1914] Griundl: Manniials an, I liinU of tin Colorado VnUcy 



95 



area in which it is able to get the food necessary for itself by the 

 method which its anatomical structure and psychological equipment 

 prescribe. 





Fig. F. Diagram showing frequency of capture of Peroyiiathus s. spinatus 

 in the several associations. One hundred and ten individuals were trapped, of 

 wliich assoeiational occurrence was satisfactorily recorded. While the asso- 

 ciational preference of this species is almost identical with that of P. inter- 

 medius, the ranges of the two species are wholly distinct, being separated 

 by the Colorado River. Assoeiational preference is also seen to be similar to 

 that of P. formosus, which occupies apparently identical ground. But P. spiii- 

 atus belongs to a different subgenus (Chactodipus) from P. formosus (subgenus 

 Perognathns), hence the two are not nearly related and probablj' do not come 

 into close ecological competition. 



Not infrequent are the cases where food-.supply is located in one 

 place, and the refuge or breeding site in another. Animals of such 

 habit are neces.sarily of relatively great powers of locomotion, and 

 may live regularly in two or more as.sociations situated remotely from 



