34 ANIMAL ECOLOGY 



outer world. In solving ecological problems we are con- 

 cerned with what animals do in their capacity as whole, living 

 animals, not as dead animals or as a series of parts of animals. 

 We have next to study the circumstances under which they 

 do these things, and, most important of all, the limiting factors 

 which prevent them from doing certain other things. By 

 solving these questions it is possible to discover the reasons for 

 the distribution and numbers of different animals in nature. 



2. It is usual to speak of an animal as living in a certain 

 physical and chemical environment, but it should always be 

 remembered that strictly speaking we cannot say exactly where 

 the animal ends and the environment begins — unless it is 

 dead, in which case it has ceased to be a proper animal at all ; 

 although the dead body forms an important historical record 

 of some of the animal's actions, etc., while it was alive. The 

 study of dead animals or their macerated skeletons, which has 

 to form such an important and necessary part of zoological 

 work, and which has bulked so largely in the interest of 

 zoologists for the last hundred years, has tended to obscure 

 the important fact that animals are a part of their environment. 

 There are numerous gases, liquids, and solids circulating 

 everywhere in nature, the study of which is carried on by 

 physicists, chemists, meteorologists, astronomers, etc, ; certain 

 parts of these great systems are, as it were, cut off and formed 

 into little temporary systems which are animals and plants, 

 and which form the objects of study of physiologists and psycho- 

 logists. Ecological work is to a large extent concerned with 

 the interrelations of all these different systems, and it must be 

 quite clear that the study of the manner in which environmental 

 factors affect animals lies on the borderline of a great many 

 different subjects, and that the task of the ecologist is to be a 

 sort of Haison officer between these subjects. He requires a 

 slight, but not superficial, knowledge of a great many branches 

 of science, and in consequence must be prepared to be rather 

 unpopular with experts in those sciences, most of whom will 

 view him with all the distaste of an expert for an amateur. 

 At the same time, although his knowledge of these other sub- 

 jects can only be slight, owing to the absolute impossibility of 



