Arthropod communities and passerine diet: effects of shrub expansion in Western Alaska Item Type Thesis Authors McDermott, Molly Tankersley Download date 26/09/2021 06:13:39 Link to Item http://hdl.handle.net/11122/7893 ARTHROPOD COMMUNITIES AND PASSERINE DIET: EFFECTS OF SHRUB EXPANSION IN WESTERN ALASKA By Molly Tankersley McDermott, B.A./B.S. A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Biological Sciences University of Alaska Fairbanks August 2017 APPROVED: Pat Doak, Committee Chair Greg Breed, Committee Member Colleen Handel, Committee Member Christa Mulder, Committee Member Kris Hundertmark, Chair Department o f Biology and Wildlife Paul Layer, Dean College o f Natural Science and Mathematics Michael Castellini, Dean of the Graduate School ABSTRACT Across the Arctic, taller woody shrubs, particularly willow (Salix spp.), birch (Betula spp.), and alder (Alnus spp.), have been expanding rapidly onto tundra. Changes in vegetation structure can alter the physical habitat structure, thermal environment, and food available to arthropods, which play an important role in the structure and functioning of Arctic ecosystems. Not only do they provide key ecosystem services such as pollination and nutrient cycling, they are an essential food source for migratory birds. In this study I examined the relationships between the abundance, diversity, and community composition of arthropods and the height and cover of several shrub species across a tundra-shrub gradient in northwestern Alaska. To characterize nestling diet of common passerines that occupy this gradient, I used next-generation sequencing of fecal matter. Willow cover was strongly and consistently associated with abundance and biomass of arthropods and significant shifts in arthropod community composition and diversity. Key nestling prey items were positively associated with both willow and ericaceous shrubs. Diet composition varied significantly among bird species and spatially within species, however, I found that temporal variability in prey abundance did not have a strong relationship to the probability of consumption. I predict that the wide temporal window of prey availability and high diet diversity may protect these birds against negative impacts from climate-driven shifts in prey phenology and abundance. Taken together, my results suggest that shrub expansion could result in a significant shift in Arctic food-web structure and an increase in food availability for insectivores, although future ecosystem change in the Arctic is likely to be heterogeneous as shrub types are expanding at different rates and in different places across the Arctic. iii iv TABLE OF CONTENTS Page TITLE PAGE ..... i ABSTRACT...............................................................................................................................................iii TABLE OF CONTENTS.......................................................................................................................... v LIST OF FIGURES..................................................................................................................................ix LIST OF TABLES....................................................................................................................................xi ACKNOWLEDGMENTS ..................................................................................................................... xv CHAPTER 1. GENERAL INTRODUCTION.......................................................................................1 1.1 REFERENCES................................................................................................................5 CHAPTER 2. ARTHROPOD COMMUNITIES ACROSS TUNDRA-SHRUB ECOTONES OF NORTHWESTERN ALASKA: IMPLICATIONS OF CONTINUED SHRUB EXPANSION .... 9 2.1 ABSTRACT........................................................................................................................ 9 2.2 INTRODUCTION.............................................................................................................10 2.3 METHODS.........................................................................................................................14 2.3.1 Study System ..............................................................................................................14 2.3.2 Arthropod Sampling ..................................................................................................17 2.3.3 Habitat Sampling....................................................................................................... 19 2.3.4 Statistical Analysis ................................................................................................... 20 2.3.4.1 Data preparation ................................................................................................ 20 2.3.4.2 Overall abundance and biomass ......................................................................21 2.3.4.3 Taxon-specific abundance ................................................................................23 2.3.4.4 Diversity............................................................................................................. 24 v 2.3.4.5 Community composition 24 2.4 RESULTS..................................... 25 2.4.1 Overall Abundance ................................................................................................... 26 2.4.2 Overall Biomass ........................................................................................................27 2.4.3 Taxon-specific Abundance ...................................................................................... 29 2.4.4 Diversity.....................................................................................................................32 2.4.5 Community Composition .........................................................................................33 2.5 DISCUSSION...................................................................................................................35 2.6 REFERENCES ..................................................................................................................40 2.7 APPENDICES ...................................................................................................................45 CHAPTER 3. HIGH DIET DIVERSITY OF ARCTIC PASSERINE NESTLINGS REVEALED BY NEXT-GENERATION SEQUENCING....................................................................................... 65 3.1 ABSTRACT......................................................................................................................65 3.2 INTRODUCTION............................................................................................................ 66 3.3 METHODS........................................................................................................................ 71 3.3.1 Study A rea ..................................................................................................................71 3.3.2 Dietary Sampling.......................................................................................................71 3.3.3 Arthropod Sampling ................................................................................................. 72 3.3.4 DNA Sequencing Protocol...................................................................................... 74 3.3.5 Statistical Analysis ....................................................................................................75 3.4 RESULTS.......................................................................................................................... 77 3.4.1 Diet Composition .....................................................................................................77 vi 3.4.2 Prey Availability and Consumption ....................................................................... 80 3.4.3 Diet Diversity ............................................................................................................ 85 3.5 DISCUSSION...................................................................................................................86 3.6 REFERENCES ..................................................................................................................92 3.7 APPENDICES ...................................................................................................................99 CHAPTER 4. GENERAL CONCLUSION........................................................................................125 4.1 REFERENCES........................................................................................................... 130 vii viii LIST OF FIGURES Page Figure 2.1 Location of 13 plots at our coastal and interior sites on the Seward Peninsula, northwestern Alaska, USA, and the years in which arthropods were sampled ................................15 Figure 2.2 Photos taken near pitfall arrays in northwestern Alaska, USA, showing (a) typical tundra vegetation characterized by graminoids and mixed low ericaceous shrubs and (b) mixed willow and birch shrub thicket ................................................................................................................16 Figure 2.3 Vegetation (a,b) and landscape (c,d) variables measured over 69 transects on the Seward Peninsula, USA, and used as predictors of arthropod abundance, biomass, and diversity. 26 Figure 2.4 The relationship of willow cover, ericaceous cover, and birch height to total