| Numerous studies indicate that many types of ants affect plant species composition and distribution in grasslands around the world. The red imported fire ant (Solenopsis invicta Buren) currently infests over 111 million hectares in the southeastern United States and is considered a major nuisance pest, yet there is little information on this species' effects on plant species composition or distribution. Results of a series of field and laboratory studies indicate that seeds of Monarda citriodora var. citriodora, a common aromatic annual forb, are collected by ants, not consumed, and discarded around the perimeter of mounds. The result is often a dense "ring" of Monarda plants growing around mounds the following growing season.; Field studies indicate that Ambrosia psilostachya and Solidago altissima may also form rings around fire ant mounds and be affected by ant foraging activities across larger areas. Other species, including Croton monanthogynus, Eustoma granidiflorum, Bifora americana, Chaerophyllum Tainturieri, Agalinis purpurea, and Schizachyrium scoparium var. scoparium showed differences related to mounds, disturbance type and/or the presence of foraging ants.; A computer simulation model was designed to estimate the area occupied by active and abandoned fire ant mounds and the canopies of Monarda rings. Results show that in heavily infested areas (1,000 mounds/ha) ant mounds account for an average of only 3-4% of available area with Monarda accounting for another 1-2%. The model also indicates that proper timing of ant suppression with Monarda seeding may reduce populations of both species simultaneously. Nevertheless, such losses in forage production area alone do not justify the costs of chemical treatments. |
