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NATURALIST'S GUIDE TO THE AMERICAS 



and 1880) there is nothing in zoological 

 literature representing the essence of 

 modern synecology as do Clements' 

 two works on plants. (Succession, 1916, 

 and Plant Indicators, 1920.) Clements 

 has for some time recognized the im- 

 portance of considering animals in 

 plant ecology. Plant ecologists in gen- 

 eral are prone to describe formations 

 and associations, often without giving 

 a comprehensive idea of the nature of 

 an area as an animal habitat. For 

 example the combination grassland and 

 streamside and grove forest of the 

 Mississippi Valley which, on account 

 of animal movement, seems best named 

 savanna, was referred to in several 

 manuscripts as deciduous forest and 

 prairie without any statement as to 

 arrangement and relative area of the 

 two. Many of the original large and 

 small animals of this region, charac- 

 teristically divided their time (usually 

 seasonally) between the two plant 

 communities or lived at the shrubby 

 border between them. Plant ecologists 

 appear to have recognized the symbiotic 

 relation of plants and animals in com- 

 munities only to a small degree. Ani- 

 mal ecologists have of course not con- 

 tributed their share of knowledge for 

 reasons already noted. Movement of 

 animals from one small plant community 

 to another may be as important to the 

 general biota as is number of dominants 

 or at least secondary considerations 

 concerning plants in communities. 



While faunistic zones agree with 

 vegetation in some cases, those who use 

 life zones often divide regions with 

 similar climate and uniform vegetation 

 into two or more zones because the 

 species are different, though physiolog- 

 ical relations may be supposed to be 

 similar (Chapman, 1917). It may be 

 said that floristic and faunistic geog- 

 raphy including life zone work rests 

 on a background of evolution and migra- 

 tion, while ecological plant and animal 

 geography have a similar relation to 

 (climatic) conditions and physiology. 



No one doubts that the life zones as 

 used mainly by zoologists are a correct 



representation of certain facts of rela- 

 tionship, and are worthy of scientific 

 recognition. They do, however, vio- 

 late two important principles or methods 

 of modern ecology. In the first place 

 they fail to separate the local communi- 

 ties determined by soil, water, etc., 

 from the extensive communities which 

 are commonly regarded as determined 

 by climate. Life zone index organisms 

 are as likely to belong to local areas 

 such as stream margins or other early 

 stages in succession as otherwise. 

 Second, the life zones sometimes divide 

 a uniform climax association into two 

 or three parts as in the case with de- 

 ciduous forest and mixed prairie. In 

 much of the United States life zones 

 are separated by east and west lines 

 and plant communities by north and 

 south lines. To the north in Canada 

 the two appear to be in better agree- 

 ment. In the Rocky Mountains they 

 are sometimes in agreement and some- 

 times not. In the tropics most of the 

 life zone studies have been carried on 

 in mountainous regions. While the 

 work is largely descriptive, the expres- 

 sion of the viewpoint is found in Chap- 

 man's introduction, in which he states 

 that "To determine the boundaries of 

 zones and faunas as they are manifest 

 by birds and mammals is our first aim 

 . . . and trust that we may throw 

 some light on laws governing the origin 

 of species. . . ." This is not the 

 object of modern ecology, which is on 

 the contrary concerned with symbiosis 

 (sense broad) succession, climax types, 

 and physiological relations to the 

 physical environment and its rhythmic 

 phenomena, etc. 



However, it is true that the life zones 

 pointed out by investigators in Central 

 and South America do consist of one 

 or more landscape aspect areas. The 

 investigators along this line possess an 

 excellent knowledge of the landscape 

 aspect types. Accordingly, a measure 

 of agreement has been reached for the 

 tropics; though starting from two quite 

 different viewpoints, it is evident that 

 agreement cannot be general. Parallel 



