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1801. [Article] Implications of cougar prey selection and demography on population dynamics of elk in northeast Oregon
Mule deer (Odocoileus hemionus hemionus) and Rocky Mountain elk (Cervus canadensis nelsoni; hereafter elk) populations in northeast Oregon have declined in the past 10 to 20 years. Concurrent with these ...Citation Citation
- Title:
- Implications of cougar prey selection and demography on population dynamics of elk in northeast Oregon
- Author:
- Clark, Darren A.
Mule deer (Odocoileus hemionus hemionus) and Rocky Mountain elk (Cervus canadensis nelsoni; hereafter elk) populations in northeast Oregon have declined in the past 10 to 20 years. Concurrent with these declines, cougar (Puma concolor) populations have apparently increased, leading to speculation that predation by cougars may be responsible for declining ungulate populations. However, empirical data on cougar diets, kill rates, and prey selection are lacking to support this speculation. Furthermore, the common assumption that cougar populations have increased in northeast Oregon may not be well founded because cougar populations in other areas within the Pacific Northwest region have declined in recent years. My primary research objectives were to (1) estimate kill rates and prey selection by cougars in northeast Oregon, (2) document causes of mortality and estimate survival rates for cougars, (3) estimate population growth rates of cougars in northeast Oregon and simulate the effects of hypothetical lethal control efforts on the cougar population, and (4) investigate the relative influence of top-down, bottom-up, and climatic factors for limiting population growth rates of elk in northeast Oregon. Results from my research will help guide cougar and elk management in northeast Oregon and provide a framework for assessing relative effects of top-down, bottom-up, and abiotic factors on population growth rates of ungulates in this and other areas. I implemented a 3-year study in northeast Oregon to investigate diets, kill rates, and prey selection of cougars in a multiple-prey system to better understand mechanisms by which cougars may influence ungulate populations. During my research, 25 adult cougars were captured and fitted with Global Positioning System (GPS) collars to identify kill sites. I monitored predation sequences of these cougars for 7,642 days and located the remains of 1,213 prey items killed by cougars. Cougars killed ungulates at an average rate of 1.03 per week (95% CI = 0.92 – 1.14); however, ungulate kill rates were variable and influenced by the season and demographic classification of cougars. Cougars killed ungulates 1.55 (95% CI = 1.47 – 1.66) times more frequently during summer (May-Oct) than during winter (Nov-Apr), but killed similar amounts of ungulate biomass (8.05 kg/day; 95% CI = 6.74 – 9.35) throughout the year. Cougars killed ungulates more frequently in summer because juvenile ungulates comprised most of the diet and were smaller on average than ungulate prey killed in winter. Female cougars with kittens killed more frequently (kills/day) than males or solitary females. After accounting for the additional biomass of kittens in cougar family groups, male cougars killed on average more biomass of ungulate prey per day than did females (R = 0.41, P < 0.001), and female cougars killed more biomass of prey per day as a function of the number and age of their kittens (R = 0.60, P < 0.001). Patterns of prey selection were influenced by season and demographic classification of cougars. Female cougars selected elk calves during summer and deer fawns during winter. In contrast, male cougars selected elk calves and yearling elk during summer and elk calves during winter. My results strongly supported the hypothesis that cougar predation is influenced by season, gender, and reproductive status of the cougar and these patterns in cougar predation may be generalizable among ecosystems. The observed selection for juvenile elk and deer suggested a possible mechanism by which cougars could negatively affect population growth rates of ungulates. I investigated survival and documented causes of mortality for radio-collared cougars at 3 study areas in Oregon during 1989 – 2011. Mortality due to hunter harvest was the most common cause of death for cougars in the Catherine Creek study area and the study area combining Wenaha, Sled Springs, and Mt. Emily Wildlife Management Units (WSM study area) in northeast Oregon. In contrast, natural mortality was the most common cause of death for cougars in the Jackson Creek study area in southwest Oregon. Annual survival rates of adult males were lowest at Catherine Creek when it was legal to hunt cougars with dogs (Ŝ = 0.57), but increased following the prohibition of this hunting practice (Ŝ = 0.86). This latter survival rate was similar to those observed at Jackson Creek (Ŝ = 0.78) and WSM (Ŝ = 0.82). Regardless of whether hunting of cougars with dogs was permitted, annual survival rates of adult females were similar among study areas (Catherine Creek Ŝ = 0.86; WSM Ŝ = 0.85; Jackson Creek Ŝ = 0.85). I did not document an effect of age on cougar survival rates in the Catherine Creek study