COMMUNITY ORGANIZATION: PERIODISM 



529 



ences. Such coordination must exist in com- 

 munities having a seasonal rhythm in the 

 physical portion of environment, if the com- 

 ponent species populations are to survive, 

 and flourish. Consequently selection oper- 

 ates at the community level, as well as at 

 the populational and organismal levels, for, 

 although the relatively self-sustaining com- 



fluences are suggested by arrows, the width 

 of which indicates their relative community 

 value. Nevertheless, it must be remembered 

 that each operating influence is subject to 

 seasonal variation in the communities being 

 discussed at this time. 



Such seasonal variations enormously 

 complicate the community concept. Aside 



Fig. 177. Seasonal variable in most communities: direct and indirect action by primary, 

 secondary, and tertiary influences on the animate and inanimate environment. 



munity is independent of adjacent com- 

 munities for survival in a periodic environ- 

 ment, its totality of adjustment is an inte- 

 grated response of its components. This is 

 one of the points of contact between the 

 almost continuous selection of behavior, 

 function, and structure which takes place 

 in nature. 



At present, we must not lose sight of the 

 complex interactions between parts of the 

 community. This interplay is shown par- 

 tially in Figure 177. Here, important in- 



from the obvious and fundamental rhyth- 

 mic seasonal changes in temperate latitudes 

 in the magnitude of both basic and second- 

 ary physical factors, the apparent, over-all 

 seasonal changes affect different types of 

 communities differently. Thus the inani- 

 mate medium of fresh-water communities 

 is reactive to lowering of air temperature, 

 followed in certain latitudes by freezing of 

 the upper strata, wholly or in part; the 

 most obvious change in terrestrial com- 

 munities is the effect upon the animate por- 



