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



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.
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.
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
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.
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Kraig Adler: A Lifetime Promoting Herpetology ................................................................................................ Michael L. Treglia 234
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Front Cover. Shannon Plummer.
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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
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
Copyright © 2012. Wilfredo Falcón. All rights reserved.
IRCF REPTILES & AMPHIBIANS • 19(3):150–160 • SEPT 2012
vulnerable to invasions of I. iguana across the Greater Caribbean
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,,
and the HerpNet2 Portal,, 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, 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:// 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,
maxent/). MaxEnt is a machine learning method that uses presence-
This Green Iguana has taken up residence at the “Paseo Lineal” in the Central Park of San Juan, Puerto Rico.
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
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 ( 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.
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.
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.
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.
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.
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.
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.
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.
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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... Reptile species are not typically considered pests from an agricultural standpoint, though they are invasive alien species in over two dozen countries (Fritts and Leasman-Tanner 2001;Kraus 2009;Meshaka 2011). The invasive green iguana (Iguana iguana Linnaeus, 1758), a reptile from Central and South America, may become a pantropical agricultural pest and thus require the same concerted management action as other agricultural pests (Falcón et al. 2012;Knapp et al. 2020;van den Burg et al. 2020). ...
... Numerous countries cite invasive green iguanas as a threat to agricultural production (Kern 2009;Van Veen 2011;López-Ortiz et al. 2012;Thomas et al. 2013), yet qualitative or quantitative analyses of the potential impact of green iguanas on agriculture are lacking. As the green iguana spreads (Falcón et al. 2012(Falcón et al. , 2013van den Burg et al. 2020) and increases its range, the need to understand its potential impact on agricultural food production becomes even more pressing. ...
Full-text available
Agricultural communities and crop production are negatively impacted by invasive species, with the effects of pathogenic fungi, parasitic insects and weedy plants being well studied. Mammals and birds are also recognized as impacting crops, but reptiles, such as non-native green iguanas (Iguana iguana), are typically not considered agricultural pests. Research on non-native green iguanas has largely focused on the lizard's interactions with native species with little attention given to its impact in the agricultural landscape. We conducted semi-structured interviews with farmers from 20 farms in Puerto Rico to explore the effect of the invasive green iguana on the production of crops and how farmers manage impacts, if any. A total of 34 of 55 crop species reported by farmers were negatively affected by the green iguana. We found that green iguanas were absent from 20% of farms, did not consume crops in 10% of the farms and caused negative impacts in 70% of the remaining farms. Negative impacts included crop loss and infrastructural damage, which had behavioral, emotional, and economic effects on farmers. Specific outcomes of these effects were revenue loss, refurbishing costs, changes in crop selection, management costs and emotional stress. Farmers considered management strategies as mitigation measures that needed to be constant to produce any positive effects on crop yield. They reported use of mesh fencing, hunting, and domestic animals as attempts to reduce negative effects of green iguanas on crop production. Recognition of this species as an agricultural pest is warranted in Puerto Rico and perhaps elsewhere in its introduced range. Agricultural extension agents should consider providing guidance on strategies to reduce negative impacts of green iguanas including cultivating less susceptible crops when possible.
... Maxent (Phillips et al., 2006) is one of the most popular methods for modeling species distributions (Merow et al., 2013) and is widely used in the study of non-native reptiles (Angetter et al., 2011;Buckland et al., 2014;Cohen, 2017;Dowell et al., 2016;Falcón et al., 2012;Jarnevich et al., 2018;Mothes et al., 2019;Mutascio et al., 2018;Nania et al., 2020;Pyron et al., 2008;Rödder et al., 2008;Weterings & Vetter, 2018). Maxent has been shown to generally outperform equivalent methods (Elith et al., 2006;Gogol-Prokurat, 2011), returning highly accurate predictions even with small sets of presence-only data (Gogol-Prokurat, 2011;Merow et al., 2013;Pearson et al., 2007). ...
... Florida is home to more established non-native species of reptile and amphibian than anywhere else on Earth (Krysko et al., 2016), and SDMs based wholly or partly on climate-matching techniques have been developed for a wide range of non-native herpetofauna in the state (e.g., Mothes et al., 2019), including the Burmese python (Python bivittatus) (Pyron et al., 2008;Rodda et al., 2009), Argentine black-and-white tegu (Salvator merianae) (Jarnevich et al., 2018), Nile monitor (Varanus niloticus) (Cohen, 2017;Dowell et al., 2016), and green iguana (Iguana iguana) (Falcón et al., 2012), all of which are considered to be problematic invasive species. ...
