The Role of Physiology 

 in the Distribution of 

 Terrestrial Vertebrates 



George A. Bartholomew 



Department of Zoology, University of California, 

 Los Angeles 



1 he inclusion of this paper in a symposium on 

 the origins and affinities of the land and freshwater fauna of western 

 North America may be taken as an expression of the tacit assumption 

 of most biologists that physiology plays a determining role in the 

 complex problems of animal distribution. I have accepted this 

 assumption, but in attempting to formulate conclusions available 

 from present knowledge, I find that the relation of physiology to 

 distribution in terrestrial vertebrates is neither direct, simple, nor 

 obvious. All that a brief essay such as this can do is offer a point of 

 view with regard to certain groups. To attempt a taxonomically 

 extended treatment of a topic so broad would be presumptuous, and 

 I shall concentrate on the animals that I know best — the amniotes. 

 The literature cited is not exhaustive, but most of the papers are 

 quite recent, and all include extensive bibliographies that offer 

 convenient access to the literature relevant to the role of physiology 

 in the distribution of terrestrial vertebrates. 



Biology is a continuum, but we biologists, because of our limita- 

 tions, divide ourselves into categories, and then we pretend that 

 these categories exist in the living systems that we study. From the 

 functional point of view, of course, an animal is indivisible, and 

 physiology is not in any sense an isolatable component of an organ- 

 ism. If physiology is defined as the study of vital functions, it be- 

 comes inseparable from morphology and behavior. When one defines 

 physiology as broadly as this and then undertakes to discuss its role 

 in distribution, one attempts the impossible — nothing less than an 



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