The green iguana, Iguana iguana is a popular pet trade species not
native to Florida, but increasingly encountered as an escaped exotic in the
southern half of the state.
I. iguana is variable in color, young animals being bright green and
then becoming more uniform grayish green in color with age. Green iguanas also
have a limited ability to alter color based on mood or social interaction or in
response to environmental conditions, with males exhibiting more color
variation than females (Frye 1995).
A prominent hanging dewlap under the throat, a dorsal crest of robust dermal
spines running from neck to tail, a set of large scales on each side of the
head, a membrane-covered tympanum, and a long, tapering, variably ringed tail
are distinguishing features of the species (Oldham and Smith 1975, De Vosjoli
1992; Frye 1995, Gingell and Harding 2005). The eyes are laterally positioned
and are protected by an immovable upperlid and a movable lower eyelid. A
light-sensing organthe parietal "eye"is present on top of the head and is
important in cueing diel coordination and gonadal maturation. The parietal eye
exhibits rudimentary visual sensory abilities, namely the ability to perceive
shadows from above the animal (Frye 1995).
Potentially Misidentified Species
Although a growing assortment of exotic iguanids, polychrotids (anoles), geckonids (geckos), and other non-native
lizards are now encountered in Florida, relatively few of these could be easily
misidentified as I. iguana. Black spinytail iguanas (Ctenosaura
similis) and Mexican spinytail iguanas (C. pectinata) are
potential exceptions, but looking for the diagnostic features described above
should allow Iguana iguana to be differentiated from these animals.
HABITAT AND DISTRIBUTION
The green iguana is native to Latin America, including parts of Mexico,
mainland and island regions of Central- and South America, and the Lesser
Antilles. It has been introduced into Florida, Hawaii and Puerto Rico where it
is considered a serious pest (McKeown 1996, Engeman Smith and Constantin 2005,
Iguana iguana has been reported from south Florida (Dade County) since 1966,
and has probably been established and breeding there since 1980 (King and
Krakauer 1966, Butterfield et al. 1997). More recently (2003), a presumed new
breeding population has been identified from Palm Beach County, while an
increasing number of animals (not reported breeding) are being encountered in
Martin and St. Lucie counties (Krysko et al. 2005).
The apparent northward expansion of I. iguana into the central IRL
watershed is of potential concern. Animal Control offices in both Martin and
St. Lucie Counties have reported an increase in the number of green iguana
sightings throughout the Treasure Coast area (Indian River Press Journal
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Hatchlings are typically 17-25 cm in length. Growth is relatively rapid, and a
12 g hatchling can grow to a 1 kg adult in 3 years. Mature animals can
attain total lengths of 2 m and can weigh as much as 8 kg, although 4-6 kg is
more typical (De Vosjoli 1992, Gingell and Harding 2005).
Captive-reared green iguanas can live for more than 20 years, while wild
individuals are believed to have a lifespan of around 8 years (De Vosjoli 1992,
Data collated by the Florida Fish and Wildlife Conservation
Commission suggests breeding populations of I. iguana are established in
at least 5 Florida counties. The statewide trend appears to be expansion of
the overall population and invasive range.
Reproduction is sexual, sexes are separate and fertilization is internal.
Individuals generally become reproductive at 3-4 years of age, although some
animals mature up to a year earlier or later. Females remain reproductive for
several years (Frye 1995). Peak breeding occurs in the dry season, ensuring
that most young hatch in the wet season when food resources are most abundant.
A polygynandrous mating system (both males and females pair with multiple
mates) seems to be typical of the species, and a variety of male-male
antagonistic displays (e.g., head bobbing, dewlap exhibiting) and male-female
courtship displays (e.g., nuzzling, biting) are usually involved. Dominant
males mark territories and mates with a pheromone-containing substance secreted
from femoral pores (De Vosjoli 1992, Frye 1995, Meshaka et al. 2004).
Females can store sperm for several years after mating, using it to fertilize
eggs at a later date (De Vosjoli 1992, Frye 1995).
Clutch sizes are relatively large, averaging 20-70 eggs. Females deposit eggs
approximately 65 days after mating, usually over the course of three days, into
nests excavated to a depth of 0.45-1 m. If suitable nesting sites are limited,
several females can share nests (De Vosjoli 1992, Frye 1995).
Incubation takes 90 to 120 days at a nest tenperature of 30-32°C. Hatchlings
break through egg shells with the aid of a caruncle (egg tooth) that is shed
shortly after hatching. Young are precocial and independent from the time of
hatching, but they derive most of their nourishment in the first few weeks of
life from yolk that has already been absorbed (Gingell and Harding 2005).
Green iguanas are exothermic and rely on environmental temperatures and
behavioral thermoregulation (e.g., basking) to maintain optimal temperature.
Active foraging typically occurs at daytime temperatures of 25-35°C; low
temperature suppresses both apatite and digestion (Frye 1995).
Northern range expansion of Iguana iguana in Florida appears to be limited
by winer low temperatures, althouh population numbers in the wake of a south
Florida freeze in 2002-2003 were reduced only temporarily (Meshaka et al.
Iguana iguana is primarily herbivorous, consuming leafy plants and ripe
fruits as preferred dietary items. A small percentage of invertebrate matter
and carrion is also typically consumed (Gingell and Harding 2005).
Green iguanas are known carriers of several Salmonella spp. bacterial
strains considered to be pathogenic. Salmonella colonize the intestines
and is shed in feces. Tortora at al. (1998) note that the carriage rate in pet
reptiles may be as high as 90%.
The pet trade has provided a steady source of introduction of Iguana iguana
to Florida. Iguanas escaped from captivity were reported from south Florida as
early as 1966, at Key Biscayne, Hialeah, Coral Gables, and near the Miami
International Airport (King and Krakauer 1966). Populations have since become
established at least as far north as Palm Beach County on the Atlantic coast
and Lee County on the Gulf coast of the state, and an increasing number of
animals (not yet reported breeding) are now reported from Martin and St. Lucie
counties (Bartlett 1980, Bartlett and Bartlett 1999, Townsend et al. 2002,
Krysko et al. 2005). The animals are frequently encountered in Everglades
National Park, and have been reported in the Keys at least as far south as
Stock Island (Meshaka et al. 2000).
In addition to Florida, I. iguana has been introduced to Hawaii where it
is also a nuisance species (McKeown 1996).
Potential to Compete With Natives
I. iguana is the largest known lizard to occur in the U.S. (Conant and
Collins 1998, Campbell 1998). McKie et al. (2005) reported concern over the
potential for iguanas to disrupt native bird nests or destroy nestlings and
Possible Economic Consequences of Invasion
The potential economic consequences associated with expanding Florida green
iguana populations are believed to be minor, mostly related to the destruction
of tropical garden and landscape foliage caused by iguana foraging (Gingell and
Harding 2005). Health-related issues arising from iguanas being carriers of
Salmonella are anticipated to be very minimal.
In other parts of the world, green iguanas are an important source of food and
leather, but they are unlikely to be utilized in this manner in Florida.
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