To seed or not to seed: Harvester ant grass seed preferences and the factors that influence preference

Overgrazing and extreme drought have contributed to the degradation of southwestern rangelands since the mid-1800’s, including rangeland grasses being displaced by shrubs. This has led to the loss of native biodiversity, reduced livestock carrying capacity, and increased soil erosion by wind and water. Rangeland restoration is crucial to offset losses, but there are numerous challenges to restoration. While harvester ants may be problematic for restoration projects, they are regarded as a keystone species due to their trophic interactions and ecological engineering, such as nest rims containing higher nutrient content than surrounding soils. To improve rangeland management seeding choices, we studied harvester ant preferences of 8 native grass seeds commonly used in rangeland restoration projects. We established cafeteria-style choice tests at harvester ant nests at the Jornada Long-Term Experimental Range, located northeast of Las Cruces, NM. We used pitfall traps at each cafeteria to capture all visiting arthropods, and pitfall trap contents were counted and keyed to species. We also measured grass seed removal at each cafeteria to quantify seed preference. Seed characteristics, soil type, and local plant community was described at each site to understand any variation in preference. Understanding harvester ant seed preferences will give us a better understanding of a prolific desert granivore and may improve rangeland restoration success by identifying patterns in harvester ant grass seed preference.