Relationship of Diet to Body Size in Texas Horned Lizards (Phrynosoma cornutum)

Abstract

Age determination is important when monitoring populations of conservation concern. Reptiles often have a positive relationship between age and snout-to-vent (SVL) length and so one can get an estimate of the age distribution of individuals in a population based on their size. Texas horned lizards are a threatened species in the state of Texas yet they are highly cryptic and difficult to find. Horned lizard scat on the other hand is relatively easy to find and recognize. We used the length of scat we found to determine if it was correlated to the SVL of its respective horned lizard. We first genotyped DNA extracted from individual scat to match them to previously captured and measured horned lizards. We found that as feces length increases, the SVL of the same horned lizard also increases. We then used this relationship to reconstruct the size distribution of the population using only feces and compare it to the size distribution of captured lizards. Collecting data on the size of Texas horned lizard feces may provide a relatively easy method to determine the size distribution of horned lizards in a population, especially in areas that need to be quickly or sporadically surveyed.