The Brown Anole, Anolis sagrei, is a small, highly prevalent lizard species commonly encountered across the Southeastern United States and the Caribbean islands. This reptile has become a familiar sight on fences, sidewalks, and low vegetation throughout its introduced range. Its success stems from its adaptability to various environments, including highly urbanized areas. This lizard’s presence in North America has created a complex ecological dynamic, particularly concerning native lizard populations.
Identifying the Brown Anole
The Brown Anole typically reaches a total length of 5 to 9 inches, with males generally being larger than females. Its coloration is highly variable, ranging from light gray or tan to dark brown or nearly black, and it can slightly change its shade to match its surroundings. Females are often lighter and display a distinct pattern of dark diamonds, chevrons, or a scalloped stripe running down the center of their backs.
The male’s dewlap, an extensible flap of skin under the throat, is used for communication. When displayed, this dewlap is a vibrant orange or red, often bordered by yellow, and is flashed during territorial disputes or courtship rituals. The Brown Anole is distinguished from the native Green Anole (Anolis carolinensis) by its shorter, stockier head shape and its consistent earth-toned base color, as the Green Anole can shift its color to a bright green.
Invasion and Habitat
The Brown Anole is native to the islands of the northern Caribbean, specifically Cuba and the Bahamas, as well as parts of Central America. Its establishment in the United States began in the late 19th century, with the first documented introduction occurring in Key West, Florida, around 1887. The species spread rapidly due to accidental transportation via cargo shipments and the horticultural trade, with eggs often concealed in the soil of potted plants.
The species has dispersed throughout Florida and across the Gulf Coast states, reaching as far west as Texas and as far north as Georgia and parts of the Carolinas. The Brown Anole’s success is tied to its generalized habitat preference, thriving in areas frequently disturbed by human activity. It is commonly found in urban and suburban environments, utilizing low-lying structures like fences, walls, and the trunks of trees.
Behaviors and Diet
The Brown Anole is an active, diurnal predator and an opportunistic insectivore, feeding primarily on small arthropods. Its diet consists of insects like ants, beetles, and crickets, along with spiders and other small invertebrates. This generalist approach means the lizard will consume whatever prey is most readily available, contributing to its ecological success.
The Brown Anole is highly territorial, particularly the adult males. Males utilize a series of head-bobbing motions and push-ups, often culminating in the extension of their bright dewlap, to signal dominance and to warn rival males. This display behavior is also used to court females during the breeding season. The Brown Anole typically occupies lower perches, such as tree trunks close to the ground, where it can quickly scurry to capture prey or evade threats.
Competition with Native Green Anoles
The presence of the Brown Anole in the southeastern U.S. has led to significant competitive displacement of the native Green Anole (Anolis carolinensis). The two species share a similar diet and often occupy the same habitat, leading to intense competition for resources and space. The Brown Anole is known to be more aggressive in direct interactions, and adult Brown Anoles have been observed preying on the eggs and hatchlings of the native species.
This pressure has forced a rapid form of “niche partitioning,” where Green Anoles have shifted their preferred perching location upward into the higher, thinner branches of the tree canopy. This behavioral change has driven a measurable evolutionary response in the native species. Within a period of just 15 years, or about 20 generations, Green Anoles in areas co-inhabited by Brown Anoles developed significantly larger toe pads with more sticky scales. This physical adaptation allows the Green Anoles to better grip the smoother, narrower perches high in the trees, illustrating a swift evolutionary change.