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The brown anole is a small Caribbean lizard that colonized south Florida and Mexico about 50-60 years ago, and more recently, Hawaii. At least eight other Caribbean lizards have become established in south Florida, but only the brown anole is expanding its range into other southeastern states. This species is arguably the most abundant terrestrial vertebrate in peninsular Florida, and often reaches densities of more than one individual per square meter in disturbed habitats! The brown anole is thought to be responsible for a dramatic decline of previously stable urban and rural populations of the green anole, the only anole native to the United States. Green anoles often undergo a habitat shift and disappear within a few years after brown anole arrival. The two species are similar in size and overlap considerably in their diets, suggesting dietary resource competition. Predation on green anole hatchlings has also been demonstrated, suggesting that an ecological double-whammy termed "intra-guild predation" (competitors that also eat each other) might better describe the interaction. Despite declines, green anole populations often remain viable in the face of dense brown anole populations when understory vegetation is present, suggesting that suitable cover for hatchlings is important for long-term green anole survival. This illustrates how a powerful synergism between habitat alteration and biological invasions can affect native species.
English common names for this species include Cuban brown anole, Bahamian brown anole, or simply brown anole. Guyer and Savage (1996) proposed the generic name Norops for all of the "beta anoles" (Etheridge 1960, Williams 1969), a sub-generic group of which Anolis sagrei is a member, hence, they invoke the scientific name Norops sagrei for this species. However, their proposal has apparently not been widely accepted, as very few authors of scientific publications have used Norops as the generic name for this, or any other beta anole. Wilson and Porras (1983) propose that because this species was named after Ramon de la Sagra that the species name should be sagrai, however, following the rules of scientific nomenclature, the original species description uses sagrei, so although it is misspelled with reference to its namesake, the name sagrei stands.
Similar Species: Similar species of anoles are numerous throughout the New World, making this a difficult species for laypersons to identify as nonindigenous. The look-alike most deserving of attention is the native green anole, Anolis carolinensis Voigt 1832, found throughout the southeastern United States and the sole Anolis lizard native to North America north of Mexico (Conant and Collins 1991). It is but one of 12 "alpha anoles" (Etheridge 1960) in the "carolinensis complex" (Williams 1969), a group of medium sized, slender, greenish trunk-crown anoles with long, wedge-shaped heads (see photo). This native lizard is capable of changing color to dark brown or even nearly black (often in early morning or near dusk), so it is often confused for A. sagrei by laypersons in Florida. However, A. sagrei, with its short, wide head and robust body, looks a bit more "dinosaurian" than its green counterpart.
Eight other species of Caribbean Anolis lizards have become established around the Miami area (Butterfield et al. 1997, Meshaka et al. 1997), including the Puerto Rican crested anole, A. cristatellus, which looks very similar to A. sagrei. That so many similar Caribbean island species have invaded the mainland seems contrary to the notion that mainland areas are resistant to invasion by island species, but is probably explained by increased invasibility of severely altered habitats in especially south Florida. However, only A. sagrei appears to be expanding its range (Godley et al. 1981, Campbell 1996, Campbell and Echternacht in prep.). Other exotic lizards such as the curly-tail lizard, Leiocephalus carinatus, are present in Florida, and may be negatively affecting native lizards and other species through synergistic interactions (J. Losos pers. comm.). Introductions of any species of anole in Old World regions should be obvious, if only for the presence of the dewlap, although some agamid lizards (Agamidae) are iguanid look-alikes and might be mistaken for more robust anoles. Visit Todd Jackman's Anole Page for photos of many species.
Other photographs are posted on my Dissertation Page. Also see Todd Jackman's Anole Page. Quality photographs of both male and female brown anoles, the green anole, and many other species of exotic lizards in Florida are found in a pictorial guide by Carmichael and Williams (1991). Although their statements regarding the interaction between A. sagrei and A. carolinensis are unsupported, the images will certainly help with identification of this, and other exotic lizards in Florida. The popular Petersen's Guide (Conant and Collins 1998) is an industry standard for the identification of North American herpetofauna, and includes exotic species. The Audubon Field Guide also has photographs. If you find a lizard egg you suspect to be A. sagrei, compare it with the photo below showing the shell of both species. Notice the difference in surface patterns, discovered by Vincent (1999).
