84 G. A, BARTHOLOMEW 



On land an almost infinite series of physical situations is available. 

 Plants, generally speaking, meet the impact of the terrestrial environ- 

 ment head on, although of course they in turn modify the physical 

 environment by adventitious group activity. The individual plant 

 cannot select its habitat ; its location is largely determined by the 

 vagaries of the dispersal of seeds or spores and is thus profoundly 

 affected by chance. Because of their mobility and their capacity for 

 acceptance or rejection terrestrial animals, in contrast, can and do 

 actively seek out and utilize the facets of the environment that 

 allow their physiological capacities to function adequately. This 

 means that an animal by its behavior can fit the environment to its 

 physiology by selecting situations in which its physiological capaci- 

 ties can cope with physical conditions. If one accepts this idea, it 

 follows that there is no such thing as The Environment, for there 

 exist as many different terrestrial environments as there are species 

 of animals. 



We can now take a somewhat closer look at the relation of physi- 

 ology to distribution. First of all, we must consider what questions 

 the student of ecological animal physiology is trying to answer. (A 

 more realistic approach might be to ask to what questions can con- 

 veniently obtained physiological data be applied.) It usually de- 

 velops that after much laborious and frustrating effort the investi- 

 gator of environmental physiology succeeds in proving that the 

 animal in question can actually exist where it lives. It is always 

 somewhat discouraging for an investigator to realize that his efforts 

 can be made to appear so trite, but this statement does not belittle 

 the ecological physiologist. If his data assist the understanding of 

 the ways in which an animal manages to live where it does, he makes 

 an important contribution to the study of distribution, for the pres- 

 ent is necessarily a key to the past. 



The contributions of physiological knowledge to an understanding 

 of distribution are necessarily inferential. Distribution is a historical 

 phenomenon, and the data ordinarily obtained by students of physi- 

 ology are essentially instantaneous. However, every organism has a 

 line of ancestors which extends back to the beginning of life on 

 earth and which, during this immensity of time, has invariably 

 been able to avoid, to adapt to, or to compensate for environmental 

 changes. By examining in retrospect this prolonged exercise in the 

 art of survival and at the same time bearing in mind the physio- 



