INTRODUCTION 



culty in biology is associated with the in- 

 trinsic complexity of the materials to be 

 analyzed or synthesized. 



Biologists working with the social hfe of 

 insects, or of other animals, are frequently 

 tempted to regard their own work as more 

 precise than that done by equally compe- 

 tent students of human sociology; and those 

 deahng with human material often feel 

 compelled to explore subjective psychologi- 

 cal aspects of sociology that are almost or 

 completely closed to the student of social 

 insects. 



Much of human sociology is an integral 

 part of ecology. There are reciprocal in£u- 

 ences between these two sciences, influ- 

 ences that are especially apparent in such 

 practical matters as the development of the 

 Canal Zone in Panama, with the details and 

 outreach of the Tennessee Valley Author- 

 ity, with stream pollution, and with the 

 whole set of problems centering about the 

 potential or actual dust bowls of semiarid 

 regions of the world. Much that is now be- 

 ing done in such projects is recognized as 

 ecology. 



A major difference between human rela- 

 tionships and those of other animals is the 

 role played by the symboHc language of 

 man, and by ideas, as contrasted with the 

 restricted use of both among nonhuman 

 populations. The extent to which animals 

 other than primates communicate with each 

 other, and the means employed, are still 

 matters for investigation. We know much 

 about the importance of odors as signals, 

 particularly among such animals as dogs, 

 ants, and moths. We also know about var- 

 ious cries, songs, and visual displays that 

 reveal sexual receptivity, or nonreceptivity, 

 that faciUtate aggregation or warn of dan- 

 ger. We have evidence that the complex 

 activities within the ant colony are integrat- 

 ed primarily by touch and odor; to regard 

 such manifestations as language emphasizes 

 the distinctiveness of human speech. The 

 demonstration of ideas— particularly of ab- 

 stract ideas— among the mental processes of 

 nonhuman animals is still more diflBcult. 



We have purposely avoided emphasis on 

 human sociology, but we hope that in time 

 a maturing ecology will be properly fused 

 with that field. 



The line between ecology and physiology 

 is equally difiBcult and perhaps equally im- 

 possible to draw with exactness. One of the 

 most helpful distinctions concerns the work- 



ing imits in the respective subject matter. 

 The physiologist seldom gets beyond con- 

 sidering an individual as his upper limit; 

 often he is content with some organ or even 

 with an individual nerve fiber; his research 

 may focus finally at the molecular level. In 

 contrast, the ecologist usually regards an 

 individual organism as his smallest unit, ex- 

 cept as he needs information about the 

 functioning of the fiver, pancreas, muscles, 

 or other organs in order to understand the 

 general environmental relations of the 

 whole organism, or of the community. The 

 kidneys give a remarkably good illustration 

 of the close correlation that may exist be- 

 tween an inner organ of the body and the 

 general environment. For ecology, the 

 supra-individuafistic units are real entities. 

 Aggregations, populations, societies, and 

 various units at or near the community 

 level present problems rarely recognized by 

 physiologists working as physiologists. Yet 

 the problems of this level are real and fie 

 so near the center of ecology that Shelford 

 (1929, p. 2) makes the statement that 

 ecology is the science of animal communi- 

 ties. 



A single Asellus moving upstream in a 

 small brook has an ecology of its own, even 

 though it is not at the moment in direct as- 

 sociation with any organisms other than the 

 bacteria and other nannoplankton of the 

 water or those minute forms residing on its 

 own surface or acting as its parasites. We 

 have no reason to befieve that this partic- 

 ular isopod remembers or anticipates con- 

 tacts with another fiving creature. It is es- 

 sentially alone, a creature of the moment, 

 responding to an innate urge to move up- 

 stream against the current of water. The 

 positive reaction is not free from environ- 

 mental influences; it is dependent on such 

 external relations as the amount of oxygen 

 and of carbon dioxide present, and on the 

 ionic content of the surrounding water. The 

 isopod is also, without knowing it, a mem- 

 ber of the community of the brook and so 

 is related to the ground water that feeds 

 the stream and, to some extent, to the bodv 

 of water into which the brook flows. At a 

 different level, the single, isolated isopod 

 may well have been and may soon become 

 again a member of an isopod aggregation 

 with which other animals are also asso- 

 ciated. 



The physical environment impinges di- 

 rectly on the individual as it does on popu- 