Full-text available
Aim To investigate whether the frequently advocated climate-matching species distribution modeling approach could predict the well-characterized colonization of Florida by the Madagascar giant day gecko Phelsuma grandis. Location Madagascar and Florida, USA. Methods To determine the climatic conditions associated with the native range of P. grandis, we used native-range presence-only records and Bioclim climatic data to build a Maxent species distribution model and projected the climatic thresholds of the native range onto Florida. We then built an analogous model using Florida presence-only data and projected it onto Madagascar. We constructed a third model using native-range presences for both P. grandis and the closely related parapatric species P. kochi. Results Despite performing well within the native range, our Madagascar Bioclim model failed to identify suitable climatic habitat currently occupied by P. grandis in Florida. The model constructed using Florida presences also failed to reflect the distribution in Madagascar by overpredicting distribution, especially in western areas occupied by P. kochi. The model built using the combined P. kochi/P. grandis dataset modestly improved the prediction of the range of P. grandis in Florida, thereby implying competitive exclusion of P. grandis by P. kochi from habitat within the former's fundamental niche. These findings thus suggest ecological release of P. grandis in Florida. However, because ecological release cannot fully explain the divergent occupied niches of P. grandis in Madagascar versus Florida, our findings also demonstrate some degree of in situ adaptation in Florida. Main conclusions Our models suggest that the discrepancy between the predicted and observed range of P. grandis in Florida is attributable to either in situ adaptation by P. grandis within Florida, or a combination of such in situ adaptation and competition with P. kochi in Madagascar. Our study demonstrates that climate-matching species distribution models can severely underpredict the establishment risk posed by non-native herpetofauna.
... The establishment of invasive I. iguana in numerous countries highlights the ever-present risk of this species spreading to other tropical and subtropical regions (Falcón et al., 2012;De Jesús Villanueva et al., 2021;Knapp et al., 2021). Species-distribution modelling by van den Burg et al. (2020a) has shown that broad To date, no jurisdictions with breeding populations of I. iguana have successfully eradicated them (Knapp et al., 2021), which emphasizes the importance of wildlife managers and scientists investigating early detections of I. iguana in new areas. ...
... In recent years, however, the Invasive Alien Green Iguana (IAGI) has become a species of high worldwide concern as an invasive species. From its origins in South America, it has spread extensively throughout the Caribbean (Falcón et al. 2012) and is now rapidly spreading elsewhere throughout tropical and subtropical regions of the world, including Asia (Falcón et al. 2013, Van den Burg et al. 2020). ...
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The Invasive Alien Green Iguana (IAGI), Iguana iguana, has spread worldwide via the pet trade, as stowaways and via other means and has become a pest species of global concern. It also represents a major threat to the endemic Lesser Antillean Iguana, Iguana delicatissima, on St. Eustatius. Following the capture of an adult female IAGI on St. Eustatius in early 2016, we conducted a Rapid Response Removal Campaign (RC) from April 2016 to January 2017. Three sets of directed visual surveys totaling 409.5 observer hours and covering a combined trajectory of 114.2 km realized only a single detection of a hybrid that was later removed. During the remainder of the campaign period, an additional four IAGI hybrids were opportunistically detected and removed thanks to park staff or community involvement. Since the end of the campaign, eight additional detections and removals have been realized, three of which were IAGIs caught while offloading freight in the harbour and five of which were hybrids caught in surrounding suburban areas. We suggest that at least four distinct IAGI introductions to St. Eustatius occurred between 2013 and 2020. Our results show the value of motivating and mobilizing stakeholders and the public at an early stage of an invasion. Since the program’s initiation, eight of the 13 iguanas detected for culling were thanks to public and key stakeholder support and involvement. Four years after our campaign, the number of IAGIs and their hybrids still appear to be limited and concentrated in and around inhabited areas. Additional removal campaigns should be initiated as soon as possible, firmly based in public outreach, motivation and engagement. New legislation is needed to prohibit the importation, possession and harbouring of IAGIs or hybrids and to provide a framework for long-term structural funding required for effective control and removal. Routine fumigation and rigorous inspection of arriving cargo to eliminate the risk of stowaway IAGIs are also recommended. Culling of IAGIs is recommended for the port of St. Maarten, which serves as a major point of dispersal of IAGIs to St. Eustatius and likely also other islands in the region.
