SPATIAL DYNAMICS OF COLONY INTERACTIONS IN YOUNG-POPULATIONS OF THE FIRE ANT SOLENOPSIS-INVICTA

Newly founded colonies of the fire ant Solenopsis invicta compete inte nsely by brood raids, which result in a rapid reduction of colony dens ity. Experimental plantings of colonies and analyses of sequential map s were used to examine the importance of spatial pattern in the dynami cs of young populations. Colony positions were initially clumped in na turally founded cohorts, but were regular in most mature populations. Incipient colonies planted in clumped patterns were more likely to eng age in brood raids than colonies planted in regular hexagonal patterns at the same average density. However, contrary to what would be expec ted if local crowding increased mortality no significant increases in spatial regularity were observed during brood raiding either in the ex perimentally planted populations or in a natural population of more th an 1200 incipient colonies. These results show that it may be difficul t to infer the degree of past or current competition by passive analys is of spatial data even when held experiments show that the probabilit y of mortality depends on local spacing.