70 John B. Calhoun 



In other unpublished studies by Dr. Barbehenn, Sorex catches nearly 

 doubled those of Peromyscus. 



IX. A Theoretical Conceptualization of the Evolution of a Social Hierarchy 

 among Species in the Utilization of Space 



The concept of social inhibition of home range represents an inference 

 derived from the observed differential probability of capture by snap 

 traps. Reduction of extent of home range must result from an increase in 

 the probability of terminating trips away from home. We have seen that 

 an increase in the structuring of the environment, with stimuli which 

 elicit responses, does lead to an increase in the probability of terminating 

 trips. This structuring of the environment represents an increase in the 

 amount of stimuli impinging on the organism. For this reason I believe 

 that one is justified in making the following tentative generalization: Any 

 increase in the frequency or intensity of stimuli to which the animal has 

 responded in the past will lead to an increase in the probability of termi- 

 nating trips. 



It follows that genera such as Sorex or Pitymys frequently are char- 

 acterized by such small home ranges that we may conclude that they ex- 

 perience a high frequency or intensity of relevant stimuli. At the same time 

 their associates, Peromyscus or Clethrionomys, hsixe large home ranges. 

 This being so, we may conclude that the latter are not unduly exposed to 

 an excess of relevant stimuli. And yet we may suspect that any stimulus 

 which Sorex or Pitymys can detect can also be detected by Peromyscus or 

 Clethyrionomys. Thus, their differential response to stimuli must involve 

 some internal mechanism through which stimuli produce an effect indicating 

 relevancy or irrelevancy. 



So far it has appeared that auditory stimuli of the class represented by 

 vocalizations of members of the small mammal community might represent 

 the class of stimuli producing alterations of home range. If this inference 

 proves correct, it means that some species respond to a broad spectrum of 

 different auditory stimuli whereas others "ignore" all except those emitted 

 by their own species. 



Broadbent (1958) elaborates a theory of perception and communication 

 which may serve in conceptualizing how vocal communication functions in 

 leading to an organization of the small mammal community. Briefly this 

 theory is as follows: 



The central nervous system may be conceptualized as a signal flow 

 system possessing the following connections and characteristics. Stimuli 

 impinging upon the sense organ generate signals which pass into a tempo- 



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