Identification ................................................................13 Floral Community Sampling..................................................................................14 Statistical Analyses ................................................................................................16 RESULTS ..........................................................................................................................19 DISCUSSION....................................................................................................................24 LITERATURE CITED ......................................................................................................33 vi LIST OF TABLES Table Page 1 A summary of site attributes for each of the 16 sites. Each site consisted of a fen and its surrounding upland. Latitude is given as decimal degrees. Size refers to the fen sampling area only ......................................11 vii LIST OF FIGURES Figure Page 1 Map of study area within the Siskiyou Mountains of northwest California and southwest Oregon. Each symbol represents a study site which comprised a fen and upland habitat. Circles represent the 8 sites burned in the Biscuit Fire of 2002 and triangles represent the 8 unburned sites ..............................................................10 2 Bee species richness for unburned (n = 23) and burned (n = 16) sites, (A) and bee species abundance, pan data only, for unburned (n = 51) and burned (n = 39) sites, (B). Horizontal lines represent mean value for each group. Each site includes one Darlingtonia fen and its immediate surrounding upland habitat. Burned sites were within the boundary of the 2002 Biscuit Fire of northern California and southern Oregon........................................................................................................................21 3 Non-metric multidimensional scaling (NMDS) ordination of bee communities based on Bray-Curtis similarity values (final stress = 14.369). Marginally significant differences in bee community composition between 8 unburned sites and 8 burned sites were assessed using multiple response permutation procedures (MRPP; P = 0.0964). Each symbol represents the bee community at one of sixteen sites surveyed in the summer of 2005............................................................22 4 Plant species richness for unburned (n = 29) and burned (n = 30) sites, (A) and floral abundance in m 2 for unburned (n = 8.69) and burned (n = 7.77) sites, (B). Horizontal lines represent mean value for each group...............................................23 viii LIST OF APPENDICES Appendix Page A Summary of plant species surveyed. Species are listed by family; “Species Code” is the alphanumeric code assigned to each species