There are two sides to every lizard: Understanding the Northern Curly Tail’s impact on South Florida
- stephanieoduardo
- May 24, 2024
- 5 min read
Updated: Jun 20, 2024
Please note, this article is part of multipart series published that will be published periodically.
Part 1
Do you think the Northern Curly Tail is harmful to native Floridian flora and fauna?
Yes
No
Unsure
Before reading, please participate in the poll!
Where do we draw the line between invasive and nonnative?
Ecologically, the answer is simple. For a plant or animal to be invasive, it must do harm. Simply being nonnative is not cause for concern.[1] The nonnative Northern Curly Tail Lizard is a species of lizard that has become ubiquitous in Palm Beach and Miami-Dade County. Lizards in South Florida are easily observable and incredibly common. They quickly exhibit characteristics that make their geographic movement and population establishment an appealing candidate for study. Some experts consider the Northern Curly Tail (Leiocephalus carinatus) to be harmful to Florida’s native fauna and therefore classify the lizard as invasive. But, Leiocephalus carinatus is not extensively researched and the lizard’s impact is relatively unknown. It may be that the Northern Curly Tail, given its history and diet, is not as bad as we think. The Curly Tail Lizard is misunderstood due to its aggressive and dominating appearance, but it is actually more docile than it looks. In this series, I delve into the biology and history of these reptiles to answer the pressing question: “Are these lizards genuinely harmful to our region’s ecosystem?”
The Florida legislature, working with the Florida Fish and Wildlife Conservation Commission (FFWCC) classifies only three species of lizard as highly invasive and thereby strictly prohibited. One of these prohibited species is the Green Iguana (Iguana iguana). Both the Green Iguana and the Curly tail lizards belong to the sub-order Iguania, indicating they share a common evolutionary ancestor. But, they belong to different families within this sub-order and the Northern Curly Tail is not considered to be invasive by the FFWCC.
Could the Northern Curly Tail population establish itself to the level of the Green Iguana and become prohibited in the future? The life history, or the pattern of survival and reproduction events in the life of an organism, including traits such as longevity, age at maturity, and size, indicate that this may occur. For example, cold tolerance traits in the Northern Curly Tail have been documented by Christopher Searcy, PhD, an associate professor of biology at The University of Miami and head of the Conservation Ecology Labs. The evolutionary ancestors of these lizards originally haled from the Caribbean. As they moved north and into South Florida, the cooler winters and frost line have acted as population control. But as the lizards who successfully tolerate the cold reproduce, the trait is becoming more dominant, and thus may contribute to success of the species in the South Florida clime.
Iguana iguana at Morikami Japanese Gardens in Boca Raton on August 6, 2022
For now, the Northern Curly Tail is not considered as harmful to the native flora and fauna of South Florida as its distant iguana cousins are. Last updated in February of 2021, every other animal on the FFWCC prohibited nonnative species list is higher on the trophic level than the Northern Curly Tail Lizard. The trophic level of an organism is the position it occupies on the food web. Generally, less is known about the effect of lower trophic organisms. Herpetologist, Christopher Searcy, PhD, in his 2023 paper Patterns of Non-Native Species Introduction, Spread, and Ecological Impact in South Florida, the World's Most Invaded Continental Ecoregion states that “Non-native species may not have demonstrable negative effects. . . especially if they primarily consume plants or invertebrates, as these lower trophic levels are less likely to be extensively monitored.”[2] Searcy suggests, considering that “we lack sufficient (or any) evidence across most of the lower trophic level species in South Florida”[3] there potentially is less or more of a negative impact on plants and invertebrates (even lower on the food web than lizards) by the Northern Curly Tail Lizard. We simply are unsure.
Although not all nonnatives are invasive, they do carry an innate risk to native species. Predation of native species by nonnative species, increased competition for food, and the introduction of novel parasites and diseases to an environment all pose a threat to established populations of native species. Looking more closely at the terrestrial Northern Curly Tail, the lizard theoretically competes with the other, native, terrestrial lizards of Florida. These are the Florida Scrub lizard (Sceloporus woodi) and the Eastern Six-lined Racerunner (Aspidoscelis sexlineata sexlineata). The preferred habitat of these species, however, differ. The Northern Curly Tail Lizard’s preferred habitat is “disturbed, open, sandy rubble-strewn areas in coastal Florida. . .[areas] degraded by human infrastructure. . . and sightings [are] frequently are in association with. . . human produced habitat conversions.” [4] The species may appear more numerous than it really is, since native Floridians often see the Northern Curly Tail around sidewalks and buildings, while the other species habitat areas further away from human development.
