1976] 
Bernstein — Polymorphism in an Alpine Ant 
181 
Methods 
The general ecology and thorax color of F. neorufibarbis gelida 
were examined at several different alpine tundra sites on the east 
slope of the Rockies during the summers of 1975 and 1976. Inten- 
sive study and data collections were from a single tundra site, Niwot 
Ridge, located approximately 20 miles northwest of Boulder, Colo- 
rado. This area is supervised by the Institute of Arctic and Alpine 
Research, University of Colorado, and therefore relatively undis- 
turbed by human activities. 
Weekly visits were made to the Niwot Ridge study site between 
June 21 and August 10, 1976. Records were kept of the number 
and color of foragers, type of food collected, the times of day when 
foraging took place and where the foragers searched for food. 
Developmental stages of the brood were observed by turning over 
rocks near midday, when the brood is brought to the surface of 
the nest. 
Samples of 20 foragers each were taken from various different 
foraging heights (ground, flowers, and shrubs of heights ranging 
from 20 cm to one meter) and at different times of-the day. Because 
several environmental factors, including light intensity, tempera- 
ture and humidity, change in a regular fashion with time of day 
when the effects of the sun are not obscured by clouds, all collections 
were made on cloudless days. The samples of foragers were then 
taken to the laboratory, the color of each individual noted, and its 
head width measured with a Lietz eyepiece micrometer. 
Results 
More than 85% of the food collected by the colonies on Niwot 
Ridge consisted of liquid material from plants. From the beginning 
of the season through peak flowering time, most of the food was 
nectar from flowers, primarily that of Acomastylis rossii. Later 
in the season, major foraging activity occurred on the stems of 
plants, where the ants sucked liquids from the area around the 
axil. Of the other types of food collected, seeds comprised less 
than 5% and dead insects about 10% of the diet. Regardless of 
the abundance of food, once the brood had matured, all foraging 
ceased for the season. 
Head width measurements of foragers with red thoraxes and 
of those with dark thoraxes were plotted according to frequency 
