March of the Green Iguana: Non-native Distribution and Predicted Geographic Range of Iguana iguana in the Greater Caribbean Region

Abstract

Green iguanas (Iguana iguana L. 1758) have been introduced outside their native range mostly through the pet trade industry. In many places, exotic populations have become established or invasive. Of special concern is the Greater Caribbean Basin, were several exotic populations of green iguanas are causing negative impacts, and may threaten the conservation of several native species, including possible native and distinct forms of I. iguana in the Lesser Antilles, and the endangered Lesser Antilles Iguana (I. delicatissima Laurenti 1768). We assessed the risk of spread and invasion by green iguanas in the Greater Caribbean Basin, using the maximum entropy niche-modeling algorithm (MaxEnt) to predict the potential distribution of this reptile. We used a total of 187 location points that represented occurrences from both the native and the invasive range, coupled with environmental data as predictor variables. Our model had average training and test AUC values of 0.90 and 0.87 respectively, indicating a high predictive ability. The model predicts suitable conditions for I. iguana in south and central Florida (mainly along the coast), and in regions of all the islands in the Caribbean. Given the known negative impacts of green iguanas and their dispersal capabilities, governments in the Greater Caribbean Basin should manage non-native populations to prevent further spread, and revise and enact laws that allow management agencies to respond quickly in the case of new green iguana incursions.

Full text

IRCF REPTILES & AMPHIBIANS • 19(3):150–160 • SEPT 2012
species and perhaps one of the reptiles with the most extensive geo-
graphic ranges in the Americas is not surprising.
During the last half-century, Green Iguana populations have
suffered heavy losses in their native range through collection and
exportation to satisfy the pet trade industry (Fitch et al. 1982,
Harris 1982, Muñoz et al. 2003). As a result of the introduction of
I. iguana outside its native range, some populations became estab-
lished and even invasive (e.g., in Florida and Puerto Rico; Kraus
2009). We have now begun to see impacts associated with the estab-
lishment and spread of Iguana iguana.
As with any invasive species, prevention would be the best
option to deal with these reptiles, both in economic and logisti-
cal terms (Leung et al. 2002, Powell et al. 2011). Considering the
negative impact caused by Green Iguanas in their invasive range,
assessing the risk of invasion in order to assist in development of
sound preventive strategies would be advantageous. In this article,
we employ niche-modeling techniques to identify areas likely to be
Keywords: Iguana iguana, exotic species, risk assessment, niche
modeling, Caribbean Basin.
Introduction
Many animals have been introduced outside their native ranges. In
the Greater Caribbean Region, thousands of reptiles and amphib-
ians have been imported as food, through the pet trade, or as hitch-
hikers on cargo (Powell et al. 2011). A high profile example of this
is the Green Iguana (Iguana iguana L. 1758). Green Iguanas are
large (up to 2 m long), arboreal, herbivorous lizards native to the
Neotropics. These reptiles can be found from xeric to mesic hab-
itats, from coastal areas to inland mountain ranges, and in both
open and forested areas (Moberly 1968, Müller 1972, Distel and
Veazey 1982, van Devender 1982, van Marken Lichtenbelt et al.
1993, Benítez-Malvido et al. 2003). Moreover, they also inhabit
and reproduce well in urban areas. With such a wide tolerance to
variable conditions, that I. iguana is the most widespread iguanine
March of the Green Iguana:
Non-native Distribution and Predicted
Geographic Range of Iguana iguana
in the Greater Caribbean Region
Wilfredo Falcón1, James D. Ackerman1, and Curtis C. Daehler2
1Faculty of Natural Sciences, Department of Biology, University of Puerto Rico, P.O. Box 70377, San Juan, Puerto Rico 00936-8377, USA
(wilfredo.falcon@upr.edu)
2 Department of Botany, University of Hawai’i, 3190 Maile Way, Honolulu, Hawaii 96822-2279, USA.
Photographs by the senior author except where indicated.
Abstract.—Green Iguanas (Iguana iguana L. 1758) have been introduced outside their native range largely through the
pet trade. In many places, exotic populations have invaded and many have become established. Of special concern is
the Greater Caribbean Basin, where several exotic populations of Green Iguanas have had a negative impact, and may
threaten the conservation of several native species, including possible native and distinct forms of I. iguana in the Lesser
Antilles, and the endangered Lesser Antilles Iguana (I. delicatissima Laurenti 1768). We assessed the risk of spread and
invasion by Green Iguanas in the Greater Caribbean Basin using the maximum entropy niche-modeling algorithm
(MaxEnt) to predict the potential distribution of this reptile. We used a total of 187 location points that represented
occurrences from both the native and the invasive range, coupled with environmental data as predictor variables. Our
model had average training and test AUC values of 0.90 and 0.87 respectively, indicating a high predictive ability. The
model predicts suitable conditions for I. iguana in south and central Florida (mainly along the coast), and in regions
of all the islands in the Caribbean. Given the known negative impact of Green Iguanas and their dispersal capabilities,
governments in the Greater Caribbean Basin should manage non-native populations to prevent further spread, and
revise and enact laws that allow management agencies to respond quickly in the case of new Green Iguana incursions.
