Species Description: The brown anole Anolis sagrei is small, semi-arboreal ("trunk-ground") lizard with relatively long toes and reduced toe pad surfaces (relative to congeners), well suited for running and jumping (Williams 1983).
Color is variable, ranging from light gray to brown to almost black, commonly with irregular patches or mottled patterns, spots, chevrons and a series of light-colored lines. The tail is somewhat laterally compressed. A prominent identifying feature of this species is the extensible dewlap or throat fan which can be yellow to red-orange in color and is used in territorial and mating displays.
Sexual dimorphism is pronounced with males reaching a larger terminal size and weight (see below). The dewlap of males is also usually larger than that of the females. Female brown anoles often exhibit a dorsal line that can appear as a light-colored wave, zig-zag or diamond pattern that males typically lack. Mature males also exhibit a pronounced crest-like ridge running down the back (Williams 1983).
Potentially Misidentified Species: Anolis carolinensis, the southeastern US native green anole, is slightly smaller and more delicate in build, with a longer and more slender head and snout. Anolis carolinensis is capable of impressive color change from bright green to brown to nearly black, but is still recognizable as distinct from Anolis sagrei.
A number of other Anolis lizard species not native to the United States (e.g., the knight anole A. equestris, bark anole A. distichus, and others) now occur in Florida, most notably around Miami (Rocus and Mazzotti 1996). These lizards can be difficult for untrained individuals to recognize as distinct from Anolis sagrei, particularly A. distichus which looks quite similar but does not grow as large and is more strictly arboreal in habit.
Regional Occurrence: Genus Anolis belongs to the New World lizard family Polychrotidae and encompasses more than 300 species of diurnal, arboreal to semi-arboreal primarily insectivorous lizards (Frank and Ramus 1995). The genus is native to the islands of the Caribbean and mainland South and Central America, with only the green anole (Anolis carolinensis) occurring as a temperate North American native (Schwartz and Henderson 1991).
Anolis sagrei is native to Cuba, the Bahamas, and nearby islands. Six distinct subspecies have been identified, including the principal subspecies of Cuba (Anolis sagrei sagrei) and the Bahamas (A. sagrei ordinatus) (Schwartz and Henderson 1991). The range of the brown anole in the eastern United States includes all of peninsular Florida (SREL).
The brown anole has been described as a habitat generalist that generally prefers open vegetation within disturbed sites and urbanized areas. It spends most of its time on the ground or on trees at trunk level up to several feet off the ground (Williams 1969).
IRL Distribution: A. sagrei can be found throughout the Indian River lagoon watershed, including populations that inhabit most of the IRL spoil islands.
Age, Size, Lifespan: Adult male Anolis sagrei reach a snout-to-vent length of more than 6 cm and a weight of 6-8 g. Females rarely exceed 5 cm and 3-4 g.
Maturation occurs rapidly with individuals becoming reproductively active by their second summer and pronounced adult mortality the following winter. Published reports suggest the species in Florida has a maximum life span of less than 18 months although some reports suggest individuals may live twice as long. (King 1966, Lee et al. 1989).
Abundance: In areas where this exotic species has become established, it is very often the most abundant reptile species present. Anolis sagrei is among the most abundant lizards throughout Florida (SREL).
Reproduction: Breeding in Florida populations of adult brown anoles occurs in spring and summer with individuals establishing breeding territories in March or April and defending them for the next five to six months (Lee et al. 1989). Territorial fighting in males is fierce, with combatants repeatedly fighting by locking jaws and knocking one another from their perch (Estrada and Rodriguez 1986). During the breeding season, males display their extended dewlaps as a component of agonistic same-sex interactions and also in courtship behavior directed toward females (West-Eberhard 1983).
Gordon (1956) reported that females lay single eggs approximately every week throughout the breeding season, but other references indicate that two eggs per clutch is typical. Oviposition alternates between the left and right ovaries with each clutch (Gordon 1956).
Embryology: The eggs are typically laid under decaying vegetation on the ground and hatch within 60-90 days, as opposed to an approximate 1-month incubation period for green anole eggs. Hatchlings emerge at about 15-18 mm snout-to-vent length beginning in June (Duellman and Schwartz 1958).
Temperature: Like all reptiles, the brown anole is a poikilotherm that relies on external warmth to raise its body temperature and employs behavioral thermoregulatory techniques (i.e., basking) to maintain its body temperature within acceptable limits.
The northern limits of the brown anole in the United States, into central Georgia, appear to be temperature related; cold winters are capable of reducing population densities in the northern portions of their range (Campbell 1996, Parmley 2002).
Trophic Mode: Natural dietary items of these generalist predators include arthropods, worms and molluscs. Cannabalism of adult Anolis lizards on their hatchlings is also well documented, and this behavior may be prevalent in A. sagrei (Cochran 1989, Nicholson et al. 2000).
Invasion History: The brown anole was first documented in the Florida Keys in the 1880s. By the 1940s the species had also become established on the Florida mainland. Lee (1985) concludes that introduction to peninsular Florida in the 1940s occurred on at least six different occasions.
By 1980, established brown anole populations existed in all or most of Florida's large urban centers south of Gainsville (Lee 1985).
The Florida range of this species continues to expand into the northernmost and panhandle counties and populations have also become established in Georgia, Louisiana, and near Houston, TX. Accidental transport via motor vehicles and as accidental introductions (particularly as eggs) with transported live plants has been suggested as the likely source of these introductions (Campbell 1996).
Although both the Cuban and Bahamian subspecies have been introduced to Florida, the genetic identies of these distinct lines has been lost through outcrossing (Lee 1985).
Campbell notes that the species has also been introduced into Hawaii and Jamaica, and Green et al. (2002) and Kolbe et al. (2004) report their presence in Granada. The ISGG database additionally includes Belize, Mexico, and Taiwan as part of the brown anole's alien range and lists Guam as a country into which the species was introduced but whose subsequent establishment was intercepted.
Potential to Compete With Natives: The first anecdotal suggestions implicating the exotic brown anole in the decline of native green anole populations in Florida were published in the 1960s (Collette 1961, King and Krakauer 1966). Direct studies of interspecific associations between the two congeners appear much less significant than intraspecific (within-species) competitive interactions within these aggressive, territorial animals (Brown and Echternacht 1991).
Field observations and experimental manipulations have demonstrated that brown anoles in Florida prey directly on other small vertebrates, including hatchlings of the native green anole. (Campbell 2000, Campbell and Gerber 1996). Campbell (2000) reported that adult green anoles also consume brown anole hatchlings. The lack of documented among-species interactions notwithstanding, Campbell (2000) reports that where Anolis sagrei and Anolis carolinensis populations co-occur, Anolis carolinensis individuals shift their spatial niche upward to occupy arboreal perches from trunk to tree canopy, abandoning the ground perches they otherwise also utilize when populations occur in the absence of Anolis sagrei. The author speculates that this spatial shift may lead to a change in the number and types of prey available to native Anolis carolinensis populations.
Wardle (2002) reports that Anolis sagrei feeding activity is capable of reducing the numbers and diversity of spiders on which they prey, although Campbell (2006) has suggested that the overall impact of the species on prey populations is probably too small to be considered economically important.
Possible Economic Consequences of Invasion: No steps have been taken to eradicate or control brown anoles in Florida, and the abundance, fecundity, and generalist habits exhibited by the species make it highly unlikely that eradication could ever be achieved (Campbell 1999).
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