area, which I attributed to selective harvest of prime-aged, male cougars when it was legal to hunt cougars with dogs. In contrast, I observed an effect of age on annual survival in both the WSM and Jackson Creek study areas. These results indicate that sub-adult males had significantly lower survival rates than sub-adult females, but survival rates of males and females were similar by age 4 or 5 years. My results suggest that survival rates of cougars in areas where hunting cougars with dogs is illegal should be substantially higher than areas where use of dogs is legal. I used estimates of cougar vital rates from empirical data collected in northeast Oregon to parameterize a Leslie projection matrix model to estimate deterministic and stochastic population growth rates of cougars in northeast Oregon when hunting cougars with dogs was legal (1989 - 1994) and illegal (2002 - 2011). A model cougar population in northeast Oregon that was hunted with dogs increased at a mean stochastic growth rate of 21% per year (λ[subscript s] = 1.21). Similarly, I found that a model cougar population that was subjected to hunting without dogs increased at a rate of 17% per year (λ[subscript s] = 1.17). Given that hunting cougars with dogs typically results in increased harvest and reduced survival rates of cougars, it was unexpected that the cougar population subjected to hunting with dogs was increasing at a faster rate than one that was not hunted with dogs. However, cougar populations in Oregon were subjected to low harvest rates when hunting cougars with dogs was legal and harvest was male biased. This resulted in high survival rates of female cougars and correspondingly high population growth rates. The Oregon Cougar Management Plan allows the Oregon Department of Fish and Wildlife to administratively reduce cougar populations to benefit ungulate populations, reduce human-cougar conflicts, and limit livestock depredation. Consequently, I was interested in modeling the effects of a hypothetical lethal control effort on a local cougar population. Using empirically-derived vital rates and a deterministic Leslie matrix model, I found that the proportion of the cougar population that would need to be removed annually to achieve a 50% population reduction within 3 years was 28% assuming a closed population, and 48% assuming maximum immigration rates into the population. Using a stochastic Leslie matrix model, I also determined that the model cougar population would likely return to its pre-removal size in 6 years assuming a closed population, and 2 years assuming maximum immigration rates. These model results indicate that current management practices and harvest regulations, combined with short-term, intensive, and localized population reductions, are unlikely to negatively affect the short-term viability of cougar populations in northeast Oregon. However, at this time, it is not known if intensive lethal control efforts funded by state agencies will be cost-effective (i.e., increased sales of tags to hunt deer and elk will offset the costs of control efforts). Further research is needed to investigate the cost-effectiveness of cougar control efforts in Oregon. I developed a Leslie matrix population model, parameterized with empirically-derived vital rates for elk in northeast Oregon, to investigate the relative influence on elk population growth rates of (1) survival and pregnancy, and (2) top-down, bottom-up, and climatic variables. I then estimated the effect of varying the strength of top-down factors on growth rates of elk populations. Growth rates of the model elk population were most sensitive to changes in adult female survival, but due to the inherent empirical variation in juvenile survival rates explained the overwhelming majority of variation in model population growth rates (r² = 0.92). Harvest of female elk had a strong negative effect on model population growth rates of elk (r² = 0.63). An index of cougar density was inversely related to population growth rates of elk in my model (r² = 0.38). A delay in mean date of birth was associated with reduced juvenile survival, but this had a minimal effect on population growth rates in my model (r² = 0.06). Climatic variables, which were used as surrogates for nutritional condition of females, had minimal effects on population growth rates. Likewise, elk density had almost no effect on population growth rates (r² = 0.002). The results of my model provided a novel finding that cougars can be a strong limiting factor on elk populations. Wildlife managers should consider the potential top-down effects of cougars and other predators as a limiting factor on elk populations.
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1802. [Article] Linking Moral Obligations, Assumption-based Research, and Structured Decision Making to Inform Bull Trout Recovery
More than 1500 species of plants and animals in the United States are listed as threatened or endangered under the Endangered Species Act (ESA). The U.S. Departments of Interior and Commerce are required, ...Citation Citation
- Title:
- Linking Moral Obligations, Assumption-based Research, and Structured Decision Making to Inform Bull Trout Recovery
- Author:
- Brignon, William R.
