68 LABORATORY DIRECTIONS IN 



3&. The American Bison and the Moose, on one map. (From Seton, 

 Life Histories of Northern Animals). 



3c. The Willow Ptarmigan, White-winged Cross-bill, and Road 

 Runner on one map. (From Chapman, Handbook of the Birds of Eastern 

 North America, and Bailey, Handbook of the Birds of Western United 

 States. These books contain descriptions, not maps, of ranges.) l 



4. Plot upon outline maps of North America the distribution of one or 

 more semi-aquatic species. The North American minks are suggested 

 for this purpose (Seton, Life Histories of Northern Animals). 



5. Compare the distribution maps which you have made with the map 

 showing the natural regions in North America as indicated by the domi- 

 nant vegetation and summarize the distribution of the species in terms of 

 natural regions and geographic location. (Example: The range of 

 species X is the coniferous forest region in eastern North America from the 

 Atlantic coast to the 100th meridian and from Hudson Bay on the north 

 to Lake Superior on the south.) 



In which cases, if any, does the range approximately correspond to the 

 distribution of certain types of vegetation? (See map prepared in 

 paragraph 1 above.) In which cases, if any, does the range bear no 

 relation to the vegetation areas? Explain the difference in the two 

 cases. 



It will be noted that the ranges of the animals do not correspond 

 exactly to the natural regions. There are several reasons for this, such as 

 incomplete knowledge of the extent of the range, too general summaries of 

 the distribution, the fact that the regions merge gradually into each other 

 or interdigitate where they come in contact, and the different effects of 

 the environments upon different animals. 



The intermediate regions are characterized to some extent by inter- 

 mediate conditions, but at least frequently the environments interdigi- 

 tate. For an example of the latter phenomenon consult " Principles of 

 Animal Biology," by Shull, LaRue and Ruthven. 



C. ADAPTATIONS OF ANIMALS TO THE CONDITIONS 

 IN THE REGIONS WHICH THEY INHABIT 



As brought out in the exercise on ecology animals are adapted to the 

 conditions in which they live. It follows from this that a difference in 

 any conditions of the environment may serve to limit the distribution of a 

 form. Owing to the complexity of the relationship between animals and 

 their surroundings it is difficult to determine the exact factor or factors 

 restricting the distribution of a given species at a given point, but certain 

 very general adaptations may be easily recognized. 



1 Other ranges of terrestrial animals may be substituted for the ones mentioned, or 

 used in addition to them. 



