1982] 
Cole — Sawgrass-Inhabiting Ants 
355 
with another species of ant, there is at least one intervening, empty 
internode between S. picta and the other species. 
Of the total sawgrass culms, 71% are occupied by at least one 
species. Let C be the average probability that a species will colonize 
a sawgrass culm and E be the average probability that a colony will 
go extinct. Then the equilibrium fraction of sawgrass culms occu- 
pied is C/ C+E = 0.7 1 . One can then obtain an estimate of the rate of 
extinction relative to the rate of colonization as C = 2.5E. 
If colonization takes place on an annual cycle, then one can esti- 
mate that the average lifespan of a colony which becomes estab- 
lished is about 2.5 years. This estimate assumes that the occupancy 
of sawgrass culms is at equilibrium. In addition, data from several 
species, each of which may not have the same demographic charac- 
teristics, are combined. This is not as bad as it seems, however, due 
to the fact that the bulk of the species’ occurrences are of P. pallida. 
The estimate of average colony longevity is principally an estimate 
based on P. pallida. 
The inside diameter and position of the lower nest chamber of P. 
pallida colonies that inhabit two internodes is comparable to the 
inside diameter and position of the internode occupied by P. pallida 
in a single nest chamber. This suggests that P. pallida move up to 
occupy a second internode. The fact that the queen of P. pallida 
tends to be found in the upper chamber suggests that the queen 
moves into the newer, smaller or higher nest chamber. 
The average inside diameter of sawgrass culms occupied by Z. 
varians (3.13 mm) is not significantly different from the average 
inside diameter of hollow stems of red mangrove occupied by Z. 
varians (2.95 mm, Cole 1979, n = 1 14, t s = 0.94, p > 0.2). The major 
workers of Z. varians are morphologically modified for passive col- 
ony defense (Wilson 1976, Cole 1980). It is reasonable to suppose 
that there is selective pressure of Z. varians to choose, as nest sites, 
hollow stems that are of a suitable size to allow the major workers to 
block off the stem and bulldoze out intruders. 
This research supported, in part, by a grant from Sigma Xi. 
References 
Cole, B. J. 1979. Assembly of mangrove ant communities. Ph.D. dissertation. 
Princeton University, vi + 123 pp. 
