Theses and Dissertations at Montana State University (MSU)
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Item Evaluating aspen responses to changes in elk abundance, distribution and behavior following wolf reestablishment in West-Central Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2011) Shafer, Timothy Lee; Chairperson, Graduate Committee: David RobertsThe reintroduction of wolves to Yellowstone National Park (YNP) in the mid-1990's has created a unique natural experiment for the investigation of trophic cascades operating at large spatial scales and involving large terrestrial mammals. Wolves have been directly linked to changes in elk density/behavior and have been hypothesized to be the driving force behind observed changes in woody plant growth in the system. The primary objectives of this study were to investigate the occurrence of a trophic cascade among wolves, elk and aspen in an area of YNP where elk abundance and distribution changed dramatically as a direct result of wolf reestablishment in the system. In Chapter 2, I determined the distribution and demographic characteristics of aspen in the Madison headwaters study area (MHSA) and identified the environmental attributes associated with its distribution on the landscape. Additionally, I evaluated the morphology, productivity, and persistence of aspen in both clonal and seedling-established. In Chapter 3, I established a climate-growth relationship for aspen to investigate the occurrence of a shift in productivity related to climate coincident with the timing of wolf reestablishment. I used standard dendrochronology techniques to investigate growth trends and identified which climate variables are most important to aspen productivity in this region. Additionally, I established the timing of historic aspen recruitment in the MHSA using age of mature trees. In Chapter 4, I investigated a trophic cascade among wolves, elk and aspen. I reconstructed historical browse conditions for aspen to look for a shift in browse regimes that occurred concurrently with the changes in elk abundance/distribution by performing a dendrochronological analysis of aspen architectural morphology. I also evaluated plant height, productivity, and longevity of aspen where elk densities had declined dramatically in order to capture the expected growth response. I used ANOVA's and multiple comparison procedures to evaluate browse conditions and aspen growth among sites where elk densities have declined dramatically and those where elk densities have remained relatively constant.Item Applying risk allocation theory in a large mammal predator-prey system : elk-wolf behavioral interactions(Montana State University - Bozeman, College of Letters & Science, 2004) Gude, Justin Albert; Chairperson, Graduate Committee: Robert A. Garrott; Scott Creel (co-chair)Understanding the behaviorally-mediated indirect effects of predators in ecosystems requires knowledge of predator-prey behavioral interactions, and the risk allocation hypothesis can be used to make predictions about such interactions. In predator-ungulate-plant systems, empirical research quantifying how predators affect ungulate group sizes and distribution, in the context of other influential variables, is particularly needed. We determined non-predation variables that affect elk (Cervus elaphus) group sizes and distribution on a winter range in the Greater Yellowstone Ecosystem (GYE), using regression analyses of 1219 elk groups counted and mapped over 12 years prior to wolf (Canis lupus) recolonization. We next examined the relevance of these non-wolf-predation variables in the presence of wolves using logistic and linear regression on surveys of 513 1-km2 areas conducted over 2 years. Using model selection techniques, we evaluated risk allocation and other a priori hypotheses of elk group size and distributional responses to wolf predation risk while accounting for influential nonwolf- predation variables. We found little evidence that wolves affect elk group sizes, which were strongly influenced by habitat type. Following predictions from the risk allocation hypothesis, wolves likely created a more dynamic elk distribution in areas that they frequently hunted, as elk tended to move during the period of safety following wolf encounters in those areas. We predict that this distributional response to wolf predation risk should decrease the spatial heterogeneity of elk impacts on grasslands in areas that wolves frequently hunt. We also predict that this response should decrease browsing pressure on heavily-browsed woody plant stands in certain areas, which is supported by recent research in the GYE. This research highlights the importance of predator-prey behavioral interactions in large mammal systems.Item Behavioral responses of elk to winter wolf predation risk in the Madison Headwaters area, Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2009) Gower, Claire Natasha; Chairperson, Graduate Committee: Robert A. GarrottOver the past few decades a large body of literature has provided evidence that predators can influence the ways in which prey behave. This in turn may influence prey demography and predator-prey dynamics and therefore predators may influence the structure and function of populations and communities, independent of direct killing. Using data collected from 1991 to 2007, I evaluated the behavior of elk (Cervus elaphus) in the Madison headwaters area of Yellowstone National Park in response to the colonization and establishment of wolves (Canis lupus). Changes in home range size, fidelity, group size, foraging behavior, and large-scale spatial responses were evaluated. After wolf colonization, elk movements were more dynamic as elk moved more over the landscape as they were increasingly encountered, attacked, and displaced by wolves. Home range sizes were larger, with slight decreases in fidelity. These results show that elk made modest adjustments in space use presumably to reduce their vulnerability from predators at a fine-scale within their range. More dramatic larger scale spatial shifts were also documented as radio-collared elk adopted long-distance dispersal and migratory movements away from high-density wolf areas. These apparent predator-avoidance movements were never observed prior to wolf colonization or from areas where the risk of predation was lower. Prior to wolf colonization, the grouping behavior of elk was relatively stable and predictable as elk attempted to conserve energy and decrease starvation risk in the absence of wolves. Following wolf reintroduction group size and group size variation increased. This more dynamic behavior likely reflects a strategy to minimize