D3407: Investigating harvester ant seed foraging for improving rangeland restoration

Overgrazing by livestock and extreme drought have contributed to degradation of rangelands in the southwestern, United States. Rangeland restoration with native plants is crucial to offset losses, but there are many challenges, including harvester ants (e.g., Pogonomyrmex spp.). While harvester ants may pose challenges for restoration, they are keystone species due to their trophic interactions and ecological engineering. Therefore, rather than managing harvester ants to improve reseeding efforts, restoration projects may seek to avoid seeding in areas with high harvester ant colony density or to seed plant species not preferred by harvester ants. In this project, we assessed harvester ant seed preferences and temporal dynamics. Experiments were established at two sites in New Mexico: Las Cruces (Chihuahuan Desert) and Corona (grassland/juniper), using both biased and unbiased sampling designs. In the biased design, seed cafeterias with 50 seeds each of Bouteloua eriopoda, Oryzopsis hymenoides, Ratibida columnifera, and Sprorbolus airoides were placed 3 m from a P. rugosus colony for 24 hours, after which cafeterias were collected and remaining seeds counted (10 replications). For the unbiased design, a 100 m x 100 m grid (nodes spaced at 25 m – 25 sampling points total) was established in an area with mapped harvester ant colonies. Cafeterias were collected and the remaining seeds were counted after 24 hours. Trials were conducted in July, August, September, and October 2024. Ants harvested more seeds on in the biased experiment and took more seeds in August. This project will provide information to facilitate improved restoration via seeding.