As urbanization continues to reshape landscapes, its effects on wildlife have become a subject of growing concern. In the unique context of Cuba, a recent study focused on an endemic lizard species, Anolis homolechis, found in both natural and suburban environments. This in-depth study relied on adapted tracking methods deployed over several years and explored a wide range of characteristics. This approach provides a comprehensive view of the impact of urbanization on a native species, expanding our understanding of the increasingly intricate consequences of urban expansion on biodiversity.
The lizard Anolis homolechis is medium-sized trunk anole that is common and widespread in Cuba. This small reptile is not only found in natural habitats but is also thriving in suburban environments. Its ability to navigate these varied landscapes has drawn the attention of researchers. Dr. Annabelle Vidal, a Cuban-born researcher, dedicated her doctoral thesis to understanding how urbanization affects this species.
Monitoring lizards
Vidal chose two natural and two suburban sites where she conducted several parallel studies on the lizards, with complementary objectives, all relying on a capture-mark-recapture method. All lizards spotted along established study paths (including both sexes and adults and juveniles) were captured using a fishing pole. They were then marked with colored implants or numbered tags (depending on the aim of the study), enabling the identification of individuals in subsequent captures. All animals, a remarkable number exceeding 1000 lizards, were then released at the exact location of capture.
Each capture involved documenting numerous parameters. Before being released, all animals were measured and weighed, and their sex and developmental stage (juvenile vs. adult) were determined. They were also inspected for scars indicative of tail autotomy, a common anti-predator behavior in anoles where the attacked individual voluntarily sheds part of its tail as a distraction to escape. Other parameters were also considered depending on the aim of each study. For instance, for a study dedicated to the behavior, the height at which the animal was perched, an important behavioral parameter known to be influenced by various factors, was noted. For another study dedicated to age-class structure, female lizards were examined to ascertain if they were gravid (about to lay eggs) or not.
Lizards differ in their morphology
The first study, published in 2022, revealed important morphological differences between the two types of environments. Lizards were overall larger in suburban areas compared to forests and were in better body condition. These results suggest an easier access to food resources around cities, notably thanks to the many insects attracted by the accumulation of garbage. The overall larger size of the reptiles around cities would be a direct consequence of their better body condition, with a supposedly longer survival allowing them to reach larger sizes.
In addition, lizards from suburban environments also had longer legs (for equal size), compared to forests ones. Researchers suggested that the increased legs size could result from phenotypic plasticity and might help lizards to better climb in an environment with broad surfaces such as manufactured structures.
An impact on lizards’ behavior
To better document the effect of urbanization on the climbing behavior of A. homolechis, a second study was conducted, published in 2023. In addition to measuring the perch height at capture, Vidal also recorded videos of 81 individuals in the wild to collect information about their behavior.
As expected, the behavior of anoles differed between the two types of sites, with lizards perching overall higher in suburban environments. Several environmental parameters could explain this variation, such as higher temperature in urban areas (known to influence the perch height of anoles), or an improved visibility of the surroundings in open suburban areas, compared to closed spaces such as forests.
The same study also found another effect of urbanization: lizards from suburban environment showed variations in their behavior according to the time of day, while lizards from forests did not. Indeed, around cities, lizards perched higher in the afternoon compared to the morning. The authors explain that predation risk could be higher in the afternoon in urban areas, but not in forests, causing this behavioral response.
Consequences for the population structure
All the differences highlighted in the two studies could impact the demographic success and population dynamics of native species. A third study was thus conducted to explore this topic, this time focusing on the age-class structure of the species.
The results from this last study, published in 2024, reveal a four-fold lower proportion of juveniles in suburban habitats compared to forests. This lower proportion of juveniles near cities was however not explained by a difference in female fecundity, as this parameter did not differ between the two types of sites.
The proportion of tail autotomy might bring another explanation. Indeed, this phenomenon was much more often observed among juveniles in suburban areas compared to forests. The same result was also found in adults in the first study. It is possible that the predation pressure is higher in suburban environments. In particular, the pattern of autotomy observed suggests an important rate of predation on juveniles in around cities.
Conclusion and perspectives
Overall, many differences were discovered in A. homolechis between the two types of environments (including other parameters not detailed here), some of which suggesting differences in survival. It is possible that the specific environmental pressures of suburban habitats lead to directional and/or stabilizing selection on anoles populations. This significant research topic, the following study in preparation by Vidal, aimed at understanding how urbanization affects anole populations through differential survival and selection, represents the next crucial step toward a comprehensive understanding of the impact of urbanization on this native species.
About Dr. Annabelle Vidal
Annabelle Vidal completed her doctoral thesis in 2022 on the adaptation of Anolis lizards to the urban environment, with the support of Caribaea Initiative, an international NGO dedicated to studying and conserving biodiversity in the insular Caribbean. After her PhD, she joined a project leaded by Caribaea Initiative dedicated to invasive exotic reptiles. She currently lives in Cuba where she continues her research within the Institute of Ecology and Systematics.
References
Featured image: © Annabelle Vidal, some rights reserved (CC-BY)
- The many consequences of urbanization on an endemic Cuban lizard - February 8, 2024
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