150
IRCF REPTILES & AMPHIBIANS • VOL15, NO 4 • DEC 2008 189TABLE OF CONTENTS
TABLE OF CONTENTS
FEATURE ARTICLES
Chasing Bullsnakes (Pituophis catenifer sayi) in Wisconsin:
On the Road to Understanding the Ecology and Conservation of the Midwest’s Giant Serpent ...................... Joshua M. Kapfer 190
The Shared History of Treeboas (Corallus grenadensis) and Humans on Grenada:
A Hypothetical Excursion ............................................................................................................................Robert W. Henderson 198
RESEARCH ARTICLES
The Texas Horned Lizard in Central and Western Texas ....................... Emily Henry, Jason Brewer, Krista Mougey, and Gad Perry 204
The Knight Anole (Anolis equestris) in Florida
.............................................Brian J. Camposano, Kenneth L. Krysko, Kevin M. Enge, Ellen M. Donlan, and Michael Granatosky 212
CONSERVATION ALERT
World’s Mammals in Crisis ............................................................................................................................................................. 220
More Than Mammals ...................................................................................................................................................................... 223
The “Dow Jones Index” of Biodiversity ........................................................................................................................................... 225
HUSBANDRY
Captive Care of the Central Netted Dragon ....................................................................................................... Shannon Plummer 226
PROFILE
Kraig Adler: A Lifetime Promoting Herpetology ................................................................................................ Michael L. Treglia 234
COMMENTARY
The Turtles Have Been Watching Me ........................................................................................................................ Eric Gangloff 238
BOOK REVIEW
Threatened Amphibians of the World edited by S.N. Stuart, M. Hoffmann, J.S. Chanson, N.A. Cox,
R. Berridge, P. Ramani, and B.E. Young .............................................................................................................. Robert Powell 243
CONSERVATION RESEARCH REPORTS: Summaries of Published Conservation Research Reports ................................. 245
NATURAL HISTORY RESEARCH REPORTS: Summaries of Published Reports on Natural History ................................. 247
NEWBRIEFS ...................................................................................................................................................................................... 248
EDITORIAL INFORMATION ..................................................................................................................................................... 251
FOCUS ON CONSERVATION: A Project You Can Support ............................................................................................... 252
Front Cover. Shannon Plummer.
Totat et velleseque audant mo
estibus inveliquo velique rerchil
erspienimus, quos accullabo. Ilibus
aut dolor apicto invere pe dolum
fugiatis maionsequat eumque
moditia erere nonsedis ma sectiatur
ma derrovitae voluptam, as quos
accullabo.
Back Cover. Michael Kern
Totat et velleseque audant mo
estibus inveliquo velique rerchil
erspienimus, quos accullabo. Ilibus
aut dolor apicto invere pe dolum
fugiatis maionsequat eumque
moditia erere nonsedis ma sectia-
tur ma derrovitae voluptam, as
IRCF
REPTILES & AMPHIBIANS
CONSERVATION AND NATURAL HISTORY
Copyright © 2012. Wilfredo Falcón. All rights reserved.
WWW.IRCF.ORG/REPTILESANDAMPHIBIANSJOURNAL

IRCF REPTILES & AMPHIBIANS • 19(3):150–160 • SEPT 2012
151
vulnerable to invasions of I. iguana across the Greater Caribbean
Basin.
Methods
In order to generate niche models that allowed us to identify
areas vulnerable to Green Iguana invasions, we used herpetologi-
cal specimen occurrence records obtained from data published
by Arctos, California Academy of Science, Carnegie Museum of
Natural History, Colecciones Instituto Alexander von Humboldt,
Comisión Nacional para el conocicmiento y uso de la Biodiversidad
(Mexico), Conservation International, Finnish Museum of Natural
History, Instituto de Biología Universidad Nacional Autónoma
de México, Los Angeles County Museum of Natural History,
Museum of Comparative Zoology (Harvard University), Museum
of Vertebrate Zoology (University of California), National Museum
of Natural History, Staatliches Museum fur Naturkunde Stuttgart
(Germany), University of Colorado Museum of Natural History,
and Yale University Peabody Museum (accessed through the Global
Biodiversity Information Facility Portal, http://data.gbif.org/species/,
and the HerpNet2 Portal, http://www.herpnet2.org), along with
occurrence records that we collected in Puerto Rico. After scrutinizing
each location to remove duplicates from the dataset and to set a mini-
mum distance of 10 km between each point (to prevent overfitting),
we had 187 location points including both the native (166) and the
invasive (21) ranges. Locations from the invasive range were restricted
to jurisdictions inside the calibration area where breeding has been
reported: Florida (2) and Puerto Rico (19). Although I. iguana has
been reported as established and/or invasive in other places within the
Caribbean Basin, no precise geo-referenced locations were available to
us, so those sites were not included in our analysis.
