98 
Psyche 
[March 
(1975) found it to be common in the summer. McCluskey (1963) 
reported foraging in V. andrei on warm nights. P. californicus some¬ 
times works at night (Cole 1932), and P. rugosus does so when 
warm (Whitford and Ettershank 1975). 
Evaluation of variables as taxonomic characters 
By virtue of the replicates it was possible to test each variable for 
species difference by one way analysis of variance, or in the case of 
phase variables, by the circular distribution test of Watson and 
Williams (1956) (Table 1). The differences are significant for 42 of 
the 51 hourly and 18 of the 23 processed variables, suggesting value 
as species characters. The hourly variables for the last third of the 
day are more discriminating than those earlier. 
Thus most of the individual variables distinguish species at least 
in a general way. As a group would they distinguish between the 
members of each pair of species? Multidiscriminant analysis was 
used to answer this (somewhat as Brown and Shipp, 1977, did to 
evaluate wing morphometric characters). 
M. mimicus, with only one replicate, was omitted. Manova 
indicates a significant (P < .01) difference among the other five 
species, whether based on processed or on hourly variables. There¬ 
fore it is appropriate to use multidiscriminant analysis for further 
examination of the differences. For the set of processed variables. 
Figure 2 shows the maximum discrimination possible in two- 
dimensional space. The replicates are well segregated into their 
respective species. The same was true if based on either of the two 
stratified subsets of 17 hourly variables tried (not shown). Further 
analysis is not attempted here because of small sample size. 
The method was checked by deliberately assigning half the repli¬ 
cates initially to incorrect species. The variables then failed to segre¬ 
gate the replicates well into the artificial species, or even to show a 
significant species difference by MANOVA. 
Later experiment 
As laboratory projects in a comparative physiology course, the 
same species of Pogonomyrmex and Veromessor were compared 
simultaneously as before, but the conditions were different. Most 
notably, the season was October instead of May; and the tempera¬ 
ture was cycled between 20° C at night and 30° (35° in hottest part 
of arena) at midday, instead of being held constant. 
