1. The Social Use of Space 51 



factors examined all suggest that the optimum interval between home 

 range centers should be of the order of a 2 home range sigma distance. 

 From an evolutionary standpoint, the most important of these probably is 

 the fact that utilization of the environment becomes uniform at slightly 

 more than 2 sigma distance between home range centers. This factor should 

 have been the major one in the evolution of those characteristics of in- 

 dividuals pertaining to the frequency of trips, the velocity of the individuals, 

 and the aggressive acts elicited when two individuals meet. It is probably 

 strictly coincidental that the properties of the sign and signal field are also 

 likely to be such as to make an interval of about 2 sigma between home 

 range centers optimum. It is at this distance between home range centers 

 that both signs and signals become most constant and thus more pre- 

 dictable. Also, the intensity of the signs and signals most nearly approxi- 

 mate any receptor's own behavior near its home, which can serve for it as a 

 standard in evaluating the intensity of the actions of its neighbors impinging 

 on it. 



L. The Number of Neighbors Perceived 



When home range centers are 2.7 sigma apart, an indi\ddual at its home 

 range center can just perceive all its six nearest neighbors. However, as it 

 begins to move away from home it begins to lose contact with those nearest 

 neighbors lying on the opposite side of its home range center. By the time 

 it reaches half the distance to its nearest neighbors in the direction in 

 which it is traveling, it can detect only three of its nearest neighbors. 

 Toward the periphery of its home range, it can detect only two of its nearest 

 neighbors. In addition, it can detect one, and only one, of its next-nearest 

 neighbors, w^hich are members of the group of twelve forming the second 

 hexagonal tier of neighbors about its home range center. Thus, with this 

 fairly large interval between home range centers, any one individual has 

 poor contact with its associates. When home range centers are 2.1 sigma 

 apart, any one individual can maintain contact with all six of its nearest 

 neighbors out to about 0.7.") sigma. Even when an individual has journeyed 

 halfway in a direction of a nearest neighbor it is still in contact with four 

 of its six nearest neighbors, in addition to one of the twelve neighbors 

 lying in the next tier. As he proceeds still farther, losses of nearest neighbors 

 are compensated for by next-nearest neighbors. Thus, at all times when 

 home range centers are 2.1 sigma apart, an individual is in contact or po- 

 tential contact with five or six of its neighbors. 



By the time home range centers are of l.o sigma apart, an individual is 

 in potential contact with ten other indi\'iduals though not always the same 



