16 NATURE AXD RELATIONS OF BIO-ECOLOGY 



coordination. The discussion of the microplankton by Gran takes 

 account of the usual division into neritic and oceanic communities 

 and further suggests the major regions or climaxes of the Atlantic 

 Ocean. Appelof has described the bottom fauna without defining 

 communities, but with such a treatment of composition and distribu- 

 tion as to indicate their general outlines. 



Hjort has recognized and described a number of pelagic communi- 

 ties in both the Atlantic and Pacific Oceans. He has dealt with the 

 vertical ranges of dominants in such detail as to suggest the basis for 

 the distinction of the most important layers. The concept of domi- 

 nance is more or less clearly in evidence, thus making it possible to 

 outline a number of associations and faciations in a preliminary 

 manner. 



Oliver (1915, 1923). In addition to Oliver, Hedley (1915) and 

 Johnston (1917) have studied litoral communities in Australasia from 

 the biotic approach, but the more detailed work of the first will serve 

 to illustrate their general outlook. In his study of the New Zealand 

 shore (1923), Oliver defines the animal-plant formation as a biotic 

 community with its principal ecological groups in definite combina- 

 tion and relation to the habitat. The community is thus based upon 

 growth forms and environment, and formations are distinguished by 

 differences in the dominant ecological forms. The dominants of the 

 littoral formations are attached animals and plants or in some cases 

 sedentary animals. The effect of the substratum is considered to be 

 of major importance. Accordingly, littoral formations are classed 

 as those on rock, with the dominant form varying from algae to 

 shelled animals, and those on sand and mud, ranging from animal to 

 plant by virtue of height above low tide. These two groups are 

 divided into formations, subformations, and associations, but, since 

 this is without reference to climax or successional criteria, it is uncer- 

 tain how closely these accord with the units employed in the present 

 book. 



Limnology. The rapid development of this field has been an out- 

 standing feature of biological progress during the past two decades. 

 In a recent monograph by Naumann (1932), hardly a tenth of the 

 350 titles given in the bibliography had appeared before 1917. It 

 represents in some measure a movement independent of ecology, ap- 

 parently deriving its initial impulse largely from practical considera- 

 tions but going far beyond these in its synthesis of related fields. The 

 number of workers concerned has been large, but the organization of 

 the subject and the formulation of concepts are probably to be cred- 

 ited more to Naumann and Thienemann than to any other two 

 men. 



It scarcely needs to be pointed out that limnology is that portion 

 of ecology which deals with fresh-water biomes and habitats. It 

 is characteristically ecological in its emphasis upon the measurement 

 of factors and has perforce devoted more attention to the biotic com- 

 munity than any other portion of ecology. As indicated previously 

 it has been quick to perceive the significance of the concept of the 

 complex organism, and likewise the importance of its reaction upon 



