1965] 
Taylor — Pristomyrmex 
53 
1 8 colonies listed were found in soil under or between stones, one was 
in a rotting log (RWT acc. 819), and one in a rotting wood frag- 
ment (RWT acc. 721). Nesting behavior thus contrasts with that 
of the sympatric bicolored form of quadridentatus , which has been 
found nesting only in rotting logs. Lowery’s six Cunningham’s Gap 
colonies each contained 18 to 36 workers and one queen. At Binna 
Burra I searched extensively for foragers of wheeleri but encountered 
only one (acc. 1210), which was taken two hours after sunset on top 
of a small rock, later found to shelter a colony. Foraging behavior 
presumably is unlike that of P. quadridentatus (see p. 48). 
Relationships. See below. 
DISTRIBUTION AND VARIATION IN THE QUADRIDENTATUS GROUP 
All known bicolored series of Pristomyrmex quadridentatus were 
collected in immediate geographical and temporal sympatric associ- 
ation with P. wheeleri , while the self-colored form has never been 
taken in such association. This correlation invites the hypothesis that 
character displacement of quadridentatus has occurred wherever the 
species is sympatric with wheeleri. 
Character displacement is the situation, usually involving several 
related species, where interspecific differences are more distinct in 
areas of sympatry than in areas of allopatry. This phenomenon has 
long been recognized, but was first crystalized by Brown and Wilson 
( 1956) , who reported its occurrence in birds, frogs, fishes, crabs and 
various insects. Subsequent reports involve many animal groups, 
including the South African cyprinid fishes, Barbus marequensis and 
B. natalensis ( Farquharson, 1962), the North American salamanders 
Plethodon cinereus (Green) and P. richmondi Netting and Mittle- 
man (Highton, 1962), the Central American iguanids. Basiliscus 
plumifrons Cope and B. vittatus Weigmann (Maturana, 1962), 
the East African gekkonids Holodactylus africanus Boettger and H. 
cornii Scortecci (Laurent, 1964), several pairs of Indian nuthatches 
of the genus Sitta (Ripley, 1959) and the New Zealand pelecypods 
Bassinia yatei (Gray) and B. parva Marwick, which apparently 
underwent displacement on becoming sympatric in the Lower Pleisto- 
cene (Fleming, 1959). Few of these cases have been studied in detail 
aimed at elucidating the selective significance of the displacement, 
though it seems clear that secondary reinforcement of premating 
isolating mechanisms, or special adaptation to greater niche specificity 
resulting from competitive displacement, are involved in some cases. 
This hypothesis is invoked to explain the origin of the bicolored 
form of P. quadridentatus on limited distributional evidence, which 
needs supplementation. A selective mechanism is difficult to envisage 
since there is no evidence that color is involved in interspecific relations 
