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The evolution of the native land mammals of the Queen Charlotte Islands and the problem of insularity Foster, J. Bristol

Abstract

The Queen Charlotte Islands are the most isolated islands in British Columbia and are populated by eight species of indigenous land mammals, all except one of which are represented by at least one endemic form. Geological and botanical evidence lend strong support to the hypothesis that the Islands could have been a refuge to most of these mammals during the last (Vashon) glaciation. Their unique mammal fauna could be the product of insular evolution, or due to the fact that it is of geographical relicts. Absence of fossil material prohibits a final solution to this problem, but circumstantial evidence suggests that the mammals have evolved their unique characteristics as a result of living in an insular environment. This conclusion is reached after the study of the most common mammals living on the Islands; the deer mice (Peromyscus maniculatus keeni and P. sitkensis prevostensis) and the dusky shrews (Sorex obscurus elassodon and S. o. prevostensis), and after a wide literature survey of mammals found on other islands. The most important evidence favouring the insular evolution theory is the uniformity displayed when the characteristics of insular birds and mammals are compared with relatives living on the nearby mainland. Birds living on islands often possess longer tarsi and culmens; artiodactyls, lagomorphs and carnivores tend to be smaller on islands, while rodents are usually larger, live longer and possess shorter tails. A corollary of the relict hypothesis holds that a large reliot rodent can not survive active competition with the smaller form and is displaced by the latter when they come into contact. This theory could not be substantiated by the present study; on the contrary, the two would likely interbreed. The differences between the insular populations of large Peromysous are greater than one would expect if they owed their similarity to a common origin. Finally, the relict hypothesis would hold that such a characteristic as large size is conservative, whereas evidence indicates that this is not generally true. Reasons are suggested for the characteristics which are commonly found in insular mammals and herein lies the most interesting area for future work.

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