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Ferguson & Bohlen 
Table 3. Summary of social interactions of juvenile spiny lizards on 
Pottowattomee Co., Kansas, study area. 
Number of hours observed 5.8 
Dates observed 8/10-9/15/1972 
Number of interactions 12 
Percent of interactions aggressive 100 
Percent of interactions in which the larger lizard dominated 100 
Mean snout to vent length of combatants (range) 34.5 mm (26-55) 
Mean percent size difference of combatants (range) 22.8 (7-40) 
Mean percent size differences of combatants in most vigorous encounters 14.7 
Mean percent size difference of combatants in least vigorous 
encounters 26.8 
Probability that difference between mean percent size differences of 
combatants in more and less aggressive encounters is due to chance 
(Mann Whitney U-test) 0.055 
dominant, were between lizards significantly 
more similar in size than those involved in 
the eight less vigorous encounters (p=.055). 
The less vigorous encounters involved only 
a single chase by the dominant and did not 
result in the subordinate’s being chased from 
the view of the dominant. 
Another observation of interest was that, 
while a number of juvenile lizards of all 
sizes were present in the sector where obser- 
vations were conducted, the mean size differ- 
ence between interacting lizards was 23 per- 
cent (Table 3). Thus, the stronger aggression 
between size peers seemed to cause the size 
peers to disperse and reduce their probability 
of encounter. Interactions between juveniles 
of different sizes had less of a dispersal 
effect. Rand (1967) demonstrated similar 
size peer territories in juvenile Anolis lineo- 
topus lizards, in Jamaica. 
Effect of Density on Dispersal 
The effect of density and presumably 
higher rates of aggressive interaction on dis- 
persal was assessed by comparing the density 
change on “more crowded” sectors with those 
“less crowded” (Table 4). The criterion for 
a more or less crowded sector was arbitrary, 
and it differed in 1971 and 1972. We rea- 
soned that, if aggression between lizards 
was causing dispersal, more crowded sectors 
with higher rates of aggressive interaction 
should show more dispersal (or a greater 
lowering of density) than less crowded sec- 
tors, which might increase in density due 
to immigration. In both 1971 and 1972, 
early in the hatching season, the difference 
between crowded and noncrowded sectors in 
density change was in the predicted direc- 
tion but was not significant. Later in the 
hatching season the difference was highly 
significant and in the predicted direction, 
suggesting that dispersion was greater later 
in the hatching season than it was earlier. 
Effect of Density on Survival 
The effect of density and presumably 
higher rates of aggressive interaction on 
survival was assessed by comparing the sur- 
vival of lizards beginning on more crowded 
sectors with that of lizards beginning on less 
crowded sectors (Table 5). As in density 
change, survival was affected more by high 
initial density that occurred later in the 
hatching season, but only in 1972 was there 
a significant trend. 
Comment on Field Study 
The seasonal increase in population and 
its effect on both density change and sur- 
