FIRST FOUR DECADES OF THE TWENTIETH CENTURY 



61 



tion furnished by earlier ecological training. 

 These two origins were wedded later, par- 

 ticularly in the fourth decade. Perhaps a 

 brief elaboration of this subject is in order. 



Approaching these studies through the 

 ecological door were men like W. C, Alice 

 and Royal N. Chapman, both feehng ap- 

 parently that there was much to be de- 

 sired in terms of environmental control 

 even for natural populations. The method 

 of such men was to bring into the labora- 

 tory an animal that could be cultured 

 there successfully and study its various 

 group responses under reasonably con- 

 trolled conditions.* Chapman transferred 

 his attention to the flour beetle, Tribolium 

 confusum, and in this organism found an 

 answer to his problem. His most important 

 paper appeared in 1928, in which he set 

 forth the concepts of "biotic potential" and 

 "environmental resistance" and substanti- 

 ated them with empirical evidence. We 

 shall return to these ideas in later sections 

 of the book and discuss them carefully 

 (p. 303). 



Alice continued his work on communities 

 and natural populations, but brought cer- 

 tain phases of these problems into the lab- 

 oratory for solution. Particularly was this 

 true of his investigations on aggregations. 

 An examination of his writings shows that 

 between 1921 and 1930 he studied, as ex- 

 perimental populations, isopods, the brittle 

 starfish (Ophioderma) , the marine flat- 

 worm (Procerodes) and planarian worms. 

 Unlike Chapman, Alice's interest was not 

 so much in the total analysis of the pop- 

 ulation as in studying in the laborator)' 

 certain responses largely protective in 

 character that arose as a consequence of 

 aggregation or population density. 



The other approach through experimental 

 population studies is typified by the work 

 of Raymond Pearl and his colleagues. Be- 

 tween 1921 and 1930 Pearl and his group 

 published an astounding amount of ma- 

 terial in journal, lecture, and book form 

 on experimental populations of Drosophila 

 melanogaster. It is not our province here 



" A somewhat idealized definition of an ex- 

 perimental population would be: a group of 

 inbred organisms cultured under controlled, yet 

 manipulatory, environmental conditions for 

 which repeated censuses of all stages can be 

 readily taken. Extensions and modifications of 

 this definition will appear in the section on 

 Populations. 



to evaluate these studies. It is our respon- 

 sibility to indicate the aspects of the sub- 

 ject covered by them and attempt to weigh 

 their impact on third decade ecology. 



Pearl was interested in experimental 

 populations from the following five view- 

 points: 



1. The form of population growth. This 

 work was largely the demonstration that 

 various populations (e.g., yeast, Parame- 

 cium, Drosophila, man) followed a sigmoid 

 growth curve (the "logistic"). 



2. The analysis of population density and 

 its end effects. Pearl was thoroughly con- 

 vinced of the biological importance of this 

 matter. In 1930 he said, "In general there 

 can be no question that this whole matter 

 of influence of density of population, in all 

 senses, upon biological phenomena, de- 

 serves a great deal more investigation than 

 it has had. The indications all are that it is 

 one of the most significant elements in the 

 biological, as distinguished from the phys- 

 ical, environment of organisms" (p. 145). 

 Population density was analyzed primarily 

 as it affected reproduction and mortality. 



3. The problem of longevity and those 

 factors, both genetic and ecologic, that in- 

 fluence it. These studies were actuarial in 

 character, and the data were summarized 

 to good advantage in life tables. 



4. The possible growth analogies be- 

 tween experimental and human populations. 



5. An illustration of the applicability of 

 quantitative methods to biological research. 



In sum, experimental population studies 

 appealed to the workers of the decade (as 

 well as in the 1931 to 1940 period) for 

 these major reasons : 



1. The results can be expressed in quan- 

 titative terms. 



2. The end responses that can be studied 

 include such variables of patent biolog- 

 ical importance as: 



(a) The factors contributing to 

 population growth— fecundity, 

 fertility, fission rate, success 

 and rate of development. 



(b) The factors contributing to 

 population decline— differential 

 morbidity and mortality. 



(c) The factors concerned with se- 

 lection pressure. 



3. There is an absence of terminology 

 in these studies. 



