Factors that determine the spatial distribution of an introduced species, <i>Phrynosoma cornutum</i>, in South Carolina
The study of spatial distribution can give us insight into which factors are most important for a species to survive and reproduce and can allow scientists to determine species most vulnerable to extinction. Texas horned lizards (<i>Phrynosoma cornutum</i>) are native to the western U.S. and are declining throughout their native region. There are introduced populations of this species scattered along areas of the southeastern U.S. coast. There has been very little research done on the spatial distribution of this species, and no research of the distribution of the introduced populations. I examined which factors govern the spatial distribution of Texas horned lizards, focusing on habitat, prey, and predator characteristics. I performed four transect surveys from May to August 2017 on Sullivan’s Island, South Carolina. Transects and invertebrate pitfall traps were deployed every 20 meters across the dune habitat in a total of 14 consecutive areas. Five microhabitat characteristics were quantified: open sand, shade, grass, shrub, and herbaceous vegetation. I had a total of 1,134 sampling stations and collected and identified 7,580 invertebrates. I located 52 horned lizard fecal pellets that were used to represent horned lizard distribution. I found that Texas horned lizard distribution is significantly influenced by all microhabitat characteristics. Areas with higher abundance of the ant genera (<i>Pogonomyrmex</i>, <i>Dorymyrmex</i>, and <i>Pheidole</i>) and Coleoptera predicted significantly fewer lizards. The abundance of <i>Solenopsis</i> (fire ants) had no significant effect on horned lizard presence. Significantly fewer lizard fecal pellets were found in areas with ghost crab holes and tracks. This study can help managers and biologists better identify which factors are most useful for the conservation of Texas horned lizards in their native range and can serve as a baseline for other threatened or endangered species. This research will also serve as a baseline for understanding the impact of this introduced lizard on native species in the barrier island coastal dune ecosystem.