More than 1500 species of plants and animals in the United States are listed as threatened or endangered under the Endangered Species Act (ESA). The U.S. Departments of Interior and Commerce are required, under Section 4(f)(1) of the ESA, to develop recovery plans for ESA-listed species under the respective agency jurisdictions. However, developing recovery plans that are both scientifically defensible and consistent with a diversity of stakeholder (e.g., states, tribes, private landowners) values is often difficult. Structured decision making is a framework that resource managers can use to integrate diverse, and often conflicting, stakeholder value systems into species recovery planning. Within this framework difficult decisions are deconstructed into the three basic components: 1) explicit, quantifiable objectives that represent stakeholder values; 2) mathematical models used to predict the effect of management decisions on the outcome of objectives; and 3) management alternatives or actions. The goal of my dissertation was to acknowledge and understand the uncertainty of bull trout Salvelinus confluentus reintroduction strategies and provide an ethical and scientific foundation for an enduring and biologically sound conservation program. My objectives were to (1) describe how incorporating stakeholder values into scientifically defensible recovery planning using structured decision making will fulfill legal and moral obligations to recover species, (2) determine how captive rearing environments affect the development and survival behaviors of bull trout and how these effects may influence the efficacy and ultimate success of reintroduction and recovery programs, and (3) use structured decision making to evaluate the tradeoffs of alternative bull trout reintroduction decisions. I developed this research project to be multifaceted by incorporating components of philosophy (Chapter 2), assumption-based research (Chapter 3), and statistical modeling (Chapter 4). The collective results my research should serve as an example of how to incorporate diverse stakeholder value systems, assumption-based research, and evaluations of alternative management actions into species recovery and reintroduction decisions. This approach promotes transparency and consensus in decision making. Recognizing these benefits, the U.S. Fish and Wildlife Service has adopted a similar approach to manage species and their habitats into the future (i.e., Strategic Habitat Conservation). The impediments to species recovery are numerous. Some of the biggest impediments to recovery planning are conflicting values and interests among stakeholders. I believe that these types of conflicts and related issues are best addressed by integrating the diverse values and interests of stakeholders with the best scientific information available, and doing so in a clear and transparent manner that will broaden acceptance for enduring recovery planning. Science, in and of itself, cannot dictate which management decisions ought to be made; it purely offers a biological and physical basis for estimating the outcomes of decisions. An understanding of humanities is needed to provide context for the myriad of societal obligations. Three moral philosophies; consequentialism, deontology, and virtue theory, suggest that structured decision making is a justified method that can guide natural resource decisions in the future, and will honor legal and moral obligations to recover ESA listed species and their habitats. The ability to recover and delist species in the future depends on an increased understanding of natural ecosystems through scientific discovery and the ability to incorporate stakeholder values into the recovery planning process in a manner that is objective, systematic, and transparent. Animals reared in barren captive environments exhibit different development and behaviors than wild counterparts. Hence, the captive phenotypes may influence the success of reintroduction and recovery programs for threatened and endangered species. I collected wild bull trout embryos from the Metolius River Basin, Oregon and reared them in differing environments to better understand how captivity affects the bull trout phenotype to aide in the development of informed recovery strategies for the species. I compared the development of the brain and eye lens, and boldness and prey acquisition behaviors of bull trout reared in conventional barren and more structurally complex captive environments with that of wild fish. I found that wild bull trout exhibited a greater level of boldness and prey acquisition ability, followed by captive reared bull trout from complex habitats, and finally fish reared in conventional captive environments. In addition, the eye lens of conventionally reared bull trout was larger than complex reared captive fish or that of wild fish. Unexpectedly, I detected wild fish had a smaller relative cerebellum than either captive reared treatment. My results add to the existing literature that suggests rearing fish in more complex captive environments can create a more wild-like phenotype than conventional rearing practices. Rearing fish