Ctenosaura Similis) on Gasparilla Island, Florida, USA

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2014

Invasive black spiny-tailed iguanas (Ctenosaura similis) on Gasparilla Island, Florida, USA

Michael L. Avery United States Department of Agriculture, [email protected]

Eric A. Tillman USDA/APHIS/WS National Wildlife Research Center, [email protected]

Conny Spurfeld USDA/APHIS/WS National Wildlife Research Center

Richard M. Engeman USDA-APHIS-Wildlife Services, [email protected]

Kelin P. Maciejewski United States Department of Agriculture

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Avery, Michael L.; Tillman, Eric A.; Spurfeld, Conny; Engeman, Richard M.; Maciejewski, Kelin P.; Brown, Jessica D.; and Fetzer, Emily A., "Invasive black spiny-tailed iguanas (Ctenosaura similis) on Gasparilla Island, Florida, USA" (2014). USDA National Wildlife Research Center - Staff Publications. 1454. https://digitalcommons.unl.edu/icwdm_usdanwrc/1454

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 Michael L. Avery, Eric A. Tillman, Conny Spurfeld, Richard M. Engeman, Kelin P. Maciejewski, Jessica D. Brown, and Emily A. Fetzer

This article is available at DigitalCommons@University of Nebraska - Lincoln: https://digitalcommons.unl.edu/ icwdm_usdanwrc/1454 Integrative Zoology 2014; 9: 590–597 doi: 10.1111/1749-4877.12085

1 ORIGINAL ARTICLE 1 2 2 3 3 4 4 5 5 6 6 7 Invasive black spiny-tailed iguanas (Ctenosaura similis) on 7 8 8 9 Gasparilla Island, Florida, USA 9 10 10 11 11 12 12 13 Michael L. AVERY,1 Eric A. TILLMAN,1 Conny SPURFELD,2 Richard M. ENGEMAN,3 Kelin P. 13 14 14 1 4 1 15 MACIEJEWSKI, Jessica D. BROWN and Emily A. FETZER 15 16 1United States Department of Agriculture, Wildlife Services (USDA-WS), National Wildlife Research Center, Florida Field Station, 16 17 Gainesville, Florida, USA, 2USDA-WS, Gainesville, Florida, USA, 3USDA-WS, National Wildlife Research Center, Fort Collins, 17 18 18 Colorado USA and 4Berryman Institute, Mississippi State University, Starkville, Mississippi, USA 19 19 20 20 21 21 22 22 23 Abstract 23 24 24 25 The native range of Ctenosaura similis extends from southern Mexico through Panama. From an initial intro- 25 26 duction of 3 animals in 1979, the species now numbers in the thousands on Gasparilla Island in southwest Flor- 26 27 ida. In response to complaints of property damage from residents and threats to native species, local officials 27 28 and the US Department of Agriculture Wildlife Services began a removal program in 2008. Through 2011, trap- 28 29 pers removed 9467 ctenosaurs. The number removed declined from 32 iguanas/day in 2008 to 1.9 iguanas/day 29 30 in 2011 despite no easing of the control effort. We necropsied 2757 ctenosaurs to document aspects of their nat- 30 31 ural history. Females outnumbered males overall, although the largest size class (>300 mm snout–vent length) 31 32 included 32 males and just 2 females. Reproduction was seasonal. We found oviducal eggs in females from ear- 32 33 ly Apr to early Jun, approximately 2 months later than C. similis in its native range. We trapped hatchlings from 33 34 late Jul to early Oct coincident with the summer rainy season. Clutch size increased with female body size, with 34 35 62 being the largest clutch size recorded. In general, the biology of the invasive population on Gasparilla Island 35 36 resembles native C. similis populations in Central America, except for the lack of large individuals. We suggest 36 37 that shorter day length and colder temperatures create environmental conditions that are suboptimal for individ- 37 38 ual growth compared to those in the native range. 38 39 39 Key words: Ctenosaura similis, Florida, invasive reptile, population control, spiny-tailed iguana 40 40 41 41 42 42 43 43 44 INTRODUCTION 44 45 45 46 Ctenosaura similis (Gray, 1830) occurs natural- 46 47 ly throughout southern Mexico and Central America, 47 48 Correspondence: Michael L. Avery, USDA/Wildlife Services, where it is widely exploited for its purported medic- 48 49 National Wildlife Research Center, Florida Field Station, 2820 inal properties and as a food source (Fitch & Hack- 49 50 East University Avenue, Gainesville, FL 32641, USA. forth-Jones 1983; Savage 2002; Stephen et al. 2011). 50 51 Email: [email protected] This species is also part of the international pet trade. 51

