Professor Brigham Young University, Utah, United States
Abstract: In western North America, novel fire regimes driven by invasive annual grasses have emerged, threatening the biological resilience and stability of desert ecosystems. Native consumers including ants and rodents likely have critical roles in defining native desert vegetation and plant invasion responses to these altered fire regimes. The objective of this study was to understand how western harvester ants (Pygonomyrmex occidentalis) in the Great Basin Desert respond to fires and rodent exclusion. In 2011, we created five 60m by 60m blocks that were each divided into four 30m x 30m treatments. Each block had a randomly assigned full factorial arrangement of treatments. The treatments for each plot, within the block, were either burned or unburned and either excluded rodents or allowed rodent access. In September 2022, eleven years after the treatments were established, we measured ant disc and mound size and density, along with a direct measure of ant activity in each treatment. The presence of rodents decreased ant activity by a factor of 1.4, while there were no noticeable effects of fire on ant activity. Fire increased mound density by a factor of 2.3 compared to unburned plots. Rodents decreased mound density 1.6-fold compared to when rodents were absent. Ant disk diameter increased due to rodent presence by a factor of 1.3. Rodent presence decreased ant mound diameter 1.1-fold compared to plots without rodents. Ant mound height decreased due to the presence of small rodents by a factor of 2.7 compared to rodent exclusion plots. The results suggest ants may benefit from more frequent fires while decreasing rodent populations also benefit ant communities.
