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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.

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