234 CLIMAX AND SERE 



done on succession in fresh-water communities, the existence of true 

 chmaxes is barely demonstrated in rivers and large lakes. In the 

 ocean, in spite of the paucity of successional studies on marine com- 

 munities, the age and stability of these justify considering them as 

 climax, provisionally at least. 



THE STRUCTURE OF CLIMAXES 



Evaluation of Constituent Species. It is sufficiently obvious that 

 the first requisite to the evaluation of a biotic community is a list of 

 component species, showing relative abundance and size. In the case 

 of a climax such as a prairie or a lake, this can be obtained only by 

 means of quantitative studies in which all available methods of collec- 

 tion and enumeration are employed. Through the several seasons and 

 for two or more years at the very least, sample catches over a wide 

 extent of territory are indispensable. The range within which im- 

 portant species retain their dominant or influent character must be de- 

 termined. The important species of a community will vary within 

 extreme limits in practically all their characteristics, ranging from 

 size to number and role, and the next essential task is to take account 

 of these in accordance with their significance. 



Composition of the Biome. Constituent species differ with respect 

 to life form and life history, size, abundance, frequence, constancy, 

 and space and time relations, such as aspection, annuation, and suc- 

 cession. Practically all these have some significance in the role of 

 each organism, but life form and life habit, size, and abundance are 

 regularly the most decisive. On the one hand, they determine the 

 response to the habitat and the reaction upon it, and on the other 

 the interrelations of the species in terms of competition and coaction, 

 such as food and shelter. Moreover, these processes exhibit essential 

 differences in plants and animals, or with respect to their location on 

 land or in the sea, and in climax or sere. However, in spite of the 

 distinctions between terrestrial climates and hydroclimates and cli- 

 maxes, the bases for the ecological classification of the organisms 

 involved are identical for the most part. These have long been ap- 

 plied, in part, to the role of plant species in land climaxes and their 

 seres, and the present task is to employ them for the evaluation of 

 land animals, and of both plants and animals in water communities. 



In the three succeeding chapters, the biome constituents have been 

 classified as dominants, major influents, subdominants, influents, sub- 

 infiuents, and secondary species. When the categories are extended to 

 include animals and cover the phenomena of the waters, often no 

 sharp line of demarcation between the categories remains. 



