On small, isolated islands, researchers often observe a striking phenomenon: species that are rare on the mainland reach exceptionally high population densities. This is known as density compensation. It occurs because the reduced biodiversity on islands often results in less pressure from predators, competitors, and parasites, allowing a single species to flourish.

A prime example of this is the spiny woodlizard (Enyalioides heterolepis) on Gorgona Island, Colombia. The island's high lizard population makes it an ideal "natural laboratory" for exploring the ecology and natural history of this species. During visual encounter surveys conducted in 2023 and 2024, researchers tracked the woodlizards across both day and night, documenting microhabitat preferences, perch heights, and perch diameters.

Across the lowland tropical forests of Gorgona, the study revealed a distinct circadian shift in behavior. In daytime most lizards were found on the ground, specifically within shadowed microenvironments. At night, instead, individuals moved to elevated perches, such as fallen trunks, branches, and leaves. This transition to sleeping perches likely serves as a defense mechanism against ground-based predators or provides thermoregulatory advantages as the sun rises.

Interestingly, while males were found to be significantly larger than females—a form of sexual dimorphism often linked to male-on-male competition—there was no significant difference in how the two sexes utilized their habitat. Both males and females chose similar perch sizes and elevations.

The study also noted a moderate-to-low rate of caudal autotomy (tail shedding). In the world of herpetology, low rates of tail loss typically suggest one of two things: either predation pressure is remarkably low on Gorgona Island, or the lizards' antipredator strategies are exceptionally efficient.

Want to dive deeper into the data? Read the full paper for a comprehensive look at the lizards of Gorgona!

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