FAUNAL DIVISIONS OF EASTERN NORTH AMERICA. 217 



region of the Great Plains, conditions a very characteristic fauna. This I have 

 called the Grassland Fauna from its most notable vegetation feature. Manx 

 forms of mammals, birds, and reptiles are peculiar to it. The effect of greater 

 precipitation in its eastern portion (prairies proper) determines a mon or less 

 different type of flora and fauna from that obtaining over the arid steppe-like 

 region of the so-called "Great Plains" of the West. Two types within this 

 Grassland Fauna are thus defined — (a) the Prairie Type, and {b) the Steppe Type. 

 The above outline is more in accord with the conditions that prevailed before 

 the opening up of the country by European settlement and the consequent wide- 

 spread disturbance of the natural balance of existence in the adjustments between 

 organisms and their environment. The cultivation of the land over the greater 

 portion of the prairie country, incident to the growth of crops, has almost entirely 

 exterminated the primitive flora in many places. Disturbances in the fauna must 

 necessarily follow, some forms disappearing, others, like certain species of birds, 

 increasing with greater food facilities from crop growth. The cutting off of wide 

 tracts of forest in the eastern part of the United States likewise profoundly dis- 

 turbed the faunal relations. Our fallow fields and pastures are in reality prairie- 

 land, and prairie types, both of fauna and flora, have migrated to these places 

 from the similar natural region lying on the western edge of the forest. Many of 

 our present field birds (e. g., certain species of sparrows, meadow-lark, etc.) 

 have undoubtedly thus found a habitat in our eastern fields and pastures since 

 the earliest settlements. The opening of areas in the northern coniferous forest 

 has had the effect of letting in more sunlight and has induced the spread of t he 

 deciduous type of woodland into these open spaces. This has been accompanied 

 by a marked movement of certain species of the faunal type, notably among 

 birds. Even some species of the alluvial forest type have invaded these areas 

 of "second growth." 1 



A discussion of the faunal features of the western portion of the continent is 

 not within the scope of this paper. I do not believe, however, that we are justi- 

 fied in assuming the presence of a continuous faunal zone extending across the 

 entire land. The extension of the coniferous forest far into the northwest (Boreal 

 Zone of Merriam and other writers) has certainly spread some of the species of 

 its faunal type on the higher mountain ranges, but south of this (in the so-called 

 "Austral Zone") there is a marked difference in specific forms, even to a difference 

 in generic types in certain instances, between the eastern and the western portions 

 of the continent. I have tentatively called this western element as a whole the 

 Plateau Fauna, recognizing in a general way its division into two quite distinct 

 types as conditioned by the broader features of vegetation dependent upon rain- 

 fall— (a) the Cactus Desert Type, and (6) the Mountain Forest Type— leaving the 

 matter for some more competent investigator to analyze. 



16-23 



Western 



Oct., 1909, p. 384. 



tptdar Science Monthly 



