EVOLUTION OF INTERSPECIES INTEGRATION AND ECOSYSTEM 



727 



in telephone poles on the outskirts of a 

 town (Ithaca, New York). Wrens (Trog- 

 lodijtes aedon) have ultimately won nest- 

 ing sites from sparrows in such "tension 

 zones" or ecotones as the vicinity of houses 

 m the Indiana sand dunes (Breed, 1945). 

 More such observations would lead us to a 

 better understanding of the exact nature 



Pliocene times. 



Experiments show that a species may 

 exclude another closely related and ecolog- 

 ically similar one (p. 657). Two species 

 of flour beetles, Tribolium confusum and 

 T. castaneum, are competitive under ex- 

 perimental conditions (Birch, Park, and 

 Frank, 1946). When parasitized by a sporo 



SYNTERMES 



Fig. 263. Phylogenetic tree of certain genera of termites ( Nasutitermitinae ) , showing pro- 

 files of the heads of the soldier caste and the imago-worker mandibles. Convergent develop- 

 ment of the "squirt gun" and reciprocal convergent reduction of the soldier mandible are 

 shown in Subulitermes and Nasutitermes, both of which are tropicopolitan, while the more 

 primitive genera with mandibulate soldiers are all neotropical. 



of the biotic barrier limiting the successful 

 invasion of this "foreigner." 



Eight genera of termites originating in 

 South America have reached no farther 

 than Costa Rica since the Pliocene connec- 

 tion, while one genus (Tenuirostritermes) , 

 originating in Central America, has been 

 unable to push south of northern South 

 America. One may postulate competition 

 between termite genera as a possible ex- 

 planation for this mutual exclusion since 



zoan (Adelina tribolii), T. confusum usu- 

 ally replaces T. castaneum in mixed cul- 

 tures, because T. castaneum is more sus- 

 ceptible to the pathogenic effects of the 

 parasite. In nonparasitized cultures, T. cas- 

 taneum usually eliminates T. confusum, 

 probably in part because of the higher re- 

 productive potential of T. castaneum (T. 

 Park, 1948). These experiments show how 

 competition between closely related species 

 differs in effect through the influence of 



