1981] 
Mac Kay — Nest Phenologies of Pogonomyrmex 
63 
with P. rugosus (Figure 10). Pogonomyrmex montanus, and to 
some extent P. subnitidus, are in habitats with winter snow cover. In 
such habitats foraging during the winter is not possible. Pogono- 
myrmex rugosus occupies a low altitude habitat where there are 
many warm sunny days during the winter. During these days, it does 
not forage, although a few workers are on the nest surface either 
sunning themselves or working on nest reconstruction. 
The higher altitudes had shorter growing seasons, resulting in 
fewer annual seed producing plants. As a result P. montanus and P. 
subnitidus foraged on various materials but began to rely heavily on 
seeds later in the year (Figure 13). This was especially the case in P. 
montanus, which relied heavily on plant parts early in the year. 
Later when seeds became more available, they almost completely 
replaced plant parts in the diet (Figure 13). 
Allocation of resources between worker and reproductive produc- 
tion. 
As was expected, the highest altitude species was exposed to a 
shorter foraging season, but this did not result in lower production. 
The highest altitude species, P. montanus, invests a larger propor- 
tion of energy into production than do the other two species. The 
amount invested in reproductives is especially high (Table 4). 
Pogonomyrmex subnitidus and P. rugosus invested about equally in 
production, with investment in reproductives very low compared to 
P. montanus (Table 4). 
Most Pogonomyrmex spp. are low altitude desert species (Cole 
1968). Pogonomyrmex montanus appears to be in a marginal 
habitat for Pogonomyrmex spp. in that it occurs in a high altitude 
pine forest. The nest populations are among the smallest for the 
genus (Table 3) and the nests are also very shallow (Appendix 1). 
Both P. montanus and P. subnitidus have shorter foraging seasons 
and apparently are not able to exploit their optimal food source 
(seeds) until late in the season (Figure 13). Simulations of the effects 
of bad years on the nests indicate that P. rugosus and P. subnitidus 
are able to withstand moderately large reductions in food input 
whereas P. montanus is not (MacKay in prep.). As a result, nests 
may be short-lived as compared to the other two species and nest- 
extinction may be a common phenomenon. Apparently, as a 
response to such conditions, P. montanus invests a larger propor- 
tion of energy in the production of reproductives than do the other 