1 During 2001–2008, approximately 13 000 were import- thermore, C. similis feeds on the same native plants as 1 2 ed into the USA. This practice has declined in recent the gopher tortoise, potentially depriving the tortoises of 2 3 years, and only 78 were imported in 2008 (Stephen et food resources, and iguanas usurp gopher tortoise bur- 3 4 al. 2011). C. similis was first released in Florida in 1979 rows, potentially compromising the tortoises’ reproduc- 4 5 when a resident brought 3 animals from southern Mex- tive success (McKercher 2001; Krysko et al. 2003; En- 5 6 ico and liberated them on the southern end of Gasparil- geman et al. 2009). 6 7 la Island, Lee County (Krysko et al. 2003). A recent ge- Gasparilla Island comprises 2 separate jurisdictions, 7 8 netic analysis showed that the current Gasparilla Island Lee County and Charlotte County. In response to steadi- 8 9 population is most closely allied with C. similis popu- ly increasing numbers of iguanas, in 2007 Lee County 9 10 lations in Nicaragua, Costa Rica and Honduras, and not residents hired a private trapper to remove iguanas from 10 11 as closely allied with those from Mexico (L. Buckley, that county’s part of Gasparilla Island. In 2008, Char- 11 12 Rochester University, unpubl. data). lotte County residents contracted the US Department 12 13 In Florida, 56 species of introduced reptiles and am- of Agriculture Wildlife Services to remove iguanas and 13 14 phibians are now established, including 43 lizard spe- that effort continued through 2011. A concurrent remov- 14 15 cies (Krysko et al. 2011a). C. similis breeds through- al effort continued in Lee County, but we are not privy 15 16 out Gasparilla Island and on the adjacent mainland. to those results. Many of the iguanas taken in Charlotte 16 17 The species seems to be most widespread in southwest- County during 2008–2011 were sent to the US Depart- 17 18 ern Florida, but populations are also established along ment of Agriculture wildlife research facility in Gaines- 18 19 Florida’s southeastern coast and on the Florida Keys ville for necropsy, and we report on those findings here. 19 20 (Townsend et al. 2003; Krysko et al. 2011b; Meshaka Our objectives were to describe the general biology of 20 21 2011). The species has tremendous reproductive poten- this invasive population, to document temporal changes 21 22 tial, with a single annual clutch containing 12–88 eggs within the population and to compare the invasive pop- 22 23 (mean = 43) (Fitch & Hackforth-Jones 1983), with an ulation with published information from a portion of 23 24 invasive female reported to have 82 oviducal eggs on the native range, specifically Costa Rica and Nicaragua, 24 Key Biscayne (Krysko et al. 2003). 25 corresponding to the putative origin of the invasive pop- 25 26 Gasparilla Island has become increasingly developed ulation. 26 27 with residential communities since the introduction of 27 28 C. similis in 1979. Such land use changes are compati- 28 29 ble with the natural history of the species; in its native MATERIALS AND METHODS 29 range, C. similis is abundant in human-altered environ- 30 Study area 30 31 ments (Fitch & Henderson 1978). This adaptability, re- 31 32 fugia and nest sites (provided by gopher tortoise bur- Gasparilla Island is an 11 km barrier island just off 32 33 rows), and minimal human persecution have created a the southwest coast of Florida (Fig. 1). It has typical 33 34 situation in which the C. similis population can easily low-relief barrier island topography and includes 5 dis- 34 35 persist and expand. tinct natural communities: beach dune, coastal strand, 35 36 On Gasparilla Island, C. similis eats expensive land- marine unconsolidated substrate, maritime hammock 36 37 scape plantings and invades houses, causing monetary and estuarine tidal swamp (Florida Natural Areas In- 37 38 damage and aggravating homeowners (Reed 2006). In ventory 1990). Many of these natural communities have 38 39 addition to creating problems for residents, the species been invaded by exotic plant species, such as Australian 39 40 also threatens sensitive native flora and fauna (Krysko pine (Casuarina equisetifolia), Brazilian pepper (Schi- 40 41 et al. 2003). Although these iguanas are primarily her- nus terebinthifolius), beach naupaka (Scaevola sericea) 41 42 bivorous, they will opportunistically eat other lizards, and burrnut (Tribulus cistoides). Gasparilla Island expe- 42 43 small birds, rodents and invertebrates (Fitch & Hack- riences a mild sub-tropical climate, with average sum- 43 44 forth-Jones 1983), and we have documented them to mer high temperatures exceeding 30 °C and average 44 45 eat juvenile gopher tortoises [Gopherus polyphemus winter high temperatures approximately half that. Pre- 45 46 (Daudin, 1802)] (Avery et al. 2009). There is also the cipitation (>140 cm/year) occurs mostly during the Jun– 46 47 possibility of iguanas preying on various Florida bird Sep rainy season (http://wildernet.com/). The island in- 47 48 species, such as the least tern (Sternula antillarum Les- cludes many neighborhoods of single and multi-family 48 49 son, 1847), the snowy plover [Charadrius nivosus (Cas- residences as well as resort and condominium develop- 49 50 sin, 1858)] and the burrowing owl [Athene cunicularia ments, and a golf course. The northern portion of the is- 50 51 floridana (Ridgway, 1874)] (Krysko et al. 2003). Fur- land is in Charlotte County, and the rest is in Lee Coun- 51

