10 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 125 
environment from the lizard’s point of view. They have been called the 
lizard’s “structural niche” (Rand, 1964). When the term was pro- 
posed for West Indian anoles, it was found that certain measurements 
of the perches on which the lizards were seen provided a useful descrip- 
tion. Though the concept of structural niche seems useful for Belém 
lizards, measurements used for West Indian anoles are not sufficient 
and other environmental parameters must also be considered. In the 
case of Uranoscodon superciliosa, the proximity of water seems im- 
portant. No system of quantifying the various aspects of structural 
niches was devised, and they have been described verbally in the fore- 
going species accounts. 
Another set of parameters, in addition to structural niche, must be 
considered in describing the ecological distribution of lizards. These 
can be grouped as the lizard’s “climatic niche.” There are a variety of 
environmental factors that show parallel gradients here, among them 
insolation, light, temperature, and humidity. In general, one set of 
extremes for all these factors in the area is reached on or near the floor 
of the mature forest, and the other set is reached on the ground in 
clearings devoid of vegetation. Edges, second growth, and the top of 
the canopy show intermediate conditions. 
The various lizards arrange themselves differently with respect to 
these gradients. To understand better the relationships of the lizards to 
the microclimates, we took a number of cloacal temperatures of the 
former while they were active in periods when the sun was shining; 
behavioral thermoregulation was possible at this time. In West Indian 
anoles similar data showed that the lizards in shaded habitats had 
lower body temperatures than those in open habitats (Ruibal, 1961; 
Rand, 1964). 
The Belém data are a bit more complicated. Figure 2 shows the body 
temperature plotted against air temperatures taken in the immediate 
vicinity at the same time. These plots suggest that there are two very 
different kinds of thermal] relationships represented among the Belém 
lizards : those whose temperature approximates that of the surrounding 
air and those whose temperature is much above it. A review of observa- 
tions made of the various species shows that those in the first class 
were not seen basking while those in the second class were observed 
with definite basking behavior. Regarding this behavior, it seems safe 
to conclude that the high temperatures of the second group are due to 
behavioral thermoregulation and that they are heliotherms while the 
other group is not—at Jeast at the ambient temperatures observed. 
(Since their temperature approximates the air and there is no evidence 
that they use substrates for thermoregulation, we prefer not to use 
“thigmotherm” but rather the more neutral “nonheliotherm.”) 
