DEMOGRAPHICS AND MOVEMENT OF A SKY-ISLAND POPULATION OF SCELOPORUS OCCIDENTALIS (WESTERN FENCE LIZARD)
Arthur Barraza, Angela Castanon, Brian Rivas, Evelyn Ruelas, Prarthana Shankar, William Hoese, Christopher Tracy.
California State University Fullerton, Fullerton, CA.
Populations isolated on mountain peaks, or sky islands, often have lower genetic diversity and are subject to increasing periods of drought due to climate change, both of which increase the risk of local extinction. Therefore, sky-island populations could make good indicators of the effects of climate change. We studied the sky-island population of Sceloporus occidentalis (western fence lizard) on Ord Mountain, California, in the Mojave Desert, to examine population demographics and measure individual movement. Based on the demographics of non-isolated populations of Sceloporous occidentalis, we hypothesized we would find 3 distinct age classes on Ord Mountain and that individuals would disperse throughout the habitat. We established 4 half-hectare plots (50 × 100 m), 2 north and 2 south of a long-term monitoring site on Ord Mountain. We captured S. occidentalis over 2 days in June, marked each individual, and measured mass, snout-vent length (SVL), substrate temperature, and GPS coordinates. Individuals fell into 3 age classes based on SVL: juveniles, sub-adults, and adults. Based on recapture data, we estimated the population density to be 35 individuals/hectare, similar to other populations. Movement among individual lizards varied greatly. Individual movement ranged from 1 to 68 meters (mean: 12.76 m ± 17.19, SD). Movement was generally on the east-west axis and may have followed rock formations. Our findings suggest that some individuals dispersed rather than moved within their home range. Population density and the presence of multiple age classes indicate that the Ord Mountain population is robust.