INTRODUCTION 



Just at the beginning of the present century, there seems to have 

 been a revival of interest in plants and animals in relation to their 

 environments, and various workers have turned from the study of 

 anatomy and classification in the laboratory to the study of organisms in 

 nature. In this, the botanists have preceded the zoologists, in success 

 if not in time. In 1901 Dr. H. C. Cowles published a bulletin on the 

 Plant Societies of the Chicago Area. This was one of the first attempts of 

 an American biologist to treat all the plants of a given area in a strictly 

 ecological manner. This study of all the organisms of an area, from the 

 point of view of their relations to each other and to their environment, 

 is still a new or at least a renewed idea. Zoologists have devoted most 

 of their attention to the study of animals from the standpoint of a single 

 individual and of single species. Practically all of the more general 

 study has been comparative. We have comparative anatomy, compara- 

 tive embryology, comparative physiology, and comparative psychology. 

 These are comparisons of the structure or physiology of one species, or 

 group of species, with that of another species or group of species. 



Our point of view is very different. We shall deal with many species 

 from the standpoint of their dependence upon each other and their 

 relations to their environments. We shall attempt to present what has 

 been learned upon this subject during several years of investigation and 

 field teaching. In the spring of 1903, the writer made his first field 

 excursion in the Chicago area, and from that time has been engaged in 

 further study of the subject. 



The study of organisms in relation to environment is entitled ecology. 

 The definition of ecology, like that of any growing science, is a thing to 

 be modified as the science itself is modified, crystallized, and limited. At 

 present, ecology is that branch of general physiology which deals with the 

 organism as a whole, with its general life processes, as distinguished from 

 the more special physiology of organs (51), and which also considers the 

 organism with particular reference to its usual environment. 



Undertaking such a study from the point of view of many organisms 

 involves matters of both ecological and taxonomic classification. Classi- 

 fication of animals is difficult because animals are so exceedingly numer- 

 ous. There are probably from 10,000 to 20,000 species of animals which 

 the naturalist may encounter in the area which we are treating, while 