For predictive variables, we used the Bioclim global climatic lay-
ers dataset (WorldClim, http://www.worldclim.org/current). These
climatic layers have a resolution of 30 arc-seconds (~1 km2) and are
derived from monthly temperature and rainfall values that include
annual trends, seasonality, and extreme or limiting environmental fac-
tors calculated from 1950 to 2000 (Hijmans et al. 2005). BIL layers
were converted into GRD and ASC layers using DIVA-GIS (http://
www.diva-gis.org/) and trimmed to focus on the Neotropics. From
the available climatic information, we selected a priori the mean,
extreme, and seasonality values in temperature and precipitation vari-
ables (layers) to represent conditions that are biologically important to
and may limit the distribution of Green Iguanas (e.g., Moberly 1968,
van Devender 1982, Bock and Rand 1989, van Marken Lichtenbelt
et al. 1993, van Marken Lichtenbelt et al. 1997).
To model the realized distribution of I. iguana, we used the
MaxEnt software, which employs the maximum entropy method for
niche modeling (MaxEnt, http://www.cs.princeton.edu/~schapire/
maxent/). MaxEnt is a machine learning method that uses presence-
FALCÓN ET AL.
This Green Iguana has taken up residence at the “Paseo Lineal” in the Central Park of San Juan, Puerto Rico.

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152
only data in combination with predictive variables to model a spe-
cies’ geographic distribution (Phillips and Dudík 2008 and refer-
ences therein).
To predict the potential for invasion, we constructed a model
using the combination of points from the native and invasive ranges
(e.g., Steiner 2008). The calibration area, which includes all the cli-
matic information for the occurrence locations of I. iguana in our
dataset, was defined as the smallest rectangle that encompassed all
the location records that we used in the model (longitude -107–
-35°, latitude -23– 26°) and does not include information from oce-
anic areas. For the model, we ran 10 replicates with bootstrapping
and randomly selected 80% of the presence records for training and
20% for testing in each run. The model was run without using the
Threshold feature (i.e., the Auto and Threshold features were set to
off) to correct for overfitting based on the response curves. For the
evaluation of the model, we utilized AUC statistics, that is, the Area
Under the ROC (Receiver Operating Characteristic) Curve, and
reported the average AUC values. This summary statistic provides
a single measure of the model’s performance by comparing the pre-
dicted geographical distribution of the species to the background
data (Phillips et al. 2006). The Training AUC indicates how well
the resulting predicted distribution matches the locations of the
training data and the Test AUC indicates how well the resulting
prediction of the geographic distribution matches occurrence sites
that were reserved for model testing (points not used to build the
model). Since the Test AUC for our model measures model perfor-
mance outside the model training points, the Test AUC provides
a better indication of predictive ability of the model. Models with
AUC values >0.90 are considered to have excellent predictive per-
formance, whereas values <0.90 are interpreted as having a good
(0.80–0.90) to poor (<0.70) predictive performance (Swets 1988,
Manel et al. 2001, Franklin 2009). We ran simulations using the
climatic layers selected a priori and evaluated the performance of
the model by removing individual layers based on the percent con-
tribution of each variable, Jackknife test of variable importance,
Jackknife of test gain, and Jackknife of the AUC, and selected the
combination of layers that resulted in the highest mean, train-
ing, and test AUC values. These layers included the annual mean
temperature (BIO1), isothermality (BIO3), temperature seasonal-
ity (BIO4), minimum temperature of the coldest month (BIO6),
the mean temperature of the warmest quarter (BIO10), the annual
precipitation (BIO12), precipitation seasonality (BIO15), and the
precipitation of the warmest quarter (BIO18; for clarifications on
the definitions, refer to http://www.worldclim.org/bioclim).
