Reproductive potential of colonies of desert harvester ants (Pogonomyrmex desertorum): effects of predation and food.

To ascertain what factors affect reproductive output of colonies of the Desert Harvester Ant, Pogonomyrmex desertorum, colonies were subjected to two experiments. The first was a 3-way factorial design, which varied (i) artificial predation intensity, (ii) seed addition, and (iii) insect matter addition. The second experiment used fences to prevent horned lizards (Phrynosoma spp.) from foraging on concentrations of worker ants found at colony entrances. Increased artificial predation caused a decrease in alate production. The effect of predation was strongest in colonies also receiving insect matter. The treatments of adding seeds and adding insect matter by themselves did not have a measurable effect on alate production. Exclusion of horned lizard predators using fencing also had no effect on alate production. Although this study shows that predation has the potential to affect reproductive output (and therefore the potential to have been important in the evolutionary history of P. desertorum) the present study shows no evidence that either present levels of predation or scarcity of food limit reproductive output.