60 



THE HISTORY OF ECOLOGY 



thesis, and, by that token, not much de- 

 velopment of ecology as a unified science. 

 It would be incorrect to say that this uni- 

 fication exists today, although some notable 

 steps were to be made during the decade 

 1931 to 1940. 



When the zoologist started to ask him- 

 self the quantitative question "How many?" 

 in addition to the qualitative question 

 "What Idnd?", natural population studies 

 began to emerge from natural history and 

 community investigations. Many ecologists 

 felt that community analyses with their 

 many variables were too complex to be 

 feasible methodologically. Accordingly, 

 they sought to better the situation by count- 

 ing certain species of animals that hved 

 within the framework of the total com- 

 munity and were of enough ecological im- 

 portance to warrant such careful scrutiny. 

 These counts were population censuses. 



It is inaccurate to suggest that such 

 studies appeared de novo in the third dec- 

 ade. There were several historical preced- 

 ents for them. One important precedent 

 lay in earlier ecological work itself, both 

 botanical and zoological. A basis for pop- 

 ulation studies had been established in the 

 literature before 1900 (see p. 24). In fact, 

 we mentioned earlier a number of papers 

 that could be cited appropriately. Another 

 precedent came from the work of biologists 

 with a flair for biometry and an interest 

 in biological groups as such. Many of these 

 men have already been mentioned. Still an- 

 other precedent stemmed from the devel- 

 opment of statistics as a method for han- 

 dling biological data, as a technique for ra- 

 tionalizing and formulating biological inter- 

 actions (e.g., Lotka, 1925; Volterra, 1926), 

 and as a basis for the philosophical inter- 

 pretation of scientific evidence. These vari- 

 ous fields in one way or another were 

 forcing themselves into the ecologist's 

 thinking. From them the population ap- 

 proach, as did many other approaches, be- 

 gan to crystallize. 



The early work on natural populations 

 frequently had an economic focus and 

 motivation, as, to a large degree, is still 

 true today. The investigators were con- 

 cerned with certain species, frequently an 

 insect, that as populations in nature had 

 a significant relation to some problem of 

 human disease, diseases of other animals, 

 or agriculti're. Analvsis of the former prob- 

 lem yielded data on epidemiology, actually 



an 



ail excellent example of quantitative ecol- 

 ogy. The distinguished British sanitarian, 

 Major Greenwood (1932), says of this 

 subject: 



"Epidemiology displays the general factors 

 which operate upon populations or aggregates, 

 and lead to the outbreak of a sickness afltecting 

 several organisms within a short time. The unit 

 of the epidemiologist is the population ..." 



Thus many of the natural population studies 

 were epidemiological in character and 

 stressed the statistics of host-parasite inter- 

 action. A masterly summary of the prin- 

 ciples vmderlying this science was written 

 by Wade Hampden Frost in 1927. 



Analyses of insect pest populations fre- 

 quently yielded many data on the abun- 

 dance of such forms in relation to climatic 

 cycles and to predation and parasitization 

 pressures. Some representative studies of 

 the decade were those of Cook (1924) on 

 cutwoiTn populations, Bodenheimer (1925) 

 on the Mediterranean fruit fly, Shelford 

 (1927) on the codling moth, and Swynner- 

 ton (1921) on tsetse fly populations as a 

 vector for trypanosomes. 



Natural population studies also were 

 concerned with cycles of abundance of 

 mammals and birds. In the literature of 

 the period we find studies on lemmings, 

 mice, rabbits and hares, marmots, musk- 

 rats, and certain ungulates and birds. 

 While the factors controlling these cycles 

 were not analyzed critically in many cases, 

 the information in the literature suggests 

 that the common causes are epidemics, 

 variation in quality and quantity of food, 

 and sunspot or climatic influences. Elton 

 was much taken with this research, as evi- 

 denced by his own papers (1924, 1925) 

 and Chapter 9 in his text. Other represen- 

 tative publications are those by Hewitt 

 (1921) on the wolf, hare, lynx, and red 

 fox; Soper (1921) on hares; and Brooks 

 (1926) on deer. 



Experimental or laboratory population 

 studies had their essential inception in the 

 decade 1921 to 1930 and grew out of two 

 groups of investigators. On the one hand, 

 ecologists with a traditional background 

 turned their attention, in part at least, to 

 such studies. On the other hand, general 

 biologists and biometricians interested in 

 the experimental approach to growth of 

 groups became interested in such popula- 

 tion studies without the impetus or motiva- 



