THE FAUNAL DIVISIONS OF EASTERN NORTH AMERICA IN 



RELATION TO VEGETATION. 



By Spencer Trotter, M.D. 



Two quite distinct ideas are associated in the word fauna — the one zoological, 

 the other geographical. The term blends these two conceptions most happily, 

 for it connotes the natural surroundings that are so inseparably interwoven in 

 our thought of the living animal world. Its place is in the vocabulary of science, 

 yet the word savors of a remote past when woods and fields were haunted by 

 strange animal divinities and men were closer to the life about them, and knew 

 it more sympathetically and more intimately, if less accurately, than in later 

 times. In its modern scientific usage, fauna signifies the varied assemblage of 

 animal species inhabiting a particular region. It may be, and frequently is, 

 broadly applied to the animal life of an extensive area of land or sea, and likewise 

 to some particular class of animals, as birds or fishes, in relation to their distri- 

 bution. In a more restricted and technical sense the word denotes the collective 

 animal life of an area of more or less uniform and distinctive environmental 

 conditions. In such a sense it is used by zoogeographers to designate the sub- 

 divisions of the large regional zones of distribution that characterize a continent. 



The current classification of North American faunal areas is that of Dr. C. 

 Hart Merriam 1 who recognizes the continent as primarily divided into two 

 dominant zones which extend across its entire breadth — a northern or Boreal 

 Zone, of environmental conditions similar to the northern zone of Eurasia, and a 

 southern Austral or Sonoran Zone. Between these two Merriam recognizes a 

 more or less narrow area of overlap which he calls the Transition Zone. This 

 zonal arrangement of life is based on temperature. The Austral or Sonoran is 

 further divided into an upper and lower zone based on observed differences of 

 temperature and differences in faunal distribution. The Sonoran is further 

 divided east and west into a humid and an arid province. Within these zones are 

 recognized certain regional subdivisions characterized by an assemblage of 

 animal species of more restricted distribution. These subdivisions have been 

 termed faunas. Their recognition long antedates Merriam's zonal scheme. 

 The late Prof. Edward D. Cope in an essay on geographical distribution accom- 

 panying his list of North American Batrachia and Reptilia 2 uses the term "dis- 

 trict" to define these faunal subdivisions, while he calls the larger, primary 

 divisions "regions." Cope did not regard the distribution of North American 

 life as any way zonal in character. Merriam, on the other hand, lays particular 



*See reference in North American Fauna, No. 3 (1890); also The Geographic Distribution of 

 Life in North America, by C. Hart Merriam, M.D., from the Smithsonian Report for 1891, p. 365. 

 * Bulletin of the U. S. National Museum, Washington, 1875. 



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