Anolis cristatellus. Photo by Janson Jones.

If you ever come to Puerto Rico, the first thing you’ll probably notice is the warmth. Yet, for an anole, things are not that simple. Different habitats can have different thermal regimes that potentially influence the lizard’s biology and natural history in different ways. What might be a hot and humid urban park for us can be a heterogeneous thermal landscape for a small lizard.

This is the case for Anolis cristatellus, a lizard common in most parts of Puerto Rico. Back in the early70’s, Ray Huey (1974) studied how habitat influenced this anole’s thermal biology. He found that in open and sunny habitats, this lizard actively thermoregulates and has relatively high and stable body temperatures, but that in shaded forests it is a thermoconformer and has relatively low and variable body temperatures.

Also back in the early ’70s, George Gorman and Paul Licht (1974) found that altitudinal and seasonal variation in temperature had major effects on reproductive cycles of Puerto Rican anoles. So, do reproductive cycles differ between lizards living in thermally distinct — but contiguous — habitats? Ray Huey, George Gorman and I teamed up to find out, and you can find the answer in our recent paper just published in The American Naturalist.

We studied seasonal reproductive cycles of this lizard in two localities in lowland Puerto Rico. Both localities have contiguous but thermally distinctive habitats: open parks and forests, separated by only a few meters. We caught female lizards every month for more than two years and palpated their bellies to establish reproductive condition. At both localities, lizards living in open habitats were more often gravid than were those in the forest. This difference was especially marked during winter months (of course… in a tropical sense). During these cooler months, more than 20% of open lizards were gravid, while essentially none of the forests ones were.

Large-scale geographic variation in reproductive cycles has been described in many taxa, but this is one of the few examples on a micro-geographic scale. Very likely these difference will have significant effects on the population ecology of the species, and these will be reported on soon. But in the meantime, we can say that at least for the reproductive output of Anolis cristatellus, a few meters matter!