ISIS] Dice: Land Vertebrates of Southeastern Washington 335 



The idea that temperature is the fundamental factor in limiting 

 the distribution of species is dominant in the conception of life-zones, 

 and in 1894 Merriam made an attempt to determine the temperature 

 limits of each life-zone. By running various isothermal lines he de- 

 termined that the northern limits of the life-zones agreed fairly well 

 in having the same total quantity of heat. The total quantity of heat 

 is the sum for the year of the daily mean temperatures above 6° C. 

 This temperature is assumed to be the point at which life begins 

 activity. The southern limits of the life-zones, however, did not agree 

 with the isotherms thus determined, but did approximately agree with 

 isotherms of the hottest period of the year. 



One criticism which should be made of this correlation of life-zones 

 and isotherms is that the northern and southern limits of the life-zones 

 are not determined by the same temperature criteria and that there- 

 fore in some places the life-zones may not meet each other. If de- 

 pendence be placed on these temperature criteria alone, some regions 

 must be placed in two life-zones and theoretically some in none at all. 

 Along the Pacific Coast in particular there is much oveiiapping of the 

 life-zones. Merriam (1894, p. 233-235) considers that in that region 

 the northern forms are able to come far south on account of th(? low 

 temperature of the summers, while the southern forms are able to 

 extend their ranges far to the north on account of the long growing 

 season. Thus is explained the great overlapping of northern and 

 .southern forms in the "Pacific Coast strip." However, it cannot be 

 considered proved that the temperature relations established by 

 Merriam are the particular ones which determine the limits of dis- 

 tribution of any species of animal. 



Another criticism of Merriam 's determination of life-zone tem- 

 peratures is that no thorough attempt has been made to determine if 

 these temperatures actually do apply to all parts of the life-zones as 

 they have been plotted in North America. Indeed, the temperatures 

 of some parts of the life-zones in the West were obtained by applying 

 temperature data obtained in the corresponding faunal areas of the 

 eastern United States (Merriam, 1890, pp. 31, 32). There are some 

 facts which seem to indicate that the temperatures determined by 

 Merriam do not apply in parts of some life-zones. For instance, ac- 

 cording to temperature Walla Walla and the Columbia Basin prairie 

 area of southeastern Washington would be placed well within the 

 Upper Austral zone, but the faunal relationships are with the Transi- 

 tion zone, or at least are not definitely Upper Austral. 



