Sprovach Thesis
Total Page:16
File Type:pdf, Size:1020Kb
! ii Acknowledgements To my advisor, Dr. Michael Draney, I cannot thank you enough for your guidance, encouragement, and mentorship. Your lessons have helped me the past when writing this thesis and leading me through my studies, are helping me in the present for helping to get my results published, and will help me in the future for wherever my ecology career takes me. To my committee members, Dr. Matthew Dornbush and Dr. Patrick Robinson, thank you for your valuable input for making my thesis the best that it could be, especially in regards to interpreting sparse data and expanding my conclusions to the greater picture. To the Heirloom Plant fund and the Office of Graduate Studies at the University of Wisconsin - Green Bay, thank you for the financial support necessary to fund both this thesis project and my travel to Golden, CO to present preliminary data at the 20th International Congress of Arachnology. To statistician Dr. Megan Olson-Hunt, thank you for helping me navigate the sometimes complicated world of statistical analysis. Your suggestions and viewpoints helped me make sense of some of my more difficult analyses and made me a convert to R. To Kathryn Corio of the Fewless Herbarium and Kate Hau of Bay Beach Wildlife Sanctuary, thank you for helping me identify the trickier plant species and saplings that I encountered in my field sites. To Mike Reed of Bay Beach Wildlife Sanctuary, Mark Konlock of the Green Bay Botanical Garden, and the Friends of Peninsula State Park, thank you for helping me locate a suitable field site to research garlic mustard. To all of my colleagues who helped me with various tasks at my field site, from vegetative sampling, to setting up and breaking down plots, to taking plant measurements, thank you for your kindness and helping hands. Mia Spaid, Holly Harpster, Candace Kraft, Claire Rebman, Ellie Roark, and Wilson Gaul, there was no way I could finish this project alone. To my family and friends, thank you for your emotional support during some of the more difficult periods of my graduate studies. Also, thank you for your advice on topics such as beating writer's block and designing figures that are easier for the reader to see. To anybody else that I did not mention by name, but helped me finish this thesis and earn my Master's degree, thank you. No matter how great or small your contribution, this thesis could not be done without you. ! ! iii Abstract Spider diversity response to garlic mustard (Alliaria petiolata) invasion in a Wisconsin forest understory Megan Sprovach The invasive herb garlic mustard is considered a major contributor to biodiversity loss in forest understories throughout the United States, including in northeastern Wisconsin. Research on the effect of garlic mustard invasion on spiders is limited. The purpose of this project is examine the effect of garlic mustard invasion on the spider community structure at Bay Beach Wildlife Sanctuary in Green Bay, Wisconsin. Four pitfall traps per each of thirty 5 X 5-meter plots, representing a gradient of garlic mustard cover, were sampled monthly from June to September in 2015. Time-controlled vegetative sampling was conducted in each plot at the beginning and end of the collection season and all vegetation within each plot was identified to species. Spider species richness, spider Shannon diversity, and the ratio of web-building to wandering spider species were quantified at the plot level. The spider richness, diversity and guild ratios were modeled against garlic mustard cover. Individual spider species were examined for correlation with garlic mustard cover. When accounting for plant height deviation, the relationship between Shannon diversity and garlic mustard cover is inconclusive, but spider species richness increased with greater garlic mustard cover. The ratio of web-building to wandering spiders was not correlated with garlic mustard cover. June vegetative samples of the native linyphiid Ceraticelus fissiceps were also positively correlated with garlic mustard, but not strongly enough to be used as an indicator for plot-level ecological change. The opportunistic native linyphiid Diplostyla concolor and the native salticid Pelegrina proterva were also commonly found in the plots. These results suggest that the presence of an invasive species in a habitat could benefit spider populations under unusually low biodiversity conditions, but caution must be exercised when considering these results for policy implications. ! ! iv Table of Contents Acknowledgements ........................................................................................................... ii Abstract ............................................................................................................................ iii Table of Contents ............................................................................................................. iv List of Tables ..................................................................................................................... v List of Figures .................................................................................................................. vi Introduction ...................................................................................................................... 1 Methods ............................................................................................................................. 8 Research Site .......................................................................................................... 8 Sampling Methods ................................................................................................. 8 Plant Identification .............................................................................................. 10 Statistical Analyses .............................................................................................. 11 Results .............................................................................................................................. 14 Summary of Sampling Data ................................................................................ 14 Pitfall Trap Data Analysis ................................................................................... 22 Vegetative Sample Data Analysis ........................................................................ 24 Plant Height as a Fixed Effect ............................................................................ 30 Discussion ........................................................................................................................ 32 Policy Implications ......................................................................................................... 38 References ....................................................................................................................... 42 ! ! v List of Tables Table 1 List of plant species found at Bay Beach Wildlife Sanctuary in Brown County, Wisconsin .................................................................................... 15 Table 2 List of all identified spider families and species from pitfall and vegetative samples at Bay Beach Wildlife Sanctuary in Brown County, Wisconsin . 17 Table 3 Correlation matrices for pitfall trap and vegetative sample variables of interest ...................................................................................................... 21 Table 4 Ranked abundance of spider species (adult specimens only) sampled from pitfall traps at Bay Beach Wildlife Sanctuary in Brown County, Wisconsin ................................................................................................. 23 Table 5 Ranked abundance of spider species (adult specimens only) sampled from vegetation at Bay Beach Wildlife Sanctuary in Brown County, Wisconsin ................................................................................................................... 25 ! ! vi List of Figures Figure 1 Number of garlic mustard stems versus number of active spider webs. Adapted from Smith and Schmitz (2015), Appendix A1 ........................... 5 Figure 2 Diagram of the quadrat used for vegetative sampling ............................... 11 Figure 3 Frequency of Alliaria petiolata percent cover values in the Bay Beach Wildlife Sanctuary research site by number of plots ................................. 14 Figure 4 Species accumulation curves for pitfall and vegetative sampling data from June, July, August, and September at Bay Beach Wildlife Sanctuary in Brown County, Wisconsin ........................................................................ 20 Figure 5 Relationship between garlic mustard cover and the Shannon diversity of adult spiders sampled from pitfall traps placed in June, July, August, and September ................................................................................................. 24 Figure 6 Relationship between garlic mustard cover and the Shannon diversity of adult spiders sampled from vegetation in June and September ................ 26 Figure 7 Relationship between garlic mustard cover and adult spider species richness sampled from vegetation in June and September ........................ 27 Figure 8 Square-transformed Shannon diversity of spider species sampled from June vegetation according to stratified categories of garlic mustard percent cover ......................................................................................................... 29 Figure 9 Relationship between number of Ceraticelus