in captivity is an important tool that can be used to accomplish a suite of management objectives including providing fish for research and reintroduction programs, or in worst case scenarios maintaining refuge populations. An understanding of the effects of captivity on the development and behavior of bull trout is important if life in captivity is the only option to ensure existence of some populations, and can inform rearing and reintroduction programs through prediction of the performance of released individuals. Stakeholders can be divided on what is the optimal reintroduction strategy to use (i.e., translocation, captive rearing, or artificial production) or how many individuals to collect for a program. These decisions are further complicated by a limited understanding of how captivity affects an animal’s phenotype and how well animals will survive upon release. Structured decision making allows natural resource decisions to be made in spite of uncertainty by linking reintroduction goals with alternative management actions through predictive models of ecological processes. Predictive models represent competing hypothesis that describe the belief of the structure and function of the ecological system and can be updated as new information is generated by monitoring and research (i.e., adaptive management). I developed a structured decision model to evaluate the tradeoffs between six bull trout reintroduction alternatives with the goal of maximizing the number of adults in the recipient population, up to 300 individuals, without reducing the donor population to an unacceptable state. The six alternative decisions that were evaluated are to 1) do-nothing, 2) translocate 1000 juveniles, 3) translocate 60 adults, 4) translocate 1000 juveniles and 40 adults, 5) captive rear 20,000 wild embryos, or 6) artificial production of 60 wild adults. The model was parameterized with published demographic parameters where available and consists of three stage-based Leslie matrix models that represent the donor, captive, and recipient populations. A state dependent policy was created that identifies the optimal decision over a combination of possible donor and recipient adult abundance states. One-way sensitivity analysis suggests that the value of the decision outcome was most influenced by survival parameters that resulted in increased adult abundance in the recipient population, and increased juvenile survival in the donor and recipient populations. The decision outcome was also sensitive to small and large adult fecundity rates and sex ratio. The outcome was least sensitive to survival parameters associated with the captive population, a survival reduction of naive reintroduced individuals, and juvenile carrying capacity of the reintroduced population. Two-way sensitivity analysis with all combinations of model parameters identified interactions that influence the decision outcome and identity. For example, a comparison of the juvenile density dependent parameters for the donor population indicated that when above a maximum egg survival of 0.14, the juvenile carrying capacity had a greater influence on the expected outcome of the decision. When juvenile carrying capacity in the donor population was less than ~5500 individuals, the optimal strategy was to do nothing, which most likely avoided an unacceptable reduction in the donor population. Whereas, translocating adults was the optimal decision when both density dependent parameters (i.e., juvenile carrying capacity, maximum egg survival) were in the upper end of their range and resulted in a decision outcome of greater than 60 adults in the recipient population. The optimal decision was to captive rear embryos when there was minimal effect of captive rearing and translocation on the survival of released fish. Whereas, translocating adults was the optimal decision when the probability of survival was less than 0.75 for captive reared fish as compared to translocated fish. As the survival penalty for captive reared fish neared 1.00, which indicated little to no effects of captivity on a fish’s survival after release, artificial production became the optimal decision regardless of the effects of a translocation on post-release survival. This model and sensitivity analyses can serve as the foundation for formal adaptive management and improved effectiveness, efficiency, and transparency of bull trout reintroduction decisions. Ongoing bull trout reintroductions and research will continue to lessen uncertainty and new information can be incorporated into decision models to guide future reintroduction decisions and maximize the benefit from limited resources available for bull trout recovery.
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Given the vital role of forest ecosystems in landscape pattern and process, it is important to quantify the effects, feedbacks, and uncertainties associated with forest disturbance dynamics. In western ...
Citation Citation
- Title:
- Mapping disturbance interactions from earth and space : insect effects on tree mortality, fuels, and wildfires across forests of the Pacific Northwest
- Author:
- Meigs, Garrett W.
