Behavioral responses of a predator, the round-tailed horned lizard, <i>Phrynosoma modestum</i> and its prey, honey pot ants, <i>Myrmecocystus</i> ssp.

The round-tailed horned lizard <i>Phrynosoma modestum</i> was active and feeding throughout the day from 2 hr after sunrise until sunset. <i>Phrynosoma modestum</i> remained in the shade of large mesquite during midday where they preyed on honey pot ants (<i>Myrmecocystus depilis/mimicus</i>) which were foraging in the canopy and moving across the shaded substrate. <i>Phrynosoma modestum</i> fed at an average of 3.9 +- 2.2 ants bout-1 and average of 7.0 +- 1.7 bouts hr-1. The species diversity of the diet of <i>P. modestum</i> doubled (H' = 0.78 to H' = 1.41) following rainfall when many species of small ants extended their activity to overlap with the activity of <i>P. modestum.</i> Honey pot ants <i>Myrmecocystus mimicus/depilis</i> were, however, the only dependable prey. Simulated predation of 20 ants day-1 and 40 ants day-1 affected activity of <i>M. mimicus/depilis</i> , while simulated predation of 10 ants day-1 had no effect. We estimate that <i>P. modestum</i> removes approximately one-half of the early summer standing crop of <i>M. mimicus/depilis</i> during the summer.