EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



so distributed. With certain exceptions which we have given, the species 

 of Hippodamia and Coccinella are in quite general competition. They are 

 characterized for the most part by very wide distribution and extensive 

 overlapping of other species. With the exception of a few species like 

 Cleis hudsonica, there is little zonal distribution. The apparent zones of 

 distribution, as given for New T Mexico by Cockerell (1898), are in marked 

 disagreement with other regions. 



The abundance of the several species is also very erratic from place to 

 place. At Cold Spring Harbor the order of abundance of the several 

 species differs from year to year and is quite different from that given for 

 other localities not far distant. The conclusion seems evident that the 

 exigencies of the death-rate are great and that these species have diffi- 

 culty in leaving 2 progeny for each pair, not because of overcrowding, but 

 from some other unfavorable circumstance. Small considerations, such as 

 the activity of some disease of aphids here or there, turn the balance 

 against this or that species, though it may be in the middle of its range. 

 If this be the case, then just such wide overlapping ranges should be 

 found. The distribution of the varieties as opposed to that of the species 

 must be separately considered, for here we have different conditions. The 

 facts of the varietal distributions apply also to some species of a narrow 

 range which are closely related to some species of wide range and which 

 are more or less certainly derived from them at a relatively recent date. 

 These are young species not far removed from varietyhood and, not unnat- 

 urally, distributed much as varieties are. They will be distinguished as 

 minor species in distinction from major species. 



In Hippodamia, especially, we have wide-ranging major species. Some- 

 times on the outskirts, sometimes on the interior part of its range, are 

 found the lesser ranges of the varieties and minor species. This is illus- 

 trated diagramatically in fig. 91 for Hippodamia con rer gens and its deriv- 

 atives. Such a .distribution is, I believe, very significant in the study of 

 evolution in this group. It points strongly to the directive influence of 

 the environment and to the role of segregate heredity in the evolution 

 of a species up to the varietal stage, at least, within the territory occupied 

 by the mother species. The difficult step by which the variety acquires 

 intersterility and thus becomes a species must be discussed in a later 

 section. 



When the new species has arisen, the extension of its range, as we have 

 seen, is not checked by any coccinnellid saturation of the environment, 

 and depends largely upon the degree of success it has in the distribution 

 of its eggs and in its success in hibernation. If relatively successful, it 

 takes its rank as a major species; if less so, it continues as a species of 

 narrow range; if still less so, it continues as a rarity which persists, in 

 spite of its high death-rate, through the mass of recruits constantly fur- 

 nished by the mother species. 