 Brown anole (left) and green anole (right) egg shells.
Contacts: If you need more information about this species, please contact: Dr. Arthur C. Echternacht Dr. Todd S. Campbell
If you see or hear this species outside its native range, contact Todd Campbell at lizardman@utk.edu.
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February 2001 Text and photos by Todd Campbell Contents: Taxonomy - Description - Native Range & Biology - Introduced Range & Biology - Known & Potential Impacts - Similar Species - Identification Aids - Literature Cited - Contacts Description: The New World family Polychrotidae includes a number of small, tropical, diurnal, arboreal, territorial, insectivorous lizards in the genus Anolis. Anoles are native to all the islands of the Caribbean (Schwartz and Henderson 1991) and are widespread in mainland South and Central America (Etheridge and DeQuiroz 1988), but only the green anole (Anolis carolinensis) is native to North America. In fact, over 300 species of Anolis lizards are currently recognized (Frank and Ramus 1995), making this one of the most extensive vertebrate radiations on earth. This statement holds regardless of whether one presents the genus Anolis as monophyletic (Etheridge 1960) or as a polyphyletic assemblage of four genera (Guyer and Savage 1986). Before discussing our invader of the month, some background on this interesting group of lizards is warranted. Anoles occur in many types of three dimensional habitats. Early on, it was recognized that Caribbean anoles in complex habitats segregated themselves vertically (Oliver 1948) and by temperature (Ruibal 1961). The relationship between ecology and morphology was first mentioned by Collette (1961), refined by Rand (1964), and later attributed to the outcome of competitive interactions which led to the evolution of distinct ecologically influenced morphologies, or "ecomorphs" (Williams 1969, 1972, 1983). This term describes their preferred perching positions in three-dimensional space in vegetation (e.g. "trunk-crown" or trunk-ground") and applies certain attributes to their size, shape, and limb morphology. That recurring combinations of ecomorphs occur in unrelated species on each large island of the Greater Antilles is a classic example of convergent evolution (Losos 1992, Losos et al. 1998, Beuttell and Losos 1999). The most identifiable feature of the anoles is their dewlap (see photo above), a colorful flap of skin below the neck that is stretched like a drum over a highly modified hyoid apparatus and used for territorial and mating displays. Females generally have a functional dewlap, however, it is usually much smaller than that of males. Skin color is mediated by melanophores and can change very rapidly, often spanning their entire range of possible colors in only a few minutes, depending on the temperature, time of day, level of territorial aggression, or reproductive activity. Less obvious to the casual observer is their expanded toe-pads which, like those of gecko lizards, help anoles cling to even the smoothest of surfaces, and the extent of which varies with their degree of arboreality. Anolis mating systems are various iterations of male resource-defense polygyny without parental care (e.g. Jenssen et al. 2000). Females generally deposit a single egg in leaf litter about every week or two during their reproductive season, which is year-round in many tropical locations, or if seasonal, is often triggered by temperature or precipitation (Fitch 1982). The two sexes are often highly dimorphic in their morphology and behavior, whether due to resource partitioning, the nature of their mating system, or both (Stamps et al. 1997). Adults of both sexes vigorously defend three-dimensional territories against conspecific intruders (Evans 1938), and two or more female territories are generally nested in the territory of one