The Lonely Clouded Anole on a Pacific Island

Anolis nebulosus. Photo by Hugo Siliceo-Cantero.

By H. Hugo Siliceo-Cantero and A. Garcia

In the late 1980´s, the scientists Bradford C. Lister and Andrés García discovered an interesting population of clouded anoles inhabiting the small 3.3 ha island of San Agustin located just off the Pacific coast of Jalisco, Mexico. This island was also close to the actual protected area of tropical dry forest on the mainland in the Chamela-Cuixmala Biosphere Reserve. Lister and García reported that the abundant anole population on San Agustin was maintained a decade later at much higher densities than the mainland population. We began to study this population in 2007 as a graduate student. Since then, we have studied several aspects of the ecology of this island population comparing this with the ecology of anoles on the mainland.

The existence of such island populations enables scientists to carry out natural experiments that provide invaluable information helping us to understand ecological and evolutionary processes.

This Clouded Anole (Anolis nebulosus) species that is on San Agustin Island is endemic to Mexico, and is of particular interest as this population has evolved in the absence of similar species of the same genus, or congeners. The species on the island also occupies a broad niche of perch height and a low number of lamellae, and is one of the most sedentary anoles known. Our work demonstrated that San Agustin population of the Clouded Anole has distinct morphological and genetic traits compared to conspecifics on the mainland.

Recently, we found that the insular population also presents distinct ecologic traits compared to those of the mainland population. In our manuscript “Assessing the relative importance of intra- and interspecific interactions on the ecology of Anolis nebulosus lizards from an island vs. a mainland population”, we suggest that the processes that drives the ecology and evolution of this insular population (intraspecific competition) differs from those that are important in the mainland (interspecific competition).

We believe that the results of our research on the insular population of anoles on San Agustin Island complement the scenario of Caribbean anoles, where congeneric competition is the key evolutionary driver. Furthermore, in our study, we used video cameras to provide direct evidence of predation, interspecific and intraspecific encounters and aggression, which was possible because the Clouded Anole is a sedentary lizard.

It has been a pleasant and rewarding experience for me to study the Clouded Anole. Although spending hours in the field observing a largely sedentary lizard may seem a little boring and tedious, the data from our studies have revealed a fascinating adaptation to the natural and social environment with unique physical, genetic, and ecological characteristics.

Currently, the population of Clouded Anoles on San Agustin has been dramatically reduced, almost to the point of extirpation. We think that two natural events, the hurricanes Jova in 2011 and Patricia in 2015, as well as invasive studies such as Hernández-Salinas et al. (2016) where they extracted 77 anoles from this small island, are the cause of the dramatic reduction in the Clouded Anole of San Agustin Island. As ecologists, we believe that research should not be done at the expense of the species or population under study, but should ensure that the population remains intact to continue along its evolutionary path, and further elucidate our understanding of the natural world around us.

We are currently monitoring both insular and mainland populations in order to understand and evidence the ecological implications of such natural and anthropogenic reduction on anole populations.