Why is this important? There is an ecological theory known as the empty niche hypothesis that predicts in “areas with a depauperated native fauna are more susceptible to invasion. It is hypothesized that non-native species are able to exploit empty or vacant niches.” [5] When we apply this to the Curly Tail Lizard’s predilection for industrial habitats resulting from human development, it is less likely than not that there is no significant competition amongst the Northern Curly Tail Lizard and Floridian lizards. The Florida Scrub lizard and the Eastern Six-lined Racerunner both prefer sandy scrublands with loose soil and sand for burrowing. This differs from the Northern Curly Tail which, when threatened, will retreat to pre-existing recesses under concrete structures (like crevices in seawalls or under sidewalks) for shelter and escape. It is reasonable to conclude that given the difference in preferred habitats and the empty niche hypotheses that the Northern Curly Tail lizard has established extensive populations in areas highly visible to people that would be otherwise vacant.
Let’s assume that the Northern Curly Tail did exist in the same habitat as native scrub lizards and competed with them for food. Would the Northern Curly Tail be predatory to the native lizards? An examination of the stomach contents of adult Northern Curly Tail found that the most commonly consumed items, by percent total volume, are crickets, grasshoppers, beetles, roaches, and isopods.[6] Although carnivorous, the only vertebrate the Northern Curly Tail has been observed to consume is the brown anole (anolis sagrei). The brown anole is another nonnative species and threatens native Green Anoles (Anolis carolinensis). Thus, there is little evidence to support risk of predation. Because the primary food source of the Northern Curly Tail is low trophic level organisms, plants and invertebrates, with “short generation times and high reproductive output” the traits of the Northern Curly Tail’s prey “may lower or negate the impact of predation from invasive species.”[7] In short, the primary food source of the Northern Curly Tail reproduces so plentifully and rapidly that there is an even lower likelihood that the Northern Curly Tail’s impact on the food source of native species is significant enough to cause harm to established populations by competition or predation.
In the next blog, we will explore the relationship between the Northern Curly Tail and another nonnative that is commonly seen throughout South Florida – the brown anole.
Citations, Footnotes, and Research
[1]National Park Service. (n.d.). Learn - Invasive & Non-Native Species. U.S. National Park Service. Retrieved May 23, 2024, from https://www.nps.gov/subjects/invasive/learn.htm
[2] Searcy, C. A., Howell, H. J., David, A. S., Rumelt, R. B., & Clements, S. L. (2023). Patterns of non-native species introduction, spread, and ecological impact in South Florida, the world's most invaded continental ecoregion. Annual Review of Ecology, Evolution, and Systematics, 54(1), 195-218. https://doi.org/10.1146/annurev-ecolsys-110421-103104
[3] Ibid.
[4] Smith, H.T., and R.M. Engeman. 2003. A Review of the Range, Distribution, and Ecology of the Invasive Northern Curly-tailed Lizard in Florida. Florida Park Service "Parknership" Technical Report. 5 pp.
[5] Searcy, C. A., Howell, H. J., David, A. S., Rumelt, R. B., & Clements, S. L. (2023). Patterns of non-native species introduction, spread, and ecological impact in South Florida, the world's most invaded continental ecoregion. Annual Review of Ecology, Evolution, and Systematics, 54(1), 195-218. https://doi.org/10.1146/annurev-ecolsys-110421-103104
[6] Smith, H.T., and R.M. Engeman. 2003. A Review of the Range, Distribution, and Ecology of the Invasive Northern Curly-tailed Lizard in Florida. Florida Park Service "Parknership" Technical Report. 5 pp.
[7] Searcy, C. A., Howell, H. J., David, A. S., Rumelt, R. B., & Clements, S. L. (2023). Patterns of non-native species introduction, spread, and ecological impact in South Florida, the world's most invaded continental ecoregion. Annual Review of Ecology, Evolution, and Systematics, 54(1), 195-218. https://doi.org/10.1146/annurev-ecolsys-110421-103104
Comments