Speciation of the Wandering Shrew Part 11

3. The sympatric existence of the terminal subspecies of the _Sorex vagrans_ ra.s.senkreis is made possible by marked differences between them in size and in ecological preference.

4. The west-coast subspecies, _sonomae_, _pacificus_, _yaquinae_, _bairdi_, and _permiliensis_ probably differentiated from the Great Basin and Rocky Mountain subspecies, _vagrans_, _obscurus_ and _monticola_, during a separation caused first by aridity in the Great Basin, and secondly by glaciation of the Cascade Mountains and the Sierra Nevada, possibly in the Sangamonian and Wisconsinan ages respectively.

5. _Sorex v. vagrans_ originated in the Great Basin and arrived on the Pacific Coast after the last deglaciation of the Cascades and Sierra Nevada.

6. In _S. vagrans_, heterogonic growth is ill.u.s.trated; the larger the skull, the larger the rostrum in proportion to the skull as a whole.

7. In the species _S. vagrans_, size and color vary geographically more than do other features.

8. The _S. ornatus_ group, _S. longirostris_, and _S. veraepacis_ had a common ancestor with _S. vagrans_, possibly in the Illinoian Age.

9. _S. vagrans_, the _S. ornatus_ group, _S. veraepacis_, _S.

longirostris_, _S. pal.u.s.tris_, _S. bendiri_, and the _S. cinereus_ group, because of structural resemblances, should be placed in a single subgenus, _Otisorex_. _S. trowbridgii_, the _S. arcticus_ group, the _S. saussurei_ group, _S. merriami_, _S. fumeus_, and _S. dispar_, should be included in the subgenus _Sorex_.

10. _Sorex cinereus_ occurs with the medium-sized and large-sized _S.

vagrans_ in the Rocky Mountains and in Canada, but does not occur with the smaller subspecies of _S. vagrans_, probably because compet.i.tion between two shrews of like size excludes _S. cinereus_.