NO. 3658 LIZARDS—-RAND AND HUMPHREY tia | 
There is a definite relationship, but not unvarying, between thermal 
relationship and habitat used. The nonheliotherms are all inside the 
forest, and this is thermally the most constant habitat. The heliotherms 
occur in the more extreme environments in clearing, second growth, 
and canopy. One species of heliotherm, however, is almost entirely 
restricted to the area within the forest (Hentropyx), where it basks 
in the numerous patches of sun that reach the forest floor. 
URANOSCODON PLICA UMBRA 
SUPERCILIOSA 
ANOLIS ANOLIS 
FUSCOAURATUS PUNCTATUS 
| 
POLYCHRUS CNEMIDOPHORUS 
MARMORATUS LEMNISCATUS 
Ficure 2.—Temperature relationships in Belém lizards: Cloacal temperature plotted 
against ambient air temperature at time of capture (temperatures in centigrade of just- 
captured lizards in natura! habitat during day). 
It should be noted from figure 2 that, under the conditions tested, the 
nonheliotherms in the forest are about as homeothermic as are the 
heliotherms that practice behavioral thermoregulation outside the for- 
est (see Rand and Rand, 1966, for details of thermoregulatory behavior 
in Tropidurus). It certainly seems likely that the body temperatures of 
the open habitat animals would fluctuate much more than they are ob- 
served to do if the lizards did not practice some sort of thermo- 
regulation. These data suggest that, if heliothermy has evolved to 
increase homeothermy rather than to produce high body temperature 
per se, then it has probably evolved in response to the fluctuating con- 
ditions in open environments. The data also suggest that the high body 
temperatures observed in heliotherms reflect the general principle 
