Mound Dispersion and Population of Formica exsectoides Forel (hymenoptera: formicidae), and an Evaluation of the Accuracy of Using the Lincoln Index to Estimate the Population of Ground Dwelling Ant Nests

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Mound dispersion of Formica exsectoides Forel was determined in two plots in Michaux State Forest, Franklin County Pennsylvania by measuring nearest-neighbor distances and calculating indices of dispersion. Dispersion indices in both plots indicated significant clumping of nests. Dispersion indices calculated from subplots of the main plots indicated random dispersion, illustrating the importance of scale in the use of nearest neighbor analyses. Behavioral observations using mark-release-recapture (MRR) techniques indicated clump, but not mound, fidelity by workers. There was no agonistic behavior between workers from different mounds or mound clumps. Population estimates of eighteen F. exsectoides mounds calculated through the use of MRR methods and the Lincoln Index (LI) were compared to actual counts from excavated mounds. Counts of ants collected from excavated mounds averaged 24,964 workers/mound. An average of 83.8% of marked ants were recollected during excavations. When only workers collected on a mound surface were used to calculate the LI, estimates of worker population averaged 8,306 workers. When the LI was calculated from all ants collected during excavation, estimated worker population averaged 29,923 workers/mound, indicating an average of 29.4% of the worker population worked on the mound surface during our sampling period. We found a high correlation (R2 = 0.96) between estimated forager population and estimated total worker population.