University of Tennessee, Knoxville Trace: Tennessee Research and Creative Exchange Masters Theses Graduate School 5-2016 Urbanization Impacts on Land Snail Community Composition Mackenzie N. Hodges University of Tennessee - Knoxville, [email protected] Recommended Citation Hodges, Mackenzie N., "Urbanization Impacts on Land Snail Community Composition. " Master's Thesis, University of Tennessee, 2016. https://trace.tennessee.edu/utk_gradthes/3774 This Thesis is brought to you for free and open access by the Graduate School at Trace: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of Trace: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Mackenzie N. Hodges entitled "Urbanization Impacts on Land Snail Community Composition." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Geology. Michael L. McKinney, Major Professor We have read this thesis and recommend its acceptance: Colin Sumrall, Charles Kwit Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official student records.) Urbanization Impacts on Land Snail Community Composition A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Mackenzie N. Hodges May 2016 i DEDICATION I dedicate this research to my late grandmother, Shirley Boling, who introduced me to snails in the garden in very young age. I believe her love and constant presence in my early years has changed my life in unknowable ways. I also dedicate this to Philip Moore, my partner in love, life, and happiness. His support and rationale throughout this process has been nothing short of life-saving. ii ACKNOWLEDGEMENTS I would like to sincerely thank Dr. Michael McKinney for his constant support and all the knowledge he has imparted upon me, which started on my first day of college when I sat in the front row of his biodiversity class. I credit him for developing my love of nature and understanding of the environment, which includes the tiniest snails and the most beautiful phenomenon. I would like to thank my committee member Colin Sumrall, who is a constant voice of reason, and who introduced me to hydrogen peroxide, which saved innumerable hours of time. I thank Charlie Kwit who graciously agreed to join my committee late in the process, and provided a wealth of ecological knowledge and enthusiasm. The assistance of Philip Moore, Barbara Dinkins, Matthew Blair, Nicholas Gladstone, and Evan Norton was immeasurable in helping to collect and process over 12,000 snails. Amy and Wayne Van Devender, Ron Caldwell, Tim Pierce, Daniel Douglas, and Francisco Borreo all graciously lent their knowledge of snails to turn “unknown snails” into identifications. I thank David Withers, the Tennessee State Zoologist, whose interest and advice in my work was very encouraging and appreciated, and Rusty Boles of the TWRA who assisted me in obtaining collection permits. I thank the Parks and Recreation Departments in Nashville, Knoxville, and Chattanooga who let me make other visitors uncomfortable by crawling around in the dirt and bushes looking for snails. I thank Dr. Arnold Saxton, brilliant statistician, who finally spoke about statistics in a way that left me in tears of happiness instead of despair. The knowledge I gained from his class and advising appointments was absolutely invaluable. Finally, I want to acknowledge my parents, whose encouragement and love has gotten me so far in life. Your daughter, the snail counter, sincerely thanks you for all of your support. iii ABSTRACT Urbanization has tremendous impacts on most native species. Urban ecosystems are becoming increasingly prevalent, while urban ecology is a relatively underdeveloped field. This is especially true for terrestrial mollusks, which are a surprisingly understudied organism. Due to their low mobility and dispersal potential, land snails are valuable indicators of ecosystem disturbance. For this study, land snails were collected in 54 city parks along an urban gradient to understand influences of urbanization on snail communities. Sampled parks include small extensively landscaped downtown parks, neighborhood and community parks, district parks, and large nature parks, each with variable vegetation, soil characteristics, disturbance regimes, and human activities. Sampling recovered 12,153 individual snails, representing 20 families, 43 genera, and 95 species. Seven new Tennessee state and 87 new county occurrences were recorded for Davidson, Knox, Hamilton, and Marion counties. Five non-native and one extra-limital invasive species were found, four of which are new Tennessee state records. Results show that urbanization greatly alters land snail community structure. Nature and district parks have significantly greater species richness, species diversity and species evenness than community, neighborhood, and downtown parks. Degradation of parks, distance from the park to the city center and percent of coarse woody debris explained most of the variation between park types. Non-metric multidimensional scaling shows that downtown snail communities are similar across all three cities, whereas snail communities in nature parks are distinct. This suggests that urbanization promotes homogenization among land snail communities in Tennessee. iv TABLE OF CONTENTS CHAPTER 1 INTRODUCTION .............................................................................................................. 1 Urbanization Impacts on Biodiversity and Community Similarity ............................................... 1 Introduction to Terrestrial Gastropods ................................................................................................... 2 The Importance of Terrestrial Gastropods ............................................................................................ 4 Habitat Factors that Influence Terrestrial Gastropod Communities ........................................... 6 Urbanization Impacts on Land Snails .................................................................................................. 7 Study Goals ......................................................................................................................................................... 9 CHAPTER 2 MATERIALS AND METHODS .................................................................................. 10 City and Site Selection ................................................................................................................................. 10 Sampling Overview ....................................................................................................................................... 15 Visual Survey and Processing ................................................................................................................... 15 Soil and Litter Collection and Processing ........................................................................................ 18 Snail Identification ........................................................................................................................................ 20 Habitat Data Collection ............................................................................................................................... 20 Data analysis ................................................................................................................................................... 21 Analysis of Variation ............................................................................................................................... 21 Regression Models ................................................................................................................................... 23 Indicator species analysis ..................................................................................................................... 23 Nonmetric multidimensional scaling ................................................................................................ 24 CHAPTER 3 RESULTS ......................................................................................................................... 25 Descriptive Statistics .................................................................................................................................... 25 Analysis of Snail Communities across Park Types and Cities ...................................................... 34 Abiotic and Biotic Factors Influencing Snail Communities ........................................................... 39 Indicator Species Analysis for Park Type ............................................................................................ 43 Indicator Species Analysis with Invasive Ground Cover ........................................................... 46 Synanthropic species analysis ............................................................................................................. 46 Nonmetric Multidimensional Scaling Ordination ........................................................................ 49 CHAPTER 4 DISCUSSION ..................................................................................................................