SPATIAL MODEL FOR TERRITORIAL COMPETITION AND POPULATION-DYNAMICS IN THE FIRE ANT SOLENOPSIS-INVICTA (HYMENOPTERA, FORMICIDAE)

We developed a simulation model of monogyne red imported fire ant, Sol enopsis invicta, populations that operates by competitive interactions of individual colony territories. This model describes six major aspe cts of colony life history: nest founding, brood raiding, territory ex pansion, queen death, possible requeening, and colony death. Individua l colony territories are represented by rectangles, whose sides change independently depending upon the presence and size of neighboring col onies. Growing colonies try to occupy free space, while retaining squa re territorial dimensions whenever possible. The growth of fire ant po pulations in the model compared well with available field data. The mo del predicted that competitive exclusion caused by territorial interac tions should occur when areas reach 70-90% territory coverage. Several computer experiments were conducted with the model to examine the imp ortance of colony growth rate, brood raiding activity, and other param eters on the relative success of sequentially founding colony cohorts. A 1-wk advantage in founding generally increased the long-term surviv al of young colonies by 40-80%. We also examined the factors affecting average coverage of an area by colony territories. Maximum coverage w as achieved under a continuous influx of 50 queens/(ha.wk) or a single settlement of 1000 queens/ha; both values were much less than actual magnitudes of queen influx observed in the field.