The Brown Anole, Anolis sagrei, is one of the most commonly sighted lizards across Florida, frequently seen skittering along sidewalks, fences, and palm trees. Despite its widespread presence, this small reptile is not a natural part of the state’s ecosystem. The Brown Anole is officially classified as an invasive species in Florida, confirming its non-native origin and capacity to harm the local environment. Its successful colonization has led to significant shifts in the habits and distribution of Florida’s native lizard populations.
Status and Historical Establishment
The Brown Anole is native to islands of the northern Caribbean, primarily Cuba and the Bahamas. Its arrival in the United States was documented in the late 1800s, making it the first established non-native reptile species in Florida. The initial recorded presence of Anolis sagrei occurred around 1887 in Key West.
The introduction was likely accidental transport, with the lizards or their eggs stowing away in cargo shipments arriving from the Caribbean. Florida’s numerous international ports and subtropical climate provided an ideal environment for the species to thrive. From its initial foothold in the Keys, the lizard rapidly expanded its range across the peninsula. By the early 2000s, Brown Anoles had established breeding populations in every county of peninsular Florida, solidifying their status as a widespread invasive species.
Distinguishing Brown Anoles from Native Species
Differentiating the invasive Brown Anole from Florida’s sole native anole, the Green Anole (Anolis carolinensis), relies on clear physical and behavioral distinctions. The Brown Anole typically exhibits a color range of gray to brown, often displaying intricate patterns like a pale stripe or diamond shapes along its back. While the Green Anole can change its color from bright green to brown, the Brown Anole cannot display vibrant green coloration.
Male Brown Anoles possess an extensible dewlap—a throat fan—that is typically orange or reddish-orange, often framed with a white edge. This contrasts with the male Green Anole, which displays a pink or reddish-pink dewlap. Behaviorally, the Brown Anole is generally found on lower surfaces, such as the ground, fence posts, and tree trunks, preferring sunnier, open microhabitats. The native Green Anole is more slender and now primarily occupies higher, more arboreal perches in the canopy.
Ecological Displacement and Competition
The invasive status of the Brown Anole is driven by its direct ecological impact on the native Green Anole population. Brown Anoles are more robust and aggressive, leading to intense competition for resources like food and basking sites. This interaction has forced the native Green Anole to retreat into a different part of the environment, a phenomenon known as niche partitioning.
In areas where the two species coexist, Green Anoles have shifted their preferred perching height significantly higher into the tree canopy to avoid the invasive newcomer. Studies indicate the native species may move up to 17 times higher on vegetation to escape competition. This displacement stresses the native lizards and limits their access to optimal thermal and foraging resources.
Brown Anoles also affect the native population through predation, as adults readily consume Green Anole hatchlings. Their aggressive behavior and ability to tolerate higher population densities allow them to outcompete the native species by sheer numbers. This pressure has been linked to a reduction in the abundance and reproductive success of the native Green Anole in many parts of Florida. Furthermore, this intense competition has prompted a rapid evolutionary response, with Green Anoles in invaded areas evolving larger toe pads to better grip the higher, thinner perches.