... Other studies documented ten predatory carnivorous mammals of iguana (eight wild and two domestic) and presumably L. longicaudis (de Lima et al., 2020). On the other hand, and not less important, humans are regarded as their main enemy (Falcón et al., 2012); the consumption of iguana by humans is a common issue and in some places the rate of overexploitation is not sustainable (Bock, 2013). In summary, here we report the first known case of predation by P. brasiliensis on a large lizard (I. ...
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The Giant otter (Pteronura brasiliensis) is a semi-aquatic mammal listed as Endangered (EN) at national and international levels. On 20 th April 2021, a P. brasiliensis was sighted and a video recorded the killing a Common green iguana (Iguana iguana). In this short note we report the first record of attack and consumption of iguana by giant otter and includ the Giant otter in the list of the occasional predators of these widespread lizards in a tributary of Tillavá River, tributary of the Vichada River, department of Meta, Colombia.
... We found that more than a third of the 24 verified observations outside of the Florida populations were in localities adjacent to streams or bodies of water. Green Iguanas frequently are associated with water, which is a key predictor of their presence in their natural range (Falcón et al. 2012). The proportion of reports near watercourses could reflect people discarding iguanas near water or a pattern in which iguanas liberated near water survive at higher rates than those released in other situations. ...
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Presently, the only established populations of invasive Green Iguanas (Iguana iguana) on the mainland USA occur in Florida. We examined observation data from the online citizen-science application iNaturalist to determine the frequency of reports of free-living Green Iguanas in Florida and identify where iguanas have been reported in other parts of the mainland USA. Observations from Florida comprised 99.6% of the 5,929 verified Green Iguana observations from the mainland USA. The largest proportion were observations from 2016 to 2021, corresponding with an increasing number of application users contributing to the dataset during this period. The majority of Green Iguana observations from latitudes of 27–41°N in 11 other mainland states were from California. However, we noted no obvious concentrations of sightings to indicate the presence of established populations in any of those 11 states. The majority of observations from outside Florida were adults and were most frequently reported from suburbia and urban parks, suggesting that released or escaped pets were the likely source. More than one third of iguanas reported outside Florida were near water, which is worrisome because iguanas are known to use waterways to disperse. This study clearly demonstrates the value of public participation in assembling sighting records of non-native animals, and we encourage engagement campaigns that leverage reports from members of the public to achieve early detections of potentially invasive species.
... Green Iguanas exploit a range of habitat strata from arboreal perches to aquatic habitats. The species' adaptability corresponds with a wide natural range throughout the Neotropics and subsequent invasions of some West Indian islands, Florida, Hawaii, Fiji, Japan, Taiwan, Singapore, and Thailand (McKeown 1996;Krysko et al. 2007;Falcón et al. 2012;van den Burg et al. 2020;De Jesús Villanueva et al. 2021). The anthropogenic spread of the Green Iguana is largely associated with their popularity as pets (Knapp et al. 2020). ...
... Native and non-native geographical ranges (established populations) of the specie were obtained from the Global Invasive Species Database (, the Reptile Database (, and previous studies (e.g., Mitrus and Zemanek, 2000;To, 2005;Albino and Carlini, 2008;Falcón et al., 2012;Martínez et al., 2015;Burgos-Rodríguez et al., 2016;Mo, 2019;Spitzweg et al., 2019). ...
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Trade of non-native reptiles is an important and increasing driver of biodiversity loss and often compromises the standards required for protection. However, the growing interest in non-native reptiles as pets has posed serious concerns to wildlife managers and conservationists. Instituting effective policies regarding non-native reptiles requires a thorough understanding of the potential range of species in new environments. In this study, we used an ensemble of ten species distribution models to predict the potential distribution for 23 of the most commonly traded species of reptiles across the Middle East. We used ten modeling techniques implemented in the Biomod2 package and ensemble forecasts. Final models used thirty environmental variables, including climatic, topographic, and land cover/land use variables. Our results indicate that all Middle Eastern countries included suitable habitats for at least six species, except Qatar, Kuwait and Bahrain, for which the models did not predict any suitable habitats. Our study showed that Lebanon, Palestine, Turkey, and Israel face the highest risk of biological invasion based on the area of suitable habitats for all studied species. Also, the results showed that turtles posed the highest risk of spreading in in the Middle East. Information on which species pose a greater danger as invaders and the possible impacts of their introduction will be a valuable contribution to the development of conservation plans and policies.
