82 G. A. BARTHOLOMEW 



interpretation of all the ways in which the dynamic capacities of an 

 organism influence its distribution. In the present paper therefore, 

 we shall restrict our discussion to the kinds of data that comparative 

 physiologists and physiological ecologists gather. In this way we can 

 confine our topic to reasonable limits and also insure that we have 

 at least some data on which to base our conjectures. 



Once an organism has been identified, two of the most obvious 

 questions to ask are first, "How many are there?" and second, 

 "Where do they live?" Simple as these questions are, they are 

 usually extremely difificult to answer. But let us assume that, by 

 years of unremitting effort, we have succeeded in obtaining approxi- 

 mate answers to these obvious questions. Since abundance and dis- 

 tribution may be considered as different aspects of the same problem 

 (Andrewartha and Birch, 1954, p. 5), two additional and inextricably 

 interlocked questions inevitably present themselves: first, "Why are 

 there as many as there are?" and second, "Why do they live where 

 they do?" We may start our inquiry concerning the role of physi- 

 ology in distribution by asking the straightforward question, 

 "What information do physiologists supply that relates more or less 

 directly to the above questions, particularly to the last one, which is 

 a major concern of most students of distribution?" Unfortunately it 

 is useless to pretend that answers to these questions can supply us 

 with much that is specifically and immediately relevant; first, 

 because of the complexity of both physiology and distribution, and 

 second, because physiologists have only infrequently considered 

 these questions. 



It is obvious that an organism's distribution is a complex integra- 

 tion of all facets of its present biology, together with a past history 

 in which chance has played an indeterminable but not necessarily an 

 unimportant role. Moreover, the occurrence of an organism is 

 dependent not only on a complex summation of its present and past 

 activities plus chance; it is often profoundly influenced by the occur- 

 rence or non-occurrence of other organisms, and these organisms 

 may be of quite a different nature and have difi'erent physiological 

 tolerances, requirements, and reactions from the one whose distri- 

 bution is being studied. 



Viewed in this context it is obvious that most present knowledge 

 of the physiology of terrestrial vertebrates is likely to have either no 

 apparent distributional importance or to have a contribution so 



