362 
Psyche 
[December 
Fig. 3. Latitudinal gradients in species richness for Indo-Australian and 
Eastern Asian Papilionidae. 
that permit the coexistence of several species of butterflies should 
probably be sought in the larval rather than the adult stages has 
been obtained by Young (1972). The critical dimension of the 
niche (or ecotope) may in fact be something other than the range of 
larval hostplants utilized ; however, as well as being one that is rela- 
tively easy to measure, it is assumed here to be a crucial parameter 
in most cases. 
In a relatively recently speciated group of swallowtails in the U.S., 
the polyphagous Papilio glaucus (L.) is apparently entirely excluded 
geographically by three species which are sympatric and which have 
subdivided the range of plant families utilized by P. glaucus 
(Brower, 1958a; 1959). Besides their specialized feeding habits, 
isolating mechanisms such as seasonality, coloration, and mating 
preferences appear to have been involved in the Pleistocene specia- 
tion. There is no clear cut distinction between ecological and evolu- 
tionary time, and the importance of trophic specialization is uncertain 
