Proceedings of 
the United States 
National Museum 
SMITHSONIAN INSTITUTION +« WASHINGTON, D.C. 
Volume 125 1968 Number 3658 
Interspecific Competition 
in the Tropical Rain Forest: 
Ecological Distribution 
Among Lizards at Belém, Para 
By A. Stanley Rand and Stephen S. Humphrey! 
The ecological differences between sympatric species have proved 
useful foci for ecological studies, particularly those with an evolu- 
tionary viewpoint. The information provided by such studies is 
relevant to considerations of interspecific competition and to the 
problem of the causes of tropical species diversity. In general, it is 
assumed that a species’ closest competitors in an area are its nearest 
relatives. This is probably true within generic and specific groups, 
but, as this study suggests, it may not be true for higher categories. 
Studies on the ecology of sympatric lizards (usually restricted to 
sympatric congeners) have been made at several localities by various 
workers, among them Milstead (1957), Inger (1959), Collette (1961), 
Rand (1964). Little has been published about the ecology of the 
lizards of lowland tropical forests and almost nothing about those in 
the rain forests of the Amazon. The study most comparable to the 
present one is that of Sexton, Heatwole, and Knight (1964) in 
Panama. 
*Rand: Smithsonian Tropical Research Institute, Balboa, Canal Zone; 
Humphrey: 612 Louisiana St., Lawrence, Kansas. 
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