- 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.