ALPINE ANIMALS 



495 



tion in this continent has largely been studied with reference to these 

 life zones. 



This zonation does not mean that every species of animal is con- 

 fined to a distinct zone. The closeness of this correlation varies among 

 different animals, and we may distinguish stenozonal forms 23 which are 

 confined to a single zone, and euryzonal forms which range through 

 more than one zone. Grinnell and Storer, 24 in their account of the zonal 

 distribution of the vertebrates of the Sierra Nevada, have diagrammed 

 the zonal range species by species (Fig. 129a). Schmidt has studied 



Fig. 129a. — Zonal distribution of the owls in the Yosemite region; an example 

 of contrasting euryzonal and stenozonal distribution among related animals. 

 From Grinnell and Storer. 



the mainly stenozonal salamanders of the genus Oedipus on the Guate- 

 malan volcanos. 25 Invertebrates may likewise be either stenozonal or 

 euryzonal. In the Alps, the moth, Maniola glacialis, is stenozonal, 

 Pieris callidice is less distinctly so, while Vanessa urticae is euryzonal 

 (Fig. 130) , 26 The Apollo butterflies, favorites with collectors in both 

 hemispheres, are strictly limited to the boreal zone in lower latitudes. 

 Difficult terrain. — The steepness of slope encountered in high 

 mountains is one of the characteristics of the mountain environment. 

 Erosion is more active owing to the force of rain and wind, tempera- 

 ture differences are extreme, and streams, swelled by melting snow, 

 gouge deep ravines even in the hardest rock. Steep and vertical slopes 

 thus become frequent. Rock surfaces are frequently laid bare even 

 on less steep slopes, and coarse rock debris covers great areas. Rock 



