Urban ecology and conservation of Texas Horned Lizards living in small towns
Williams, Dean A.
Wall, Ashley E.
Biffi, Daniella
Ackel, Alexis
Alenius, Rachel
Mirkin, Steven
Rhoads, Dustin D.
Tucker, Mary R.
Department of Biology
Texas Christian University
Fort Worth, Texas, USA
Texas horned lizards (Phrynosoma cornutum) have faced significant declines and local extinctions across much of their eastern range due to habitat loss, the introduction of red imported fire ants (Solenopsis invicta), and declines in their main prey, harvester ants (Pogonomyrmex spp.). Urbanization represents an extreme change to natural environments and yet this species used to be a common wildlife component in small towns. We conducted a study of Texas horned lizards in the small towns of Kenedy and Karnes City (~3,000 people) in south Texas to determine how this species persists in human altered landscapes. We monitored 16 sites from 2013-2021 that included alleyways, school yards, parks, and abandoned lots. Genetic diversity in town is low and dispersal is hindered by urban infrastructure. The density of lizards at some sites (20-70 lizards/ha) was much higher than found in more natural areas (4-10 lizards/ha). Home range sizes were also smaller (0.25 ha) than found in more natural areas (1-2 ha). Alleyways had the highest thermal quality of the habitats we monitored and had the highest density of lizards. Our findings suggest these lizards experience lower predation pressure in town, possibly contributing to their high densities and a diet shift from large harvester ants towards smaller ants (Pheidole, Dorymyrmex spp.) and surface-foraging termites (Tenuirostritermes cinereus). The long-term survival of these populations remains uncertain due to small effective population sizes and ongoing habitat degradation. Kenedy, named the “Horned Lizard Capital of Texas” in 2001, lost most of its lizard population by 2019, while Karnes City also experienced declines. In some cases, these declines were caused by large construction projects like the construction of a new prison and in other cases efforts to “clean-up” alleyways and parks resulted in a 79% decrease in the number of lizards in areas that experienced vegetation and brush pile removal. Texas horned lizards are considered a highly desirable species by most residents, however there will need to be effective landscaping and continuing education to maintain suitable habitat and corridors to ensure this species remains in these towns.