34 



John B. Calhoun 



the trends of the 15-day trap-out as shown in the left-hand graph of Fig. 

 13 for eight NACSM lines also run on Mt. Desert Island. 



In New York, where Peromyscus had the same density as in Maine but 

 Clethrionomys was four times as numerous as Peromyscus, a striking differ- 

 ence in the trends resulted. Clethrionomys exhibited a typical, though some- 

 what slow, decline through the three consecutive days. In contrast, despite 

 removal trapping and thus fewer deer mice available for entering traps, a 

 greater number of Peromyscus entered traps each successive day. I wish 

 to emphasize that competition for entering traps contributed negligibly 

 to these trends. Three times as many traps were set each day as there were 

 total animals caught for the entire 3-day period. 



• • Clethrionomys 



A -A Peromyscus 



■5(- 



B. NEW YORK 



DAY 



DAY 



Fig. 14. Capture rates for Clethrionomys and Peromyscus in Maine and New York. 

 Nearly codominance, or lack of dominance, is reflected by the Maine data, whereas in 

 New York Peromyscus is clearly subordinate to Clethrionomys. See Table VI. 



In Alberta, where both species are on the average relatively abundant 

 (Table VII), there exists a marked seasonal difference (Fig. 15) in the 

 trend of input over time between these species. During the spring, when 

 low densities characterize both species, each exhibits a rapid rate of de- 

 cline. In contrast, by fall when high densities have developed for both 

 species, Clethrionomys shows a relatively constant input. Note the reversal 

 of the trends of input for Clethrionomys and Peromyscus when Fig. 1 1 and 

 Fig. 15B are compared. 



VII. Toward a General Theory of Interspecific and Intraspecific Use of Space 



The data presented in Section VI reveal that a continuous decline in 

 catch from one day to the next during removal trapping is the exception 



