factors, those for which all the organisms living together in the environment 

 are responsible. Every individual inhabiting a particular environmental 

 situation exerts efTects on its surroundings and on other organisms and thus 

 constitutes a factor in their environment. Ecology has been defined as the 

 study of the action of the environment on the organism, and the reaction of 

 the organism on the environment. In seeking to elucidate the complex inter- 

 relationships implicit in such a definition, students of ecology have developed 

 the field into a broad and very active area of investigation. 



The environmental relationships of organisms have interested observers 

 since the beginnings of biological science; the work of early naturalists 

 and systematists, and much of the field of "natural history" in later years, 

 formed the foundation of the modern science of ecology. It has been said, 

 indeed, that ecology is "scientific natural history," which has developed 

 from the older observational science by the application of experimental 

 methods and rigorous quantitative treatment to recognized problems. 

 Modern ecology makes use of the techniques of chemistry, physics, analytical 

 and statistical mathematics, population genetics, and other highly specialized 

 fields, in addition to the more general methods of biology. The importance 

 of ecological studies cannot be overemphasized. Like all scientific work, 

 they increase our knowledge of the world about us. In addition, these 

 studies make it possible to plan intelligently the proper utilization and 

 conservation of natural resources, and to predict the probable consequences 

 of current practices in the many areas in which human activities come into 

 contact, and often interfere, with the environment. 



It is a common observation, and it is evident from much that has been said 

 in previous chapters, that animals are well adjusted to the environments 

 in which they occur. It might better be said that animals are found in en- 



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