We then projected the selected model to a set of layers focusing
on the Neotropics (longitude -126– -34°, latitude -43– 43°) to visu-
alize the predicted distribution of Green Iguanas in the Americas
using Diva-GIS (http://www.diva-gis.org/) and the logistic output
format from MaxEnt, which estimates the probability of presence of
the species in a given grid, with values ranging from 0 to 1 (Phillips
and Dudík 2008). This was done after subtracting the “Clamping
layer” provided by MaxEnt, which provides information about cli-
matic values in a given pixel of the predictive layers that are outside
the climatic conditions of the training data, thus avoiding incorrect
predictions (as recommended by S.J. Phillips, May 2008, MaxEnt
Google Group). To generate a binary map of presence/absence, we
used the average of the logistic threshold value that maximizes the
sum of the test sensitivity and the specificity (MTeS+S) as the cutoff
point. The sensitivity is the proportion of correctly predicted pres-
ence observations, whereas the specificity is the proportion of cor-
rectly predicted absences in terms of the fractional area predicted.
This threshold criterion minimizes the mean of the error rate for
positive and negative observations (Manel et al. 2001, Freeman and
Moisen 2008). When compared to other criteria, the Maximum
Sensitivity plus Specificity threshold performs comparably or bet-
ter than other threshold selection methods in providing accurate
presence predictions (Jiménez-Valverde and Lobo 2007, Liu et al.
2005, Freeman and Moisen 2008). In the map, we also present the
This male Green Iguana was captured by the senior author in the Piñones
State Forest in Loiza, Puerto Rico. Note the wounds inflicted by a large
lizard equipped with teeth, claws, and a tail that can be used like a club.
Photograph by Noramil Herrera.
A pregnant female Green Iguana killed by dogs in Humacao, Puerto Rico.
Of 69 eggs, 55 contained developing embryos.

FALCÓN ET AL. IRCF REPTILES & AMPHIBIANS • 19(3):150–160 • SEPT 2012
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pixels within the range of the MTeS+S minus 1 standard deviation
(MTeS+S –s). This was done to consider the lower level disper-
sion from the mean threshold value obtained from the 10 replicates,
since some combinations of points yielded a lower threshold value
for the presence-absence cutoff point.
Results and Discussion
Our model showed a good performance, with AUC values of
≥0.90, which indicates that the combination of occurrence records
and predictive variables used to model the distribution of I. iguana
was adequate. The model yielded an average training and test AUC
value of 0.90 (SD < 0.01) and 0.87 (SD = 0.02) respectively, and a
Maximum Test Sensitivity plus Specificity threshold value of 0.30
(SD = 0.11). Based on this threshold cutoff point, the omission rate
for the training data is 0.19 (SD = 0.10) and 0.20 (SD = 0.09) for
the test points.
In terms of the average variable contributions to the model,
the minimum temperature of the coldest month (BIO6) had the
greatest contribution (21.7%) and was followed by the mean tem-
perature of the warmest quarter (BIO10, 20.4%), precipitation
seasonality (BIO15, 16.0%), the precipitation of warmest quarter
(BIO18, 15.1%), and temperature seasonality (BIO4, 14.0%). The
remainder of the variables had individual average contributions of
<10%: isothermality (BIO3, 5.6%), annual precipitation (BIO12,
5.4%), and annual mean temperature (BIO1, 1.9%).
From the presence records, we were able to extract the climatic
information, which shows the variable climatic conditions that
Green Iguanas experience through their range (Table 1). The mean
annual temperature throughout the range of Green Iguanas in our
sample was 25.5 °C, the mean maximum temperature of the warm-
est month was 32.5 °C, and the mean minimum temperature of the
coldest month was 18.5 °C. Moreover, the mean annual precipita-
tion according to the presence records of I. iguana was 1,754 mm,
with a mean precipitation during the wettest month of 305.81 mm
and a mean precipitation during the driest month of 33.0 mm.
In general, the predicted distribution of our model within
its native region is in agreement with the native distribution of I.
iguana as described in the literature (Map A). Green Iguanas can be
found from Sinaloa, México to Ecuador on the Pacific versant and
to northern Paraguay on the Atlantic versant (Etheridge 1982, de
Queiroz 1995, Lever 2003, Townsend et al. 2003). Some patchi-
ness in terms of suitable distribution areas is evident. For example,
Although this iguana is reacting defensively toward the photographer, many Green Iguanas become accustomed to humans and often allow a close
approach. This individual was basking near the Piñones State Forest in Loiza, Puerto Rico.

