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movement and head amplitude changes 
through time are important considerations 
for defining a display. The head amplitude 
is the best single criterion of vertical body 
movement, whether it is effected by the neck 
muscles, forelimbs, and/or hindlimbs ; 
ideally, however, each group of effectors 
should be monitored for its contribution. 
My objective in a descriptive analysis is 
to isolate display elements that are stereo- 
typed in order to distinguish display types, 
and to place elements of display variability 
into recognizable categories. To formally 
categorize display stereotypy and variability, 
I suggest the following four concepts (Table 
1) : Intra-population stereotypy, intra-in- 
dividual stereotypy, intra-population vari- 
ability, and pattern variability 
Intra-population stereotypy refers to the 
permanent elements of a display behavior as 
performed by a population. These permanent 
elements form the core of a predictable and 
recurring pattern of movements and postures 
which define a display type. These elements 
may be used to distinguish one display type 
from others of a species’ repertoire. Display 
elements characterized by intra-population 
stereotypy promote species recognition. 
Intra-individual stereotypy refers to those 
elements of a display (especially the perma- 
nent elements) which are consistent for an 
individual, but are absent or show wide 
variability between members of a population. 
Consistent, individual-unique elements pro- 
mote individual recognition. 
The following examples demonstrate the 
concept of intra-individual stereotypy. Even 
though all observed A. nebulosus performed 
an identical signature display pattern (Fig. 
7A), each individual performed its display 
with a consistent duration which tended to 
be different from the display durations of 
the other lizards (Fig. 9). An analysis of 
variance showed that only 2 percent of the 
variability in display duration existed within 
groups and 98 percent between groups 
(Jenssen, 1971). Each lizard tended to have 
its own particular display duration. 
Stamps and Barlow (1973) also found a 
very stereotyped bob pattern for the signa- 
ture display of A. aeneus. The duration of 
each display unit for the overall aeneus 
pattern was fairly constant within individ- 
uals, but varied much more from one indi- 
vidual to another. 
Table 1. Proposed classification for partitioning stereotypy and variability in lizard 
behavior. 
Term 
Defining Characteristic 
Possible Function 
Intra-population 
Stereotypy 
Any element of a display which reflects 
population-wide stereotypy, is species 
unique, and helps define the core dis- 
play. 
Can facilitate species recogni- 
tion. 
Intra-individual 
Stereotypy 
Any element of a display which exhibits 
little intra-individual variability and 
much interindividual variability. 
Can facilitate individual rec- 
ognition. 
Intra-population 
Variability 
Any element of a display which exhib- 
its much intra-individual variability 
and little interindividual variability. 
Can provide information on 
relative level of arousal. 
Pattern Variability 
Variation in the stereotyped portion of 
the population’s display sufficient to 
disrupt that pattern, as produced by 
(a) a few population members on oc- 
casion, or (b) all population members 
consistently. 
Function of variability not 
apparent; may denote (a) 
anomalous behavior or (b) 
relaxed selection pressure 
for stereotypy. 
