Home range, habitat use, and conservation of the Texas horned lizard (phrynosoma cornutum) in Central Texas

The Texas horned lizard (Phrynosoma cornutum) lives in a wide variety of habitats throughout its range. Although several studies have been conducted on the general ecology and home range for this species, none have been performed in central Texas – an area of special concern for this species as populations there have experienced sharp declines. I collected natural history and home range data at two sites in central Texas, Camp Bowie and Blue Mountain Peak Ranch, in order to understand how natural history characteristics may vary in this part of the species’ range from what has been recorded elsewhere. In general, aspects of the natural history examined (sex ratios, morphology, survival estimates), coincided with what has been previously found in other parts of this species’ range. Home range size also was within what has been previously reported, though home ranges of lizards at Camp Bowie appear to be largely confined to roads. Although little cause-specific mortality could be identified, road mortality has been substantial elsewhere and may be playing a role in the continued local decline of lizards at Camp Bowie. Habitat data were also collected at these sites. Habitat data were collected at both the microhabitat and macrohabitat level. Microhabitat data were analyzed primarily for ground cover using a Daubenmire frame and digital photographs analyzed in SamplePoint. Transect data ground cover was collected in the same way, along with measurements of other habitat variables along 100 m by 2 m transects. Overall, similar patterns of habitat use were observed between the two sites. At Blue Mountain Peak Ranch, lizards appeared to be located in areas with the mosaic of ground cover types observed in previous studies. Although similar results were observed at the macrohabitat level between sites, the mosaic of ground cover types is not as pronounced at Camp Bowie, limiting lizards to use of the roads and road margins. Prescribed burns could be implemented to create this preferred ground cover mosaic. In order to better understand what could be causing the range-wide declines observed, I also conducted a population viability analysis for this species. Life history data were obtained from the literature. I constructed a age-based matrix model to estimate population growth rate and conducted a sensitivity analysis to determine which ages are particularly important for population growth. Results show that P. cornutum populations are particularly impacted by survival of juvenile lizards and that populations do not likely have a high capacity for growth. Researchers should make a concerted effort to better understand the habits of young lizards – particularly dietary composition and cause-specific mortality – to gain further insight into the decline of this species.