Demographic Analysis 
239 
Table 9. Survivorship of hatchlings maintained in outdoor enclosures at different densities 
(see Table 2 for experimental treatments). + = p <.l. Other significance value designa- 
tions as in Tables 4 and 5 (Chi square or Fisher exact probability tests). 
# Surviving 
First 3 Weeks 
of Experiment 
# Not 
Surviving 
Proportion 
Surviving 
A. Isolated Hatchlings 
early hatchlings 
(experiment 2) 
6 
3 
.67 
late hatchlings 
(experiment 1) 
6 
1 
.86 
B. Grouped Hatchlings 
early hatchlings 
(experiment 2) 
25 
2 
.93 
late hatchlings 
(experiment 1) 
*** 
15 
21 
.42 
C. Early Hatchlings (experiment 2) 
isolated hatchlings 
25 + 
3 
.67 
grouped hatchlings 
2 
.93 
D. Late Hatchlings (experiment 1) 
isolated hatchlings 
6 * 
1 
.86 
grouped hatchlings 
15 
21 
.42 
in both social and nonsocial contexts, the dis- 
plays are considered by most observers to be 
primarily involved in adaptive conspecific 
communication. Experimental evidence of 
their communicative functions is available 
(Hunsaker, 1962; Jenssen, 1970). 
The signature display of the side-blotched 
lizard Uta stansburiana is geographically 
variable (Ferguson, 1971). One possible ex- 
planation for this variability might be char- 
acter displacement (Ferguson, 1971 ; Brown 
and Wilson, 1956). Thus, in each “zone of 
pushup similarity” (Table 10) side-blotched 
lizards were sympatric with different spe- 
cies of iguanid lizards. In each zone a dif- 
ferent direction of evolutionary change might 
have resulted to render side-blotched liz- 
ards (1) distinct from those species most 
likely to be encountered, and (2) less likely 
to be involved in nonadaptive hybridization. 
Another possible explanation for geo- 
graphic variation of the signature display 
was the effect of plant density on the visibil- 
ity of Uta to predators and to each other 
(Aubert, 1966; Ferguson, 1971). Thus, in 
the deserts in which the lizards occupied 
sparsely vegetated habitats (e.g., Lahonton 
Basin and Mohave Desert), the display in- 
cluded only one or two brief pushup units. In 
those regions in which the lizards were more 
closely associated with heavier vegetation 
(e.g., Chihuahuan — desert grassland. Chap- 
arral), the display included four or more 
pushup units (Table 11). This suggested an 
alternative model relating the evolution of 
display complexity to predator avoidance and 
communication efficiency. 
The Model 
Two consequences of a lizard display are 
conspecific communication and predator 
detection. In the sparsely vegetated habitat, 
where visibility is good, a simple display will 
be as likely to catch the attention of a nearby 
resident conspecific as a more complex dis- 
play. However, the simple display will be 
more likely to escape the notice of a search- 
ing predator than a complex display for the 
