Graduate Thesis Or Dissertation
 

Small mammal micro- and macrohabitat selection in streamside ecosystems

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  • During summer and fall of 1981 to 1983, mark-recapture was conducted in riparian and upland habitats within old-growth and mature forests in the Cascade Range of Oregon. Number of individuals and species richness were greater in riparian than upland habitat. For most species, the mean adult weights and the percentages of reproductively active males and females were greater in riparian habitat. Insectivora had higher numbers of captures, densities, and biomass per ha in riparian habitat. Four rodents had higher numbers of captures, densities and biomass per ha in upland habitat. An additional five rodents had higher values for these parameters in riparian habitat. Both mustelids captured had higher numbers of captures, densities, and biomass in riparian habitat. Three sympatric voles, Microtus oregoni, Microtus richardsoni, and Clethrionomys californicus, were studied relative to microhabitat separation because they are potential competitors due to similarities in morphology and life history. Discriminant analysis identified significant separation based on cover of lichen and deciduous trees and distance from the creek. Specifically, C. californicus selected microhabitats with a high percent cover of lichen and western hemlock and low percent cover of deciduous trees. M. oregoni selected microhabitats high in deciduous and evergreen herbs and deciduous shrubs. Microhabitats selected by M. richardsoni had a high soil exposure, greater length of recently fallen logs, and reduced cover of Douglas-fir. To investigate patterns of competition, Peromyscus maniculatus, the most abundant small mammal, was removed from four grids in 1983. All species of the order Insectivora increased with the removal of P. maniculatus relative to most parameters measured. Captures were significantly higher on removal grids for Sorex monticolus, Sorex bendirii, Sorex trowbridgii, and Scapanus orarius. Two rodents, Zapus trinotatus and Glaucomys sabrinus, also increased with the removal of P. maniculatus, suggesting responses to release from exploitative competition. Tamias townsendii had significantly fewer captures and individuals on experimental grids. Removal of P. maniculatus left T. townsendii the most abundant small mammal on experimental grids. It is possible that predators "switched" to T. townsendii thereby effectively depressing densities of T. townsendii on the removal grids.
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