Scientific evidence should inform environmental policy, but rapid environmental change brings high ecological uncertainty and associated barriers to the science-management dialogue. Biological ...invasions of aquatic plants are a worldwide problem with uncertain ecological and economic consequences. We demonstrate that the discrete choice method (DCM) can serve as a structured expert elicitation alternative to quantify expert opinion across a range of possible but uncertain environmental outcomes. DCM is widely applied in the social sciences to better understand and predict human preferences and trade-offs. Here we apply it to Alaska's first submersed invasive aquatic freshwater plant, Elodea spp. (elodea), and its unknown effects on salmonids. While little is known about interactions between elodea and salmonids, ecological research suggests that aquatic plant invasions can have positive and negative, as well as direct and indirect, effects on fish. We use DCM to design hypothetical salmonid habitat scenarios describing elodea's possible effect on critical environmental conditions for salmonids: prey abundance, dissolved oxygen, and vegetation cover. We then observe how experts choose between scenarios that they believe could support persistent salmonid populations in elodea-invaded salmonid habitat. We quantify the relative importance of habitat characteristics that influence expert choice and investigate how experts trade off between habitat characteristics. We take advantage of Bayesian techniques to estimate discrete choice models for individual experts and to simulate expert opinion for specific environmental management situations. We discuss possible applications and advantages of the DCM approach for expert elicitation in the ecological context. We end with methodological questions for future research.
•Identified critical salmon habitat characteristics for invaded habitat.•Demonstrated use of a discrete choice model for ecological expert elicitation.•Applied Bayesian approach to estimate individual expert opinions.•Analyzed expert coherence by combining model results with risk rating.•Discussed applicability for informing resource management decisions.
Climatically driven changes in snow characteristics (snowfall, snowpack, and snowmelt) will affect hydrologic and ecological systems in Alaska over the coming century, yet there exist no projections ...of downscaled future snow pack metrics for the state of Alaska. We updated historical and projected snow day fraction (PSF, the fraction of days with precipitation falling as snow) from McAfee et al. We developed modeled snowfall equivalent (SFE) derived from the product of snow-day fraction (PSF) and existing gridded precipitation for Alaska from Scenarios Network for Alaska and Arctic Planning (SNAP). We validated the assumption that modeled SFE approximates historical decadally averaged snow water equivalent (SWE) observations from snowcourse and Snow Telemetry (SNOTEL) sites. We present analyses of future downscaled PSF and two new products, October–March SFE and ratio of snow fall equivalent to precipitation (SFE:P) based on bias-corrected statistically downscaled projections of Coupled Model Intercomparison Project 5 (CMIP5) Global Climate Model (GCM) temperature and precipitation for the state of Alaska. We analyzed mid-century (2040–2069) and late-century (2070–2099) changes in PSF, SFE, and SFE:P relative to historical (1970–1999) mean temperature and present results for Alaska climate divisions and 12-digit Hydrologic Unit Code (HUC12) watersheds. Overall, estimated historical the SFE is reasonably well related to the observed SWE, with correlations over 0.75 in all decades, and correlations exceeding 0.9 in the 1960s and 1970s. In absolute terms, SFE is generally biased low compared to the observed SWE. PSF and SFE:P decrease universally across Alaska under both Representative Concentration Pathway (RCP) 4.5 and RCP 8.5 emissions scenarios, with the smallest changes for RCP 4.5 in 2040–2069 and the largest for RCP 8.5 in 2070–2099. The timing and magnitude of maximum decreases in PSF vary considerably with regional average temperature, with the largest changes in months at the beginning and end of the snow season. Mean SFE changes vary widely among climate divisions, ranging from decreases between −17 and −58% for late twenty-first century in southeast, southcentral, west coast and southwest Alaska to increases up to 21% on the North Slope. SFE increases most at highest elevations and latitudes and decreases most in coastal southern Alaska. SFE:P ratios indicate a broad switch from snow-dominated to transitional annual hydrology across most of southern Alaska by mid-century, and from transitional to rain-dominated watersheds in low elevation parts of southeast Alaska by the late twenty-first century.
Establishing species conservation priorities and recovery goals is often enhanced by extinction risk estimates. The need to set goals, even in data-deficient situations, has prompted researchers to ...ask whether general guidelines could replace individual estimates of extinction risk. To inform conservation policy, recent studies have revived the concept of the minimum viable population (MVP), the population size required to provide some specified probability of persistence for a given period of time. These studies conclude that long-term persistence requires ≥5000 adult individuals, an MVP threshold that is unaffected by taxonomy, life history or environmental conditions. Here, we re-evaluate this suggestion. We find that neither data nor theory supports its general applicability, raising questions about the utility of MVPs for conservation planning.
Rates of glacier mass loss in the northern Pacific coastal temperate rainforest (PCTR) are among the highest on Earth, and changes in glacier volume and extent will affect the flow regime and ...chemistry of coastal rivers, as well as the nearshore marine ecosystem of the Gulf of Alaska. Here we synthesize physical, chemical and biological linkages that characterize the northern PCTR ecosystem, with particular emphasis on the potential impacts of glacier change in the coastal mountain ranges on the surface–water hydrology, biogeochemistry, coastal oceanography and aquatic ecology. We also evaluate the relative importance and interplay between interannual variability and long-term trends in key physical drivers and ecological responses. To advance our knowledge of the northern PCTR, we advocate for cross-disciplinary research bridging the icefield-to-ocean ecosystem that can be paired with long-term scientific records and designed to inform decisionmakers.
