A female Anolis allisoni, no worse for the wear, from Roatan, Honduras
In advance of our trip out to Swan Island, I’ve come to Roatan, one of the Bay Islands just off the coast of Honduras, to check out its anole fauna. Of particular interest is the mixture of island and mainland faunas: A. allisoni¸ a trunk-crown member of the carolinensis group, somehow found its way here from Cuba, whereas A. roatensis (nee lemurinus) represents the mainlanders. And, as a bonus, A. sagrei is here, too, apparently introduced. I’m looking forward to seeing how they mix it up.
Things didn’t get off to a good start yesterday when I arrived mid-afternoon. It was very overcast and drizzly, and the temperature probably barely topped 70. Brrr! With more of the same forecast for today, I was not optimistic.
But although it looked like it was on the verge of raining all day, it held off until after dark. The sun was in and out, and so were the lizards. My expectation was that the balance of color would be like it is in other places where carolinensis and sagrei group anoles co-occur: lots of brown anoles on the ground and low on trees, bushes and buildings, and a small to moderate number of greens at eye level up to the treetops.
I couldn’t have been more mistaken. Green anoles were seemingly everywhere—as thick as anywhere I’ve ever been. And the browns? I saw three. The greens were on the buildings, on the fences, in the bushes up the trees, even doing their best grass-bush anole imitation along the roadside. They were everywhere, except one place: the ground. And therein lies the explanation for this green:brown inversion. There were brown lizards in great abundance—at least in open sunny localities—but although they skittered about and occupied the same place, they weren’t anoles. Rather, they were these fellows.
Brown basilisk on Roatan
Brown basilisks, Basiliscus vittatus. Many of them were sagrei-sized, and if you weren’t paying attention, their abundance might have convinced you they were anoles. But then there were the bigger fellows, not as abundant, but plenty of them. My hunch is that they’re why brown anoles haven’t gotten much of a foothold. The little guys compete with the sagrei, and the bigger ones eat ‘em. I speculated earlier this year about interactions between basilisks and introduced A. cristatellus in Costa Rica—there, they seemed to coexist and cristatellus was doing fine. Here, I think the story is different. Of course, brown basilisks have also been introduced to Miami, where they coexist with sagrei, so maybe I’m barking up the wrong tree, but the great abundance of basilisks, living exactly where you’d expect to see the sagrei, seems too much of a coincidence to me.
The proverbial lizard in the grass
Whatever the cause, the absence of sagrei seems to have given allisoni the green light to go crazy. They’re enormously abundant and use many off-the-ground habitats—fences, buildings, etc.—where you’d expect to see sagrei. At least in open places, like hotels, they are very common from 1-2 meters in height, or even lower. In more forested areas (and remember, this is based on one day’s observations, and the forested areas were visited in the afternoon), they seem mostly high up, generally in sunny spots. I was particularly struck that they were very common in the thick grass, while at the same time as high up in the tree as I could see them. Those of you who live with green anoles in other places (I’m thinking of certain Georgians and Little Caymanians), I’d appreciate your thoughts. Does this seem different from your abundant greens?
Now, as for the other native anole, A. roatensis, today I was shut out. They’re supposed to be in forested areas, and I have a hot lead for a spot tomorrow, so hopefully will have more to report then.
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Pat Shipman
Fascinating! I have never ever seen A. maynardi in the grass. Sagrei is, as predicted, on the ground or less than 1 meter up, but maynardi? nope. Now I will have to go check that I haven’t missed a lizard in the grass, but I don’t think so.
On another topic, I’ve been checking out the back patterning on sagrei in an unsystematic fashion and I have two questions: 1) how do I keep from counting the same sagrei twice? 2) I have a few times seen a sagrei (or a few) that has NO light-colored pattern on its back at all. Am I being fooled by color changes, or is there a fourth possibility in addition to bars, chevrons, or intermediate chevron-bars?
Philip M. Fortman
I may be in a area where Basilisk predation on sagrei is ripe for study. Since the last winter freeze cycles in southern Broward County Florida, the Basilisk population has rapidly spread, even overwhelming the large A. equestris. I have plenty of photos to verify. While a casual lay observer, I have witnessed Basilisks eating sagrei. What you observed on Roatan may be in transition now in my area.
Skip (James) Lazell
At our winter digs in Jackson, Mississippi, there are lots of carolinensis, often less than a meter up, and feeding sometimes on the ground. They also climb high. We have no other anoles and only a few, scarce, skinks. I would say, where naturally all alone carolinensis is quite broad-niche generalized.
Kevin de Queiroz
Did you see any of the endemic ctenosaurs?
Jonathan Losos
You bet, and on Utila, too, where they are working hard on conservation.
James Stroud
Interesting thoughts on the B. vittatus/A. sagrei co-occurrence. My only experience of their interactions is at Fairchild Botanical Gardens. It is a really interesting system, with two large predatory agamids quite well established; B. vittatus and A. agama. The garden itself is interesting as it is so highly spatially structured, and offers a huge range of habitat types, which in turn will influence diet types, thermal niche availability and other vegetative/structural variables.
What I have seen so far is that in ‘Open’ habitats, i.e. with little to no canopy cover (therefore maximum basking potential), the agamids appear to almost exclusively dominate, so similar to what you have seen. However instead of brown anoles continuing to persist in low abundances and not displacing green anoles, they are in very high densities in areas with partial canopies, which one would assume are sub-optimal for the agamid heliotherms. Green anoles in this case remain to be pushed higher up in the tree.
Robert Powell
Basilisks can certainly affect the abundance of anoles. Some years ago, while studying A. barkeri at Los Tuxtlas, we found that anoles were almost completely absent in open areas around lakes, where basilisks were abundant. In sharp contract, anoles were abundant along shaded streambeds, where basilisks were absent. I’m pretty sure this isn’t a coincidence. See Birt et al. (2001. Natural history of Anolis barkeri: A semiaquatic lizard from southern México. Journal of Herpetology 35: 161-166).