South Florida’s heat key to boom of python and cold-blooded cousins

The tokay gecko was one of 14 invasive lizards and geckos used to predict where invasive reptiles are more likely to spread in Florida.
The tokay gecko was one of 14 invasive lizards and geckos used to predict where invasive reptiles are more likely to spread in Florida.

If Florida ever wants to rid itself of Burmese pythons, tegus and other slithery invaders, pray for cold.

A new University of Florida study has confirmed what scientists have long suspected: temperature, more than habitat, determines where reptiles invade. Using the kind of risk assessment strategy normally used in business, researchers modeled where invasive lizards and geckos were likely to occur based on native habits, then compared that to where they live in Florida. Temperature, it turns out, creates an invisible barrier.

And that means South Florida will likely remain the nation’s hottest spot for all things invasive.

Scientists started thinking about the power of temperature after a severe 2010 cold snap froze iguanas like popcicles and wiped out pythons in unprecedented numbers, said Frank Mazzotti, a UF biologist and one of the study’s five authors..

“That’s when people really began to appreciate that acute cold events may often be as important or more important than regular cold weather,” he said. “It’s not how cold it gets all the time. It how cold it gets when it really gets cold.”

To test their theory, researchers looked at the menagerie of invasive reptiles on the Florida landscape, from crocodiles to turtles. They then whittled down the list to include only reptiles that are well understood in their native ranges, which could provide enough data to feed into their models. Pythons, while a bigger threat, didn’t make the cut. Neither did tegus or Nile monitor lizards, two more aggressive egg-eating, cat-consuming invaders.

Instead, they came up with 14 geckos, lizards and anoles, everyday invaders like the Hispaniola green anole and common wall gecko that get stepped over daily without grabbing headlines. They then compared their native ranges to their appearance in Florida.

The models showed that when it comes to reptiles, temperature matters most and in particular minimum, or cold temperatures. While temperature most accurately predicted location for the whole group, the type of land played a varying role depending on the species. Mediterranean house geckos were less picky about whether they lived in wetlands or a pine rockland. Star lizards were far more finicky, leading researchers to conclude that adding land type improves predictions.

Researchers also found, no surprise here, that most exotics thrive in South Florida’s steamy tropics, which tend to more closely match native ranges.

Being able to target likely hotspots could provide a valuable tool in fighting the spread of invasive species that can destroy native wildlife and cost far more to remove once they become established, Mazzotti said.

“It helps us set our priority on where to look in South Florida,” he said.