1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 Figure 1 The study site comprised the 17Charlotte County portion, approximately 17 18the northern quarter, of Gasparilla Island in 18 19southwest Florida. 19 20 20 21 21 22 22 23 23 24 ty. Gasparilla Island State Park (52 ha) is at the southern devices and strategies within a day made the standard 24 25 end of the island and provides a natural protected area 8 h working day the only practical definition for unit 25 26 for iguanas and other wildlife. of effort. Thus, we expressed efficacy of the control ef- 26 fort as the number of iguanas removed per day. We in- 27 Animals and methods 27 28 cluded only carcasses actually recovered; some iguanas 28 29 Removal efforts throughout Charlotte County start- that were shot retreated to burrows or fell into water and 29 30 ed in Feb 2008 and continued each month through 2011, death could not be verified. 30 31 except Dec 2008. In an integrated approach, field per- For each animal necropsied, we recorded body mass 31 32 sonnel simultaneously employed various strategies to to the nearest gram on a digital scale and snout–vent 32 33 remove iguanas. Due to the mixture of habitats, includ- length (SVL) to the nearest millimeter using a metal rul- 33 34 ing natural, residential and other developed areas, as er. We verified gender by dissection, and assessed re- 34 35 well as the behaviors of the animals and restrictions im- productive condition of females by counting the number 35 36 posed by community residents, great flexibility was re- of oviducal eggs or vitellogenic follicles and by weigh- 36 37 quired to integrate tools and strategies while optimizing ing the ovary or egg mass. We considered females with 37 38 human and material resources for maximizing cteno- broad, convoluted oviducts to have already laid eggs, 38 39 saur removal. Trapping strategies included placing bait- and we categorized those with straight, narrow oviducts 39 40 ed live traps in shaded areas frequented by iguanas, de- as not yet reproductive. For males, we measured length 40 41 ploying unbaited live traps in the mouths of gopher and width of testes using digital calipers and calculat- 41 42 tortoise burrows where iguanas had entered, and placing ed testes volume following Møller (1991). We summa- 42 43 unbaited live traps along the base of walls or other bar- rized the results by month of capture and compared re- 43 44 riers where iguanas traveled. Trappers employed com- sults between years. 44 45 mercial live traps with 2.54 × 2.54 cm or 1.27 × 2.54 cm We plotted SVL versus month and applied simple lin- 45 46 mesh and baited with fresh cantaloupe or watermelon. ear regression to estimate the rate of growth from hatch- 46 47 Trappers dispatched captured lizards with a pistol load- ing to sexual maturity. We considered hatchlings to be 47 48 ed with birdshot or .22 caliber bullets. Field personnel animals with SVL 60 mm or less (Fitch & Henderson 48 49 shot iguanas when prudent and safe during regular pa- 1978; Fitch & Hackforth-Jones 1983). In Nicaragua, the 49 50 trols of the study area using a .22 caliber rifle or air rifle. sex ratio for C. similis is reportedly “strongly skewed 50 51 The dynamic and ever-changing integration of control 51

