ECOLOGY OF ISLE ROYALB. 3P3 



margins, where many go to feed in the openings at dusk. With the 

 . dryer substratum and more diversified vegetation the conditions are 

 evidently more favorable for the White-footed Mouse, which with the 

 Squirrels and Hares become dominant forms, and prove attractive to 

 Weasels, Marten and Lynx. These mammals are the representative 

 balsam-spruce forest types; and it is not improbable that if such a 

 forest becomes transformed into a maple-yellow birch type, the char- 

 acter of the mammals but little changed, with the possible exception of 

 the relative abundance of some species. 



Briefly summed up, the general succession of mammal types — from the 

 "rock clearing" to the balsam-white spruce or hardwood forest — is thus 

 seen to be a change from the dominance of the forms frequenting the 

 open to those of the forest. The final result of both the lake and the 

 land series is thus seen to be practically the same — both lead to the 

 dominance of the forest types. Such observations and influences, which 

 attempt to correlate environmental changes with the habit and habitat 

 relations of the mammals, point to a general conclusion which should 

 prove useful in field work: that each habitat, swamp, conifer or hard- 

 wood forest, etc. should not only be considered as a unit of environment, 

 but even more^ — as parts of a series of changes or stages in the contin- 

 uous development of the animal environment. Standing upon the top 

 of the Greenstone Eange, one may see this entire series of conditions, 

 varied, to be sur-e, and confusing to many, yet in many ways relatively 

 simple and free from chaos. 



3. Faunal Aflinities and Migrations. 



1. The Geographic Affinities of the Fauna. — As determined by the 

 present geographic range of the species and varieties of mammals found 

 on Isle Eoyale, the fauna is emphatically of the northeastern biotic type 

 (Adams, '05, p. 58). This is the dominant fauna of the region from 

 Labrador westward, between Hudson Bay and Lake Superior into the 

 Mackenzie basin, and only enters eastern United States to a limited de- 

 gree, except on mountains. The representative forms are: Caribou, Bed 

 Squirrel, Beaver (typical form). White-footed Mouse, Bed-backed Mouse, 

 Hare, Lynx, Marten and the Small Brown Weasel. In case these forniw 

 range westward into the Rocky Mountains and to the Pacific Coast, they 

 are represented by another variety, except in the case of the Lynx. The 

 Muskrat, New York Weasel, Mink (typical form) and Say's Brown 

 Bat are forms ranging far into southeastern United States, some reach- 

 ing west to the Rocky Mountains or the Pacific Coast. Le Conte's 

 Brown Bat and the Brown Bat have such extensive ranges to the south 

 of the United States as clearly to suggest a dispersal from the south. 



To determine close faunal affinities, much weight must be given to the 

 geographic range of the varieties or forms whose affinities are to be de- 

 termined. In a region whose fauna has undergone extensive migrations, 

 within comparatively recent times, as in the case of glaciated North 

 America, many allied varieties have had a very different history and such 

 forms must be subordinated in the faunal comparison to those that have 

 had similar histories. For this reason the post-Glacial migrations of 

 the fauna "of eastern North America make the north and south rela- 

 tions stronger than those between the east and the west because there 



