COMMUNITY ORGANIZATION: PERIODISM 



547 



nal. Both types of squirrels inhabit the 

 same forest community in many localities, 

 and their different periods of activity are 

 correlated with the Hght-filtering ability of 

 their eyes and the hght intensities normal 

 for those portions of the diel cycle in 

 which they are active. 



At the level of the major community 

 much less has been accomphshed. Because 

 of the absence of dayhght, investigation of 

 the nocturnal portion of a community is 

 usually much more difficult than the 

 parallel study of the diurnal portion. The 

 few methods employed involve (1) trap- 



frequency of the calls or sounas produced 

 by nocturnal animals (Crawford, 1933; 

 O. Park, 1938); (6) the use of objective re- 

 cording apparatus in the field to record the 

 movements of an individual (Park, Barden, 

 and Williams, 1940). (7) The Norway rat 

 has been viewed by infra-red light (South- 

 em, Watson, and Chitty, 1946); conse- 

 quently this method may be applicable to 

 the large-scale study of nocturnal animals 

 in the field. (8) The use of a flash light held 

 so that the eye-shine of animals is seen 

 (jack lighting); finally (9) there is the rec- 

 ord on a light, fresh snowfall. 



TIME IN HOURS 

 Fig. 188. Diel periodicity in pH in Crystal Lake, Minnesota. See text for relation lo the me- 

 tabolism of the lake community. (After Philip.) 



ping, preferably live-trapping, or tagging, 

 animals (Hamilton, 1937, 1943); (2) 

 stomach analyses, in which the known pe- 

 riods of activity of the food-animals may 

 suggest in certain cases the coincidental 

 activity of the predator (this method is 

 useful as a corroborative measure, but im- 

 plies a great deal of foreknowledge of the 

 food-gathering habits of the carnivore in 

 question); (3) marking animals with var- 

 ious kinds of paint (Park and Sejba, 1935); 

 (4) observation of animals by artificial 

 lights (Park and Sejba, 1935; Park and 

 Strohecker, 1936); (5) tabulation of the 



All the methods have limitations. When 

 several different methods are used, over a 

 sufficient period of time, the body of evi- 

 dence is mutually supportive, and leads us 

 to the conclusion that there is a large noc- 

 turnally active segment complementing the 

 large diurnally active segment of a given 

 community, and that many of the principles 

 generally advanced for the diurnal portion 

 hold equally well for the nocturnal portion. 



This complementary nature of the diur- 

 nal and nocturnal aspects of the commu- 

 nity is basic to a full appreciation of the 

 community concept. It will be remembered 



