ECOLOGY. 355 



principle of the excess-deficit balance will make it possible to anticipate the 

 major variations in rainfall and to base the use of irrigation water upon some 

 knowledge of what will be available. The fact that the rainfall of a region 

 will be three or four times greater at the maximum than at the minimum makes 

 it evident that reclamation systems should be organized upon an expansion- 

 contraction basis and should provide for subsidiary reservoirs in the middle 

 and upper portions of a basin to store flood-waters against a drought and 

 thus insure a constant and equable supply. 



Principles and Methods of Bio-ecology, hij F. E. Clements, C. T. Vorhies, 



and W. P. Taylor. 



The concept of the biome was advanced in 1915 to emphasize the im- 

 portance of treating plants and animals together as mutually interacting 

 members of a community and hence of recognizing that plants must con- 

 stitute the basis of the different units, both climax and successional. This 

 concept has been tested during the succeeding years of field study, and the 

 entire field of bio-ecology has been sketched in outline to serve as a guide for 

 further work. The principles and methods involved in the relation of both 

 individual and community to the habitat, as well as of plants and animals to 

 themselves and to each other, have been analyzed in detail. During July 

 and August field studies in bio-ecology were made in the Sierra Nevada of 

 California on the line of the transect established for transplant and other 

 experimental work. The stations included Mather and Aspen Valley in the 

 montane forest climax, Porcupine Flat and Tuolumne Meadows in the 

 subalpine forest climax, and Benton, Mono County, in the sagebrush climax. 

 Further studies were made to determine whether animals fall properly into 

 communities of which plants form the basis, to define more accurately the 

 correlations between plants and animals, to adapt and refine census methods, 

 and to extend the knowledge of bird and mammal life-histories. Various 

 methods, especially those of plant ecology, were subjected to field test in 

 order to determine their fitness for quantitative work with birds and mam- 

 mals. Additional evidence was obtained to show that the biome is a basic 

 concept, indispensable to the causal and developmental study of biotic 

 communities, and that the climaxes and seres found in vegetation constitute 

 the groundwork in which animals find their proper place. The summer's 

 investigations emphasized the great need of definite and quantitative cor- 

 relations between plants and animals, as well as the need for ecological life- 

 histories that will take into account the factors of the habitat, the reactions 

 of the organisms, and their respective roles in the community. 



Biotic Succession in Bad Lands, by F. E. Clements. 

 As usual, a considerable number of bad-land areas have been visited during 

 the year. These ranged in time from the Permian to the Pleistocene and in 

 extent from the Red River to the Pacific. The chief areas were the Wasatch, 

 Green River, Bridger, and Uinta of northeastern Utah and southwestern 

 Wyoming, the Cretaceous Mancos and Steele of the same region, and the 

 Ohgocene and Miocene of western Nebraska and eastern Wyoming. The 

 Permian "breaks" of the Great Plains were seen from the Red River to the 

 Edwards Plateau in Texas, and the Miocene bad lands of the Pacific Coast 



