Selection of Microhabitat by the Introduced Mediterranean Gecko, Hemidactylus Turcicus: Influence of Ambient Light and Distance to Refuge

The Mediterranean gecko (Hemidactylus turcicus) is an introduced nocturnal lizard that often can be seen on and around buildings in the southern United States and in its native Old World range. However, little is known about the factors that determine its selection of microhabitat, except that it does not actively thermoregulate. For example, geckos may forage near lights due to presence of higher concentrations of flying insects or they may select darker sites near refugia to avoid predators. This study investigates the influence of ambient light level (irradiance) and distance to a refuge on selection of microhabitat. During their normal activity period, 54 geckos were hand captured. Snout– vent length, mass, sex, irradiance, and distance to the nearest refuge (crack, crevice, or hole) were determined for each lizard at the time and place of capture. Juvenile geckos tended to be in areas with higher irradiance and farther from refugia than adults. All adults generally selected sites closer to refugia. Adult male and female geckos did not differ significantly in selection of microsites. Thus, we suggest that adult lizards, especially territorial males, exclude juveniles from sites closer to refugia, which are typically of lower irradiance. RESUMEN—El gecko Mediterráneo (Hemidactylus turcicus) es una lagartija nocturna introducida en los Estados unidos que se encuentra en y alrededor de edificios en el sur de los Estados Unidos y en su territorio nativo del viejo mundo. Sin embargo, los factores que determinan su preferencia de microhabitato son en gran parte desconocidos, excepto por su inhabilidad de termoregulacion. Por ejemplo, geckos podrı́an elegir cazar cerca de lugares iluminados debido a la presencia de insectos; podrı́an escoger sitios oscurecidos y cercanos a sus refugios para evitar depredadores; podrı́an elegir microhabitatos con una combinación de estas dos alternativas; o quizas preferirian un microhabitato con otra caracterı́sticas de mayor importancia. Este estudio investiga como el nivel de luz ambiente (‘‘irradiance’’) y distancia a un refugio influyen la selección del microhabitato. Cicuenta y cuatro (54) geckos fueron capturados a mano durante perı́odos de actividad normal. La longitud del hocicovientre, la masa, el sexo, nivel de luz ambiente, y distancia al refugio más cercano (hoyo o grieta) fueron medidos al momento y lugar de captura de cada gecko. Geckos juveniles suelen encontrarse en areas de alto nivel de luz ambiente y mas lejano de refugio. Geckos adultos en general prefirieron sitios mas cercanos a refugio. Las hembras prefirieron sitios oscuros mientras que los machos fueron encontrados en microhabitatos con alta irradición, pero, geckos machos escogieron sitos más cercanos al refugio comparado a las hembras. Por lo tanto sugerimos que los geckos adultos, especialmente machos territoriales, excluyen a geckos jeveniles de sitios más cercanos a refugios los cuales tı́picamente son de bajos niveles de luz ambiente. Selection of microhabitat is of paramount importance to animals because of the high costs associated with poor choices (Huey, 1991; Webb et al., 2004). For example, if an animal chooses a thermally inappropriate microhabitat, then it will face reduced physiological performance, which would reduce its overall fitness (Huey, 1991). Because the struggle to maximize fitness is a driving force for all organisms, animals should select microhabitats that allow them to attain the greatest fitness possible (Fretwell and Lucas, 1970; Rosenzweig, 1981). Many factors, including risk of predation, access to food, and interspecific and intraspecific competition, can influence the fitness of an animal, and consequently, selection of microhabitat by that animal (Anderson, 2007). Much research on selection of microhabitat in lizards has been conducted on diurnal species with an emphasis on thermal properties (HeatTHE SOUTHWESTERN NATURALIST 52(4):578–585 DECEMBER 2007