36 ANIMAL AGGREGATIONS 



Mytilus or Ostraea. 



Beta. Individuals not organically connected. 



I. Aggregations primarily due to reactions to environment. Ani- 

 mals live at this level of group integration in a common habitat but 

 without marked organization into groups. This category would in- 

 clude the habitat communities of the ecologists. To some extent 

 the plants share with the animals in the organization of this com- 

 munity, usually, in fact, being the conspicuous factors in land com- 

 munities; hence the modern emphasis by ecologists upon the biota. 

 Further classification would depend on the physical or biotic factors 

 in the environment which dominate the habitat. 



II. Aggregations primarily due to reactions to other organisms. 

 These are generally recognized to be more closely integrated than are 

 habitat communities, being bound together by biological relation- 

 ships as well as by those of habitat. There is no sharply defined line 

 to be drawn between the two. 



In addition to the subdivisions based upon the method of inte- 

 gration, three fairly definite subdivisions can be recognized, based 

 on degree of integration. 



1 . Relatively slightly integrated groups in which the primary (in- 

 dividual) reactions predominate, and whose survival value is ap- 

 parent only after experimentation. The aggregations of isopods, 

 OpJdoderma, and Proccrodes, to be discussed later, are examples. 

 Further classification would depend on method of formation of the 

 group and on the type of integration, as well as on the different sorts 

 of animals of which it is composed. Many of Deegener's groupings 

 could be taken over here and in the next two categories. 



2. Moderately well-integrated groups in which the secondary 

 (group) reactions predominate although primary reactions are still 

 strongly in evidence. The survival value of the group is more ob- 

 vious. Schools of fish, flocks of birds, and the like would frequently 

 come under this category. 



3. Highly integrated groups in which the primary reactions are 

 decidedly in the minority and the social value is strongly in evidence. 

 Here would be classified the different insect societies, together with 



