23B 
Psyche 
[June 
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sunrise 
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Time of Day 
Figure 1. Activity patterns of the two ant species as observed in 1971. 
Solid line — solar intensity; dotted line — T apinoma antarcticum foraging 
activity; dashed line — Dorymyrmex antarcticus foraging activity. 
D. antarcticus. The Tapinoma workers continued on the bait 
throughout the midday, whereas the Dorymyrmex workers retreated 
to their nests, apparently to avoid the high midday temperatures. 
Late in the afternoon, as temperatures dropped, the Tapinoma 
workers would retreat to their nest leaving the bait to be reoccupied 
by Dorymyrmex workers. Activity at the bait seemed in general to 
parallel the apparent activity patterns of the species, which I illus- 
trated as in Figure i. The apparent tolerance of cooler temperatures 
granted an exclusive period of foraging activity to D. antarcticus ; 
aggressive dominance yielded foraging success for T. antarcticum 
during the period when both species were active simultaneously. 
In 1972 I documented these patterns quantitatively. Closely adja- 
cent nests of each species were chosen, and counts of workers passing 
the nest entrance during a two-minute period each half-hour were 
tallied with hand counters. Soil surface temperatures were monitored 
with a bulb-type thermometer placed touching the soil near the nests. 
Solar intensity values were taken from a pyroheliometer (Belfort 
Inst. Co.) stationed 150 m from the study nests. The pattern docu- 
mented for one nest of each species on 4 October is illustrated in 
Figure 2a. 
On the following day I returned to the same nests to document 
the early morning activity missed the preceding day. The patterns 
for 5 October are shown in Figure 2b. The day was cloudy and 
cool, and differences in foraging activities of the ants are of interest. 
The D. antarcticus continued active all day. The T. antarcticum 
workers emerged later and were out in fewer numbers than on the 
