1981] Ward — Rhytidoponera impressa. I 93 
DEGREES LATITUDE (South) 
Figure 1 . Altitude and latitude of 57 populations of confusa (open circles) and 34 
populations of chalybaea (closed circles). Regressions of altitude on latitude for 
confusa (upper line) and chalybaea (lower line) are highly significant (p < .001). 
rainforest gullies which are ecologically very disturbed, i.e. heavily 
encroached with introduced weeds such as Lantana, Ligustrum and 
Tradescantia. 
Sympatric associations between chalybaea and its sibling species, 
confusa, occur in some of these disturbed gully sites, with confusa 
preferentially occupying the vegetationally less disturbed portions 
of the gully. These two species also occur sympatrically in stands of 
undisturbed temperate and subtropical rainforest in northern New 
South Wales and southern Queensland. In this region chalybaea 
tends to occupy more xeric microhabitats than confusa, but in one 
locality (an isolated patch of rainforest at Boonoo Boonoo Falls, 
N.S.W.) no obvious nest site or microhabitat differences were found 
between the two species, which nested within a few meters of one 
another. 
R. chalybaea also shows an altitudinal shift with increasing 
latitude (Figure 1) and tends to occur at lower elevations than 
confusa. The general picture is one of partial ecological differentia- 
tion between these two species despite their very close morpho- 
logical resemblance (cf. Ward, 1980). 
