FIRST FOUR DECADES OF THE TWENTIETH CENTURY 



59 



real biological entity, irrespective of its 

 global location. 



The "structural" studies had two major 

 focal points, both of which are aspects of 

 the same problem. On the one hand, there 

 were extensive studies on food and feeding 

 relations within the community, such as 

 those of Sanders and Shelford (1922) and 

 Summerhays and Elton (1923) on terres- 

 h-ial communities; of Needham, Juday, 

 Moore, Sibley, and Titcomb (1922) on a 

 fresh-water community; and of Hardy 

 (1924) on a marine community. On the 

 other hand, there was a growing interest 

 in "how many" animals occupied a certain 

 niche in a community and the effect of this 

 quantitative relation on the community as 

 a whole. This aspect was really that en- 

 compassed by the natural population 

 studies, and we shall return to it shortly. 



After studying a series of papers on ani- 

 mal communities and working actively on 

 the problem himself, Elton concluded that 

 (p. 55): 



'■ . . . Animals are organised into a complex 

 society, as complex and as fascinating to study 

 as human society. At first sight we might 

 despair of discovering any general principles 

 regulating animal communities. But careful 

 study of simple communities shows that there 

 are several principles which enable us to 

 analyse an animal community into its parts, 

 and in the light of which much of the apparent 

 complication disappears. These principles are 

 food-chains and the food-cycle; size of food; 

 niches; the pyramid of numbers." 



It is not our task here to discuss these 

 problems in a technical sense. That will 

 come in later chapters. We are concerned 

 only with the historical point that the study 

 of natural groups or communities had ad- 

 vanced to such a stage in the third decade 

 that it was possible to conclude: (a) that 

 communities are integrated to a large de- 

 gree by the sum total of their feeding re- 

 lations, and (b) that these relations, al- 

 though they may be completely different 

 in detail, are the common property of all 

 communities, whatever the tvpe and wher- 

 ever located. Several other studies that ap- 

 peared during the period and which should 

 be cited are those of Weese (1924), Smith 

 (1928), and Shackleford (1929). 



Ecologists were well aware of the signifi- 

 cance of temporal factors in the organiza- 

 tion of the community. Succession was 

 firmly ensconced in ecological thought as a 



time factor that brought about eventual 

 community equiUbrium when the climax 

 was attained. We have now enough of a 

 background for this point to make unneces- 

 sary its further discussion. Other temporal 

 aspects were recognized. Some of these 

 were (1) day-night rhythms; (2) migra- 

 tions on a vertical axis that occurred at 

 certain intervals as, for example, plankton 

 migration in the sea or vertical migration 

 in a forest; (3) tidal rhythms; (4) climatic 

 rhythms of various types, including the 

 seasons; and (5) extramundane rhythms. 

 Many ecologists of the 1921 to 1930 period 

 were doing more than recognizing these 

 rhythms. They were analyzing them in re- 

 lation to the community constituents. 



Throughout this book we shall have 

 much to say about the phenomenon of ani- 

 mal aggregations and its significance for 

 ecological theory. This is a phase of ecol- 

 ogy studied with much intellectual profit. 

 As such, it needs to be considered briefly 

 in this historical review. It is brought in 

 at this point in the third decade, not be- 

 cause the subject "originated" then, but be- 

 cause it was summarized and evaluated 

 in a paper by Allee (1927a) and thus given 

 impetus for further growth. Certain phases 

 of the general problem had been consid- 

 ered earlier by botanists (especially 

 Clements), zoologists, and philosophers, and 

 their contributions must not be under- 

 estimated. But to Allee goes the credit for 

 a clear statement of the problem in terms 

 of animal ecology and "general sociology." 

 In his review Allee discussed the method 

 of formation of aggregations: general factors 

 conditioning aggregations; single-species, as 

 contrasted with mixed-species, aggregations; 

 integrative phenomena within aggregations; 

 and the social significance of aggregations. 



Despite the existence in the 1921 to 1930 

 period of considerable knowledge about the 

 physical-chemical environment, the animal 

 community, the phenomenon of aggrega- 

 tion, and, as we shall see in a moment, the 

 population, ecologists did not coordinate 

 these various phases to anv degree. When 

 Allee wrote his paper in 1927 he outlined 

 the field of animal aggregations as he 

 viewed it. But this did not mean that, over 

 night, the subject flowered and matured. 



In the third decade there was fact find- 

 ing; there was speculation; there were 

 some attempts at a synthesis of ecological 

 principles. But there was not much syn- 