This datasheet on Iguana iguana covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Biology & Ecology, Natural Enemies, Impacts, Uses, Prevention/Control, Management, Further Information.
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A Red-bellied Racer (Alsophis rufiventris) basking on the rim of The Quill, a dormant volcano on St. Eustatius. These snakes are abun-dant here, but have been extirpated elsewhere on the St. Christopher Bank, where the mongoose has become established. JOHN S. PARMERLEE, JR. I nsular populations of terrestrial animals often suffer as a con-sequence of alterations to their habitats by human agency (e.g., Fosberg 1983, Case et al. 1992). Habitat specialists and endemic species that have evolved in the absence of efficient mainland predators and competitors are particularly vulnerable (e.g., Case et al. 1992). Faunas of isolated oceanic islands are re-presented disproportionately on lists of threatened or endan-gered species (e.g., 327 of 1264 or over 25% of species included on the list of U.S. endangered species are from Hawaii ( Declines in amphibian populations throughout the world have been documented in recent years (e.g., IUCN et al. 2004), but comparable surveys of reptilian species have yet to be imple-mented. Although a few species and even some genera (e.g., West Indian Rock Iguanas in the genus Cyclura; e.g., Alberts 2000, Alberts et al. 2004) have been the focus of intensive con-servation efforts, populations of many more species, a large pro-portion of them found only on small islands, are in various stages of decline, and some are in imminent danger of extinc-tion, often with little recognition by the public or even profes-sional conservation biologists. Herein we address these concerns for reptiles inhabiting the Lesser Antilles, an archipelago of oceanic islands on which rep-tiles are frequently the most abundant and obvious naturally occurring vertebrates. General surveys of the herpetofauna include Schwartz and Thomas (1975), Schwartz and Henderson (1988, 1991), and Censky and Kaiser (1999), but the only pre-vious systematic overview of conservation needs is that of Corke (1992), and that was restricted to the Windward Islands. Although many Lesser Antillean species are ecological general-ists and some thrive in altered habitats (e.g., Henderson and Powell 1999, 2001), populations of many others are declining at alarming rates. Some recent extirpations and even some extinctions have been documented, with a majority of both attributable to human agency. Based on our own work in the region and surveys of the literature, we contend that at least 37 of 81 (45.7%) presumably native terrestrial reptilian species Abstract.—Island populations of terrestrial animals often are vulnerable to human-mediated changes to their environments. Many insu-lar endemics have become extinct, had populations extirpated, or are in various stages of decline. Herein we address the conservation sta-tus of terrestrial reptiles in the Lesser Antilles. Although many species in the region are ecological generalists and have adapted to the presence of humans, nearly half of the reptilian species native to the archipelago have suffered as a consequence of human alterations of their habitats or introductions of alien predators and competitors, often aggravated by catastrophic natural events such as hurricanes. Particularly vulnerable are species that are terrestrial and diurnally active. Although many of the listed factors have contributed to the decline or elimination of particular species from individual islands, we contend that the introduction of the mongoose is the single event most responsible for the extirpations and declines of many Lesser Antillean reptiles.
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We studied the demography and nesting ecology of two populations of Iguana iguanathat face heavy exploitation and habitat modification in the Momposina Depression, Colombia. Lineal transect data was ana- lyzed using the Fourier model to provide estimates of social group densities, which was found to differ both within and among populations (1.05 - 6.0 groups/ha). Mean group size and overall iguana density estimates var- ied between populations as well (1.5 -13.7 iguanas/ha). The density estimates were far lower than those report- ed from more protected areas in Panama and Venezuela. Iguana densities were consistently higher in sites locat- ed along rivers (2.5 iguanas/group) than in sites along the margin of marshes, probably due to vegetational dif- ferences (1.5 iguanas/group). There was no correlation between density estimates and estimates of relative abun- dance (number of iguanas seen/hour/person) due to differing detectabilities of iguana groups among sites. The adult sex ratio (1:2.5 males:females) agreed well with other reports in the literature based upon observation of adult social groups, and probably results from the polygynous mating system in this species rather than a real demographic skew. Nesting in this population occurs from the end of January through March and hatching occurs between April and May. We monitored 34 nests, which suffered little vertebrate predation, perhaps due to the lack of a complete vertebrate fauna in this densely inhabited area, but nests suffered from inundation, cat- tle trampling, and infestation by phorid fly larvae. Clutch sizes in these populations were lower than all other published reports except for the iguana population on the highly xeric island of Curaçao, implying that adult females in our area are unusually small. We argue that this is more likely the result of the exploitation of these populations rather than an adaptive response to environmentally extreme conditions.
