NO, 3658 LIZARDS—-RAND AND HUMPHREY 13 
tropyx calcaratus. Tupinambis is several times the size of the others 
and as an adult takes much larger food. Another suggestive case is the 
two forest Anolis that occupy very similar structural and climatic 
niches but differ sharply in size. The third case is the difference between 
Polychrus and Iguana, the two lizards of the tree crowns. It seems un- 
likely that this size difference is related to food competition since 
Iguana is largely and Polychrus is partly herbivorous. 
There is no evidence of the sort of temporal replacement during the 
day that Inger (1959) recorded in forest skinks in Borneo. Diurnal 
versus nocturnal replacement (perhaps involving the large nocturnal 
trunk gecko of the forest, Thecadactylus rapicaudus) is possible, but 
it is an unstudied problem. 
The only major diet difference we now know (our examination of 
stomach contents has been limited and casual and there is much still to 
be learned) lies between the two species that regularly take a consider- 
able amount of leaves and flowers, 7guana iguana and Polychrus mar- 
moratus, and the remainder, which take largely or exclusively animal 
food. This diet difference plus the difference in structural niche sepa- 
rate the two herbivorous species very sharply from the rest. 
To return to microdistribution as a mechanism for reducing species 
competition, there is considerable difference among species with respect 
to structural niches as there is with respect to climatic niches. Taken 
together, the microdistributions (fig. 1) do not show a regular pattern 
of replacement of one lizard by another because of the presence of 
overlaps between species (e.g., Plica umbra and Anolis punctatus) and 
of gaps between others (e.g., Uranoscodon and T'ropidurus torquatus) 
in distribution. Since there is a lack of regular replacement, micro- 
distribution does not suggest itself as an important factor in reducing 
interspecific competition among the lizards in general, though it may 
be so between certain species. As we have discussed, our observations 
on other strategies for reducing possible interspecific competition sug- 
gest that, even when all are considered together, no regular pattern of 
ecological separation among species appears. We are left with the im- 
pression, which we cannot prove rigorously, that the relationships of 
the lizard species to each other are not the over-riding factors in shap- 
ing their ecologies. 
There are several possible explanations. It may be that our data are 
so incomplete that we have been given a completely erroneous impres- 
sion. Further study may show that other species occur at Belém. This 
may fill the gaps in our picture and reveal differences among common 
species that would eliminate the apparent overlaps. Certainly, much 
more is to be learned and the latter possibility cannot be eliminated, 
