Multi-scale Habitat Selection of the Texas Horned Lizard in Central TexasHistorically, the Texas horned lizard ranged across the state with a few exceptions in the far Eastern counties. In 1992 and '99, researchers conducted statewide surveys along with an examination of historical records and collections that led them to conclude lizard numbers are sharply declining and populations are becoming more fragmented, especially in the Eastern and Central portions of their range. This species is now thought to be absent from 30% of lands it once inhabited in Texas.
The state took measures to protect the species: declaring collection illegal in 1967 and listing the Texas horned lizard as threatened in 1977. Initially collection was a major contributor to the decline, but after legislation banned the practice, researchers began to examine additional causes. Habitat loss and alteration, widespread pesticide use, road mortalities, and the influx of red imported fire ants are all suspected to have detrimental effects on horned lizard populations.
Slowing or even reversing the decline is a top priority for conservation of the species. The Texas horned lizard fills a unique and valuable niche in this landscape. As a specialist species (75% of their diet is comprised of harvester ants), it has been suggested that horned lizards are more vulnerable to changes in the environment and therefore can be used as an indicator of the general health of terrestrial ecosystems in Texas. The residents themselves have shown a positive response to conservation of horned lizards which is crucial considering a large portion of their range is controlled by private land owners.
My research will be focused on two populations located on sites in Central Texas. Camp Bowie is a Texas National Guard training facility and Blue Mountain Peak Ranch is a privately owned ranch managed for outdoor recreation and conservation. As I mentioned earlier, Central Texas is one of the areas experiencing the largest declines but has been the least studied of the regions. Because the range of the Texas horned lizard contains a variety of habitat, it has been shown that the behavior and ecology of the lizards themselves vary as well from region to region. Although a number of previous studies have been published on populations of horned lizards from Southern and Western portions of the state, what was found to be true for those populations may not be true for our lizards in Central Texas.
There are a number of things we wish to learn from studying these horned lizard populations. First, we want to obtain basic ecology information: specifically, growth rates and home range sizes to add to the collection of life history data that already exists for horned lizards from other regions. The main focus of the study however, will be determining patterns of habitat use at two scales: the larger scale of home range selection and the smaller scale of microhabitat selection within the home range. This data will be used to formulate a habitat model for predicting presence of Texas horned lizards on other lands in Central Texas and identifying possible sites for re-introduction of the species. In addition to habitat composition, I will also examine both fire ant and harvester ant distribution in relation to our lizard locations. What I hope to discern is whether horned lizards are restricting their home range due to prey availability or if habitat suitability is exerting a stronger influence on their distribution. All aspects of this study will be useful for developing land management suggestions that will be beneficial to the Texas horned lizard. If private land owners are willing, their participation in the conservation of this species will be paramount.
