58 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



With aggregation paramount, families are tlie rule; when the proc- 

 esses are more or less balanced, colonies prevail; with migration 

 emphasized, the mosaic of vegetation results. In closed communities, 

 it is practically impossible for annuals to persist or to enter, and the 

 pattern often reflects the tendency of perennials with offshoots to form 

 families, as illustrated by Antennaria or Erythronium. 



Aggregation among Animals. In attempting to bring together the 

 knowledge of two fields which have developed as independently as 

 botany and zoology, or more specifically, plant ecology and animal 



Fig. 12. — Aggregation of a native goosefoot {Chenopodimn IcptophyUum) in a 

 short-grass pasture covered with wind-borne silt; eastern Colorado. (Photo bj- 



Edith Clements.) 



ecology, difficulties as to the different uses of the same term arise fre- 

 quently, aside from the fact that aggregation long has been used by 

 plant ecologists to apply solely to the process of assembling in a 

 group. Alice's use of the word introduces an additional general term 

 for the communities of small size. Aggregation is accordingly used 

 here only in the sense of the process. 



As compared with plants, aggregation through reproduction is 

 comparatively rare or temporary. Temporary aggregation occurs in 

 the case of vertebrates which care for their young. Nest-building 