male (Stamps 1983). More background information on this interesting group of lizards can be obtained from Schwartz and Henderson (1991), Roughgarden (1995), Crother (1999), and the recent experimental studies by Leal et al. (1998), Losos and Spiller (1999), Spiller and Schoener (1998), and the thousands of references therein. The brown anole (Anolis sagrei) is a medium-sized, fairly robust, "trunk-ground" anole, and like many others of this ecomorph, are runners and jumpers with relatively long toes and reduced toe-pad surface areas. The two sexes are highly dimorphic in morphology and behavior, as are many species of Anolis (Stamps et al. 1997). Upon maturity, males are about 64 mm in snout-to-vent length (SVL) and weigh 6-8 grams, whereas females reach only about 48 mm SVL and weigh 3-4 grams. Male color is highly variable, ranging from light gray to nearly jet-black, and plain colored to covered dorsally with irregular dark patches or chevrons and a network of light lines. Females exhibit a large range of color, but nearly always have some type of obvious wavy dorsal pattern along the midline of their back. Native Range & Biology: The brown anole is native to Cuba, the Bahamas, and their satellite islands, and six subspecies occur throughout the Caribbean (Schwartz and Henderson 1991). Incredibly detailed natural history studies (e.g., Schoener 1968, 1975) and elegant manipulative experiments (e.g., Schoener 1983, Losos and Spiller 1999) have been done using the Bahamian subspecies, and shed light on aspects of their biology that are germane to their status as an invader. This habitat generalist generally prefers fairly open vegetation of disturbed sites, where it adopts a head-down, sit-and-wait posture, and perches low on large trunks or fence-posts (Schoener 1968, 1975, Lister 1976a, 1976b, Moremond 1979a, 1979b): a classic trunk-ground anole (Williams 1969, 1972, 1983). Evans (1938) studied the territorial behavior of brown anoles in an arboretum at Soledad, Cuba, and reported the territory size of this species to be 37.2 m2, the ground surface occupied by a large bush or hedge. Early Caribbean naturalists often remarked that the brown anole was either very abundant, or was the most abundant lizard that they had ever seen (Barbour 1904 for the Bahamas and Oliver 1948 for Bimini). Their native diet consists mainly of small arthropods, annelids, and molluscs (Schoener 1968, Schoener and Gorman 1968). A series of interesting removal and introduction experiments by Spiller and colleagues demonstrated their importance in trophic webs on Bahamian islands. In short, their removal from islands caused an increase of spiders and decrease in leaf mining insects (Spiller _____ _____ _____). Experimental introductions in the Bahamas (Schoener 1983) .....
Introduced Range & Biology: Caribbean lizards of the genus Anolis have long been considered good colonizers (Williams 1969, but see Spiller et al. 1998), and have been studied with regards to dispersal (Schoener and Schoener 1983, 1984), their ability to colonize new islands (Losos and Spiller 1999), and evolutionary diversification after colonization (Roughgarden 1995, Losos et al. 1997). Lizards in general, and anoles in particular, are good colonizers (Williams 1969), and exotic anoles often ride the coat-tails of development, as did Anolis sagrei in Grand Cayman (A. C. Echternacht pers. comm.), Anolis cristatellus in the Dominican Republic (Fitch et al. 1989) and Florida (Salzburg 1984), Anolis porcatus in the Dominican Republic (Powell et al. 1990), three anole species on Bermuda (Losos 1996), and many other cases (reviewed in Losos et al. 1993). Exotic anoles are valuable subjects for studying interspecific competition, community dynamics, and evolutionary processes (Losos 1994b), especially when more than one exotic anole species is present on a given site, as occurs in