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154
some habitat suitability gaps occur from the border of Costa Rica
and Panama to suitable areas in Colombia. This could be due to
the small sample size that we have for Panama in our dataset (only
two records). However, the locations of studies done on Green
Iguanas in Panama coincide with the predicted areas. This also is
observed in parts of South America. One factor that could explain
the patchiness of suitable habitat despite the ample distribution of
Green Iguanas could be sampling problems. Our data set might
not represent all the possible conditions in which Green Iguanas
could be present. Assuming that the predictions are correct, the con-
nectivity of climatically suitable areas through rivers and waterways
might explain the patchy distribution of suitable habitats. Green
Iguanas are commonly found along riverbanks both in their native
and invasive ranges, and in Florida and Puerto Rico, they seem to
use waterways to disperse (Rivero 1998, Meshaka et al. 2004, Joglar
2005). Although some of the occurrence points fall out of the areas
predicted with suitable climate as expected by the omission rates for
the selected threshold, the occurrence locations fall within or close
to rivers connected to suitable areas (not shown).
Green Iguanas also are considered native to several islands of
the Greater Caribbean Basin including Bonaire, Klein Bonaire,
Aruba, Trinidad, Tobago, Grenada, the Grenadines, Saint Vincent,
Saint Lucia, and Montserrat (Lazell 1973, Etheridge 1982, Powell
2004). A phylogenetic analysis of the relationships between I.
iguana lineages suggests at least three radiation events into Curaçao,
Saint Lucia, and into Saba and Montserrat (Malone and Davis
2004). All of these locations show climatic suitability for Green
Iguanas according to our model. The status of other populations in
the Lesser Antilles has been disputed as to whether they should be
considered native or introduced (Censky and Kaiser 1999, Thomas
1999, Powell 2004, Powell and Henderson 2005, Platenberg and
Boulon 2006, Platenberg 2007, Stahl 2009). Our model predicts
climatic suitability for Green Iguanas in all of the Caribbean Islands
and southeastern Florida (Map B). Most of the islands had prob-
abilities >0.60. The threshold criterion that maximizes the sum of
the sensitivity and the specificity has been regarded as a somewhat
conservative threshold for species with widespread ranges (Manel
et al. 2001, Freeman and Moisen 2008). Given that the purpose of
this model is invasion risk assessment and that the selected threshold
may under-predict the distribution of widespread species, the fact
that most of the jurisdictions within the Greater Caribbean Basin
are predicted as suitable for Green Iguanas is worrisome. The pre-
dictions for the Greater Caribbean Basin are maintained whether
we use all the occurrence points or just data from the native range
to train the model (analyses not shown).
On the Puerto Rican Bank, our model predicts highly suitable
areas, especially along the coasts. The U.S. Virgin Islands is one of
Table 1. Climatic conditions experienced by Iguana iguana throughout its range from 187 presence records and climatic variables from
Bioclim. Means are presented ± one SD (range in parentheses).
Variable Mean
Mean annual temperature 25.50 ± 2.91 °C (18.20–28.30 °C)
Maximum temperature of warmest month 32.50 ± 1.97 °C (23.30–37.30 °C)
Minimum temperature of coldest month 18.50 ± 2.78 °C (9.70–23.70 °C)
Annual precipitation 1,754.03 ± 882.35 mm (234.00–4,900.00 mm)
Precipitation of wettest month 305.81 ± 139.11 mm (68.00–759.00 mm)
Precipitation of driest month 33.70 ± 37.32 mm (0.00–190.00 mm)
Map. Predicted distribution for Iguana iguana in the Americas (A) and
the Greater Caribbean Basin (B). Gray represents absence according to
the threshold value that maximizes the sum of the training specificity and
the sensitivity (MTeS+S; <0.30), and dark gray represent the MTeS+S –
1s. Presence probabilities are represented in shades of red, with increasing
probabilities denoted by darker color.

FALCÓN ET AL. IRCF REPTILES & AMPHIBIANS • 19(3):150–160 • SEPT 2012
155
the places where the status of I. iguana is uncertain, and present pop-
ulations (which are located on the main islands) might be the result
of introductions through the pet trade (Powell 2004, Platenberg
and Boulon 2006, Platenberg 2007). In Puerto Rico, I. iguana also
has been introduced through the pet trade and is considered highly
invasive (Rivero 1998, Thomas 1999, López-Torres 2011). On the
island, the negative impact caused by iguanas is now beginning to
become apparent. These reptiles are known to interrupt air traffic
in the Luis Muñoz Marín International Airport (SJU) when they
enter the runways to bask (Engeman et al. 2005). Currently, the
FAA and the PR Ports Administration spend $98,000 annually to
prevent intrusions of iguanas onto the runways and to eliminate
nests on airport premises (B. Vázquez, pers. comm.). They also
damage gardens and ornamental plants (Carlo-Joglar and García-
Quijano 2008) and even have caused $13,000 worth of damage to
the gardens of the San Juan State Court (Joel Ortiz, El Nuevo Día
27.IV.2012). They have also severely damaged red and black man-
grove forests (Rhizophora mangle and Avicennia germinans respec-
tively), sometimes resulting in tree mortality (J. Gómez-Carrasquillo
et al., unpubl. data; Carlo-Joglar and García-Quijano 2008).
