530 



THE COMMUNITY 



tion of the community, as evidenced by the 

 onset of defoliation in temperate deciduous 

 forests; whereas the marine community is 

 less apparently changed, since the open sea 

 freezes only at high latitudes, and the or- 

 ganisms are not more obvious than the 

 liquid medium, save for highly local con- 

 centrations of plants and animals. 



Furthermore, even within a limited area 

 the seasonal changes afiFect the resident 

 communities differently. Different types of 

 communities have an inherently differential 

 response to the physical influences operat- 

 ing equally upon all of them. This differen- 

 tial response is a consequence of the total- 

 ity of the adjustments of the interdepend- 

 ent species populations of each community 

 to the occupied habitat niches. 



Certain interesting points emerge. As we 

 have seen, there are three basic drives in 

 the life cycle of an animal, namely, repro- 

 duction, sheltering, and hunger. In a sea- 

 sonal environment, such as we are discuss- 

 ing at this point, the broad outlines of each 

 of these drives are on a seasonal basis; 

 such aspects are generally qualitative. On 

 the other hand, the day to day satisfaction 

 of these drives is usually more specific and 

 quantitative. 



For example, most species have one or 

 more definite periods of copulation. Such 

 mating periods are correlated with seasons 

 of the year, but the copulation is usually 

 limited to the day or the night, depending 

 upon the species population involved. 



As to sheltering, the seasonal aspects are 

 broad adjustments to adverse weather (mi- 

 gration, hibernation, aestivation), whereas 

 the day to day aspect is concerned with 

 regular periods of physiological recupera- 

 tion in relatively sheltered habitat niches. 

 Again, this daily rest is usually either noc- 

 turnal or diurnal. 



The seasonal shift in diet is correlated 

 directly with the growth, leafing-out, flow- 

 ering, and fruiting of food plants in the 

 herbivores, and indirectly so correlated in 

 the carnivorous animals. Figure 178 illus- 

 trates seasonal shift in diet of the omniv- 

 orous raccoon, as different foods become 

 available. 



At the community level the satisfaction 

 of these three basic drives by the numer- 

 ous constituents forms a highly complex, 

 overlapping mosaic of seasonal activities. 

 Each type of community responds in a 



characteristic manner to the changing 

 rhythm of its physical and biological envi- 

 ronment. 



Another important point is that the ma- 

 jority of species that comprise any given 

 community are full-time annual residents, 

 or nearly so. Since this is the case in com- 

 munities located in seasonal, as well as 

 aseasonal environments, the general re- 



Fig. 178. Seasonal shift of available foods in 

 the diet of the omnivorous raccoon. (After 

 Hamilton. ) 



spouse to regular periods of cold or drought 

 is that of adjustment to the adverse condi- 

 tions, rather than emigration or migration. 



When attention is focussed upon the 

 seasonal abundance of organisms, or upon 

 the seasonal abundance of particular as- 

 pects of their life history, within a partic- 

 ular community (Alice, 1911; Petersen, 

 1926), the term "seasonal succession" is 

 frequently used to describe the concept. 

 Such studies may refer to events in a par- 

 ticular habitat niche or to a series of equiv- 

 alent niches, or to a stratum or to the whole 

 community. 



The concept of seasonal succession is not 

 to be confused with the concept of com- 

 munity succession. 



Clements (1905) used the term "aspect" 

 to signify the seasonal impress on a com- 

 munity; for example, the spring aspect or 

 the winter aspect. Later, Clements (1916, 

 p. 130) and Tansley and Chipp (1926, p. 

 16) broadened this usage of aspect to in- 

 clude the seasonal changes within a com- 

 munity, especially botanical features such 

 as the vegetative development and flower- 



