(B) Companion species 



(2) Indifferent (vage), occurring without pronounced 

 affinity or preference for any particular kind of 

 community 



(C) Accidental species 



(1) Strange (fremde), rare and accidental intruders 

 from another community or relicts from an earlier 

 stage of succession. 



The characteristic species, including the exclusive, selective, and 

 preferential, together with those high in constancy, including the 

 dominants, are the most important in characterizing a com- 

 munity-type. The greater the ratio of the total number of 

 constant species to the total number in a particular community, 

 the more developed is its homogeneity; and a large number of 

 characteristic species makes the floristic delineation of a type 

 sharper than a few. Community-types which have high ratios of 

 both constant and characteristic species are well established, and 

 consequently are unlikely to occur in newly formed habitats or 

 in early stages of succession. Species of high fidelity may have con- 

 siderable value in indicating ecological conditions, e.g., the 

 restriction of certain species to particular soil conditions, but 

 fidelity is primarily a sociological quality and indicator species 

 is a more appropriate term for plants that are associated with 

 such conditions. Some plant sociologists consider a high degree 

 of constancy and dominance as more important than fidelity in 

 characterizing communities; '^^-^^^ however, for completeness in 

 characterization both constancy and fidelity should be used as 

 much as possible, for one complements the other. 



A few examples indicating the importance of fidelity will be 

 given. In Iowa, some rather rare species of high fidelity are the 

 first to disappear when the prairie is disturbed, and they also en- 

 counter great difficulty in becoming re-established; therefore, 

 such plants are particularly important in describing highly 

 developed prairie. In attempting re-establishment, a grouping of 

 appropriate grasses might be considered satisfactory, but a 



Synthetic: Characteristics of the Cosnsnunity • 127 



