摘要:

A systematic account is given of the constitution, distribution and geographical affinities of the molluscan fauna occurring in fresh waters of sub-arctic Canada. The area covered is that part of western Ontario, Manitoba, Saskatchewan and Alberta lying north of N. Lat. 49°. A total of 111 species and varieties was collected and identified. Types of habitat available in this region for settlement by molluscs have been classified, and the local distribution of the species in them observed. A brief description of seven principal habitat types, with comments on their fauna in other parts of the sub-arctic region, is followed by a series of examples from specific localities. These molluscan associations, while not necessarily typical, are believed to be representative. The study is concluded with a comparison of the molluscan fauna of northern North America with that of northern Eurasia.Three geographical elements in Canadian sub-arctic Mollusca are: a group of circumboreal species, a large number of strictly North American species, and a group characteristic of this region. An explanation of the close relation between the sub-arctic molluscs and those of the Mississippi drainage probably lies in the geological history of the region. There appears to have been a greater degree of speciation in North America than in northern Asia; the total number of species and varieties in sub-arctic Canada is 111, in northern Asia it is only 50. The explanation may lie partly in the richer source of supply, the greater facility for migration, and the wider range of habitats available in Canada. Thus new species as they arose would find suitable unoccupied habitats more readily. While this is hardly the sole explanation, the existence of some connection between physiography and speciation appears to be reasonable.

ISSN:1923-4287    

DOI:10.1139/cjr38d-008

出版商:NRC Research Press    

年代:1938

数据来源: NRC