Florida (Butterfield et al. 1997). Although A. sagrei has been introduced to Mexico, Jamaica, and Hawaii, the Florida invasion has received the most attention. The brown anole arrived in the Florida Keys in the late 1800s and was inoculated to at least six separate ports in Florida in the 1940s (Lee 1985). It has spread throughout Florida and into Georgia and two other southeastern states since that time (Campbell 1996; Campbell et al. in prep., an exhaustive review of published records and unpublished museum data documenting its spread). Both the Cuban (A. s. sagrei) and the Bahamian (A. s. ordinatus) subspecies were introduced to Florida, but the genetic integrity of these lines have disappeared (Lee 1985, 1987). Other than three very detailed morphometric analyses (Lee 1985, 1987, 1992) a study of its reproductive cycle (Lee et al. 1989), and numerous studies of mating behavior by Tokarz (1998, and references therein), the basic natural history of the brown anole in North America has gone largely undocumented (W. Meshaka, pers. comm.). But much can be gleaned from recent experimental manipulations of this species in Florida (Campbell 2000) and a quick review of the basic natural history of the only truly temperate anole, Anolis carolinensis, in the southeastern United States (Gordon 1956). Small populations (12 females, 6 males) introduced onto dredge-spoil islands in east-central Florida reached densities between 8,000 and 15,000 lizards per hectare within four years (Campbell 2000). Body sizes ...... more .... Brown anoles consumed a wide variety of arthropods in Florida, including insects, amphipods, and isopods (Campbell 2000). They also prey on other small vertebrates and hatchlings of green anoles (Campbell 2000, Campbell and Gerber 1996, Gerber and Echternacht 2000). Likewise, many vertebrates consume brown anole adults (Campbell 2000) and green anoles consume brown anole hatchlings (Campbell 2000, Gerber and Echternacht 2000). Cannibalism on hatchlings has been demonstrated in Anolis lizards in general (reviewed in Gerber 1999), and brown anoles in particular (Cochran 1989, Nicholson et al. 2000). Adults of both species breed during the summer months, becoming sexually active and establishing territories in March or April, and defending territories through August or September (Gordon 1956, Jenssen et al. 1995, Lee et al. 1989). Females are reproductively active for a slightly longer period than males, possibly because they store sperm (Tokarz 1998, T. Jenssen, pers. comm.). Females of both species lay eggs singly on an approximately weekly basis for the entire summer by alternating the use of their left and right ovaries (Gordon 1956), but brown anoles exhibited shorter oviposition intervals during a cage-study employing Florida animals in Tennessee (Vincent 1999). Egg incubation is approximately 29 days for green anoles (A. C. Echternacht, pers. comm.), but varies depending on substrate temperature and moisture, and presumably, habitat type. In Florida, green anole hatchlings start life at 19 to 22 mm SVL (King 1966), and newly emerged brown anole hatchlings range from about 15 to 18 mm SVL (Duellman and Schwartz 1958). Hatchlings of both species are first seen in early June in central Florida (about 290 north latitude). Although brown anole hatchlings are usually seen first, this is probably because they are more numerous and conspicuous than are green anole hatchlings. Hatchlings of both species grow very fast, reaching adult size prior to their second summer of life (their first reproductive summer), and mortality appears to be highest in the winter thereafter (Lee et al. 1989, Gordon 1956). Each cohort undergoes a nearly complete replacement in the following year, so both species probably have a maximum average life span of less than 18 months in Florida (Oliver 1955, Gordon 1956, King 1966, Lee et al. 1989).
