Brown anoles (Anolis sagrei) are found in many urban habitats.
Invasive species are a common ecological issue worldwide. In certain situations, they can prey on, outcompete, or otherwise disrupt the ecology of native species, potentially leading to population declines or extirpation.
The brown anole (Anolis sagrei) is native to Cuba and surrounding Caribbean islands, but has been repeatedly introduced to mainland North America via Florida over the past ≈100 years. Brown anoles have continued to spread and now occupy most of Florida, along with areas of the Gulf Coast. These anoles are particularly adept at exploiting urban habitats, such as Houston and New Orleans, where they may attain higher body size and compete with the native green anole (Anolis carolinensis). Brown anoles can outcompete green anoles in habitats such as the ground or lower levels of vegetation, where they can use their larger, more muscular bodies to chase off the native anoles or even prey on young green anoles. While green anole populations are likely not extirpated by brown anoles, they shift their locations higher into vegetation, to avoid competition with brown anoles.
The ability of these species to maximize their activity at different temperatures may play a role in determining the outcomes of interactions between brown and green anoles. While green anoles are present throughout the southeastern US and can tolerate colder temperatures, brown anoles may be ancestrally adapted to higher, more tropical temperatures. Lucy Ryan, a masters student in the Gunderson Lab at Tulane University decided to investigate this possibility by monitoring the activity levels of each species at a variety of different temperatures. The research team hypothesized that, based on their thermal preferences, brown anoles would have higher activity levels than green anoles at both higher temperatures and over a wider range of temperatures. Lucy conducted focal observations of anoles to quantify activities such as feeding, displaying, and moving. They measured the temperature of each anole’s microhabitat with a copper model containing a thermocouple.
Over an 18° C range of temperatures, Ryan found that there was no difference in the activity levels of the two species. These results, while surprising, suggest that effects of temperature on activity are not driving the competitive advantage of brown anoles over green anoles. In fact, since both species’ activity rates peak at similar intermediate temperatures, this situation may increase competition between brown and green anoles. Ryan plans to continue this work through the winter and spring to determine whether there are any species differences over an entire year of activity which may impact this system. Stay tuned and follow them on Twitter!
Green anole activity rate, including dewlap displaying, shows a peak at intermediate temperatures.
