230 



CLIMAX AND SERE 



life form in the case of land climaxes, but usually to several in the 

 case of aquatic ones. In fact, a change of life form or life-form com- 

 binations is the most essential difference between biomes. This is 

 illustrated on the plant side by grassland, scrub, and forest as to 

 grand divisions, and by coniferous, deciduous, and broad-leaved ever- 

 greens as subdivisions of the tree type. Among animals, the life forms 

 are more varied, owing to the presence of sessile, sedentary, and motile 

 forms of large size. The several types of motility (and associated 

 forms), manifested in the vertebrates as flying, running, swimming, 

 and burrowing, are repeated in some of the other major divisions of 

 the animal kingdom and serve to show how complicated the field 

 becomes. 



Life form has been but little used in designating animal com- 

 munities. Coral communities have been discussed (Brooks, 1893) in 

 comparison with plants, but it has not been found possible to treat 

 them here. Shelf ord (1935) recognized bivalve-annelid, barnacle- 

 mussel, and gastropod-echinoderm communities. The last two may 

 be combined under barnacle-gastropod and the first subdivided to give 

 the classification found in Chapter 9, all of which indicates the relation 

 of life-form types to the invertebrate phyla and the diversity of form 

 that enters a community. 



TABLE 9 



Life-habit Statistics of 15 Influent Animals Each of Grassland and 



Coniferous Forest, All Occurring in Southern Manitoba 



(Shelford, 1915) 



The fact that each major marine community may be distinguished 

 by life-form combinations is readily brought out by an inspection of 

 the quadrat-content illustrations published by the Danish Biological 

 Station (Figs. 75, 76, 78, 79, 81, 82, page 335, etc.; Petersen, 1918), 

 which show several life forms: bivalve, worm, starfish, etc. By con- 

 trast, the dominants of land climaxes typically belong to a single life 

 form, such as grass, shrub, or tree, but two or more secondary forms 

 may occur in prairie, such as mid and short grass, sod and bunch grass. 



