Effect of Insularity on Sexual Dimorphism and Habitat Use in an Isolated Population of Sceloporus clarkii (Reptilia: Phrynosomatidae)

We assessed the effects of insularity, sexual size dimorphism, and habitat use in an isolated population of Clark's Spiny Lizard, Sceloporus clarkii. We captured 120 individuals from Isabel Island National Park, of which 69 were females and 51 were males. First, we compared snout–vent length between island and mainland populations of S. clarkii; second, we compared five morphological traits between sexes within the isolated population. Finally, we assessed the relationship between morphological traits and habitat use (diameter of perch and perch height) from the island population. We observed that the insular population of S. clarkii exhibited a dwarfed form compared to the mainland population. Within the island population, we observed differences in body length: females were 10% shorter than males, with smaller heads (exhibiting allometry in females and isometry in males). Females and males used similar diameters of perch and perch heights. Surprisingly, we did not observe relationships between morphological traits and habitat use in either sex.