THEORETICAL CONSIDERATIONS OF DENSITY-DEPENDENT SPACING OF A MOUND-BUILDING ANT (FORMICA-ALTIPETENS)

Nests of the mound-building ant, Formica altipetens (Hymenoptera: Formicidae), exhibit a pattern of density-dependent spacing. This pattern is observed across 12 small sites (0·0625 and 0·16 ha) and one larger site (2 ha), where F. altipetens nest density varies from 0·01-0·10 nest m-2. Nests are clumped on sites where the average density is less than 0·02 nests m-2. Nests are regularly dispersed on all sites where the average nest density is greater than 0·02 nests m-2. Nest spacing is increasingly regular on sites where there are more ant nests. A simple model that includes both clumped dispersal and local competition during nest establishment also yields a density-dependent spacing pattern. The model consists of two basic parameters: the dispersal distance (D) and the nest territory size (T). A parameterization of the model where D = 10 m and T = 2·5 m explains 75·7% of the empirical variance in an index of nest spacing (the index of dispersion, R, from the Clark & Evans nearest neighbor distance analysis). The spatial patterns of F. altipetens differ quite strongly from "null" versions of the model (no competition with either random dispersal or clumped dispersal). Thus, a model that includes both competition and clumped dispersal explains the spatial arrangement of a mound-building ant in both a qualitative and a quantitative sense. © 1991 Academic Press Limited.