1976] 
Bernstein — Polymorphism in an Alpine Ant 
183 
Because no correlation was found between forager size and 
foraging height (which should reflect different temperatures and 
humidities at a given time of day), the observed change in forager 
size and color with time of day is likely to be the effect of changes 
in the amount of solar radiation. This interpretation is strength- 
ened by the fact that all of the samples taken in June, when light 
intensity is lower than in later months (Taussig, 1962), lie below 
the line of best fit. 
Discussion 
Each colony of F. neorufibarbis gelida consists of a mixture of 
both red and dark foragers, the red tending to be larger in size than 
the dark. As foraging progresses through the morning, the pro- 
portion of large, red foragers increases. It seems likely that the 
small, dark forms have an advantage early in the day, in that they 
are able to warm up more quickly so that foraging can begin. As 
solar radiation increases throughout the morning, the advantage 
shifts to the larger, red forms because a larger body tends to heat 
up more slowly and the red color probably reflects more solar 
radiation than would a dark color. A colony made of both forms 
of foragers is able to withstand greater variations in solar radiation 
and therefore utilize more foraging hours per day than a colony 
containing only one form or the other. The lower foraging limit 
of this subspecies is about 12°C soil surface temperature (Taussig, 
1962); the upper limit is not known because foraging has never 
been observed to cease during the heat of midday. Taussig (1962) 
reports active foraging at a soil surface temperature of 52° C. 
Both small body size and dark color are characteristics of other 
high altitude insects and considered adaptations to cold tempera- 
tures (Mani, 1962). Another characteristic is that the activities of 
these insects are usually restricted to cold temperatures and they 
actually show a drop in activity during midday (Mani, 1962). The 
colonies of F. neorufibarbis gelida, however, were never observed 
to decrease their foraging activities during high environmental 
temperatures, a feature perhaps due to the presence, in these col- 
onies, of not only the small, dark individuals typical of alpine en- 
vironments, but also the large, red individuals. 
It is concluded from this study that the color and size differences 
observed in F. neorufibarbis gelida enable each colony to utilize 
a greater range of environmental conditions for foraging than if 
