Response of small mammals in native tallgrass prairie to an invasive species, red imported fire ants (Solenopsis invicta Buren)

The red imported fire ant (Solenopsis invicta Buren) is an introduced predator that aggressively defends its mounds and foraging territories, adversely affecting many native species of vertebrates and invertebrates. Previous studies investigating the impact of imported fire ants on small mammals have produced inconclusive or contradictory results. At Leonhardt Prairie, a preserve in Falls County, Texas, owned by the Nature Conservancy of Texas, small-mammal populations were monitored in 3 pairs of plots from May 2002 through April 2004. One plot in each pair was treated with Distance RTM Fire Ant Bait to reduce the abundance of fire ants. Ant-foraging intensity measured every 6 weeks indicated ant abundance was significantly reduced in treated plots. In 39,168 trap nights, 1,530 cotton rats ( Sigmodon hispidus Say and Ord) were captured 5,947 times; 581 pygmy mice (Baiomys taylori Mearns) were captured 1,040 times; and 455 fulvous harvest mice (Reithrodontomys fulvescens J. A. Allen) were captured 915 times. Abundance, survivorship of adults and neonates, mean mass, growth rates, proportion of transients to residents, and mean squared distance moved (MSD, an index of home range) were compared between treated and control plots in each pair of plots. Cotton rats showed no response to the reduced abundance of ants in the treated plots compared to the control plots. For pygmy mice and fulvous harvest mice several comparisons could not be made for some time intervals or pairs of plots due to small sample sizes. However, the comparisons that could be made for these 2 species generally showed no response to the reduction of fire ants. The effectiveness of ant control in the treated plots was comparable to results of similar studies. Populations of common small mammals at Leonhardt Prairie do not appear to be affected by red imported fire ants.