366 Psyche [December 
Fig. 5. Latitudinal gradients in feeding specialization for the Papilioni- 
dae of the world. 
ecological release from competition upon islands (MacArthur and 
Wilson, 1967), various workers have found some evidence that spe- 
cies niches do appear to broaden in the sense that there is increased 
morphological variance, behavioral plasticity, and dominance (Grant, 
1967; Lack and Southern, 1949; Patrick, 1967; Vaurie, 1957; Wil- 
liams, 1969; and Wilson, 1961). There is, however, some question 
whether these measures actually reflect niche breadth of the species 
(Soule and Stewart, 1970 ; Willson, 1969). I have employed a 
somewhat different measure here, and by altering the number of 
families or genera used as a criterion for ‘generalist’, the amplitude 
of the observed latitudinal gradient would vary but probably not the 
overall pattern. Other studies have described a ‘generalist’ in some- 
what different terms as those species able to maintain populations 
over a broad range of environmental types or substrates (McNaugh- 
ton and Wolf, 1972), or those exhibiting a greater variance or 
breadth of morphology or feeding behavior (Levins, 1968; Rough- 
garten, 1972; Schoener, 1971). These also may or may not reflect 
actual niche breadth as such, but latitudinal comparisons within a 
taxocene would probably be possible to prepare in these terms as well. 
It is interesting that many species of Papilionidae are relatively 
specialized on certain tropical and sub-tropical plant families (Sian- 
