Florida is the land of invasive species. Because of our status as a center for the importing of exotic pets and houseplants from overseas, and our neo-tropical climate, we have been invaded by everything from kudzu plants to Burmese pythons. The most common of our invaders is the Brown Anole Lizard. Every tourist has seen this ubiquitous little lizard running along sidewalks, tree trunks, or fences, conspicuously bobbing their heads and displaying their brightly-colored extendable throat fan at each other.
|The Daily Bucket is a regular feature of the Backyard Science group. It is a place to note of any observations you have made of the world around you. Insects, weather, meteorites, climate, birds and/or flowers. All are worthy additions to the bucket. Please let us know what is going on around you in a comment. Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
A Brown Anole lizard sunbathing on a sidewalk. This one is a female.
Male Brown Anole displaying his dewlap on a tree trunk.
There are about 400 different species of Anole lizards, all of them found in the tropical Americas. Taxonomically, they have been recently moved from the Iguanid family into a new family of their own, the Polychrotids. Anolis contains the largest number of species of any vertebrate genus. A proposal has been made (but not widely accepted) to separate about 150 of these and place them into their own genus, Norops. Among these proposed species is Anolis (Norops) sagrei, the Brown Anole.
The Brown Anole is just a little fellow, not more than seven or eight inches from nose to tail. Native to Cuba, and found as a subspecies in the Bahamas and several other Caribbean islands, it was first described scientifically in 1837. It is a brownish-tan color, lighter at the sides and darker on the back, though like most members of the Anolis group it can change its skin color, usually according to temperature--pale brown when warm, and darker brown to almost black when cool. Like all reptiles, the lizards are cold-blooded, and darker colors help them absorb more heat from the sun.
The females have a light-colored zigzag stripe along their back. The much larger males have faint vertical rows of light-colored spots on their sides, an erectable crest running down their neck and back, and also have a large dewlap under their chin, brightly colored yellow-orange or reddish. They are fiercely territorial, and males spend much of their time patrolling their turf, head-bobbing and displaying their dewlaps to each other as a warning.
As with many lizards, Brown Anoles have the ability to voluntarily cast off their own tails, known as "autotomy". If seized by a predator, the lizard can break off its own tail, which then twitches spasmodically and distracts the attacker while the lizard escapes. Although the tail eventually grows back, it's not unusual to see Brown Anoles with half their tail missing. They are insectivores, and eat any sort of small arthropod that they can catch. In captivity they can live as long as 6 or 7 years, but in the wild they seldom live more than 18 months.
Another member of the genus is Anolis carolinensis, the Green Anole. Generally a bit smaller in size than the Brown Anole, the Green Anole is found throughout the southeastern US, from Texas to North Carolina--the only Anolis native to the US. Because it can change its skin color from green to brown, it is also known as the American Chameleon (though it is not related to the true chameleons from Madagascar). From the 1950's on, it was very commonly sold in pet stores. And, as it turns out, many imported Brown Anoles were also sold as pets. And there begins our problem . . .
The first recorded sighting of a Brown Anole in Florida was way back in 1887, in the Keys. Very likely, the lizards had been reaching Florida for millennia, rafting over on floating driftwood or trees that were blown to the mainland during hurricanes. During this time, the Brown Anoles were not able to successfully compete with the native Green Anoles, and were never able to establish themselves.
By the 1940's, however, circumstances had changed. The human population of Florida surged, and large cities appeared on both coasts. These ports, particularly in Miami and Tampa, served as major entries for wildlife from the Caribbean and South America that were imported for the pet trade--and among these was the Brown Anole. By the 1950's, wild Brown Anoles were being reported in several cities, and by 1980, they could be found throughout most of Florida. Originally there were two distinct subspecies present, the Cuban Anole Anolis sagrei sagrei, and the Bahaman Anole Anolis sagrei ordinatus. But in Florida they have now interbred so much that the ordinatus subspecies is no longer recognizable. They do not seem to interbreed with the native Anolis carolinensis.
The establishment of the Brown Anole invaders had an immediate effect on the native Greens. While the Green Anole was largely arboreal and prefers high branches with lots of foliage in forested areas, the Brown Anole is largely terrestrial, spending most of its time on the ground and on the bare lower branches and trunks of trees and bushes. It particularly likes open shrubby areas--such as urban parks and suburban lawns. With its higher birth rate (and its larger size), the Brown Anole was able to quickly push the native Green out of the urban areas, and the Green Anoles retreated to the remaining forested tracts in Florida where the Browns preferred not to go (the arboreal Green Anoles are apparently better able than the ground-dwelling Brown Anoles to avoid predators in forested areas). Today, it's rare to see a native Green Anole in the city, and the Brown Anoles have completely taken over. From Florida, they have advanced into southern Georgia. Being less cold-tolerant than the native Green Anoles, this may be as far as the Browns can go.
I'm a lizard lover, and the Brown Anoles are entertaining to watch, but they are not supposed to be here, and they crowd out our sole native species. So I squish them underfoot whenever I get the chance--a futile gesture that nevertheless makes me feel a little bit better.