Measurements from Antweb.org
Measurements of worker and sexual size were done on specimens from
Antweb.org; images were downloaded and measured using ImageJ2 v2.3.0
(Rueden et al. 2017) relative to the scale printed on the image. Head
width was defined as the width of the head as measured across the eyes.
To ascertain whether the data available on Antweb.org were
representative of natural variation, Pogonomyrmex harvester ant
samples from Antweb.org were compared to head width measurements that
were available from other sources. The overlap of worker size variation
as measured from Antweb.org was compared to that reported in a taxonomic
overview of the genus in North America (Cole, Arthur 1968). A t-test was
used to test whether the proportion of overlap between worker size
ranges from Antweb.org and Cole (1984) differed from 1. Note thatP. wheeleri measurements from Antweb.org (N = 2) did not overlap
Cole’s range and this 0% overlap was excluded from analysis.
Additional head width measurements were available from four species (N =
382 P. badius , N = 38 P. barbatus, N = 433 P. coarctatus ,
and N = 431 P. rugosus ). These additional samples were measured
optically using an SZX7 Stereomicroscope by Olympus with a Retiga 2000R
camera by Q-Imagine, and iSolutions Lite software by iMT Technology;
samples were from various colonies and populations sampled as parts of
other studies. Overlap of Antweb.org measurements with these more
exhaustively sampled species was qualitatively compared.