Known & Potential Impacts: "They are of a most glorious green, and very tame. This species has not yet been deemed an economic pest, and is not likely to be, and it probably does not consume enough mosquitos, cockroaches, or other pestiferous arthropods to measurably benefit humans, contrary to the beliefs of many Floridians. But many Floridians have clearly noticed a dramatic decline of the native green anole in southern Florida, at least in urbanized areas. Despite the decline, surprisingly little research has been conducted that fully addresses the impacts of the brown anole on green anoles or other native fauna. The earliest written statements suggesting that the brown anole might negatively affect the native green anole, Anolis carolinensis, were made by Collette (1961), followed by King and Krakauer (1966), and reinforced by Lee (1985), but all these statements were based on anecdotes. Tokarz and Beck (1987) made the first attempts to study the interaction directly, followed by Brown and Echternacht (1991), approaching the problem from the standpoint of interference competition (aggression), but found that intraspecific (within species) overshadowed interspecific (between species) interactions. Campbell (2000) witnessed only three interspecific interactions during thousands of hours of field surveys in sympatric populations, but witnessed hundreds of intraspecific territorial squabbles. In other words, these territorial species fight much more amongst themselves than with other species. But given this, what is the cause of the perch height shift observed in green anoles in the presence of brown anoles? Without brown anoles, green anoles occupy perches from ground to crown, but add brown anoles, and green anoles move higher in trees, occupying the trunk and crown of trees. Campbell (2000) found that green anoles shift only about 30 cm upward on average, but an important component of that biologically minimal shift is the avoidance of ground perches. The mechanism of the perch shift remains a mystery, but a recent study by Stamps (___) provides a solution based on persistence. more ... Does this upward shift alter the number and type of prey items available to green anoles in the presence of brown anoles? In a comparative study of the diets of these two species on three dredge-spoil islands in Florida (Campbell 2000), dietary overlap was high, whether measured by the number of prey or the volume of the prey items taken, indicating brown anoles may be consuming prey items once available to green anoles. But for competition to be invoked, overlapping resources must also be limited in supply, and removal or addition of the resource must be clearly shown to alter one or more demographic parameter in the species in question. Although the role of competition in the extirpation of native species can sometimes be important (e.g. Riccardi et al. 1998), it is most often minimal (Simberloff and Boecklen 1991), and the jury is still out on the occurrence and importance of resource competition in this interaction. Porter (in prep.) performed food augmentation and depletion experiments on dredge spoil islands in Florida, and results are forthcoming. Gerber and Echternacht (2000) were the first to study hatchling competition and predation of hatchlings by adults in field enclosures, and the first to suggest that these two competitors also consumed each other's hatchlings (termed intra-guild predation, or IGP). In a brief note, Campbell and Gerber (1996) confirmed predation of hatchling green anoles by adult brown anoles in the field, and hatchling brown anoles were found in the stomachs of adult green anoles collected for the diet overlap study mentioned above (Campbell 2000), indicating this phenomenon occurs under natural conditions in the field. However, the role of IGP in the green anole decline is yet unknown. Campbell (2000) introduced brown anoles onto small dredge-spoil islands containing native green anole populations, and followed their progeny for four years. Browns expanded, greens crashed ..... more ... Green anoles shifted upward ...... more .... Habitat structure has been shown to affect this interaction in field enclosures (Gerber unpublished manuscript) and on dredge-spoil islands in east-central Florida (Campbell 2000). more .... This phenomenon has precedence. In an interesting manipulative experiment using aircraft hangars on Oahu, Hawaii, Petren and Case (1998) showed that the addition of habitat structure (aluminum baffles) reduced the intensity of interspecific resource competition between native and exotic geckos. parasites..... (Campbell 2000, Goldberg and Bursey 2000) Brown anole densities - biomass - augments predator populations such as black rat snakes? Vincent (1999) studied the interaction in native hammock habitat in Florida and compared their reproductive output in outdoor enclosures in Tennessee, and