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[December 
benthos (Sanders, 1968, 1969) or coral reefs (Kohn, 1968) we 
expect closer packing and greater numbers of competitors per com- 
munity (Levins, 1968; MacArthur and Levins, 1967; Vandermeer, 
1970) with narrower realized niches and increased ecological dif- 
ferentiation and niche specificity (Whittaker, et ah, 1954; Klopfer, 
1959; Selander, 1965; Millar, 1969). 
Although species diversity varies from one community to the next, 
it is often greatest in the lower latitudes. Sanders (1969) incorpo- 
rates many of the earlier proposed explanations of differences in 
species diversity (Pianka, 1966; Paine, 1966; Connell and Orias, 
1964; MacArthur, 1965, 1969b) in his stability-time hypothesis. 
According to this hypothesis, the greater number of species in the 
tropics implies a greater number of biotic interactions than in the 
temperate regions. The results of competition would be most obvious 
in the form of niche divergence and increased specializations over a 
resource gradient. The corresponding decrease in predictability and 
stability of environmental conditions with an increase in latitude 
may mean that species in temperate regions are influenced more by 
the physical environment than by competitive interactions (Slobodkin 
and Sanders, 1969; Janzen, 1970). Realized niches may be smaller 
in the tropical or low latitudes than in higher latitudes because of 
the expected difficulties of specializing in an unpredictable environ- 
ment and of generalizing in an extremely diverse and competitive 
environment. The following investigation was undertaken in an 
attempt to determine the correctness of the premise that realized 
feeding niches are relatively more specialized in the tropical and sub- 
tropical latitudes than in the higher latitudes. 
Methods 
My approach was to choose a single taxonomic group that is cos- 
mopolitan, whose habits are relatively well known and which all 
nicely fall into a single ‘guild’ (Root, 1967). The 538 species of 
Papilionidae (Lepidoptera) of the world, based on Munroe’s classi- 
fication, met these criteria adequately. 
In order to analyze a niche breadth it was necessary to choose a 
criterion that could be compared over a range of latitudes and not 
one that varied between communities. Therfore, I investigated larval 
host plant relationships arbitrarily designating those species feeding 
on more than one taxonomic family of plants as “generalists,” or 
wide-niched, species. By using food-plant range as such, latitudinal 
comparisons of food-plant specialization, or trophic niche breadth 
