Great Basin Naturalist


Little is known about the basic characteristics of the western harvester ant (Pogonomyrmex owyheei) in the absence of anthropogenic disturbances. We examined the role of P. owyheei as an agent of disturbance in an area of semiarid vegetation in central Oregon known as the Horse Ridge Research Natural Area (HRRNA) that has been largely free of livestock grazing and other significant anthropogenic influences for over 23 yr. We determined density and size characteristics of nest sites and estimate total area cleared by P. owyheei activities on HRRNA. From random sampling of twenty-five 0.04-ha plots we found a mean nest density/standard error of 1.6 (±0.16) nests/0.04 ha. Mean area cleared per nest site was 4.8 m2, which results in an estimated barren area of 46,080 m2 on the 240-ha HRRNA. Comparing our findings to others on P. owyheei and P. occidentalis, we found nest density and mean cleared area to be in the middle range of reported observations under a variety of land-use influences. The literature suggests that moderate disturbance may increase nest site density, but little relationship exists between disturbance history and mean size of nest sites.