Mirkin Stephen, Tucker Mary R, Williams Dean A
Department of Biology Texas Christian University Fort Worth TX USA.
Ecol Evol. 2021 Mar 24;11(10):5355-5363. doi: 10.1002/ece3.7426. eCollection 2021 May.
Texas horned lizards () 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 suggest 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 ( = 126) and control pieces of foam ( = 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 ( = 1) compared with the ranch ( = 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.
德州角蜥有多种避免被捕食的方法，包括伪装、尖锐的头角、身体扁平化以及从眼睛喷血的能力。这些特征以及它们在野外相对较低的存活率表明这些蜥蜴面临着很高的捕食压力。由于城市化进程加快、农业发展以及猎物物种的减少，这些蜥蜴在其东部大部分分布范围内数量一直在下降。然而，在德克萨斯州南部的一些小镇上仍然可以找到它们，在这些地方它们的密度（约50只/公顷）比自然区域（约4 - 10只/公顷）高得多。我们推测在这些小镇观察到高密度的一个原因可能是捕食压力降低。我们使用德州角蜥模型来测试德克萨斯州南部两个小镇的捕食水平是否低于附近的牧场。我们用聚氨酯泡沫构建模型，这种材料非常适合保存捕食者留下的痕迹。在夏初和夏末，将模型（n = 126）和对照泡沫块（n = 21）分别留在每个地点的野外9天，随后根据捕食者类别对捕食痕迹进行分类。我们观察到模型上的捕食尝试明显多于对照，并且与牧场（n = 60）相比，小镇上的尝试次数明显更少（n = 1）。在牧场上，鸟类的捕食尝试似乎很常见，尤其是当模型颜色与土壤颜色不匹配时。我们的结果表明，具有合适栖息地和食物资源的人类改造环境可能为角蜥等一些猎物物种提供躲避捕食者的避难所。
