82 John B. Calhoun 



moving in at a constant speed of tra\'el per day, those invading the trapped 

 area each day will represent residents from successive bands of equal 

 width. Each successive day the majority of the captures will be from a 

 more distant band than on the prior day. In a system of concentric bands 

 of equal width, each band more distant from the center contains a larger 

 area than the next innermost one. Thus, with density proportional to area 

 and invasion into the central area transpiring from a constant rate of move- 

 ment toward it, catch per day should increase with time. 



At the time when this formulation was just crystallizing in the fall of 

 1950, Dr. Webb wrote me concerning their developing plans for long- 

 range studies of small-mammal populations of the Huntington Forest near 

 Newcomb, New York. I mentioned the interesting results obtained by 

 Hinckley, and the hypothesis generated by them. His response was to 

 replicate Hinckley's study. 



Details of these two studies have been included here (Figs. 12 and 13A). 

 However, at the time of these two studies the failure of catch per day to 

 decline over time blinded us to the story which the differences of input 

 for different genera could tell us. That is, it was not realized at that time 

 that expansion of home range by subordinate members of the dominant 

 species and by all members of the remaining subordinate species could 

 lead to results by removal trapping in which catch per day did not decline 

 even though there were no invasions. Xot recognizing this possibility the 

 results of these two studies were described (Calhoun and Webb, 1953) as 

 supporting the hypothesis that continuous removal trapping did in fact 

 lead to invasion of the trapped-out area by residents from surrounding 

 areas. 



By that time I had become associated with the Neuropsychiatry Divi- 

 sion of the Walter Reed Army Institute for jMedical Research. If this 

 hypothesis were correct it might have relevance both to lemming migration 

 (Elton, 1942) and to certain panic phenomena of troops (Ranson, 1949; 

 Caldwell, et al., 1951). In order to explore this phenomenon in more detail, 

 it was possible for Dr. Webb to negotiate Contract Number DA-49-007- 

 j\ID-325 between the ^Medical Research and Development Board (Office of 

 the Surgeon General, Department of the Army) and the College of Forestry-, 

 State University of New York. This enabled him and his associate to execute 

 a large series of studies on the response of small mammals to removal trap- 

 ping. The major details of these studies will be published elsewhere by Dr. 

 Webb. I merely wish here to present a brief outhne of one of these studies 

 because of its importance to the general theme being developed in this 

 paper. 



In the center of an extensive forested tract they established a circular 

 trapline with a 562-foot radius. Along this trapline 781 snap-traps were 



