Behavior of a Predator and its Prey: The Horned Lizard (Phrynosoma Cornutum) and Harvester Ants (Pogonomyrmex Spp.)

Abstract

Horned lizards, Phrynosoma cornutum, were observed between sunrise and sunset in order to record the time spent at different behaviors and the prey taken. Two ant species, Pogonomyrmex desertorum and Pogonomyrmex rugosus, were the most important prey. The behavioral responses of these prey species were studied by subjecting them to varying levels of simulated predation. The lizards fed most often on ants that were not associated with nest discs or foraging columns and took only a few ants at any one place. Lizards moved on average of 46.8 m/d, remaining in the vicinity of any group of ant nests <15 min. In artificial predation experiments, Pogonomyrmex desertorum ceases activity for periods of up to 5 d following losses of °25% of the forager population when foragers were removed at a rate of 5/d or 10/d. Pogonomyrmex rugosus did not respond to loss of 25% of the forager population, ceased activity of losses of 50% of the forager population, and exhibited frenzied activity upon loss of 75% of the forager population. The horned lizards have evolved a foraging strategy that allows maximization of prey availability over weeks or a month rather than per hour or day. Estimates of horned lizard densities, ingestion rates, and numbers of potential prey suggest that horned lizard numbers are regulated by the availability and productivity of Pogonomyrmex spp. These estimates also suggest Pogonomyrmex spp. colonies are extremely productive, essentially replacing the entire worker population each year.