Sociometry and sociogenesis of colony-level attributes of the Florida harvester ant (Hymenoptera : Formicidae)

This study addressed how collective, supra-organismal colony characteristic s change during growth (sociogenesis) from the founding queen to maturity a nd through the seasons. A total of 31 harvester ant colonies representing a full range of sizes was excavated on 4 sample elates during the lear. The data were analyzed for growth-related and seasonal patterns. The subterrane an nests consisted Of horizontal chambers connected by vertical tunnels. Th e total area of these nests increased more slowly than did the colony popul ation, leading to an increase in mean worker density, which also varied sea sonally. Nest area grew somewhat more rapidly through nest deepening and ad dition of new chambers than it did through the enlargement of chambers. The mean weight and headwidth of workers increased with colony size, but this size increase was limited to the minor workers. The major workers made up a pproximate to 7g of the worker population, a proportion that did not vary w ith colony size. The total weight and number of seeds stored by colonies in creased isometrically with colony size, so that the milligram of seeds per milligram of ant biomoss did not change. However, the weight of seeds incre ased more rapidly than did the population of dark (older) workers who colle cted them, so that the foragers of larger colonies each collected more seed s than their counterparts in smaller colonies. Lat ge colonies contained up to 300,000 seeds. Colonies of fewer than GO workers collected smaller seed s, but larger colonies showed no relationship between mean worker size and seed size. Brood production was limited to May-September. Sexuals were prod uced only in the early spring, before any workers, by colonies with >2,500 workers (approximate to 1/3 of maximal colony size). In the summer, colonie s of all sizes produced only workers. The seasonal patterns of colony. fat reserves suggest that colonies draw on these reserves to overwinter and pro duce sexuals, then they rebuild the reserves during the summer. The size of the fat reserves increased much more rapidly than did colony size, suggest ing that changes in colony composition and function lead to better nutritio n. All indicators of colony growth rate increased more slowly than did colo ny size. These included the ratio of brood to workers, callow workers to da rk workers, and the number of developing follicles in the queen's ovaries. These decreases were also reflected in raw birth rates (individuals per day ) that increased half as rapidly as did colony size, and colony growth rate s (percent per day) that decreased by half with each 10-fold increase in co lony size. These patterns are discussed in relation to colony function, ont ogeny and life history.