36 



THE HISTORY OF ECOLOGY 



munity. Any change in any of the relative fac- 

 tors of a bioconose produces changes in other 

 factors of the same. If, at any time, one of the 

 external conditions of hfe should deviate for a 

 long tune from the ordinary mean, the entire 

 bioconose, or community, would be trans- 

 formed. It would also be transformed, if the 

 number of individuals of a particular species 

 increased or diminished through the instru- 

 mentahty of man, or if one species entirely 

 disappeared from, or a new species entered 

 into, the community." 



S. A. Forbes (1887) apparently took over 

 and expanded the ideas of Mbbius. The 

 quotation already given (p. 32) shows that 

 Forbes recognized a "close community of 

 interest" even between predators and prey 

 in a community. Warming (1895) saw the 

 unity of plant communities as a result of 

 his study of the vegetation of Danish dunes. 

 Braun-Blanquet, disregarding the zoological 

 studies we have just reviewed, ranks Warm- 

 ing's work as the most important landmark 

 in the development of community ecology 

 since that of Heer. In one important re- 

 spect, this estimate is just: modern com- 

 munity studies have mainly been stimulated 

 by Warming's findings rather than by those 

 of his zoological predecessors, Edward 

 Forbes, Verrill, Mobius, and S. A. Forbes. 



Communities may be integrated by the 

 requirements imposed by a uniform, cir- 

 cumscribed habitat as well as by the mutual 

 uiteractions between organisms such as 

 those that characterize a biocoenosis. The 

 two kinds of integration do not necessarily 

 yield similar results. Caves furnish one of 

 the striking examples of a unity imposed by 

 the habitat. Interest in cave hfe was strong 

 in the Darwinian period of the last century. 

 Attention was focussed particularly on the 

 origin and evolution of cave faunas. This 

 involved a consideration of adaptations, 

 especially those of sense organs, the migra- 

 tion of preadapted animals into caves, the 

 degeneration of eyes and other features, and 

 the conditions of existence to be met there. 

 Food habits of cave animals, including what 

 we now call food chains, and ultimate 

 sources of food were also studied. Absolon 

 in Europe, and Packard and Eigenmann in 

 America, engaged in such investigations. 

 The summaries of progress to date and 

 bibhographies by Packard (1888, 1894) 

 indicate that a fair knowledge of the gen- 

 eral relations of cave animals had been 

 attained by the closing years of the nine- 

 teenth century. Active work along the 



same Hues continued into the new century 

 (see p. 48) and will be critically dis- 

 cussed in the section on Evolution. 



Quantitative studies of the plants and 

 animals of a given community appear to 

 date from the work Hensen began in 1882, 

 the results of which were published in the 

 latter part of 1887. Hensen was primarily 

 interested in two questions: (1) What 

 quantities of hving plankton organisms does 

 the sea contain in a given area at a certain 

 time? And (2) how does the quantity of 

 plankton vary from place to place and 

 from time to time? He attempted to find 

 answers to these questions by collecting 

 plankton quantitatively by means of small- 

 meshed nets drawn through a known vol- 

 ume of water. 



A large and critical Hterature soon de- 

 veloped, much too voluminous and compU- 

 cated for us to review thoroughly. An early 

 summary is given by Johnstone (1908), 

 and some of the more important papers 

 are fisted by Adams (1913) in his excel- 

 lent annotated bibhographies. 



Hensen's work at once stirred up con- 

 troversy. Haeckel (1890) doubted the 

 vafidity of Hensen's conclusions in a mem- 

 oir done in his usual attractive style, to 

 which Hensen (1891) repfied effectively. 

 Kofoid (1897), though also engaging in 

 quantitative studies, dissented from Hen- 

 sen's conclusions, and Lohmann (1901) 

 undertook to show that Kofoid had not 

 understood the nature of the method he 

 criticized. Kofoid (1903) gave an excellent 

 and detailed report on a quantitative study 

 of the plankton of the Ilfinois River. In 

 fact, quantitative as well as quafitative 

 plankton studies flourished to such an ex- 

 tent that Shelford used to warn his classes 

 in the early years of the present century 

 that ecology was not a synonym for plank- 

 ton study. 



Quantitative methods were soon appfied 

 to the investigation of communities of the 

 inshore bottom of the ocean by Petersen 

 (1893 and later) and to those of the land 

 by Pound and Clements (1898), Dahl 

 (1898), and others. 



HYDROBIOLOGY 



Discussion of the rise of self-conscious 

 ecology will be delayed only for a brief 

 further consideration of the development 

 of hydrobiology or, more exactly, of its 



