X 



78 John B. Calhoun 



and behavior of such distantly related genera as Cleihrionomys, Peromyscus, 

 Blarina, and Sorex, we would suspect minimum niche similarities and thus 

 little influence of one genus upon the other. 



If their niche reciuirements are really quite dissimilar, if within any 

 individual's home range each requirement is represented at many points, 

 and if in most home range-sized plots most of the niche requirements for 

 each genus abundantly occur, then, depending upon the intraspecific 

 factors leading to fluctuations in density, we might in fact anticipate that 

 one or several of these genera might occur simultaneously in high densities. 

 In fact, observed relative densities do behave in such a fashion. Were we 

 content to rest our case solely on relative densities, we would remain con- 

 tent with the satisfactoriness of such logic in revealing true relationships. 



However, the time sequence analysis of removal captures leads to a 

 formulation of community dynamics suggesting the nearly complete 

 invalidity of the concept of lack of influence of one species upon another if 

 their niche reciuirements markedly differ. In fact, the concept of competition 

 has little relevance. Instead, "home range inhibition" becomes the most 

 useful concept. Home range inhibition is the consequence of processes 

 through which the individual reacts to a signal as if it were identical to a 

 different signal with which it shares certain physical characteristics. In 

 other words, an animal may react to a signal emitted by a member of an- 

 other species as if it were the signal emitted by another member of its own 

 species with whom its interactions have led to its characterizing the signal 

 as noxious. Such a species becomes a subordinate member of the community. 



Signals of the dominant species must contain not only the basic char- 

 acteristics of the subordinate but some characteristics peculiar to itself. 

 Thus, when both a dominant and a subordinate species occur simultane- 

 ously in a habitat, members of the dominant species will come to associate 

 no.xious qualities only to that portion of the signal which is species-specific 

 since it is the only portion of the signal which always accompanies a nega- 

 tive intraspecific interaction. If we consider a commiuiitj^ composed of 

 four species A, B, C, and D (following the nomenclature of Section IX) 

 in which D is most dominant and A most subordinate, and signal compo- 

 nents a, b, c, and d are observed, then Z)'s signal should include components 

 a, b, c, and d; C's should include a, b, and c; 5's only a, and b; and A's 

 only a. 



Even though A learns to define signal a as noxious only by reacting with 

 other A associates, he will respond similarly to detection of the a compo- 

 nents of his B, C, and D associates. I have cited data indicating that the 

 greater the frec^uency of rele^'ant stimuli in the environment the greater 

 will be the probability of the origin of a neural signal leading to termination 

 of the behavior of outward movement from home. In this situation, every 