Porter (1999) performed a field study on spoil islands that addressed the effects of food depletion and augmentation on the interaction, but both of these studies lie on the brink of completion. Far-reaching effects of this species on whole systems have not been demonstrated, but given the extraordinary densities attained by this species, food web effects are highly likely. Cite Spiller ... more ... Management: No control or eradication measures have been implemented for this species, and none have been proposed by any federal agency or the State of Florida that I am aware. This species would be very difficult if not impossible to completely eradicate due to its high density, high reproductive potential, and habitat generality. On a priority list of species to eradicate or control, the brown anole should lie far below the many biologically, economically, and culturally important pests and weeds. Literature Cited: Brown, P. R. and A. C. Echternacht. 1991. Interspecific behavioral interaction of adult male Anolis carolinensis (Sauria: Iguanidae): A preliminary field study. Anolis Newsletter IV:21-30. Campbell, T. S. 1999. Consequences of the Cuban brown anole invasion: it's not easy being green. Anolis Newsletter V:12-21. Campbell, T. S. 2000. Analyses of the effects of an exotic lizard (Anolis sagrei) on a native lizard (Anolis carolinensis) in Florida, using islands as experimental units. Unpublished Ph.D. Dissertation, University of Tennessee, Knoxville, TN. Campbell, T. S. 1996. Northern range expansion of the brown anole Anolis sagrei in Florida and Georgia. Herp. Review 27:155-157. Campbell, T. S and G. Gerber. 1996. Natural History: Anolis sagrei: Saurophagy. Herp. Rev. 27:106. Cochran, P. A. 1989. Anolis sagrei behavior. Herp. Rev. 20:70. Collette, B. B. 1961. Correlations between ecology and morphology in anoline lizards from Havana, Cuba and southern Florida. Bull. Mus. Comp. Zool. 125:137-162. Conant, R. and J. Collins 1998. Reptiles and Amphibians of Eastern North America. Houghton-Mifflin, ____________ Echternacht, A. C. 1999. Possible causes for the rapid decline in population density of green anoles following invasion by the brown anole in the Southeastern United States. Anolis Newsletter V:22-27. Gerber, G. P. 1991. Anolis sagrei and Anolis carolinensis in Florida: Evidence for interspecific predation. Anolis Newsletter IV:49-53. Gerber, G. P. 1999. A review of intraguild predation and cannibalism in Anolis. Anolis Newsletter V:28-39. Guyer, C. 1988. Food supplementation in a tropical mainland anole, Norops humilis: demographic effects. Ecology 69:350-361. Goldberg, S. R. and C. R. Bursey. 2000. Transport of helminths to Hawaii via the brown anole, Anolis sagrei (Polychrotidae). J. Parasitol. 86(4):750-755. King, W. and T. Krakauer. 1966. The exotic herpetofauna of southeast Florida. Quart. J. Florida Acad. Sci. 29:144-154. Leal, M., J. A. Rodriguez-Robles, and J. B. Losos. 1998. An experimental study of interspecific interactions between two Puerto Rican Anolis lizards. Oecologia 117:273-278. Lee, J. C. 1985. Anolis sagrei in Florida: Phenetics of a colonizing species I. Meristic characters. Copeia 1985:182-194. Losos, J. B. and D. Spiller. 1999. Differential colonization success and asymmetrical interactions between two lizard species. Ecology 80:252-258. Nicholson, K. E., A. V. Patterson, and P. M. Richards. 2000. Anolis sagrei: cannibalism. Herpetol. Review 31(3):173-174. Roughgarden, J. 1995. Anolis Lizards of the Caribbean: Ecology, Evolution, and Plate Tectonics. Oxford University Press, Oxford. Schoener, T. W. 1968. The Anolis lizards of Bimini: Resource partitioning in a complex fauna. Ecology 48:704-726. Schoener, T. W. 1975. Presence and absence of habitat shift in some widespread lizard species. Ecol. Monogr. 45:233-258. Schwartz, A. and R. W. Henderson. 1991. Amphibians and reptiles of the West Indies: descriptions, distributions, and natural history. University of Florida Press, Gainesville. Spiller, D. A. and T. W. Schoener. 1998. Lizards reduce spider species richness by excluding rare species. Ecology 79:503-516. Tokarz, R. R. and J. W. Beck, Jr. 1987. Behaviour of the suspected lizard competitors Anolis sagrei and Anolis carolinensis: An experimental test for behavioural interference. Anim. Behav. 35:722-734. Vincent, T. 1999. The competitive impact of Anolis sagrei on the reproductive output of Anolis carolinensis: an enclosure study. Anolis Newsletter V:114-122. Williams, E. E. 1969. The ecology of colonization as seen in the zoogeography of anoline lizards on small islands. Quart. Rev. Biol. 44:345-389. Williams, E. E. 1983. Ecomorphs, island size, and diverse end-points in island radiations of Anolis. Pp 326-370 In Huey, Pianka, and Schoener, eds., Lizard Ecology: Studies of a Model Organism. Harvard University Press, Cambridge.
The brown anole page was last updated on 04/17/2002 |
