Management of Biological Invasions (2018) Volume 9, Issue 3: 369–377 DOI: https://doi.org/10.3391/mbi.2018.9.3.18 Open Access © 2018 The Author(s). Journal compilation © 2018 REABIC Research Article Exotic predators may threaten another island ecosystem: A comprehensive assessment of python and boa reports from the Florida Keys Emma B. Hanslowe1,4,*, James G. Duquesnel1, Ray W. Snow2, Bryan G. Falk1,2, Amy A. Yackel Adams1, Edward F. Metzger III3, Michelle A.M. Collier2 and Robert N. Reed1 1U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, Colorado 80526, USA 2South Florida Natural Resources Center, Everglades National Park, 40001 State Road 9336, Homestead, Florida 33034, USA 3Fort Lauderdale Research and Education Center, University of Florida, 3205 College Avenue, Fort Lauderdale, Florida 33314, USA 4Department of Fish, Wildlife, and Conservation Biology, Colorado State University, 1417 Campus Delivery, Fort Collins, Colorado 80523, USA Author e-mails: [email protected] (EBH), [email protected] (JGD), [email protected] (RWS), [email protected] (BGF), [email protected] (AYA), [email protected] (EFMIII), [email protected] (MAMC), [email protected] (RNR) *Corresponding author Received: 6 April 2018 / Accepted: 10 July 2018 / Published online: 31 August 2018 Handling editor: Luis Reino Abstract Summarizing historical records of potentially invasive species increases understanding of propagule pressure, spatiotemporal trends, and establishment risk of these species. We compiled records of non-native pythons and boas from the Florida Keys, cross-referenced them to eliminate duplicates, and categorized each record’s credibility. We report on 159 observations of six python and boa species in the Florida Keys over the past 17 years. Burmese pythons (Python bivittatus), boa constrictors (Boa constrictor), and ball pythons (Python regius) are the most frequently reported species, but credible records of three additional species were also reported. Among the most notable records, we report on three hatchling and multiple reproductive Burmese pythons captured on North Key Largo since 2016, indicating that the species is now established on that island. The expanding mainland Burmese python population and ongoing python and boa introductions via pet and cargo pathways are likely to keep propagule pressure high in coming years. Both effective public outreach to solicit reporting of sightings and effective early detection and rapid response networks may help to prevent further establishment and associated ecological impacts of python and boa species in the Florida Keys. Key words: invasive species establishment, propagule pressure, constrictor snake, island ecology, early detection and rapid response, Boidae, Pythonidae increasingly recognized as posing high risks to native Introduction species on islands around the world (Cabrera-Pérez et al. 2012; Monzón-Argüello et al. 2015; Quick et Geographic isolation allows island flora and fauna to al. 2005; Reynolds et al. 2013; Rodda and Savidge evolve with limited competitors and predators 2007; Savidge 1987; Vázquez-Domínguez et al. 2012). (MacArthur and Wilson 1967), thus making the intro- Due to their low detection probability (Durso et al. duction of a new predator potentially catastrophic to 2011), early detection and reporting of invasive snakes island ecosystems (Bellard and Jeschke 2016; Russell may serve to identify species and areas at risk from et al. 2016; Vitousek 1988). Invasive mammals have newly established populations of invasive snakes. caused many high-profile impacts to insular faunas The Florida Keys are a chain of limestone islands including major population declines and extinctions extending approximately 180 km from southeastern (e.g., the small Indian mongoose [Herpestes javanicus; mainland Florida (Hoffmeister and Multer 1968) with Hays and Conant 2007], domestic cats [Felis catus; mangrove, pine rockland, and tropical hardwood Medina et al. 2011]). Invasive snakes, however, are forests (Hilsenbeck 1976; Schomer and Drew 1982; 369 E.B. Hanslowe et al. Snyder et al. 1990) that provide habitat for a diversity (EDDMapS 2018), records from Everglades and of native wildlife, including five endemic mammals Biscayne National Parks, Florida Museum of Natural deemed “in danger of extinction throughout all or History, Monroe County Sheriff’s Office, media significant portion[s] of [their] range[s]” (Key deer accounts, and our own observations through March [Odocoileus virginianus clavium Barbour and Allen, 2018. We considered a report to be from the Florida 1922], Key Largo woodrat [Neotoma floridana smalli Keys if the snake was observed within the outermost Sherman, 1955], lower Keys marsh rabbit [Sylvilagus boundary of the