THE STRUCTURE OF CLIMAXES 245 



North Sea (Davis, 1925) , have been referred to as consociations (Shel- 

 ford, 1935), but when compared with plant consociations certain dif- 

 ferences are seen to exist. In view of the apparent dominant func- 

 tion of brittle stars already referred to, and the possible dominance 

 of marine fishes, further investigation may indicate that Spisula is a 

 secondary dominant. Furthermore, while Spisula outnumbers other 

 constituents a thousand to one, the latter are nevertheless present. 



The sea exhibits other groupings that resemble consociations, the 

 oyster bed constituting an example. The oysters form a substratum 

 which encourages hard-bottom species and hence serves as the basis 

 for a community that would not otherwise occur in the area, espe- 

 cially where water is quite brackish. The bivalve, Modiolus modiolus, 

 forms similar groups and supports hard-bottom communities on the 

 shells, while resting on bottom too soft to support these associates. 

 These are more far-reaching in their effects and relations than the 

 consociation dominant in a plant community. It must further be 

 recognized that, while the oyster and Modiolus communities appear 

 like fragments of other biomes, such as groves of deciduous trees in 

 grassland, they are not so, but are unique certainly so far as the oyster 

 is concerned. However, the Modiolus communities of the North Pa- 

 cific have been regarded as the subclimax stage of the Strongylocen- 

 trotus-Argbuccinum biome because (a) they support this on their 

 shells, and (5) the}^ are climax dominants of the hydroclimate above, 

 regardless of the unfavorable bottom. 



Minor Units. As has been indicated earlier, the subdominant plants 

 constitute secondary groupings within the community of dominants. 

 In the main, the life form of subdominants is that of the forb, but 

 bush and shrub are also to be included, chiefly in layered forests. 

 Communities of this rank have long been known as societies, being 

 called simple or pure when composed of a single species, and mixed 

 when comprising two or more of similar importance. The two most 

 significant categories are those of aspect or seasonal and layer socie- 

 ties, the former marking the change of tone in the plant matrix through 

 the seasons and the latter being best developed in forest. Communi- 

 ties of small animals, chiefly arthropods, restricted to the layers have 

 been called layer societies. The plants most nearly equivalent to the 

 invertebrates of these societies are the mosses, lichens, and fungi. 



The vast majority of the arthropod constituents of the layer ani- 

 mal societies of the deciduous forest biotic community (Weese, 1924; 

 Blake, 1926; Smith, 1928) move to the ground surface and under 

 fallen leaves for the winter, greatly increasing the population of that 

 layer and constituting an hiemal layer society. It is not correct to as- 



