Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

A survey of small mammals on eight islands in the Columbia and Willamette Rivers near Portland, Oregon was conducted in 1974. The islands were Govermnent , Sand, Lemon, McGuire and Sandy Islands in the Columbia River and East, Ross and Hardtack Islands in the Willamette River. The objectives of the study were to ascertain and compare the kinds, distribution and relative densitites of small mammals . A variety of traps was used to capture the animals including Museum Special Rodent Traps , back- break mouse traps, scissor and guillotine- type stab mole traps , Sherman traps , modified Young traps and pitfalls . Most traps were set in linear transects . Trapping was conducted with the objective of sampling the major habitats on each island. Observations of scats, tracks , burrows and dead animals were also noted. One species of small marmnal , Sorex vargrans , was found on all eight islands . Microtus was found on five islands and Peromyscus maniculatus on four islands . Two islands yielded Scapanus townsendii. Glaucomvs sabrinus was found on only one island. I hoped that evidence would be found to prove or disprove that current theories of island biogeography would apply to river islands. However, data in this study were inadequate to allow calculation of precise indices of population densities . Therefore, I was unable to determine if theories of island biogeography do apply to these river islands.

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. / Science, Faculty of / Zoology, Department of / Graduate