LATITUDINAL GRADIENTS IN 
LARVAL FEEDING SPECIALIZATION 
OF THE WORLD PAPILIONIDAE ( LEPIDOPTERA) * 
By J. Mark Scriber 
Department of Entomology 
Cornell University, Ithaca, N. Y. 14850 
Introduction 
A major question arising from ecological theory is whether or not 
there are relatively more specialized species in the lower or tropical 
latitudes than in the higher or more temperate latitudes. There 
exists a great deal of speculation concerning this question, but little 
actual data. This article presents an analysis of such data for one 
family of Lepidoptera ; the Papilionidae. 
The subject of niche breadth and degree of competitive overlap 
has generated tremendous interest in the field of ecology in the last 
two decades. In terms of the spatial model of the niche first pro- 
posed by Hutchinson (1957) and later expanded by Slobodkin 
(1962), Levins (1968), and MacArthur (1968), niche breadth is 
the “distance through” a niche hypervolume along a particular 
resource gradient within a community (Colwell and Futuyma, 1971 ; 
Whittaker, et al., 1973). 
Although there is presumed to be an apparent limit to the simi- 
larity and hence the number of competing species that can coexist 
(MacArthur and Levins, 1967), the packing of species (MacArthur, 
1969a) appears to be roughly proportional to the environmental 
variance, with less overlap, or looser packing, occurring with in- 
creased environmental fluctuation or perturbation. May and Mac- 
Arthur (1972) imply that niche overlap may be relatively inde- 
pendent of small to moderate environmental fluctuations, but it 
remains true that greater packing could still be attained by special- 
ization, and the question concerning what ultimately limits niche 
width remains unsettled. Also, in a more stable environment of the 
tropical latitudes, with larger productivity one might expect that 
marginally scarce resources would become adequate to support new 
species at the extremes of the resource gradient (Odum, et al., i960; 
Connell and Orias, 1964). In a more stable low-latitude tropical 
environment (MacArthur, 1969a), old lakes (Kozhov, 1963), the 
* Manuscript received by the editor October 18, 1973 
355 
