

208 FAUNAL DIVISIONS OF EASTERN NORTH AMERICA. 



stress on the zonal feature and correlates the older divisions of regions and 

 faunas with these zones. I have taken these two writers as illustrating the older 

 and the more recent views of North American zoogeographers, not mentioning 

 the many other able investigators who have done so much to enrich this branch 

 of the science. 



Merriam presents an array of distributional phenomena which he correlates 

 with the results of extensive temperature observations to show this zonal arrange- 

 ment, and he formulates from the whole mass of evidence a series of laws of 

 1 ' temperature control. m 



Unquestionably temperature does exert an influence in the distribution of 

 living beings, especially in the case of plants, but it is not, I think, as Dr. Merriam 

 would have us believe, the supreme cause of the present phases of dispersal. 

 In the first place the attempt to arrange the animal life of a land in a series of 

 zones based on temperature is, to say the least, misleading and unnatural. 

 There are, as we well know, marked contrasts between the animal life of the 

 tropics and that of the temperate regions, and the species in each are more or less 

 adjusted to the prevailing conditions of heat and moisture. The degree of 

 temperature, however, is not the cause of this contrast. Dr. Merriam claims that 

 each species is bound to its region through some special peculiarity in its repro- 

 ductive metabolism in relation to temperature, or what he calls its "physiological 

 constant.' ' It is hard to believe that the African antelopes are so widely differ- 

 entiated from other bovine species that inhabit more northerly regions by this 

 functional relation to temperature, or that the two species of reindeer, the one 

 of the Barren Grounds, the other of the woodland farther to the south, should 



be limited to their respective ranges solely through temperature conditions. 

 Or again, that one variety of tiger is limited only by this temperature control 

 to the hot, low-lying jungles of the southern peninsular lands of Asia, while a 

 nearly related one inhabits the cold and snowy region of Manchuria. Case after 

 case might be cited throughout the different groups of animals of closely related 

 species thus separated in areas of contrasted temperatures, but the "physi- 

 ological" or "heat constant" theory will hardly explain the facts. Again, how 



are we to account for the differences in the types of animals found in an east and 



west direction through this temperature relation? The aggregate of daily 



temperatures taken throughout the period of reproductive activity (i e>> ^ 

 spring and summer of the north) is regarded by Dr. Merriam as the essential 

 limiting factor in the distribution of species. Thus an aggregate of less than ten 

 thousand degrees Fahrenheit is characteristic of the Boreal Zone, and all the 

 forms of life within its borders are adjusted to temperatures below this point. 

 Undoubtedly they are, to a certain extent, but at the same time this aggregate 

 of temperature does not explain the past history of the fauna within this zone, 

 and it is altogether too vague and too sweeping a conception to be taken as 



1 Laws of Temperature Control of the Geographic Distribution of Terrestrial Animals and Plants, 

 National Geographic Magazine, vol. VI, 1894, pp. 22^-238. 



