Predation release of Texas horned lizards (Phrynosoma cornutum )
living in small towns
Stephen Mirkin1*, Mary R. Tucker2,
Dean A. Williams3
1Department of Biology, Texas Christian University,
Fort Worth, TX
*Corresponding author
Abstract: Texas horned lizards (Phrynosoma cornutum ) have a
number of ways to avoid predation, including camouflage, sharp cranial
horns, flattening of the body, and the ability to squirt blood from the
eyes. These characteristics and their relatively low survival rates in
the wild suggests these lizards are under high predation pressure. These
lizards have been declining in much of their eastern range due to
increased urbanization, agriculture, and loss of prey species. However,
they can be still be found in some small south Texas towns where they
can reach densities that are much higher (~50
lizards/ha) than in natural areas (~4-10 lizards/ha). We
hypothesized that one reason for the high densities observed in these
towns may be due to reduced predation pressure. We used model Texas
horned lizards to test whether predation levels were lower in two south
Texas towns than on a nearby ranch. We constructed models from urethane
foam, a material that is ideal for preserving marks left behind by
predators. Models (n = 126) and control pieces of foam (n = 21) were
left in the field for 9 days in each location in early and late summer
and subsequent predation marks were categorized by predator taxa. We
observed significantly more predation attempts on the models than on
controls and significantly fewer attempts in town (n = 1) compared to
the ranch (n = 60). On the ranch, avian predation attempts appear to be
common especially when the models did not match the color of the soil.
Our results suggest that human modified environments that have suitable
habitat and food resources may provide a refuge for some prey species
like horned lizards from predators.