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Jenssen 
The result is infrequent anomalous display 
performances. 
Pattern variability can also occur at the 
population level in two forms. First, a species 
may not have enough permanent display 
elements to produce a consistent display pat- 
tern. This situation is expected to be rare 
and could result if selection pressure for 
stereotypy has become relaxed, resulting in 
unexplained variability in the display behav- 
ior. Second, members of a population may 
have many permanent elements of their dis- 
plays not interindividually shared, so that 
there is no single core display pattern held 
in common by the population. The latter 
situation is an extreme case of intra-individ- 
ual stereotypy. 
As an example of pattern variability at 
the individual level, Jenssen (1971) found 
that approximately 7 percent of a population 
of A. nebulosus would occasionally vary the 
pattern of their signature display by deleting 
the first dewlap pulse or sandwiching a third 
pulse between the usual two (Fig. 12). This 
is an instance of pattern variability since 
these same animals would also perform the 
species-typical signature display pattern. 
The altered signature display pattern was 
in no way shared by the population as a 
whole and thus was not a case of intra- 
population variability or another display 
type. It is considered anomalous behavior. 
Another example of occasional pattern 
variability by a minority of population mem- 
bers is provided by Stamps and Barlow 
(1973). The normal A. aenem signature dis- 
play pattern of a male was altered by unit 
deletion. 
An example of pattern variability at the 
population level is provided by A. opalinus 
which shows population-wide disruption of 
display patterning (Jenssen, in press). Fig- 
ure 4 illustrates some displays by a male. A. 
opalinus ; these inconsistent patterns are nor- 
mal for the species. Not one discrete stereo- 
typed bob pattern was found for the species 
after analyzing 639 filmed displays. Bobs per 
display were quite variable. This in itself 
does not preclude a stereotyped display pat- 
tern. For instance, Jenssen and Hover (1976) 
found A. Umifrons had a predictable seven- 
bob display cadence to which optional num- 
bers of bobs can be added (dynamic modi- 
fier). However, no such core of stereotyped 
cadence or patterns was detected for A. opali- 
nus. For example, in one eight-bob display, 
a male distributed the bobs in a double- 
single-double-triple pattern. In another eight- 
bob display he performed a single-triple- 
quadruple cadence. The interbob pauses do 
not maintain any consistent proportionality 
between displays for this species. 
To this point I have stressed a descriptive 
approach for separating the display behavior 
of anoles. This is the first step of any taxo- 
D 
Figure 12. Four signature display patterns ob- 
served in Anolis nebulosus. Upper block repre- 
sents head amplitude movement through time, and 
lower block represents dewlap extension through 
time. Normal signature display pattern (A). 
Deviations from the normal signature display 
pattern (B, C, and D). 
