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Evidence of a trophic cascade among wolves, elk, and aspen in Yellowstone National Park, USA

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dc.contributor.advisor Ripple, William J.
dc.creator Halofsky, Joshua S.
dc.date.accessioned 2007-06-20T17:43:23Z
dc.date.available 2007-06-20T17:43:23Z
dc.date.copyright 2007-04-19
dc.date.issued 2007-06-20T17:43:23Z
dc.identifier.uri http://hdl.handle.net/1957/5546
dc.description Graduation date: 2008
dc.description.abstract According to general top-down trophic theory, in the presence of carnivores, herbivore behavior and/or densities could change and result in an overall decrease in herbivory on plant communities. In this dissertation, I examined the potential relationship between gray wolf (Canis lupus) presence and absence on elk (Cervus elaphus) herbivory of aspen (Populus tremuloides). Based on aspen tree cores and an age-diameter relationship, I approximated aspen origination dates both within and outside two elk exclosures to study long-term patterns of aspen recruitment in the Gallatin elk winter range of northwestern Yellowstone National Park, USA. From aspen data, I concluded that while a host of interacting biophysical factors may influence aspen recruitment and growth, the observed pattern of aspen decline is most correlated with elk herbivory, coincident with the presence and absence of wolves. Outside of the elk winter range, but still within the northwestern portion of the park, I studied growth patterns of clonal upland aspen thickets since wolf reintroduction. Growth patterns were compared in an area burned in the 1988 fires to an adjacent area that was unburned. From the results, I proposed that in addition to any wolf-mediated changes in elk densities, a recoupling of fire with increased elk predation risk in the presence of wolves may improve upland clonal aspen recruitment. To examine the potential for a trophic cascade from the perspective of elk, I measured vigilance behavior in female elk throughout the park during both winter and summer seasons. After vigilance behavior was recorded, I noted the distance to, and type of, objects that could have impeded observed female elk escape from predators. From my model selection procedure, I concluded elk foraging behavior appeared to vary with physical features in the landscape. This variation in foraging behavior with risk of predation provides a potential mechanism to explain the patchy release of preferred woody browse species within the Park. Therefore, in addition to density-mediated effects, the results are consistent with a behaviorally-mediated top-down trophic cascade between wolves, elk, and aspen. en
dc.format.extent 1124627 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US en
dc.subject top-down influence en
dc.subject elk behavior en
dc.subject.lcsh Food chains (Ecology) -- Yellowstone National Park en
dc.subject.lcsh Aspen -- Ecology -- Yellowstone National Park en
dc.subject.lcsh Elk -- Habitat -- Yellowstone National Park en
dc.subject.lcsh Wolves -- Reintroduction -- Environmental aspects --Yellowstone National Park en
dc.subject.lcsh Predation (Biology) -- Yellowstone National Park en
dc.subject.lcsh Ecology -- Yellowstone National Park en
dc.title Evidence of a trophic cascade among wolves, elk, and aspen in Yellowstone National Park, USA en
dc.type Thesis en
dc.degree.name Doctor of Philosophy (Ph. D.) in Forest Resources en
dc.degree.level Doctoral en
dc.degree.discipline Forestry en
dc.degree.grantor Oregon State University en
dc.contributor.committeemember Anthony, Robert G.
dc.contributor.committeemember Doescher, Paul S.
dc.contributor.committeemember Olson, Deanna
dc.contributor.committeemember Ross, Darrell W.

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