Recently, a 1–2 year-old Green Iguana reached the Mona
Island Nature Reserve on board the boat that goes to the island
from Mayagüez (PR) to collect trash (K. Barrientos, pers. com-
mun.). Luckily, when the boat reached the pier, the crew noticed
the iguana and alerted biologists and DNER personnel on the
island. The iguana was eventually captured and euthanized. The
Mona Island Nature Reserve is home to the endangered endemic
Mona Ground Iguana (Cyclura stejnegeri).
Green Iguanas were initially sold as pets in the Dominican
Republic in the early 1990s (Pasachnik et al. 2012). In that study,
Pasachnik et al. (2012) identified twelve general locations where the
presence of Green Iguanas has been confirmed by either observa-
tions or interviews in the local communities. All of these locations
fall within the areas predicted by the model as suitable for Green
Iguanas. Due to the negative impacts associated with the invasion
of Green Iguanas, the Dominican Ministry of the Environment
Green Iguanas are excellent swimmers and are known to have colonized islands after swimming or rafting considerable distances. Censky et al. (1998)
recorded Green Iguanas reaching Anguilla on rafts of floating vegetation that had drifted about 320 km from their source in Guadeloupe. This individual
was photographed at Roosevelt Roads, a former naval station in Ceiba, Puerto Rico.

FALCÓN ET AL. IRCF REPTILES & AMPHIBIANS • 19(3):150–160 • SEPT 2012
156
implemented a resolution in 2010 that prohibits the importation
and commercialization of these reptiles (Pasachnik et al. 2012).
The introduction of Green Iguanas of continental origin to some
of the Lesser Antilles has resulted in mixed populations of presumably
native I. iguana and their continental relatives, and the co-occurrence
of the introduced iguanas with the endemic and endangered Lesser
Antillean Iguana (I. delicatissima; e.g., Daltry 2009, Morton and
Krauss 2011). Introduced I. iguana (of continental origin) has been
shown to compete and displace I. delicatissima in the islands where
they co-occur and the two species hybridize, which has jeopardized
conservation efforts for the Lesser Antillean Iguana (Day and Thorpe
1996, Breuil 1997, Powell and Henderson 2005, Knapp 2007, Breuil
et al. 2010). This raises concerns because some of these native Green
Iguanas in the Lesser Antilles may warrant recognition as distinct
populations (or even species; Malone and Davis 2004, Powell 2004),
and interbreeding with introduced continental iguanas might alter
the gene pool and break up adaptive gene complexes. In Saint Lucia,
where a potentially distinct form of I. iguana is endemic, continental
iguanas were introduced through the pet trade and are a cause of con-
servation concern (Morton and Krauss 2011).
Iguana iguana was also introduced through the pet trade to
Barbuda and Saint Martin (Powell 2005). It has also been intro-
duced illegally into the UK Overseas territories of the British Virgin
Islands, the Cayman Islands, and Turks and Caicos Islands (Seidel
and Franz 1994, Edgar 2010, Reynolds and Niemiller 2010).
On Grand Cayman, Green Iguanas are spreading eastward across
the island with an exponentially growing population (interview
with Frederick Burton by Tammi Sulliman, Cayman 27 News,
21.IV.2009). They are considered a nuisance, are now causing a
variety of problems, and might pose a threat to the native critically
endangered Rock Iguana (Cyclura lewisi; Seidel and Franz 1994,
Burton 2007, Edgar 2010).
On Anguilla, one population of Green Iguanas is almost cer-
tainly descended from introduced pets, and another originated from
Guadeloupe after a hurricane in 1995 sent at least 15 iguanas rafting
on trees until they reached the Anguillan coast some 200 miles away
(Censky et al. 1998; Hodge et al. 2003, 2011). According to Breuil
(2002), Green Iguanas found on Les Îles des Saintes, Basse-Terre,
Grande-Terre, and Martinique should also be considered invasive.
All of these islands have high probabilities of predicted distribution
for Green Iguanas, so based on the climatic variables included in the
analysis, populations are expected to continue spreading.
In the U.S., these reptiles have been imported primarily from
El Salvador and Colombia (Hoover 1998), and are now consid-
ered invasive in Florida (Townsend et al. 2003, Krysko et al. 2007),
where they are known to cause extensive damage to gardens and
This imposing individual greeted tourists near the Cruise Terminal in Charlotte Amalie, St. Thomas, U.S. Virgin Islands.

