Demographic Analysis 
235 
Table 4. Ratios of final density to initial density of juvenile spiny lizards on “crowded” 
versus “noncrowded” sectors of a 4-acre study area in Pottowattomee Co., Kansas. Sig- 
nificant differences between density changes of crowded and noncrowded sectors indicated 
as follows: **p<.01, ***p<.001 (Chi squared test). 
# of Lizards at # of Lizards at 
Beginning of Interval End of Interval 
“to” “tl” #ti/#to 
1971 A. Late July to Late August Interval: 
# of crowded sectors 
(>12 lizards/6400 ft.^) 
9 
152 
147 
0.97 
# of non-crowded sectors 
(<12 lizards/6400 ft.*) 
15 
77 
92 
1.19 
1971 B. Late August to Late September Interval: 
# of crowded sectors 
(>12 lizards/6400 ft.^) 
7 
140 
88 
0.63 
# of noncrowded sectors 
(<12 lizards-6400 ft.*) 
17 
105 
** 
187 
1.78 
1972 A. Late July to Late August Interval: 
# of crowded sectors 
(>3 lizards/6400 ft.*) 
8 39 
33 
.85 
# of noncrowded sectors 
(<3 lizards/6400 ft.*) 
12 
24 
24 
1.00 
1972 B. Late August to Late September Interval: 
# of Crowded Sectors 
(>3 lizards/6400 ft.*) 
7 41 29 .71 
# of crowded sectors 
( <3 lizards/6400 ft.*) **♦ 
11 20 61 3.05 
vival can be attributed to an increase in 
competition for limited resources. However, 
because we feel that the most important 
source of mortality was predation (Ferguson 
and Bohlen, 1972) and some predators are 
known to influence their prey species in a 
density dependent fashion (Tinbergen, 
1960), we cannot rule out the possibility 
that the above effects are due to a shift in 
the importance of different predator species. 
Thus, high predation by toads early in the 
season would not show a density-dependent 
effect. Toads are largely nocturnal predators, 
but in August they concentrated around the 
shadier parts of the study area in the day- 
time in numbers that seemed sufficient to 
affect the lizard population density. On sev- 
eral occasions a toad readily devoured a 
tethered lizard offered to it on the end of 
string. Later in the season, a possible in- 
crease in the abundance of birds preparing 
for fall migration could increase the den- 
sity-dependent effect that birds are known 
to exert on their prey. 