Florida Keys National Marine palustris hefneri Lazell, 1984], Key Largo cotton Sanctuary, on U.S. Route 1 south of and including mouse [Peromyscus gossypinus allapaticola Schwartz, mile marker 113 (25.252941º; −80.437029º), or in 1952], and rice rat [Oryzomys palustris natator Florida or Biscayne Bays, with the northernmost Chapman, 1893]), thereby listing them as endangered boundary at Sands Key (25.518234º; −80.176573º; under the U.S. Endangered Species Act (U.S. House Supplementary material Figure S1). We cross- of Representatives 1973; USFWS 1999; USFWS referenced all dates, locations, and reporter identities 2018). All of these species may be impacted by the to find and delete duplicate records (per Falk et al. introduction of a new predator such as an exotic 2016) and categorized each record’s credibility as snake. Of particular concern is the Burmese python either verified (a photograph or specimen has been (Python bivittatus Kuhl, 1820), a large constrictor verified by an expert) or unverified (a photograph or snake native to southeast Asia that is established on specimen has not been verified by an expert). the Florida mainland adjacent to the Florida Keys We mapped each record in ArcMap 10.3.1 and that has negatively impacted native mammal (Environmental Systems Research Institute [ESRI], populations in the Greater Everglades Ecosystem Redlands, CA, U.S.A.). If coordinates were not (Dorcas et al. 2012; McCleery et al. 2015). Laboratory included with a report, we used locality descriptions experiments (Hart et al. 2012) and multiple observa- and Google Earth (Google LLC, Mountain View, tions of Burmese pythons swimming several kilometers CA, U.S.A.) to assign coordinates following the from the mainland in Florida Bay (EDDMapS 2018) georeferencing practices described by Chapman and and on islands in their native range (e.g., You et al. Wieczorek (2006). The terrestrial portion of our 2013) suggest that dispersal from the mainland to the study area is divided into three previously estab- Florida Keys is possible. Moreover, Burmese lished geographic regions: (1) the “Upper Keys” pythons are not the only exotic-snake introduction defined as the islands and man-made bridges from risk for the Keys; at least 15 other python and boa U.S. Route 1 mile marker 113 to 72 (24.842143º; (Squamata: Boidae, Pythonidae) species were −80.752388º) and Card Sound Road within the introduced to Florida in the past 50 years via the pet- outermost boundary of the Florida Keys National trade or cargo pathways (Krysko et al. 2016). In Marine Sanctuary; (2) the “Middle Keys” defined as short, both expanding populations elsewhere in the the islands and man-made bridges from U.S. Route 1 state and ongoing human-associated introductions mile marker 72 to 47 (24.706895º; −81.12458º); and may result in high propagule pressure for pythons (3) the “Lower Keys” defined as the islands and man- and boas in the Florida Keys. made bridges from U.S. Route 1 mile marker 47 to Greene et al. (2007) provided the first peer-reviewed zero (24.54694º; −81.812462º; Chiappone et al. 2005). report of an exotic constrictor snake from the Florida Keys, a Burmese python captured in 2007. However, Results we discovered previous reports during this inves- tigation. The credibility of these and other subsequent Between 08 March 2002 and 31 March 2018, 159 reports is highly variable, and no critical examination pythons and boas were reported from the Florida of available evidence has been conducted. In this paper, Keys (Supplementary material Table S1). Of these we evaluate these reports to better understand propa- reports, 140 were identified to species, including gule pressure, spatiotemporal trends, and establishment Burmese python (n = 97), boa constrictor (Boa risk of exotic constrictor snakes in the Florida Keys. constrictor Linnaeus, 1758; n = 24), ball python We also discuss likely invasion pathways, anticipated (Python regius Shaw, 1802; n = 16), white-lipped impacts, and possible management strategies. python (Leiopython fredparkeri Schleip, 2008; n = 1), Kenyan sand boa (Gongylophis colubrinus Linnaeus, Methods 1758; n = 1), or Saharan sand boa (Gongylophis muelleri Boulenger, 1892; n = 1). The remaining 19 We compiled python and boa records from the Florida reports were of large snakes estimated to be greater Keys using all sources we were aware of, including than one meter in total length with descriptions that the Early Detection and Distribution Mapping System did not match any native species. We classified these 370 Assessment of python and boa reports from the Florida Keys Figure 1. Annual verified and unverified reports of A) Burmese pythons, B) boa constrictors, C) ball pythons, and D) unidentified large snakes