Comparative Evolution of Biomes 



313 



pointed out that in each of several subfamihes related genera arose 

 in South America and that, probably in Cretaceous time, represent- 

 atives of only one genus spread into North America and ultimately 

 into the Old World, Seevers ( 1957 ) postulated an almost identical 

 circumstance in the beetles which live as guests in the termite 

 colonies. In the beetle subtribe Perinthina (Fig. 137), only a single 



Fig. 137. Distribution of the genera of the subtribe Perinthina of the family 

 Staphyhnidae. Lines indicate the phylogeny and paths of dispersal. (After 

 Seevers. ) 



line dispersed, in the tribe Termitohospini two lines dispersed, and 

 in the subtribe Corotocina also two lines dispersed (Fig. 138). 



With these termites and their beetle guests, the apparently cor- 

 related dispersal of several lines indicates that an entire commu- 

 nity dispersed as a unit. Many other related South American genera, 

 however, did not disperse. This difference in dispersal behavior 

 may be correlated with biome structure. Biomes are a system of 

 overlapping associations or communities in which the peripheral 

 communities may be similar in physical nature to the others but 

 different in taxonomic composition (see Chapter 9). If a land 

 bridge of limited ecological characteristics became available for 

 dispersal, it would probably be similar ecologically to the peripheral 

 community which it touched. Under these circumstances only spe- 

 cies in these peripheral communities would spread across the bridge. 