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ornamental plants (Kern 2004, Krysko et al. 2007) and might aid
in the dispersal of invasive species of plants (Meshaka et al. 2007,
Sementelli et al. 2008). The consumption of Drymaeus multilinea-
tus, a native tree snail, and interactions with the Florida Burrowing
Owl (Athene cunicularia floridana; a species of special concern)
elevates concerns about the possible negative ecological impact that
this species might have (McKie et al. 2005, Townsend et al. 2005).
Moreover, these lizards are considered an erosion hazard in the state
due to their burrow construction habits. Some areas in Florida have
more than 2,000 burrows/ha, which could result in high costs due
to erosion-related damages and repairs (Sementelli et al. 2008). The
predictions of our model agree with the areas presently occupied
by Green Iguanas in the state (Meshaka et al. 2004, Krysko et al.
2007; Florida Museum of Natural History Herpetology Database).
Suitable predicted areas also occur along the coast in Titusville and
Merritt Island, and in the Tampa Bay area, but with probabilities
<0.40 (except for the dark spots in the St. Petersburg area; see Map
B). Farther north along the Atlantic Coast, the model also predicts
suitable areas east of Jacksonville north to Brunswick (Georgia), and
from west of Live Oak to Pensacola along the Gulf Coast. Again,
the majority of the predicted areas have probabilities <0.40, with
higher probabilities in coastal areas (Map B). The cold temperatures
in northern latitudes likely limit the distribution of I. iguana in the
U.S. (Townsend et al. 2003, Krysko et al. 2007). According to our
model, suitable climatic conditions for Green Iguanas are limited to
<31° latitude along the coasts. From our Green Iguana occurrence
data, the sample average for the temperature in the coldest month
(BIO6) is 18.38 °C (~65 °F; Table 1), and in Florida, I. iguana
populations were adversely affected for a short period of time when
temperatures dropped below 10 °C (50 °F; Krysko et al. 2007). The
annual mean temperature range is 19–20 °C in northern parts of
Florida predicted as suitable, and the mean temperature of the cold-
est month goes down to 4–5 °C according to our climatic layers.
Green Iguanas are unlikely to survive prolonged periods (>1 month)
of cold temperatures (<18 °C) without behavioral modifications
(e.g., seeking shelter in burrows or water; Townsend et al. 2003).
Also, a population of Green Iguanas has been reported in the Rio
Grande Valley of Texas (Meshaka et al. 2004), but our model does
not predict suitable areas there (probabilities <0.01). Currently, the
fate of this feral population is uncertain, and no recent accounts
report established Green Iguanas in Texas, although occasional
escaped pets and Spiny-tailed Iguanas in the genus Ctenosaura are
known to occur (A. Gluesenkamp, pers. comm.).
Based on the high dispersal capabilities of I. iguana and the
suitability of climatic conditions in the Greater Caribbean Basin,
Green Iguanas clearly have a high potential for invasion. Virtually
all Caribbean Islands currently unoccupied by Green Iguanas are
vulnerable to new invasions, especially in coastal areas, based on the
climatic suitability. These lizards also have the potential to spread
from places where non-native Green Iguanas have become estab-
lished and currently remain localized. The same is true for many
islands in the Pacific. This model was projected into the Pacific
Region, where established populations of Green Iguanas have also
been reported. Suitable climatic conditions for the establishment
and spread of Green Iguanas are abundant (Falcón et al., in press).
That our model was developed using global environmental lay-
ers, in which considerable data are based on extrapolation, is impor-
tant to mention (Hijmans et al. 2005). This limits the predict-
ability of Green Iguana distribution especially at finer scales (e.g.,
Christenhusz and Toivonen 2008). Moreover, other important
factors might affect local distributions of Green Iguanas for which
we do not have information at a global scale. To address local-scale
distribution of Green Iguanas (e.g., in Puerto Rico), one should use
variables (layers) obtained at a finer scale. In the case of Florida and
Puerto Rico, Gap Analysis Projects (Pearlstine et al. 2002, Gould et
al. 2008) provided those local scale data, which included land cover
and stewardship, vertebrate occurrence, and other natural history
information. These data are collected in a standardized way as part
of the U.S. National Gap Analysis Program (Scott et al. 1987, Scott
and Jennings 1994), which makes comparable analyses between
jurisdictions in the U.S. The problem with such data is that cover-
age is limited, especially for tropical regions, making broad-scale
species distribution modeling such as that which we present here
dependent on global datasets.
Currently the possession and importation of Green Iguanas
is regulated depending on the jurisdiction where they have been
Stuffed iguanas for sale in the gift shop of El Portal Visitor Center at El
Yunque National Forest. Although not native and highly invasive, because
of their visibility, Green Iguanas have come to represent wildlife for many
tourists visiting Puerto Rico.