1 in favor of females” (Fitch & Henderson 1978, p. 496). overall in the population (P < 0.001), it was not con- 1 2 We tested the null hypothesis of equal sex ratios, over- sistent within SVL size classes, especially in the >300 2 3 all and within size classes using the one-proportion test mm SVL size class, which was 94% male (2 females, 3 4 (Minitab Inc. 2007), with the alternative hypothesis that 32 males). For each sex, mean body size of animals re- 4

5 females constituted >50% of the sample. For other sta- moved varied across years (P < 0.001). For males (F3,635 5

6 tistical analyses we used t-tests and one-way analyses of = 16.59) and females (F3,836 = 26.00), mean body size 6 7 variance as appropriate. was greatest in 2008, declined in 2009, and then recov- 7 8 ered, although not to the original sizes. The maximum 8 9 RESULTS size of male iguanas removed annually declined 14.4% 9 10 during the study, compared to 3.6% reduction among fe- 10 11 Iguana removal males. 11 12 12 13 In Charlotte County, during 2008–2011, field person- 13 14 nel removed 9467 iguanas during 616 days of effort. 14 15 The lowest daily removal rates corresponded to the on- 15 16 set of cooler weather when iguana activity was great- 16 17 ly reduced, and the highest rates reflected the abundance Table 1 Sex ratios of Ctenosaura similis collected on Gasparil- 17 18 of hatchlings in late summer. The pattern of month-to- la Island, Florida, 2008–2011 18 19 month fluctuation in the removal rate was consistent SVL (mm) N % female Z-statistic P 19 across years, although amplitudes declined (Fig. 2). Re- 20 <100 48 63.8 1.90 0.029 20 21 moval rates declined annually across the 4-year study, 21 100–149 275 53.1 1.03 0.153 22 from 29.6 iguanas/day in 2008 to 1.9 iguanas/day in 22 23 2011. 150–199 461 58.8 3.77 <0.001 23 24 Body size 200–249 459 61.9 5.09 <0.001 24 25 250–299 203 52.7 0.77 0.220 25 Body mass increased nonlinearly as a function of 26 >299 34 5.9 –5.14 1.000 26 27 SVL. After log-log transformation, slopes of the lin- 27 Total 1462 57.5 5.7 <0.001 28 ear regression lines for males (logBodyMass = 2.95 × 28 2 29 logSVL – 4.35; R = 0.980) and females (logBodyMass For each size class, the null hypothesis of an equal sex ratio 29 2 30 = 3.07 × logSVL – 4.62; R = 0.978) were statistical- was tested against the alternative hypothesis of the female per- 30 centage being >50%, using the 1 proportion test. SVL, snout– 31 ly indistinguishable (t1295 = 0.84; P = 0.40; Fig. 3). We 31 vent length. 32 determined gender for 1462 animals, 57.5% of which 32 33 were females (Table 1). Although there was female bias 33 34 34 35 35 36 36 37 37 38 38 39 39 40 40 41 41

42 LogBodyMass 42 43 43 44 44 45 45 46 LogSVL 46 47 Figure 3 Body mass of C. similis (N = 2515) increased nonlin- 47 48 early as a function of snout–vent length (SVL), Gasparilla Is- 48 49 Figure 2 Monthly variation in the number of Ctenosaura simi- land, Charlotte County, Florida, 2008–2011. Males (triangles) 49 50 lis removed per day during a control program on Gasparilla Is- and females (circles) displayed statistical identical relation- 50 51 land, Charlotte County, Florida, 2008–2011. ships between body mass and SVL. 51

