250 



SCIENCE. 



[N. S. Vol. XXIII. No. 581. 



ease is that of the western chipmunks 

 (genus Eutamias) , one of the most elegant 

 and attractive groups of American mam- 

 mals. The genus occupies a vast area in 

 western North America, extending from 

 Lake Nipissing, Ontario, westerly to the 

 Pacific Ocean, a distance of 2,000 miles, 

 and from the Mackenzie River a little north 

 of Great Slave Lake southward to the 

 mountains of Zacatecas in Mexico, a dis- 

 tance of fully 3,000 miles. Most of the 

 species dwell in forests, but a few inhabit 

 the great sage brush plains. Faunally they 

 contribute distinctive species to every life 

 zone from the Upper Sonoran to the Arctic- 



continental life zones, each of which is 

 characterized by peculiarities of climate 

 and by a definite association of species of 

 mammals, birds, reptiles, trees and shrubs. 

 There are no gaps between the belts, the 

 upper border of one being coincident with 

 the lower border of the next, so that indi- 

 vidual animals of different species meet 

 along the border lines of the several zones. 

 In some cases only a single species inhabits 

 a zone, but in one case not less than three 

 occur together. These three however, as 

 would be expected, are so very distinct 

 from one another that they could not pos- 

 sibly have arisen by mutation. 





Ub^tt Sowovoorv 



Fig. 2. Diagram Showing the Zone Ranges of Chipmunks (genus Eutamias) in an east-west sec- 

 tion of the middle Sierra and White Mountains in eastern California. 



Alpine. In mountainous regions the spe- 

 cies are commonly distributed in parallel 

 belts, the borders of which are not only in 

 absoliite contact, but even slightly overlap 

 for long distances. 



As it will be impossible in the time at 

 our disposal to consider more than a few of 

 the species, I have selected for illustration 

 those that inhabit eastern California, along 

 an east-and-west line extending from the 

 west base of the Sierra Nevada to the sum- 

 mit of the White Mountains. On the grad- 

 ually rising slopes of the Sierra the species 

 are arranged one above the other, from base 

 to summit, in definite belts or strata (see 

 diagram, Pig. 2). Field studies have shown 

 that these belts are the same as the trans- 



Beginning at the foot of the Sierra on 

 the west side, the first species encountered 

 is a large, dark, long-tailed form {Eutamias 

 merriami), whose range coincides with the 

 limits of the digger pine or Upper Sonoran 

 zone. Immediately above this is the broad 

 belt of ponderosa pines and giant sequoias 

 of the Transition zone. The chipmunk of 

 the zone below does not occur here, but is 

 replaced by a striking long-eared speci£s 

 (quadrimaculatus) which fills the zone and 

 is restricted to it. Along the line Avhere 

 the yellow pines of the Transition zone 

 change to the Murray pines of the Can- 

 adian no less than three species (amoenus, 

 senex and speciosus) begin abruptly and 

 range upward throughout the Canadian 



