Identifying plausible scenarios for the establishment of invasive Burmese pythons (Python molurus) in Southern Florida

John D. Willson^1,4, Michael E. Dorcas², and Raymond W. Snow³

¹Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA
²Department of Biology, Davidson College, Davidson, NC 28035-7118, USA
³Everglades National Park, 4001 State Road 9336, Homestead, FL 33034, USA
⁴Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and
State University, 100 Cheatham Hall, Blacksburg, VA 24061, USA

Abstract: Successful invasions of secretive alien species often go unrecognized until spread has exceeded the point where control or eradication is feasible. In such situations, understanding factors that contributed to establishment can be critical to preventing subsequent introductions of previously-successful
invaders or ecologically similar species. The Burmese python (Python molurus bivittatus), a native to Southeast Asia, is abundant in the pet trade and is now well-established in southern Florida. Although there can be little argument that the ultimate source of Florida pythons was the pet industry, there has been limited consideration of biological support for scenarios that may have lead to their establishment. In this study we use information on python capture rates and biologically-derived population growth models to evaluate the plausibility of various scenarios for python establishment. Our results indicate that scenarios involving relatively recent establishment (post-1990) require large numbers (100–1,000) of founders or unrealistically high juvenile survivorship. Intentional simultaneous release of large numbers of pythons is unlikely and accidental release of large numbers of founders is inconsistent with the spatial and temporal pattern of pythons captures in the region. We conclude that the most parsimonious scenario for establishment of pythons in Florida involves the release of a relatively small number of founders prior to 1985. Our results demonstrate that for pythons and other species with low inherent detection probabilities, early action during incipient phases of an invasion is critical and understanding likely introduction scenarios is important for preventing similar situations from occurring elsewhere or with other species.