A MULTISCALE INVESTIGATION OF SNAKE HABITAT RELATIONSHIPS AND SNAKE CONSERVATION IN ILLINOIS by Nicolette L. Cagle Department of Ecology Duke University Date:_______________________ Approved: ___________________________ Norman L. Christensen, Supervisor ___________________________ John Terborgh, Supervisor ___________________________ Dean L. Urban ___________________________ Jennifer Swenson Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Ecology in the Graduate School of Duke University 2008 ABSTRACT A MULTISCALE INVESTIGATION OF SNAKE HABITAT RELATIONSHIPS AND SNAKE CONSERVATION IN ILLINOIS by Nicolette L. Cagle Department of Ecology Duke University Date:_______________________ Approved: ___________________________ Norman L. Christensen, Supervisor ___________________________ John Terborgh, Supervisor ___________________________ Dean L. Urban ___________________________ Jennifer Swenson An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Ecology in the Graduate School of Duke University 2008 Copyright by Nicolette L. Cagle 2008 Abstract Snake populations in the North American tallgrass prairie appear to be declining, yet data unavailability impedes the development of enhanced ecological understanding of snake species-habitat relationships and also hinders snake conservation efforts. This study addresses both issues for the snakes of Illinois in two steps. In a two-year mark-recapture study at twenty-two sites within six northern Illinois prairie preserves, I investigated snake species-habitat relationships using habitat variables at three scales: microhabitat (< 100 m), landscape (1 – 10 km), and regional (> 10 km). A total of 120 snakes representing seven species was captured using drift fence arrays associated with funnel traps and sheet metal cover. The low numbers and diversity of snakes captured, when compared to historic evidence, indicate that Illinois snake populations have declined. At the microhabitat scale, non-metric multidimensional scaling and Mantel tests revealed a relationship between snake species composition and elevation. At the landscape-scale, snake species composition varied along an agricultural-urban cover gradient. Classification and regression trees and maximum entropy models (Maxent) were used to identify the scales at which snake species-habitat relationships were strongest. Six of seven regression trees for individual snakes species contained habitat iv variables at the landscape scale. Important landscape characteristics included patch size, isolation, and land cover, metrics that strongly covary with habitat loss. Microhabitat features only appeared in the regression trees of two species and in three Maxent models. This study indicates that habitat loss has shaped the current distribution of snake species in Illinois’s remnant prairies and that snake conservation efforts should emphasize the landscape-scale. Finally, I developed a risk ranking system based on natural and life history characteristics to assess the conservation status of Illinois’s 38 snake species. Cluster analysis identified eight groups of snakes, similar in terms of risk factors, with high risk species sharing characteristics such as large body size, long life span, limited habitat breadth, and a high anthropogenic threat ranking. Here, I emphasize the need for basic demographic studies on snakes and suggest that ranking systems be used with population data (when available) and expert opinion to identify snake species of conservation concern in other regions. v Acknowledgements I would like to extend my deepest thanks to everyone who has joined me in this amazing process of intellectual development. This dissertation would not have been possible without the steadfast support of my committee, my family, and my friends. First, I would like to thank my committee for fostering my growth as an ecologist and supporting me, both intellectually and emotionally, during my years at Duke University. My advisers, Norm Christensen and John Terborgh, have provided me with exceptional guidance, keeping me on a steady course as I worked on this dissertation. Norm not only taught me to examine the larger picture, but also unfalteringly demonstrated the principle of seeking first to understand and then to be understood. John patiently and judiciously compelled me to consider ecological phenomena more deeply. From him, I learned to question statistics and trust my field experience. I consider myself very fortunate to have been advised by two people both demonstrating such a rare combination of perspicacity and benevolence. I am particularly grateful to Dean Urban for his discernment, forward thinking, availability, and most of all, for his unparalleled mentorship. Dean first took me under his wing during my fledgling years, and deftly prepared me to leave the nest by providing innumerable opportunities to explore new ideas, teach, present at conferences, and mature as an ecologist. From Dean, I learned to identify when I was vi “standing too close” to my research and how to step back to re-examine my thought process. It is impossible to fully document his contribution to my intellectual and personal growth. I also thank Jennifer Swenson, as well as Bill Morris, for furthering my academic development. Jennifer not only provided discerning critiques of my work, but also stands as an inspiring model of a talented female ecologist effectively balancing career and family. Bill was instrumental in developing the framework of this dissertation, and also compelled me to consider my research critically. I would also like to sincerely thank my supportive and loving family, without which I would have no incentive to proceed with any endeavor. My affectionate and devoted parents, Eileen and Joe Flocca, have provided me with unfathomable support, both emotional and material. My mom not only provided wise counsel during these tumultous years, but bravely endured ticks and chiggers as my frequent field assistant. She deserves special recognition for not only being a kind and generous parent, but a true friend. My dad has truly inspired my research. When I imagine him catching garter snakes in empty Chicago lots as a boy or recall our expeditions to the old field in search of snakes, I can not envision so single-mindedly devoting five years of my life to the study of anything other than Illinois ophidians. My dad has been a devoted field assistant, an ingenious problem-solver, a humorous companion, and an extraordinarily loving parent. My patient and encouraging husband, Mark Cagle, has kindheartedly vii supported my work through thick and thin. I am so fortunate to have a dedicated partner who shares a passion for herpetofauna. With Mark, the global snake-hunting escapades will never cease. I thank you and love you all so much. I would also like to thank my friends and colleagues Claire Berger O’Dea, Ron Sutherland, and Krithi Karanth. Claire’s natural warmth, analytical mind, and unwavering support produced a life-long friend. Claire supported me during the most difficult period of my life so far, for which I can not thank her enough. She is also probably the only person in the world with whom I could spend twelve straight hours working on GIS! Ron, a kind friend and a fellow snake lover, has been an excellent sounding board for both snake theories and life philosophies. Krithi is an amazing friend and fellow ecologist. Our frequent lunches, dinners, and excursions will be greatly missed. Special thanks goes, as well, to Bill Kleiman and the Nature Conservancy at Nachusa Grasslands, Dan Kirk at Goose Lake Prairie, Rick Miller at Sunbury Prairie Preserve, Todd Bittner and the Illinois Department of Natural Resources, and Bill Glass and the Midewin National Tallgrass Prairie staff for allowing me access to remarkable prairie preserves, providing me with logistical support, and teaching me about the prairie remnants of Illinois. I am also compelled to acknowledge my intellectual progenitors. Thomas Jefferson, a remarkable polymath, has supplied inspiration since I was eleven years old. viii It is to him that I owe my resolve to be a generalist in an increasingly specialized world. Robert Kennicott, a 19 th century naturalist who grew up in my home town, fostered my sense of exploration and dedication to Illinois’s natural areas. Finally, Donald Culross Peattie, an evocative nature writer who drew inspiration from a prairie grove very close to my heart, motivates me to never forget the poetry and philosophy inherent to ecology. My heartfelt thanks goes out to everyone who has helped me on this incredible journey. ix Contents Abstract .........................................................................................................................................iv Acknowledgements .....................................................................................................................vi List of Tables.............................................................................................................................. xiii List of Figures ..............................................................................................................................xv 1. Introduction and Overview.....................................................................................................1 1.1 The study of species-habitat relationships in highly modified landscapes.......2