CASTELLANO, M.J.*; VALONE, T.J.; Saint Louis University; Saint Louis University: Effects of Livestock Removal and Perennial Grass Recovery on the Lizards of a Desertified Arid Grassland

The effects of livestock grazing and desertification on birds, rodents and plants have been well studied. Herpetofuana, however, have received relatively little attention. In 1958 a livestock exclosure was established in the San Simon valley in southeastern Arizona. The valley has been subjected to open-range grazing by cattle since the late 1800’s. At that time the valley was described as grassland, but shortly after the introduction of cattle there was a change in vegetation. Now shrubs are dominant with only a few scattered perennial grasses. However, inside the exclosure perennial grass cover has significantly increased in comparison to perennial grass cover outside of the exclosure. Pit-fall trapping and mark-recapture on paired transects inside and outside of the exclosure was used to determine if this vegetation difference affected lizard abundance and diversity on two different soil-vegetation associations that occur at the site. While species richness did not differ across the exclosure fence, the abundance of Sceloporus undulatus and Uta stansburiana were significantly higher inside while Phrynosoma modestum was significantly more abundant outside the fence. Possible mechanisms for the differences in abundance that were tested include predation, temporal niche breadth and prey availability.