Given the vital role of forest ecosystems in landscape pattern and process, it is important to quantify the effects, feedbacks, and uncertainties associated with forest disturbance dynamics. In western North America, insects and wildfires are both native disturbances that have influenced forests for millennia, and both are projected to increase with anthropogenic climate change. Although there is acute concern that insect-caused tree mortality increases the likelihood or severity of subsequent wildfire, previous research has been mixed, with results often based on individual fire or insect events. Much of the ambivalence in the literature can be attributed to differences in the particular insect of interest, forest type, and fire event, but it is also related to the spatiotemporal scale of analysis and a general lack of geospatial datasets spanning enough time and space to capture multiple forest disturbances consistently and accurately. This dissertation presents a regional-scale framework to map, quantify, and understand insect-wildfire interactions across numerous insect and fire events across the Pacific Northwest region (PNW). Through three related studies, I worked with many collaborators to develop regionally extensive but fine-grained maps to assess the spatiotemporal patterns of wildfires and the two most pervasive, damaging forest insects in the PNW – mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins [Coleoptera: Scolytidae]; a bark beetle) and western spruce budworm (WSB; Choristoneura freemani Razowksi [Lepidoptera: Tortricidae]; a defoliator). The proximate objectives of developing new maps and summarizing where and when insects have occurred before wildfires enable us to address the ultimate question: How does forest insect activity influence the likelihood of subsequent wildfire? In a pilot study focused on the forest stand scale (Chapter Two), we leveraged a Landsat time series change detection algorithm (LandTrendr), annual forest health aerial detection surveys (ADS), and field measurements to investigate MPB and WSB effects on spectral trajectories, tree mortality, and fuel profiles at 38 plots in the Cascade Range of Oregon. Insect effects were evident in the Landsat time series as combinations of both short- and long-duration changes. WSB trajectories appeared to show a consistent temporal evolution of long-duration spectral decline followed by recovery, whereas MPB trajectories exhibited both short- and long-duration spectral declines and variable recovery rates. When comparing remote sensing data with field measurements of insect impacts, we found that spectral changes were related to cover-based estimates (e.g., tree basal area mortality and down coarse woody detritus). In contrast, ADS changes were related to count-based estimates (e.g., dead tree density). Fine woody detritus and forest floor depth were not well correlated with Landsat- or aerial survey-based change metrics. This study demonstrated the utility of insect mapping methods that capture a wide range of spectral trajectories, setting the stage for regional-scale mapping and analysis. In a regional assessment of MPB and WSB effects on tree mortality (Chapter Three), we developed Landsat-based insect maps and presented comparisons across space, time, and insect agents that have not been possible to date, complementing existing ADS maps by: (1) quantifying change in terms of field-measured tree mortality; (2) providing consistent estimates of change for multiple agents, particularly long-duration changes; (3) capturing variation of insect impacts at a finer spatial scale within ADS polygons, substantially reducing estimated insect extent. Despite high variation across the study region, spatiotemporal patterns were evident in both the ADS- and Landsat-based maps of insect activity. MPB outbreaks occurred in two phases -- first during the 1970s and 1980s in eastern and central Oregon and then more synchronously during the 2000s throughout the dry interior conifer forests of the PNW. Reflecting differences in habitat susceptibility and epidemiology, WSB outbreaks exhibited early activity in northern Washington and an apparent spread from the eastern to central PNW during the 1980s, returning to northern Washington during the 1990s and 2000s. Across the region, WSB exceeded MPB in extent and tree mortality impacts in all ecoregions except for one, suggesting that ongoing studies should account for both bark beetles and defoliators, particularly given recent and projected increases in wildfire extent. By combining these insect maps with an independent wildfire database (Chapter Four), we investigated wildfire likelihood following recent MPB and WSB outbreaks at ecoregional and regional scales. We computed wildfire likelihood with two-way binary matrices between fire and insects, testing for paired differences between percent burned with and without prior insect activity. All three disturbance agents occurred primarily in the drier, interior conifer forests east of the Cascade Range, with recent wildfires extending through the southern West Cascades and Klamath Mountains. In general, insect extent exceeded wildfire extent, and each disturbance typically affected less than 2% annually of a given ecoregion. In recent decades across the PNW, wildfire likelihood is not consistently higher in forests with prior insect outbreaks, but there is evidence of linked interactions that vary across insect agent (MPB and WSB), space (ecoregions), and time (interval since insect onset). For example, fire likelihood is higher following MPB activity in the North Cascades and West Cascades, particularly within the past 10 years, whereas fire likelihood is lower at various time lags following MPB in the Northern Rockies, East Cascades, and Blue Mountains. In contrast, fire likelihood is lower following WSB outbreaks at multiple time lags across all ecoregions. In addition, there are no consistent relationships between insect-fire likelihood and interannual fire extent, suggesting that other factors (such as climate) control the disproportionately large fire years accounting for the majority of regional fire extent. Although insects and wildfires do not appear to overlap enough to facilitate consistently positive linked disturbance interactions, specific fire events and years – such as 2003 and 2006 in the North Cascades – demonstrate high insect-fire co-occurrence and potential compound disturbance effects at the landscape scale. The results from this dissertation highlight the key ecological roles that native disturbances play in PNW forests. WSB, MPB, and wildfire have been relatively rare at the regional scale, but all three have had and will continue to have profound effects on particular forest stands and landscapes. Because scale is such an important aspect of both the disturbance phenomena themselves as well as our ability to detect the ecological changes they render, our results also underscore the importance of geospatial datasets that span multiple scales in space and time. Given concerns about forest health in a rapidly changing climate, long-term monitoring will enable forest managers to quantify and anticipate the independent and interactive effects of insects, wildfires, and other disturbances.