536 



THE COMMUNITY 



The winter diapause of temperate com- 

 munities requires a great deal of ecological 

 preparation, just as the organismal dia- 

 pause requires physiological preparation. 

 Long before the arrival of the hibernal 

 period, the contained animals and plants are 

 preparing for the extremes of winter 

 (Morgan, 1939), Such preparations are 

 diverse, may begin in the late serotinal 

 period, and usually are completed in the 

 autumnal period. At the latitude of north- 

 ern Illinois, for example, deciduous forest 



A large hterature and a special ter- 

 minology have developed upon the subject 

 of dormancy. Numerous physiological 

 changes are associated with extended 

 periods of inactivity. In general, when the 

 dormant period occurs in winter, the ad- 

 justments are referred to collectively as 

 hibernation. Hibernation, then, is associated 

 with relatively low temperature and physio- 

 logically inaccessible water (snow and ice). 

 When the dormant period occurs in sum- 

 mer, in temperate latitudes and altitudes, or 



MJ JASONOJ FMAMJ JA SOND JFMAMJ JA S 



1926 1927 1928 



TIME IN MONTHS 



Fig. 183. Seasonal distribution of light intensity, in foot-candles, in the Chicago area, for 

 open sun, and canopy shade of the cottonwood, conifer, oak, and beech-maple communities 

 of the Indiana Dunes. ( After O. Park. ) 



communities gradually complete the de- 

 fohation of their canopy, shrub, and her- 

 baceous strata, and deposit the bulk of this 

 potential food upon the forest floor; grass- 

 land communities have their now yellowed 

 herbaceous stratum matted down under 

 early snows; the upper stratum of larger 

 aquatic communities gradually chills, with 

 the resulting disappearance of the thermo- 

 cHne, and the smaller aquatic communities 

 chill, and eventually their aqueous medium 

 freezes. 



The general response to this gradual 

 cooling of the inanimate media is a move- 

 ment away from exposed strata into more 

 protected habitat niches, or into the lowest 

 stratum; i.e., into the subaqueous and sub- 

 terranean strata. Such movements are pre- 

 cursors of dormancy. 



in dry seasons of the tropics, the general 

 adjustment is known as aestivation (estiva- 

 tion). Aestivation is usually associated with 

 relatively high temperature and physically 

 inaccessible water (drought). Both hiberna- 

 tion and aestivation are associated with, 

 physiologically, a lowered organismal me- 

 tabolism, and, ecologically, with a lowered 

 community metabolism. 



Animals react differently to these periodic 

 environmental extremes. Even between 

 closely related genera the pattern of dor- 

 mancy, or its presence or absence, may 

 depend upon the species involved, or may 

 vary among the several individuals of a 

 given species population. In the most gen- 

 eral terms, dormancy is to be regarded as 

 a broad adjustment for shelter during a 

 periodic, seasonal response of the relatively 



