14 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 125 
but, if for no other than heuristic reasons, it cannot be accepted as the 
only possibility. 
There are two other possibilities not mutually exclusive that seem 
to us more likely. One is that lizards do not make an ecological unit. 
They, as a group, do not occupy a “lizard niche” that is subdivided 
among them; rather, the broad niche or niches that lizards occupy 
are occupied also by organisms of widely differing phylogenetic rela- 
tionships with the result that several lizards in the same habitat may — 
each have as its close competitors animals that are not lizards at all but 
other vertebrates or even invertebrates. It may not be coincidental that 
the most convincing studies of interspecific competition and mecha- 
nisms for reducing it in lizards come from the arid areas of North 
America and from those areas of the West Indies where lizards are 
very abundant both as individuals and species and play an important 
role in the trophic ecology. Certainly, one has the impression in the 
Belém area that inside the forest the disappearance of all lizards would 
not greatly upset the forest ecological economy if at all. 
The relative rarity of lizards in the Belém forests suggests another 
possible explanation for the apparent lack of regularity in interspecific 
relationships. This is that populations of lizards are held at such 
low levels (perhaps by predation) that the populations never reach 
densities wherein interspecific competition for food or space occurs. 
It may be relevant that forest lizards are most common in the park 
areas, where many of the larger predatory birds, mammals, and per- 
haps snakes are rare or absent; these are also areas where the 
number of competitors may also be reduced. 
Certainly, it is striking how little agonistic behavior one sees among 
iguanids in the Belém forests. This is in contrast to desert iguanids and 
those in the West Indies, where fighting or displaying between males 
is a common sight. One has the impression that the problem the 
forest lizards are usually faced with is not that of spacing out the 
population to avoid overcrowding but rather that of bringing together 
mates at the proper time. Among Plica umbra, Anolis punctatus, and 
Gonatodes humilis, we have the impression that we found individuals 
of the opposite sex near one another more often than we would have 
expected on chance alone. It may be that these lizards form pairs or 
at least that males and females permanently establish adjacent or 
overlapping home ranges in preference to living solitarily. The 
absence of territorial defense and the large amount of potential home 
range that seems unoccupied suggest that population densities are 
so low that direct intraspecific competition for exhaustible resources 
is nonexistent, and it also suggests that probably there is no inter- 
