86 John B. Calhoun 



tioiis ill coutjuit with the traplinc would then tend to move simultaneously 

 toward it. There would then arise the situation in which out to a iv distance 

 from the trapUne few mice remained. At this time the mice in the second 

 band would begin moving more or less together after a lag in time resulting 

 from their attachment to home and to each other. No mouse could leave 

 home until several of its associates were ready to move together. Similarly, 

 residents of bands 3, 4, and 5 would start inward as soon as most of their 

 neighbors of the adjoining inner band had moved w distance toward the 

 central trapping area. In this way a "chain-reaction" was set in motion in 

 which several bands simultaneously were moving toward the central area. 



For the present this interpretation seems the most likely one. Whether 

 the phenonemon has any analogies to lemming migrations or troop panic 

 need not concern us here. Of importance are the indications that the in- 

 fluence of a signal void extends for approximately (i.O home range sigma. 

 The wavelike nature of invasion suggests that most of the mice from a 

 band of 6.0 sigma move together. That they should do so is in harmony 

 with the concept of constellation formation into groups whose mean size 

 is 12 individuals and whose spatial diameter is about 6.0 home range sigma. 



In the context of the present paper this additional support of the con- 

 cept of a constellation as a real phenomenon represents the prime impor- 

 tance of this study on an induced invasion. For it is the evolution of the 

 constellation and its later condensation into the compact colony way of 

 life that I believe represents the reason why a basic group size of 12 adults 

 is the most important one in the mammalian series. 



XII. Derivation of Compact Colonies from Constellations 



Accentuation of the social bonds among members of a constellation 

 must have increased reproductive effectiveness and permitted survival of 

 individuals exhibiting a decreased antagonism toward those neighbors who 

 become familiar through repeated contacts. As the aggressiveness became 

 reduced, beta and gamma members gradually shifted their home range 

 center toward that of their dominant alpha associate until at last theirs 

 coincided with his. A compact colony will then be formed in which all in- 

 dividuals share the same home range. Furthermore, the aggressive actions 

 of the single dominant alpha individual of a compact colony serves to 

 protect the other members of his colony from intrusion by extracolony 

 members of the same species. Whereas constellation formation may be ob- 

 served to take place within one or a few generations from a prior uniform 

 distribution of home range centers, the development of compact colonies 

 from constellations must have entailed considerable genetic change over 