1 Reproduction and growth ka et al. 2007). We then collapsed these data across the 1 2 4 years of the study to produce a composite plot, which 2 3 Reproduction was seasonal. Testes size peaked mark- reflected a growth rate of approximately 6.8 mm/month 3 4 edly during Jan–Apr, after which there was rapid tes- (Fig. 4). 4 5 ticular regression. Similarly, during Jan–Apr, 67.3% of 5 all females contained vitellogenic follicles or oviducal 6 DISCUSSION 6 7 eggs, compared to 3.8% during the rest of the year. The 7 8 number of females with vitellogenic follicles or ovidu- Characteristics of the invasive C. similis population 8 9 cal eggs declined annually from 71 in 2008 to 3 in 2011. on Gasparilla Island resembled those in the native range 9 10 Females with oviducal eggs occurred from 9 Apr to 1 in some respects, but differed in others. For example, 10 11 Jun. During these 3 months, we examined 245 females females with oviducal eggs occurred during 9 Apr to 1 11 12 of reproductive size (>185 mm SVL), 199 (81%) of Jun in Florida compared to 4 Feb to 2 Apr in Nicaragua 12 13 which possessed either oviducal eggs, vitellogenic folli- (Fitch & Henderson 1978). Thus, the very concentrated 13 14 cles or a convoluted oviduct indicating previous laying. breeding season characteristic of the species in its na- 14 15 Among females with SVL ≥ 235 mm, 99 of 100 exhib- tive range is manifested in the introduced range, but oc- 15 16 ited evidence of reproduction. We found no evidence of curs 2 months later. The sex ratio of C. similis in Nica- 16 17 multiple clutches per year. Clutch size, as determined by 17 18 the number of oviducal eggs, averaged 31.6 (SE = 1.7), 18 and increased with SVL (clutch size = 0.364 × SVL – 19 2 19 20 56.564; R = 0.67, P < 0.001, n = 56). Clutch size with- 20 21 in size classes did not differ (paired t-test, t = –0.40; P 21 22 = 0.707) from that recorded in Nicaragua (Fitch & Hen- 22 23 derson 1978); we recorded only 1 female with SVL > 23 24 300 mm (Table 2). Clutch mass (mean ± SE) as a per- 24 centage of female body mass was 18.0% ± 0.7%, and 25 2 25 26 did not vary with SVL (y = 0.0345 × SVL + 9.540; R = 26 27 0.0378, P = 0.849). 27 28 We recorded 408 hatchlings (minimum 43 mm SVL, 28 29 2.75 g body mass), beginning in the last week of Jul 29 30 (n = 4) and extending into Oct (n = 6). The remaining Figure 4 On Gasparilla Island, Florida, C. similis appeared to 30 31 97.5% of the hatchling iguanas were trapped in Aug– grow at a rate of approximately 6.8 mm/month throughout their 31 32 Sep. We plotted SVL versus month each year to identi- first 15 months post-hatching. The graph is a composite com- 32 33 fy the appearance of hatchlings in mid-summer (Mesha- prising the 4 years of the study. 33 34 34 35 35 36 36 37 37 38 Table 2 Clutch size (oviducal eggs) recorded from female Ctenosaura similis on Gasparilla Island, Florida (this study) and in Nica- 38 39 ragua (Fitch & Henderson 1978) 39 40 Gasparilla Island Nicaragua 40 41 SVL class (mm) N Mean Range N Mean Range 41 42 42 191–250 31† 25.0 6–40 16 21.7 12–27 43 43 44 251–269 14 33.4 5–56 8 36.0 29–41 44 45 270–284 7 40.7 5–57 10 40.9 29–63 45 46 285–299 3 50.7 44–62 7 42.4 29–51 46 47 300–310 1 34.0 – 14 51.6 30–66 47 48 48 311–326 0 – – 6 61.8 49–74 49 49 50 327–340 0 – – 8 69.5 59–88 50 51 †Includes 1 animal with snout–vent length (SVL) = 187 mm. Size classes are those used by Fitch and Henderson (1978). 51

