University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USDA National Wildlife Research Center - Staff U.S. Department of Agriculture: Animal and Publications Plant Health Inspection Service 2012 Environmental temperatures, physiology and behavior limit the range expansion of invasive Burmese pythons in southeastern USA Elliott L.R. Jacobson University of Florida, [email protected] David G. Barker Vida Preciosa International (VPI), [email protected] Tracy M. Barker Vida Preciosa International (VPI),, [email protected] Richard Mauldin US Department of Agriculture Michael L. Avery US Department of Agriculture, [email protected] See next page for additional authors Follow this and additional works at: https://digitalcommons.unl.edu/icwdm_usdanwrc Jacobson, Elliott L.R.; Barker, David G.; Barker, Tracy M.; Mauldin, Richard; Avery, Michael L.; Engeman, Richard M.; and Secor, Stephen, "Environmental temperatures, physiology and behavior limit the range expansion of invasive Burmese pythons in southeastern USA" (2012). USDA National Wildlife Research Center - Staff Publications. 1151. https://digitalcommons.unl.edu/icwdm_usdanwrc/1151 This Article is brought to you for free and open access by the U.S. Department of Agriculture: Animal and Plant Health Inspection Service at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USDA National Wildlife Research Center - Staff Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Authors Elliott L.R. Jacobson, David G. Barker, Tracy M. Barker, Richard Mauldin, Michael L. Avery, Richard M. Engeman, and Stephen Secor This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/ icwdm_usdanwrc/1151 Integrative Zoology 2012; 7: 271–285 doi: 10.1111/j.1749-4877.2012.00306.x 1 ORIGINAL ARTICLE 1 2 2 3 3 4 4 5 5 6 Environmental temperatures, physiology and behavior limit the 6 7 7 8 range expansion of invasive Burmese pythons in southeastern 8 9 9 10 USA 10 11 11 12 12 13 1 2 2 3 13 14 Elliott R. JACOBSON, David G. BARKER, Tracy M. BARKER, Richard MAULDIN, Michael 14 15 L. AVERY,4 Richard ENGEMAN3 and Stephen SECOR5 15 16 1 2 16 17 College of Veterinary Medicine, University of Florida, Gainesville, Florida, Vida Preciosa International (VPI), Boerne, Texas, 17 3 4 18 US Department of Agriculture, Wildlife Services, National Wildlife Research Center, Fort Collins, Colorado, US Department of 18 5 19 Agriculture, Wildlife Services, National Wildlife Research Center, Gainesville, Florida and Department of Biological Sciences, 19 20 University of Alabama, Tuscaloosa, Alabama, USA 20 21 21 22 22 23 23 24 Abstract 24 25 A well-established population of Burmese pythons resides in the Everglades of southern Florida. Prompted in 25 26 part by a report that identified much of southern USA as suitable habitat for expansion or establishment of the 26 27 Burmese python, we examined the plausibility of this snake to survive winters at sites north of the Everglades. 27 28 We integrated daily low and high temperatures recorded from October to February from 2005–2011 at Home- 28 29 stead, Orlando and Gainesville, Florida; and Aiken, South Carolina, with minimum temperatures projected for 29 30 python digestion (16 °C), activity (5 °C) and survival (0 °C). Mean low and high temperatures decreased north- 30 31 ward from Homestead to Aiken and the number of days of freezing temperatures increased northward. Diges- 31 32 tion was impaired or inhibited for 2 months in the Everglades and up to at least 5 months in Aiken, and activi- 32 33 ty was increasingly limited northward during these months. Reports of overwinter survivorship document that a 33 34 single bout of low and freezing temperatures results in python death. The capacity for Burmese pythons to suc- 34 35 cessfully overwinter in more temperate regions of the USA is seemingly prohibited because they lack the be- 35 36 haviors to seek refuge from, and the physiology to tolerate, cold temperatures. As tropical Southeast Asia is the 36 37 source of the Everglades Burmese pythons, we predict it is unlikely that they will be able to successfully expand 37 38 to or colonize more temperate areas of Florida and adjoining states due to their lack of behavioral and physio- 38 39 logical traits to seek refuge from cold temperatures. 