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158
introduced. Releasing iguanas into the wild is illegal even where
possession is allowed (e.g., Florida and Puerto Rico). In Florida,
Sementelli et al. (2008) suggested a ban on the possession of these
reptiles due to the evident negative impact. In Puerto Rico, people
are allowed to possess, hunt, and export iguanas as long as they are
not returned to the wild. However, the importation of this spe-
cies into Puerto Rico has been illegal since 2004, when they were
declared a nuisance invasive species under the regulations of the
Department of Natural and Environmental Resources. The case of
the Grand Cayman Islands is curious in the sense that I. iguana is
invasive and causes similar problems as in Puerto Rico and Florida,
but because of the general protection offered to iguanas by the
Conservation Law (Animal Law 2003 Revision) intended to safe-
guard the endemic Grand Cayman Blue Iguana (Cyclura lewisi) and
Sister Isles Rock Iguana (Cyclura nubila caymanensis), they actually
enjoyed protection until the law was finally amended in 2010.
Not everything is negative when Green Iguanas become estab-
lished outside their native range. In Florida and Puerto Rico, some
people enjoy having iguanas around, and tourists are often drawn
to these reptiles (Meshaka et al. 2004, García-Quijano et al. 2011).
The tourism industry has taken advantage of this and uses Green
Iguanas in advertisements, on apparel, and as attractions for nature
excursions — and shops even sell figures and stuffed iguanas. The
trade in iguanas as pets has generated enormous profits in the U.S.
(Hoover 1998), and in Florida, local pet stores were supplied from
local populations after the establishment of Green Iguanas in the
state. Moreover, in Puerto Rico, “Best Iguana Puerto Rico Meat
Export” is seeking permits to not only supply local restaurants with
Green Iguana meat from individuals captured in the wild, but
also to export it to the U.S. (Inter News Services, El Nuevo Día,
07.II.2012; E. Lloréns Vélez, Caribbean Business, 08.II.2012). The
potential benefits of introduced Green Iguana populations have yet
to be analyzed critically and carefully to make sure that I. iguana
does not pose a threat to local fauna and flora and is not likely to
cause negative environmental or economic impacts.
Powell et al. (2005) suggested that introduced reptiles and
amphibians in the Greater Caribbean have a 70% success rate for
establishing new populations. If unimpeded, I. iguana is likely to
Green Iguanas are invasive in Puerto Rico, and sufficiently abundant in some areas that their burrows threaten the integrity of paved roads, sidewalks, and
verandas. This burrow was along the state road along the coast near Dorado, Puerto Rico.

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159
spread throughout the Caribbean Basin as it has shown to be adept
at both natural and human-assisted dispersal. Countries in the
Caribbean Basin that do not have regulations on the importation,
possession, and release of Green Iguanas should consider laws and
regulations enacted by the jurisdictions mentioned above in order to
prevent human-mediated dispersal. We concur with the recommen-
dations by Sementelli et al. (2008) that prohibit private ownership
of Green Iguanas in places where they have the potential to cause
or are causing a negative impact. Allowing the private possession of
these reptiles in places that are suitable for their occurrence can aid
the establishment and spread of populations, as individuals escape
from captivity or are intentionally released by their owners. Where
non-native populations of I. iguana occur and the possibility of
negative impact exists, control and/or eradication measures should
be implemented immediately. Local governments should also be
aware of the possibility of natural dispersal from islands that have
already been invaded (e.g., Censky et al. 1998) and plan accord-
ingly in order to prevent the establishment of new iguana popula-
tions. Control of the Green Iguana invasion might best be under-
taken by using a regional approach that encompasses the Greater
Caribbean (e.g., Powell et al. 2011). Otherwise, the march of the
Green Iguanas will continue and the negative genetic, ecological,
environmental, and economic effects currently associated with these
beasts could soon affect the remainder of the region.
Acknowledgements
We are grateful to Dr. Andy Gluesenkamp from the Texas Parks
and Wildlife Department for providing us with information about
iguana populations in Texas, to Mr. Bernardo Vázquez, Interim
Director of the Puerto Rico Ports Authority, for providing infor-
mation about the iguanas at SJU airport, and to Jesús Gómez-
Carrasquillo for providing us with unpublished data about the
diet of Green Iguanas. We especially thank Wilnelia Recart and
Dr. Jason Kolbe for their insightful comments on the manuscript.
This work was funded by United States Department of Agriculture
Faculty and Student Training Fellowships (2010), and WF was
supported by the LS-AMP BDP (NSF-HRD 0601843).
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