predation risk and maximize food acquisition. The decision to forage was heavily influenced by local snow, habitat type, and time of day but remained relatively stable with and without the presence of wolves. The lack of any substantial change in the foraging behavior of elk in the presence of wolves illustrates that elk can maintain the same level of foraging time and retain a relatively constant level of nutrition. Together these results suggest that in a harsh winter environment such as the Madison headwaters, elk can adaptively manage their behavior to cope with environmental constraints both in the presence and absence of wolves. Landscape variation such as snow pack severity and habitat types, complexity, and patch size also influences predation risk and may dictate the way in which prey behave.Item Good animals in bad places : evaluating landscape attributes associated with elk vulnerability to wolf predation(Montana State University - Bozeman, College of Letters & Science, 2011) Dunkley, Shana Lucille; Chairperson, Graduate Committee: Robert A. GarrottVulnerability of prey to predators is heavily influenced by their respective physical and behavioral characteristics; however their interactions with landscape, and climate, collectively termed "environmental vulnerability," may also assume considerable importance. Landscape or habitat-dependent prey vulnerability is well-studied in smaller taxa systems where environmental factors primarily influence encounter rates, however the impact of environmental vulnerability in large mammal systems, where the probability of a successful attack may be more important than encounter probability, is poorly understood. This study utilized 18 years of survival and mortality data for radio-collared elk (Cervus elaphus), in concert with abundance, distribution, and habitat use data prior to and following restoration of wolves (Canis lupus) to Yellowstone National Park to evaluate the relationship between environmental vulnerability and elk mortality. Logistic regression was used to model the odds of mortality for 108 elk in 1257 animal sample intervals from 1991-2009 across a range of environmental conditions and gradients of wolf predation risk to evaluate: 1) The relationship between landscape, habitat, and environmental attributes and elk vulnerability to wolf predation and 2) Changes in the attributes related to elk mortality before and after wolf colonization. In the absence of wolf predation, mortality risk for elk was primarily associated with physical attributes of elk due to age and condition, factors that are known to influence starvation mortality. Following wolf reintroduction mortality risk was related to these elk physical characteristics, but more so to characteristics of the landscape and climate within an animal's home range. These apparent environmental influences were strong enough to result in substantial changes in distribution and abundance of elk in the study system to the extent that by the end of the study elk almost exclusively utilized areas with high probability of wolf encounter, but also a high probability of escape due to the collective characteristics of the landscape promoting predation refuges. The strong influence of environmental vulnerability is likely to affect the abundance and distribution of elk and wolves across their range, and has broad applications to large mammal predator-prey dynamics in general.Item Elk (Cervus elaphus) vigilance levels in response to predation risk from wolves (Canis lupus)(Montana State University - Bozeman, College of Letters & Science, 2007) Liley, Stewart Grayson; Chairperson, Graduate Committee: Scott CreelMany studies have shown that levels of antipredator vigilance are sensitive to variation in prey attributes, such as age, sex and group size. It is also well established that vigilance is sensitive to environmental effects, such as the presence of cover. In contrast, little is known about the sensitivity of vigilance to variation in factors associated with the predator itself, such as proximity, the size of the threatening group, and cues about motivation to hunt. Finally, little is known about the relative importance of these three classes of variables (predator, prey, and environment), or about the information content of simple versus complex models of vigilance. We quantified the vigilance levels of elk (Cervus elaphus) preyed upon by wolves (Canis lupus) in Yellowstone National Park, between January and May in 2005 and 2006, and compared a set of 38 regression models for vigilance levels, using Akaike's Information Criterion.Item Applying predator-prey theory to evaluate large mammal dynamics : wolf predation in a newly-established multiple-prey system(Montana State University - Bozeman, College of Letters & Science, 2008) Becker, Matthew Smith; Chairperson, Graduate Committee: Robert A. Garrott; Patrick J. White (co-chair)I studied wolf prey selection and kill rates during 1996-97 through 2006-07 winters in a newly established two-prey system in central Yellowstone National Park. Prey differed substantially in their vulnerability to wolf (Canis lupus) predation and wolves preyed primarily on elk (Cervus elaphus) but also used bison (Bison bison) to varying degrees within and among winters and packs. Winter severity, wolf abundance, distribution, and prey selection varied during the study, concurrent with variations in the demography, distribution, and behavior of elk and bison. A total of 759 wolf-killed ungulates were detected and prey selection by wolves was influenced by the absolute and relative abundance of prey types, the abundance of predators, and the duration of snow pack. Wolves strongly preferred elk calves relative to all other prey types, and elk calf abundance was inversely related to the occurrence of bison in wolf diets. Increasing wolf numbers also broadened prey selection from elk calves, and predation on bison and adult elk increased with increasing snow pack accumulation and duration, likely due to its long-term debilitating influence. Elk abundance and wolf pack size best explained variation in kill rates for elk while bison calf abundance and snow pack duration best explained kill rates of bison. The functional response of wolves for elk was best described by a Type II ratio-dependent model, indicating significant predator dependence. Prey-switching evaluations indicated increasing selection of bison with increasing bison:elk ratios, however no concurrent decrease in elk predation occurred. Increased bison predation is not solely dependent on relative abundance of the two prey species; therefore it is unlikely at this time that wolf prey-switching will stabilize the system.