THE AMPHIBIA OF OKLAHOMA 



Conditions of Existence iti Oklahoma 



Oklahoma is a peculiar region when considered as an environmental 

 complex. Its area is close to 70,740 squares miles and its elevation varies be- 

 tween approximately 400 feet in the southeastern corner to about 4,500 feet 

 on Black Mesa in the northwestern tip of the Panhandle. Physiographically, 

 it is essentially a tilted plane roughened and cut by the valleys of its streams 

 and by the presence of several old mountain masses, many of them now 

 eroded to mere hills. Some of these are the Ozark highlands entering the state 

 from Arkansas in the northeast, a part of the Ouachita uplift in the southeast, 

 the Arbuckle Mountains in the south, the Wichitas in the southwest, the Glass 

 Mountains or Gypsum Hills in the west, and the extensive sandstone hills 

 running roughly north and south through the east central part (see map by 

 Bruner, 1931, p. 103). Two drainage systems occur, that of the Red River in 

 the south and that of the Arkansas River in the north. Approximately the 

 southwestern fifth of the state is drained into the Red River by the Washita 

 River to the north to the Wichita Mountains and the North, Elm, and Salt 

 Forks of the Red River to the south and west of them. All of the central area 

 is drained to the Arkansas by the Canadian, North Canadian, and Cimarron 

 rivers, whereas the northern and northeastern portions drain more directly 

 into the Arkansas through a series of larger (Illinois and Grand) rivers or 

 smaller tributaries. In the southeast, the Kiamichi and Little rivers with their 

 branches drain the southern and western Ouachita Mountains, the former 

 entering the Red River in eastern Choctaw County, the latter crossing south- 

 western Arkansas first. Throughout the state, numerous creeks and gullies 

 feed the larger streams, often with an intermittent flow. The larger rivers have 

 wide valleys, those of the prairie regions being dry, sandy ribbons during 

 summer from one-forth mile to one mile wide and fringed with flood-plain 

 forests far westward into the grasslands. Their banks in some places slope 

 gently upward to the prairies, but at other places are sheer. Sometimes, after 

 heavy rains, these streams become temporarily raging torrents. 



The climate of Oklahoma varies greatly from east to west. Twenty inches 

 of annual rainfall (distributed very irregularly through the year) in the Pan- 

 handle of the state is normal but thirty to thirty-five inches is usual in the 

 central portion; the Northeast receives forty inches and the Southeast forty- 

 five. Summers are hot and dry and the prevailing hot southwesterly winds 

 of this season make rates of evaporation excessive, particularly in the south- 

 western part of the state. According to Bruner (1931), "The high evapora- 

 tion rate is due to relatively high temperatures, high and almost continuous 

 winds and low relati\'e humidity. Tanks located in western Nebraska gave 

 an evaporation rate of forty-one inches and in North Dakota only thirty-one 

 inches (as compared with fifty to fifty-five inches in western Oklahoma). This 

 great increase in evaporation southward causes the twenty inches of rainfall 

 in the Panhandle to be only as efficient as fifteen inches in western North 

 Dakota." These high evaporation rates affect greatly the lives of individual 

 salientians and, through this, the ecological distribution of species. 



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