1973] 
Scriber — Papilionidae 
367 
sky, 1972). In the higher latitudes where fewer species of most 
major families of host plants occur there has probably been some 
breakdown of the phylogenetic larval host plant preferences that tie 
some species to these major evolutionary host plant groups, perhaps 
favoring polyphagy at the plant family level. The Papilio troilus 
L. and P. glaucus L. groups, for instance, have expanded their diets 
considerably from the Lauraceae and Magnoliaceae they are thought 
to have originally fed upon. Thus, besides ‘ecological release’ and 
the inability to specialize in unpredictable and unstable environments 
as possible explanations of the observed gradients in feeding special- 
ization, a third possibility exists. Perhaps there was a necessary 
alteration of those allelochemical specializations developed over a 
long period of evolutionary time, either as species of Papilionidae 
extended their ranges into the higher latitudes where their usual host 
plant families never existed, or as they remained in higher latitudes 
where their ancestral hosts had since been eliminated, perhaps by 
climatic changes. 
The precise reason for Papilionidae being more specialized in their 
feeding habits in tropical latitudes is uncertain and will probably 
remain largely as such. One contributing factor for this is that no 
one knows whether polyphagy in general is the ancestral condition 
from which more specialized feeding habits arose or not. The fact 
exists, however, that there are greater percentages of feeding special- 
ists in the tropical latitudes, and that this percentage decreases as one 
moves toward the higher latitudes. These data do not suggest that 
species are more specialized in the tropical than temperate latitudes, 
but that more species are specialized. 
Summary 
Latitudinal gradients in food plant specialization are examined for 
the swallowtail butterflies of the world (Papilionidae). It is found 
that the absolute number of generalized feeders existing in each ten 
degree belt of latitude is fairly constant, but the relative percentage 
of generalized species is significantly higher in the higher latitudes. 
This fact is discussed in terms of trophic niche breadth and species 
diversity of the Papilionidae in tropical and temperate regions. 
Acknowledgements 
This work was supported by N.S.F. Grant #GB 33398 (P.P.F.). 
I wish to thank Drs. Paul Feeny, J. G. Franclemont, Robert 
Poole, and Frank Slansky, Jr. for reading the manuscript or supple- 
