The brown anole (Anolis sagrei) is a small, ubiquitous lizard commonly observed throughout the US Southeast, darting across sidewalks and garden walls. Its rapid proliferation across states like Florida, Georgia, and Texas has made it one of the most recognizable reptiles in the region. Many people wonder if this lizard is a natural part of the local ecosystem or a problematic intruder. Understanding the history and impact of the brown anole provides the context needed to answer the question of its invasive status.
Confirming Invasive Status and Origin
The brown anole is not native to the United States and is officially categorized as an invasive species across its non-native range. Its original distribution is centered in the Caribbean, primarily Cuba and the Bahamas. The species was first documented in the Florida Keys as early as 1887, likely arriving accidentally through international trade. Introduction pathways were primarily passive, involving stowaways on cargo ships or the transport of nursery plants containing eggs or small lizards. The brown anole becomes invasive because its aggressive establishment and measurable effects on local fauna cause ecological harm. Once established, brown anoles are highly successful at spreading rapidly, utilizing human infrastructure like roadways and cleared land to move into new territories.
How to Identify Brown Anoles
Distinguishing the brown anole from native species, such as the green anole (Anolis carolinensis), requires observing a few specific physical characteristics. Brown anoles are generally smaller and possess a stouter, stockier build compared to the slender native green species. Their base coloration is typically brown, ranging from light tan to dark gray, though they can change their skin tone depending on temperature and mood. Many individuals display a distinctive pattern along their back, such as light-colored diamond shapes or a prominent light stripe. A reliable identification feature is the male’s dewlap, the expandable throat fan used for display. The brown anole’s dewlap is usually a vibrant orange or red-orange, often bordered by a yellow margin, contrasting with the solid pink or red dewlap of the native green anole.
The Ecological Consequences of Their Spread
The colonization by brown anoles has resulted in measurable shifts within the ecosystems they inhabit, particularly through direct competition with the native green anole. Scientific studies show that the invasive species outcompetes the native lizard for desirable habitat perches, specifically those lower to the ground that receive more direct sunlight. This aggressive displacement forces the native green anoles to retreat higher into the tree canopy, where resources and thermal conditions may be less optimal for survival and reproduction. This change in vertical habitat use is a clear example of competitive exclusion, altering the community structure of arboreal lizards.
The brown anole is also a documented predator that affects local invertebrate and smaller vertebrate populations. They consume a wide variety of insects and arthropods, potentially reducing the food supply available to native insectivores. Brown anoles also prey upon the eggs and hatchlings of native lizard species, including the green anole.