COMMUNITY ORGANIZATION: PERIODISM 



559 



the sum total of such patterns conforms to 

 the normal diel rhythm, is usually in step 

 with it, and consequently gives the com- 

 munity, or at least tliose parts exposed to 

 diel rhythm, a distinctive diurnal and noc- 

 turnal aspect. 



To turn from periodic to arrhythmic ac- 

 tivity, the latter would hardly be noticeable 

 in the community, unless specifically looked 

 for, since the active individuals would al- 

 ways blend into the periodic activity of the 

 diel cycle. When looked for, aperiodic spe- 

 cies are found usually in two sorts of envi- 

 ronments. They tend to inhabit those por- 

 tions of the community structure that are 

 not affected, or are relatively httle affected, 

 by the diel rhythm of the operating factor 

 complex; or, second, they so control their 



exposed to a normal diel fluctuation (Bent- 

 ly, Gunn, and Ewer, 1941); and the flour 

 beetle {Tribolium confusum) was found to 

 be arrhythmic as a population when reared 

 under constant darkness, temperature, and 

 humidity (O. Park and Noskin, 1947). 



In the second situation noted previously 

 are such social animals as certain ants and 

 man. Thus McCook (1877), speaking of 

 the eastern mound-builder, Formica exsec- 

 toides, observed: 



"Ants at Camp Riddle, when observed dur- 

 ing every hour of the night from sunset to 

 sunrise, were found to be pursuing the very 

 same labors in the same way, and in the same 

 fields as during the day. The avenues, tree- 

 paths, feeding stations, feeding grounds and 

 hills were always thronged day and night." 



Fig. 196. Aperiodicity of the Mammoth Cave crayfish {Cambarus pellucidus) ; activity re- 

 corded under experimental conditions of constant darkness and constant temperature. Ten con- 

 secutive twenty-four hour trials are shown, with average of trials in heavy line. Note that 

 each trial is independent of the other nine with respect to time active, and in the distribution 

 of activity. ( After O. Park, Roberts and Harris. ) 



immediate environment that the individuals 

 are relatively undisturbed by the periodic 

 diel complex. 



In the first of these situations are such 

 species as the cave crayfish {Cambarus pel- 

 lucidus) of Mammoth Cave, Kentucky 

 (Park, Roberts, and Harris, 1941), in 

 which, under constant temperature and 

 darkness, some individuals are always ac- 

 tive (Fig, 196); or, again, essentially arrhy- 

 thmic species that inhabit the relatively 

 constant habitat of stored agricultural 

 products. For example, the grain beetle 

 (Ptijius tectus) was found to be arrhythmic 

 as a population when reared under constant 

 light, temperature, and humidity, but devel- 

 oped an habitual periodic activity when 



Parallel observations are numerous 

 (Flint, 1914; Park, Lockett, and Myers, 

 1931; Park and Strohecker, 1936; Talbot, 

 1946). Some ants are more active by day, 

 others by night, and still others are ape- 

 riodic with respect to the diel cycle. 



In man it is obvious that the species has 

 no inherent pattern of general diel activity, 

 and as he integrates into the complex social 

 system he tends to become more and more 

 aperiodic with respect to the diel cycle. 

 The human infant is apparently arrhythmic 

 (Szymanski, 1918); during its first year of 

 life there is an increasing range and regu- 

 larity of the twenty-four hour body tem- 

 perature rhythm (Kleitman, Titelbaum, 

 and Hoffman, 1937), and this rhythm be- 



