Population Viability of Nonnative Mediterranean House Geckos (Hemidactylus turcicus) at an Urban Site Near the Northern Invasion Front
Biological invasions are one of the most serious threats to biodiversity conservation. Although success and impacts of many invaders, particularly ectotherms, are likely to be limited by a combination of climatic and demographic factors, human modifications to the environment can facilitate distributional expansion into otherwise low-quality landscapes. We assessed factors that might promote or preclude population viability of a nonnative ectotherm, Hemidactylus turcicus (Mediterranean House Gecko), within an urban center at the northern periphery of its known North American range. Mediterranean House Geckos are increasingly apparent in the southeastern United States, but their potential for establishment and spread in more temperate regions is less well known. We gathered data using capture–recapture methods and the unique dorsal patterns of individual geckos. Despite a more temperate climate compared to other areas in their introduced range, and refuge temperatures falling below the critical thermal minimum previously documented for other introduced Mediterranean House Gecko populations, geckos survived the winter and reproduced successfully. Cormack–Jolly–Seber open population models did not provide definitive evidence regarding changes in population size over the study period. The tendency for this introduced species to establish populations primarily within urban centers may suggest that negative impacts associated with this northerly expansion are minor. Nonetheless, a high potential for range expansion suggests a need to assess a potentially growing suite of ecosystem interactions.Abstract
General location of study site, denoted by the star, alongside other observations of Mediterranean House Geckos (Hemidactylus turcicus) (diamonds) in Tennessee, from the records of the Austin Peay State University Museum of Zoology. Tennessee geographic data and border data are from the Tennessee GIS Clearinghouse (tngis.org) and U.S. Census Bureau, respectively. Map constructed in QGIS 2.18.0 (QGIS Development Team, 2016) with some additional work in Google Earth 7.1.7.2606 (Google Inc.).
Numbers of juveniles, gravid females, and adult male/nongravid female (other) Mediterranean House Geckos (Hemidactylus turcicus) captured over the course of the study in Knoxville, Tennessee, at (A) the lower wall and (B) the upper wall. All individuals per occasion sum to sample size. Bars are not horizontally spaced to scale with the intervening time intervals. Negative Julian dates denote dates in 2014.
For each sampling occasion, the percentage of Mediterranean House Geckos (Hemidactylus turcicus) that had been previously captured. Captures are shown for the lower and upper walls over the study period in Knoxville, Tennessee. Recapture status was determined from pattern recognition of photographs of gecko dorsal patterns.
One Mediterranean House Gecko (Hemidactylus turcicus) recaptured over the course of the study in Knoxville, Tennessee, with the date of each capture. SVL in centimeters is given in the inset in each photo. This individual evidently survived the 2014–15 winter.
Environmental temperature within seven refuge sites (wall crevices) between 15 October 2014 and 30 April 2015 in Knoxville, Tennessee. The shaded region between solid horizontal lines represents critical thermal limits (CTmin, CTmax) of Mediterranean House Geckos (Hemidactylus turcicus) reported by Huey et al. (1989). Optimal (Topt) and preferred (Tpref) body temperature values reported by Huey et al. (1989) and Angilletta et al. (1999), respectively.
Snout–vent lengths of Mediterranean House Geckos (Hemidactylus turcicus) over the study period in Knoxville, Tennessee. The horizontal line is at 4.2 cm, which we considered to be the size at maturity (Punzo, 2001).
Population size estimates of Mediterranean House Geckos (Hemidactylus turcicus) in Knoxville, Tennessee, from Cormack–Jolly–Seber models, for the (A) lower and (B) upper walls. Error bars represent one standard deviation.