1 ragua was female-biased 2:1 (Fitch & Henderson 1978). es activity but also limits growth rate and could retard 1 2 Gender bias also occurred on Gasparilla Island where sexual maturation (Andrews 1976). 2 3 the population was 57% female. However, just 2 of 393 Alternatively, lower growth rates on Gasparilla Is- 3 4 (0.51%) adult females we examined had SVL >299 mm. land could be the result of increased competition for 4 5 This is in contrast to a sample of 283 females from Nic- food relative to that in mainland populations in the na- 5 6 aragua, of which 82 (28.97%) had SVL >299 mm (Fitch tive range. Animal populations on islands are predicted 6 7 & Henderson 1978). The paucity of large females in our to experience lower predation, increased intra-specific 7 8 sample relative to Nicaragua could be due to vagaries of competition and higher population densities than main- 8 9 sampling, but other explanations for this difference are land counterparts (Van Valen 1973; Novosolov et al. 9 10 also plausible. 2013). For insular lizard populations, such conditions 10 11 Ctenosaura similis appears to grow more slowly in are expected to produce smaller clutch sizes and larg- 11 12 Florida than in Central American sites 1500–1800 km er hatchlings compared to mainland populations (No- 12 13 farther south, and this, in turn, might be reflected in the vosolov et al. 2013). On Gasparilla Island, we found 13 14 observed size distributions. Fitch & Henderson (1977) neither to be true. Clutch sizes we recorded were not 14 15 report that in Nicaragua hatchlings grew to >140 mm different from those reported from mainland populations 15 16 SVL and >80 g body mass within 6 months. Hatchlings in the native range (Table 2). The range of hatchling siz- 16 17 on Gasparilla Island appeared to grow much more slow- es reported from Costa Rica (48–58 mm SVL; Fitch & 17 18 ly, averaging just 91.0 mm SVL and 21.7 g body mass Hackforth-Jones 1983) and Nicaragua (55–60 mm SVL; 18 19 after 6 months (Table 3). Growth rate can be affected by Fitch & Henderson 1978) is commensurate with sizes 19 20 various environmental factors, including low tempera- we recorded (43–69 mm SVL, N = 134) during the late 20 21 ture and decreased insolation (Fitch 1973). The Florida Jul to early Aug hatching period on Gasparilla Island. 21 22 iguana population is subjected to a very different tem- We did not measure food availability on the island, and 22 23 perature regime than native C. similis (Fig. 5). In par- we have no direct evidence of competition for food. Al- 23 24 ticular, historical mean minimum monthly temperatures though we cannot rule out intra-specific competition as 24 25 in Managua, Nicaragua during winter (Dec–Feb) range a contributing factor, we have no indication that it plays 25 26 from 19.7 to 21.2 °C, whereas on Gasparilla Island a major role in limiting growth rates in the Gasparilla 26 27 during the same months mean monthly temperatures Island population. 27 28 28 range from 10.9 to 12.8 °C (www.meoweather.com/his- Until 2008, the C. similis population on Gasparil- 29 29 tory). Winter months yielded the lowest rates of removal la Island was apparently free of significant predation 30 30 during the 4-year study (Fig. 2), largely because of the pressure. The large numbers of hatchlings and subadult 31 31 reduced iguana activity. Colder weather not only reduc- iguanas removed in 2008 and 2009 attest to the health 32 32 of the population prior to management actions. Howev- 33 33 er, 4 years of persistent removal efforts greatly reduced 34 34 the iguana population across all size classes. The re- 35 35 moval program will remain a success if control efforts 36 36 37 37 38 38 39 39 40 40 Table 3 Snout–vent length (SVL) and body mass (mean ± SE) 41 41 of juvenile Ctenosaura similis from the cohort that hatched in 42 Aug 2008 and was subsequently collected through Jul 2009 on 42 43 Gasparilla Island, Florida 43 44 44 45 Month N SVL (mm) Body mass (g) 45 46 Aug 2008 (hatch) 102 63.6 ± 0.8 7.9 ± 0.3 46 47 Sep 2008 178 72.5 ± 0.8 11.8 ± 0.4 47 48 Figure 5 Mean monthly historical maximum and minimum Feb 2009 6 91.0 ± 5.0 21.7 ± 3.7 48 49 temperatures in the native range (Managua, Nicaragua) and the 49 Mar 2009 12 98.7 ± 3.2 30.6 ± 2.9 50 introduced range (Gasparilla Island, Florida) of C. similis (cli- 50 51 mate data from www.meoweather.com/history). Jul 2009 30 143.3 ± 2.5 126.6 ± 6.8 51

