The Mystery of the Disappearing and Reappearing Green Anoles

 

Most who live in SW Florida will have noticed in their yards a very common small lizard, the brown or Cuban anole. It is an exotic species which has long been established here. The males extend a colorful orange/red dewlap while doing “push-ups” to establish territorial dominance.

Brown anoles are now an important food source for many Florida predators such as the corn snake and great egret, shown here eating them. This lizard also eats many insects and is thus a significant part of the local food web.

Apparently this brown anole has displaced a native lizard, the green anole (or American “chameleon”) which used to be quite common in SW Florida, but now is rarely seen. The green anole still occurs to the north where brown anoles do not live, but in S Florida it appears to have lost the competitive battle with the invader from the Caribbean. The green anole can be bright green or change to brown depending apparently on emotional state; it has a pink dewlap except for some southern populations with a white dewlap. When the dewlap is not extended the all green or all brown lizards can be well camouflaged when on vegetation matching their color.

To my amazement within the past year I have seen green anoles in three locations in Charlotte County, my yard on Manasota Key, Myakka State Forest and Yucca Pens wildlife management area. This is the first time in decades that I have seen green anoles here. What could be happening to explain this?

An amazing study by Stuart et al. 2014 (Science 346:463) carried out on spoil islands in S Florida offers an explanation. Brown anoles were introduced to islands with green anoles; subsequently the numbers of brown anoles rose. Green anoles shifted higher into the trees on invaded islands, while continuing to perch at lower heights on nearby islands lacking brown anoles. Thus competition among these lizards seems to force green anoles to forage higher in vegetation when brown anoles are present. The structure of the feet of green anoles may have changed to cope with a more arboreal life.

Rapid Evolution in Anolis carolinensis Following the Invasion of Anolis sagrei

So what we have is a remarkable example of evolution in action during our lives and a case of how a native species can adapt to the presence of an exotic to which it is initially competitively inferior. Nature is indeed grand and as they say- ecology is not rocket science, it is far more complex!

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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