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The United States Virgin Islands (USVI) are situated along the Puerto Rico Bank near the eastern terminus of the Greater Antilles in the northern Caribbean, and comprise four major inhabited islands and more than 50 satellite cays. The small sizes of the islands, their relative isolation, and unpredictable weather events such as hurricanes make natural populations vulnerable to human-induced impacts of habitat loss and the introduction of invasive exotic species. There are currently 30 extant species of reptiles and amphibians in the USVI, 24 of which are native. Four species have been extirpated from all or part of their former distribution, four species are endangered, one is threatened, and eight are considered data deficient. Five reptiles and amphibians are fairly recent (within the last 150 years) introductions. Species of particular conservation concern are the St. Croix ground lizard (Ameiva polops), Virgin Islands tree boa (Epicrates monensis granti), and sea turtles, and recovery efforts are underway for these species. Habitat protection and reduction of exotic predators are important conservation actions required to protect herpetofauna, combined with ecological studies and population monitoring.
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The possibility and probability of over-water dispersal as a mechanism to explain the distribution of terrestrial animal species in the Caribbean has been hotly debated since the early part of this century1,2. Each theory that has been proposed — including land bridges and over-water dispersal — has involved over-water dispersal to some extent in the distribution of animals. Yet many people remain sceptical of over-water dispersal, believing that the use of rafts is improbable, unobservable and consequently untenable. Here we present evidence to support over-water dispersal as the mechanism by which green iguanas colonized Anguilla.
1. 1. In the iguana, standard metabolism increased with temperature with a Q10 of 2·24. Metabolic scope was greatest at 32°C, decreasing above and below this temperature. Resting and post-activity heart rates varied with temperatures with Q10's of 2·0.2 and 1·84, respectively. 2. 2. Energy produced anaerobically by the production of lactic acid was shown to provide at least three-fourths of the total energy used during activity. 3. 3. Glycogen reserves in the muscle were adequate to account for the production of lactate during activity. 4. 4. The rapidity with which an iguana could remove an accumulated oxygen debt was temperature-dependent, and appeared to be greatest at the temperature where the metabolic scope was greatest.
For many applications the continuous prediction afforded by species distribution modeling must be converted to a map of presence or absence, so a threshold probability indicative of species presence must be fixed. Because of the bias in probability outputs due to frequency of presences (prevalence), a fixed threshold value, such as 0.5, does not usually correspond to the threshold above which the species is more likely to be present. In this paper four threshold criteria are compared for a wide range of sample sizes and prevalences, modeling a virtual species in order to avoid the omnipresent error sources that the use of real species data implies. In general, sensitivity–specificity difference minimizer and sensitivity–specificity sum maximizer criteria produced the most accurate predictions. The widely-used 0.5 fixed threshold and Kappa-maximizer criteria are the worst ones in almost all situations. Nevertheless, whatever the criteria used, the threshold value chosen and the research goals that determined its choice must be stated.
Maps of species' distributions or habitat suitability are required for many aspects of environmental research, resource management and conservation planning. These include biodiversity assessment, reserve design, habitat management and restoration, species and habitat conservation plans and predicting the effects of environmental change on species and ecosystems. The proliferation of methods and uncertainty regarding their effectiveness can be daunting to researchers, resource managers and conservation planners alike. Franklin summarises the methods used in species distribution modeling (also called niche modeling) and presents a framework for spatial prediction of species distributions based on the attributes (space, time, scale) of the data and questions being asked. The framework links theoretical ecological models of species distributions to spatial data on species and environment, and statistical models used for spatial prediction. Providing practical guidelines to students, researchers and practitioners in a broad range of environmental sciences including ecology, geography, conservation biology, and natural resources management.