1 are maintained. Relaxation of control efforts will allow spinytail iguana), Gopherus polyphemus (gopher tor- 1 2 the iguana population to recover to pre-treatment levels. toise) concurrent burrow use. Herpetological Review 2 3 Even with potential immigration across the causeway 40, 84. 3 4 connecting the north end of the island with the mainland Fitch HS (1973). A field study of Costa Rican lizards. 4 5 (Krysko et al. 2003), the 4-year removal effort demon- University of Kansas Science Bulletin 50, 39–126. 5 6 6 strates that an established, otherwise unchecked popula- Fitch HS, Hackforth-Jones J (1983). Ctenosaura simi- 7 7 tion of invasive reptiles with high reproductive capaci- lis (garrobo, iguana negra, ctenosaur). In: Janzen DH, 8 8 ty can be successfully controlled. Other invasive lizard ed. Costa Rican Natural History. University of Chi- 9 9 species, such as the Nile monitor (Varanus niloticus L., cago Press, Chicago, pp. 393–6. 10 1758) and the Argentine tegu (Tupinambis merianae 10 Fitch HS, Henderson RW (1977). Age and sex differ- 11 Duméril & Bibron, 1839), are also well-established in 11 ences in the ctenosaur (Ctenosaura similis). Milwau- 12 Florida (Krysko et al. 2011b; Pernas et al. 2012). The 12 kee Public Museum Contributions to Biology and Ge- 13 management outcome documented here for C. similis 13 ology 11, 1–11. 14 bodes well for ultimate control of these other invasives 14 15 provided similar dedicated and persistent removal ef- Fitch HS, Henderson RW (1978). Ecology and exploita- 15 16 forts are devised, initiated and maintained. tion of Ctenosaura similis. University of Kansas Sci- 16 ence Bulletin 51, 483–500. 17 Ongoing iguana removal efforts also bode well for 17 18 gopher tortoises, which are found in appropriate habi- Florida Natural Areas Inventory (1990). Guide to the 18 19 tat throughout the island. Contrary to a previous assess- Natural Communities of Florida. Department of Nat- 19 20 ment (McKercher 2001), there are legitimate reasons to ural Resources, Tallahassee, FL. 20 21 believe that iguanas negatively impact gopher tortoises Krysko KL, Burgess JP, Rochford MR et al. (2011a). 21 22 through direct predation (Avery et al. 2009), occupation Verified non-indigenous amphibians and reptiles in 22 23 of tortoise burrows (Engeman et al. 2009) and utiliza- Florida from 1863 through 2010: outlining the inva- 23 24 tion of food resources (Krysko et al. 2009). As removal sion process and identifying invasion pathways and 24 25 efforts deplete the iguana population, there should be a stages. Zootaxa 3028, 1–64. 25 26 corresponding increase in hatchling and juvenile tortois- Krysko KL, Enge KM, Moler PE (2011b). Atlas of Am- 26 27 es observed on Gasparilla Island. phibians and Reptiles in Florida. Final Report, Proj- 27 28 ect Agreement 08013, Florida Fish and Wildlife Con- 28 29 servation Commission, Tallahassee, FL. 29 30 ACKNOWLEDGMENTS 30 Krysko KL, King FW, Enge KM, Reppas AT (2003). 31 Funding was provided by the Charlotte County resi- 31 Distribution of the introduced black spiny-tailed igua- 32 dents of Gasparilla Island and by the National Wildlife 32 na (Ctenosaura similis) on the southwestern coast of 33 Research Center. The project was conceived through 33 Florida. Florida Scientist 66, 74–9. 34 discussions with B. U. Constantin and M. L. Christie. 34 35 We thank K. L. Krysko and T. C. Mathies for insights Krysko KL, Larson KW, Diep D, Abellana E, McKerch- 35 36 on iguana anatomy and physiology. M. K. Annala pro- er ER (2009). Diet of the nonindigenous black spiny- 36 37 vided laboratory support. K. L. Krysko, S. Meiri, and tailed iguana, Ctenosaura similis (Gray, 1831) (Sau- 37 38 W. E. Meshaka contributed helpful review comments on ria: Iguanidae), in southern Florida. Florida Scientist 38 39 the manuscript. 72, 48–58. 39 40 McKercher E (2001). Ctenosaura pectinata (Iguanidae) 40 41 REFERENCES on Gasparilla Island, Florida: colonization, habitat 41 42 use, and interactions with Gopherus polyphemus (MS 42 43 Andrews RM (1976). Growth rate in island and main- Thesis). University of Florida, Gainesville, Florida, 43 44 land anoline lizards. Copeia 1976, 477–82. USA. 44 45 Avery ML, Tillman EA, Krysko KL (2009). Gopherus Meshaka WE Jr (2011). A runaway train in the making: 45 46 polyphemus (gopher tortoise), Ctenosaura similis the exotic amphibians, reptiles, turtles and crocodil- 46 47 (Gray’s spiny-tailed iguana) predation. Herpetologi- ians of Florida. Monograph 1, Herpetological Con- 47 48 cal Review 40, 435. servation and Biology 6, 1–101. 48 49 Engeman RM, Kennedy M, Constantin BU, Chris- Meshaka WE Jr, Smith HT, Golden E et al. (2007). 49 50 tie ML, Hall PT (2009). Ctenosaura similis (black Green iguanas: the unintended consequence of sound 50 51 51

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