39 40 40 41 Key words: ambient temperature, Burmese python, invasion, snake, thermal tolerance 41 42 42 43 43 44 44 45 45 46 INTRODUCTION 46 47 47 48 Correspondence: Elliott R. Jacobson, SACS, Building 2015, The zoogeography of snakes and other reptiles is 48 49 College of Veterinary Medicine, University of Florida, markedly influenced by a number of environmental fac- 49 50 Gainesville, Florida 32608, USA. tors, with ambient temperature (Ta) being a critical fac- 50 51 Email: [email protected] tor that affects their distribution and seasonal activity 51 © 2012 Wiley Publishing Asia Pty Ltd, ISZS and IOZ/CAS 271 E. R. Jacobson et al. 1 patterns. For example, two-thirds of the global varia- duced species, the Burmese python (accepted name Py- 2 tion in reptile richness can be explained by temperature thon molurus bivittatus Kuhl, 1820 by some biologists 3 alone (Qian 2010). Reptile diversity peaks in the trop- [Reed & Rodda 2009] and synonymously P. bivittatus 4 ics and decreases with an increase in latitude, with only Kuhl, 1820 by others [Jacobs et al. 2009]) has become 5 1 snake species (Vipera berus Linnaeus, 1758) reaching an established nonnative species in the Everglades of 6 the Arctic Circle and none reaching the Antarctic Circle extreme southern Florida (Reed & Rodda 2009; Enge- 7 (Darlington 1966; Arnold 1972; Schall & Pianka 1978; man et al. 2011; Krysko et al. 2011). The Burmese py- 8 Saint Girons 1980). thon, one of the largest species of snakes in the world, 9 For reptiles inhabiting the tropics, thermoregulation naturally occurs in tropical and subtropical regions of 10 is relatively passive as T is generally stable and con- Southeast Asia, where it prefers covered terrestrial hab- 11 a ducive to normal activity (Avery 1982; Huey 1982). itats (e.g. forest, jungle and scrub) and access to water 12 13 For water pythons (Liasis fuscus Peters, 1873) inhabit- (Murphy & Henderson 1997). The Burmese python’s re- 14 ing tropical Australia, few features of its ecology are in- cent establishment in the Everglades stems from a pre- 15 fluenced by thermoregulation (Shine & Madsen 1996). adaptation to mild winter temperatures, the physical en- 16 Reptiles inhabiting temperate regions of the world tend vironment that is available (e.g. scrub savanna, flooded 17 to experience much greater temporal variation in Ta than grassland and canals) and the food resources (over 25 18 tropical species, with seasonal (as well as daily) oscil- species of birds have been found in the digestive tract of 19 lations in Ta that span beyond a species critical ther- Burmese pythons; Dove et al. 2011) that can be found in 20 mal maximum (CTmax; high temperature at which activ- this region of Florida. To assess the potential expansion 21 ity is impaired and with no ability to escape will lead to or establishment of Burmese pythons, different species 22 death) and below their critical thermal minimum (CTmin; distribution models (SDMs) have been used to infer the 23 low temperature at which activity is likewise impaired potential range limits within the continental USA (Pyron 24 and with no ability to escape will lead to death) (Cowles et al. 2008; Rodda et al. 2009; Van Wilgen et al. 2009). 25 & Bogert 1944; Avery 1982; Huey 1982). Whereas all The consideration of python physiology, the profile 26 reptiles regulate body temperate to achieve an optimal of winter temperature for areas north of the Everglades 27 range of performances, temperate reptiles need also to and within the range of suitable climate projected by 28 avoid exposure to T that exceed CT and, more im- a max Rodda et al. (2009), and the recent reports on overwin- 29 portantly, possess a suite of adaptive behaviors to es- ter death of Burmese pythons (Avery et al. 2010; Dorcas 30 cape and survive a yearly episode of low T (Peterson a et al. 2011; Mazzotti et al. 2011) lead us to explore the 31 et al. 1993). As ectotherms, reptiles respond to a low- likelihood of the Burmese python to expand its distribu- 32 ering of T with a progressive depression of metabolic a tion northward, or to independently establish a new pop- 33 rate and performance that continues until the attainment ulation north of the Everglades. First we ask: Is the en- 34 of their CT and below which death is likely from hy- min vironment north of the Everglades conducive for python 35 pothermia or freezing (Peterson et al. 1993). Therefore, long-term survival? Next we ask: Do Burmese pythons 36 with the lowering of T with the onset of winter, temper- a currently inhabiting the Everglades possess the ecolog- 37 ate reptiles characteristically retreat to underground re- ical, physiological and behavioral traits to survive in 38 fugia and remain dormant (i.e. hibernate or brumate) un- 39 more temperate environments? We have examined these til T increases in the spring and they reemerge (Gregory 40 a questions by: (i) integrating recorded low and high tem- 1992). 41 peratures from October to February for the past 6 fall– Due to a climate that ranges from temperate in the 42 winter periods from 4 sites (Homestead, Orlando and north to subtropical to tropical in the south, an array of 43 Gainesville, Florida and Aiken, South Carolina) with the reptiles and amphibians have become introduced and es- 44 projected minimum temperature limits of python diges- tablished in Florida, with many of these introductions 45 tion, activity and survival; (ii) incorporating these tem- originating through the pet trade (Krysko et al.