1.7 Friday, Jan. 4 Proximal causes of diet of in the lizard Phrynosoma platyrhinos in a northern desert scrub ANDERSON, R.A.; Western Washington University Roger.Anderson@wwu.edu
Knowing the spatiotemporal patterns, causes, and consequences for both predator and prey has been a persistent challenge for ecologists. Testing hypotheses about prey use and prey availability under field conditions has been problematic. A useful system for such work includes using desert ants as prey and the ant-eating specialist lizard, the Desert Horned Lizard, Phrynosoma platyrhinos. The lizard and its prey are abundant in the Great Basin desert scrub in southeastern Oregon, and have been studied for several weeks each summer over the past decade on a 9 ha area in the Alvord Basin. Four species of ants comprise 96% of the diet by number, as analyzed by fecal pellet analyses. These ants tended to be the largest and most common ants captured by pitfall trapping, about 87% of the total ants by number. Annually 10-12 lizards were radiotracked and powdertracked, and were observed to spend most of their activity period in the open and near plant perimeters where the colony entrances to three of the four common prey species were located. Phrynosoma platyrhinos were most active in mid-morning at the same time ants were most abundant near colony entrances. Based on powdertrack trails, we inferred that the lizards knew where the colonies were. These lizards seemed to be relatively efficient foragers, judging from the length of their activity periods and their daily feeding rates.