CHAPTER XIII 



ECOLOGY 



Ecology embraces the study of the relations of animals and plants to 

 the conditions in which they hve. The discussion in this book has special 

 reference to the ecological relations of animals. It has long been recog- 

 nized that animals are dependent upon certain physical conditions, such as 

 food and water, and that different forms require somewhat different con- 

 ditions, for example that fishes require an aqueous medium, that some 

 animals require plant food, and others animal food, etc. But the ex- 

 tent to which the peculiar combinations and intensities of the various 

 physical and biological conditions existing in nature are necessary to 

 the maintenance of the individuals of particular species, and to what ex- 

 tent the absence of these combinations and intensities may cause the 

 destruction of the animals or influence thair distribution, has but recently 

 attracted the attention of zoologists. 



Several terms have been applied to the study of environmental rela- 

 tions, such as Hexiology (erroneously spelled hexicology by Mivart); 

 Physiology of Organisms (Semper), as opposed to special physiology or 

 physiology of organs; Bionomics (Lankester); and Oecology (Haeckel). 

 These terms have been differently defined by different authors, but 

 Ecology is now in general use and the conception that it comprises the 

 study of all the relations of the animal to the environment seems to 

 prevail. 



Scope of Ecology. — Defined as the relation between the animal and 

 the environment, ecology is a very broad subject and encroaches to some 

 extent upon other fields. As so defined, it includes the relations of individ- 

 uals or species to each other, such as colony formation, society forma- 

 tion, parasitism, slavery, symbiosis, and the relation of enemy and prey; 

 and their relations to the physical environment, such as the effect of the 

 chemical content and the temperature of the water, and the effect of the 

 nature of the soil, temperature and moisture on land. 



Structural Adaptations. — The relations of animals to the environ- 

 ment may be classified as structural and physiological. Characters 

 whether structural or physiological which fit an animal for life under 

 given conditions are commonly referred to as adaptations. The most con- 

 spicuous adaptations are those of structure, including color. Thus, to 

 take a simple example, a fish is adapted to life in the water by having fins 

 and gills which permit it to swim and respire in that medium, while ter- 

 restrial mammals are adapted to life on land by having legs and lungs. 



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