Appendix II: Principal components analysis of ant morphological traits
Principal components analysis (PCA) based on a correlation matrix in JMP (SAS Institute
2007) was used to describe ant species, based on continuous morphological traits.
Untransformed trait values were used for this analysis and the first four principal component
axes were plotted to evaluate the differentiation of ant subfamilies in this study in
morphospace.
The first four principal component axes were used to describe ant assemblages, based on their
morphology (Fig.s S1a,b, Table S2). Of these axes, PC1 explained 91.9% of the variation in
the data because it described assemblages in terms of body size. Larger ants in the
subfamilies Myrmeciinae and Formicinae showed greater values on this axis, while many
species in the Myrmicinae and Dolichoderinae were small. PC2 (3.3% of variation) was
positively related to eye position, with ants with dorsally (as opposed to laterally) positioned
eyes high on PC2. Dolichoderine ants were high on this axis, while Rhytidoponera and
Amblyopone had low values. PC3 (3.0% of variation) described ‘limb’ length, with ants with
long femurs and scapes and short mandibles high on this axis. Formicines and some
dolichoderines had relatively longer limbs, while Myrmecia had relatively short limbs.
Species such as Amblyopone australis, with broad heads, but small eyes were high on PC4
(1.0% of variation), while the large eyed Myrmecia were low on this axis. Myrmicine ants
were centrally positioned for all measures.
Broad patterns across subfamilies were also apparent for sculpturing and pilosity (Fig. 1c),
with smoother cuticles apparent in the Dolichoderinae and Formicinae and rougher cuticles in
the Myrmicinae, Heteroponera and Rhytidoponera. Patterns for pilosity were less clear, but
Rhytidoponera were relatively hairless, while Heteroponera were most pilose and other taxa
were clustered at intermediate levels of pilosity. These similarities in morphology within and
differences among subfamilies suggest a strong possibility for phylogenetic relatedness to
drive trait associations, which we considered by using both phylogenetically adjusted and
unadjusted regressions.
Table S1: Principal components axes for continuous traits. All values were residuals on the
regression with Weber’s length. Values greater than 0.3 are presented in bold and are
interpreted as having meaningful contributions to the axes.
Trait
Weber's length
Femur length
Head width
Mandible length
Eye width
Eye position
Scape length
PC1
0.39
0.39
0.38
0.37
0.38
0.35
0.37
PC2
-0.16
-0.16
-0.20
-0.07
0.04
0.90
-0.28
PC3
0.01
0.36
-0.28
-0.62
-0.20
0.15
0.59
PC4
0.20
-0.06
0.68
-0.20
-0.64
0.15
-0.12
Figure S1: Principal components analysis of continuous morphological traits of pitfall-trapped ants in grassy woodlands, showing the
distribution of subfamilies: a) PC1 vs PC2; b) PC3 vs PC4; and c) mean ± SE pilosity and sculpturing for subfamilies. Trait contributions to
PCA axes are shown in Table 2. Large ants are positioned high on PC1; ants with eyes positioned dorsally (rather than laterally) are high on
PC2; ants with long ‘limbs’ (femurs and scapes) and short mandibles are high on PC3; species with broad heads, but small eyes are high on PC4.
a) 2
Amblyoponinae
Cerapachinae
Dolichoderinae
Ectatomminae
Formicinae
Heteroponerinae
Myrmeciinae
Myrmicinae
Ponerinae
c) 3.5
b) 1
3
0.5
0
-1
2.5
Sculpturing
PC4
PC2
1
0
2
1.5
1
-0.5
0.5
-2
-1
-4
1
6
PC1
11
0
-2
-1
0
PC3
1
2
0
1
Pilosity
2
3