562 



THE COMMUNITY 



winter ("dormant season"), in which there 

 is relatively great inactivity. Diel periodic- 

 ity, operating within this seasonal restric- 

 tion, has two portions that diflFer in the 

 kinds of animals active, but both day and 

 night have a large active fauna. 



This basic difference results in two dif- 



Fig. 200. Diagram of a community in the 

 form of a diel wheel. Nocturnal and diurnal 

 periods are differentiated on the basis of aver- 

 age levels of activity of populations, with the 

 overlap of the crepuscular and auroral periods 

 suggested. 



ferent community symmetries (O. Park, 

 1941a). The seasonal pattern is marked by 

 the two complementary portions of gen- 

 eral activity and general inactivity with two 

 interdigitating periods of overlap between 

 activity and dormancy (Fig. 199). In this 

 general point of view, spring is the season 

 when the community is in transition to- 

 wards the rigors associated with activity, 

 and belongs to the summer; whereas aut- 

 umn is the season when the community is 



in transition towards the rigors associated 

 with inactivity, and belongs to the winter. 

 The diel pattern is characterized by 

 two complementary portions each of which 

 contains both an active and an inactive 

 fauna, with two interdigitated periods of 

 overlap between the period of diurnal and 

 nocturnal activity (Figs. 200 and 201). 



D: diurnal 

 N: nocturnal 

 A: auroral 

 C: crepuscular 



Dien Diel 2 



Fig. 201. Diagram to suggest the net diel 

 arrhythmicity of a community as the result of 

 summation of the complementary activity 

 periods of the diurnal and nocturnal faunas. 



From the general view of community activ- 

 ity, the dawn belongs to the day, whereas 

 evening belongs to the night. Thus the dis- 

 tribution of activity periods makes possible 

 a much more complete utiUzation of habi- 

 tat space and time than would be possible 

 were the community to be organized on 

 either a nocturnal or a diurnal basis. This 

 suggests that the diel community pattern 

 is much more efficient than the larger sea- 

 sonal pattern. There emerges a new con- 

 cept of total diel activity— that of ecological 

 symmetry. Thus by development of both a 

 nocturnal and a diurnal fauna, both halves 

 of the twenty-four hour cycle are utilized 

 with respect to the space-time lattice. As 

 the two halves of the diel pattern approach 

 each other, the community becomes bio- 

 logically more complex, more symmetrical, 

 and more arrhythmic with respect to day 

 and night. This general concept finds sup- 

 port in the literature cited in previous 

 pages. 



29. COMMUNITY SUCCESSION AND DEVELOPMENT' 



In the preceding chapters the concept of 

 the major community has been defined, and 

 its organization examined in terms of struc- 

 ture, metabolism, and periodism. Our 

 present purpose is to examine the develop- 



* Community succession and development 

 are to be distinguished from "community evo- 

 lution" (p. 695). 



ment and succession of the community 

 through time. 



Before doing so, it should be reem- 

 phasized that, within the concept of the 

 relatively independent major community at 

 the level of survival for interdependent 

 populations, there is an almost infinite series 

 of biocoenoses, and ecological assemblages 