In species management and conservation, surrogate species or groups of species can be used as proxies for broader sets of species when the number of species of concern is too great to allow each to ...be considered individually. However, these surrogate approaches are not applicable to all situations. In this article we discuss how the nature of the ecological system, the objectives and scale of management, and the level of available knowledge influence the decision about using a surrogate approach. We use species-area relations to define a “surrogate zone” in which the approach may be most effective. Using the Interior Columbia Basin of the northwestern United States as an example, we outline 10 steps that may enhance the effectiveness of surrogate approaches. Using a surrogate approach necessarily entails a trade-off between management tailored to individual species and less precise practices that may apply to a broader array of species. Ultimately, the use of a surrogate approach depends on the level of uncertainty that is acceptable in conducting management or conservation activities—in other words, “How good is good enough?”
1. A major paradigm shift is occurring in the approach of ecologists to statistical analysis. The use of the traditional approach of null-hypothesis testing has been questioned and an alternative, ...model selection by information-theoretic methods, has been strongly promoted and is now widely used. For certain types of analysis, information-theoretic approaches offer powerful and compelling advantages over null-hypothesis testing. 2. The benefits of information-theoretic methods are often framed as criticisms of null-hypothesis testing. We argue that many of these criticisms are neither irremediable nor always fair. Many are criticisms of the paradigm's application, rather than of its formulation. Information-theoretic methods are equally vulnerable to many such misuses. Care must be taken in the use of either approach but users of null-hypothesis tests, in particular, must greatly improve standards of reporting and interpretation. 3. Recent critiques have suggested that the distinction between experimental and observational studies defines the limits of the utility of null-hypothesis testing (with the paradigm being applicable to the former but not the latter). However, we believe that there are many situations in which observational data are collected that lend themselves to analysis under the null-hypothesis testing paradigm. We suggest that the applicability of the two analytical paradigms is more accurately defined by studies that assess univariate causality (when null-hypothesis testing is adequate) and those that assess multivariate patterns of causality (when information-theoretic methods are more suitable). 4. Synthesis and applications. Many ecologists are confused about the circumstances under which different inferential paradigms might apply. We address some of the major criticisms of the null-hypothesis testing paradigm, assess those criticisms in relation to the information-theoretic paradigm, propose methods for improving the use of null-hypothesis testing, and discuss situations in which the use of null-hypothesis testing would be appropriate. We urge instructors and practitioners of statistical methods to heighten awareness of the limitations of null-hypothesis testing and to use information-theoretic methods whenever prior evidence suggests that multiple research hypotheses are plausible. We contend, however, that by marginalizing the use of null-hypothesis testing, ecologists risk rejecting a powerful, informative and well-established analytical tool.
•Conifer mortality generally increased with bole diameter.•Patterns of mortality were influenced by management history.•Large diameter conifers near patch cuts escaped attack by bark ...beetles.•Mortality of smaller lodgepole pine was higher >15m from patch cuts.
A recent series of bark beetle outbreaks in the Rocky Mountain region of the U.S. is the largest and most intense ever recorded. Factors contributing to tree mortality from bark beetles are complex, but include aspects of forest stand condition. Because stand conditions respond to forest management, evaluating bark beetle-caused tree mortality and changes in forest structural attributes in areas previously subjected to management not only improves mechanistic understanding of beetle-caused changes in forests, but also improves prediction of future bark beetle responses to management regimes. We retrospectively assessed mortality of lodgepole pine (Pinus contorta), Engelmann spruce (Picea engelmannii), and subalpine fir (Abies lasiocarpa), and stand structure in two watersheds in south-central Wyoming, U.S.A. following outbreaks of mountain pine beetle (Dendroctonus ponderosae), spruce beetle (Dendroctonus rufipennis), and western balsam beetle (Dryocoetes confusus). One watershed received 240 patch cuts (mean area 1.5ha), a type of group selection cut, six years before the beetle outbreaks began; the other watershed received no active management (control). We conducted surveys of forest vegetation attributes over 27yrs, during pre-harvest, post-harvest, and post-outbreak periods. After the outbreak, lodgepole pine and Engelmann spruce mortality increased with increasing bole diameters and basal area of each species, but patterns of mortality were influenced by patch-cutting. Large-diameter trees in or near patch cuts tended to escape attack by bark beetles. Away from patch cuts (⩾15m), mortality of smaller lodgepole pine was higher compared to the control watershed. Based on our observed patterns of tree mortality, we hypothesize a changing pattern of host selection (i.e., selection for smaller trees) was influenced by stand conditions that created more suitable conditions for bark beetles in areas between patch cuts in the treated watershed. Snag density increased from pre-harvest to post-outbreak periods, but log density was similar, suggesting most dead trees remained standing at the time of data collection. Canopy cover did not decrease as expected, and ground cover did not change substantially from pre-harvest to post-outbreak periods. Patch-cutting improved survival probability of large-diameter lodgepole pine and Engelmann spruce during outbreaks of multiple species of bark beetle, although reduced losses were only realized for trees in or near (⩽15m) patch cuts. However, during intense, broad-scale tree mortality events, these benefits may be important in reducing the loss of mature trees to bark beetles and promoting retention of a larger cohort of mature trees post-outbreak.
The brown bear population on the Kenai Peninsula, Alaska, has not been empirically estimated previously because conventional aerial methods over this heavily forested landscape were infeasible. We ...applied a rapid field protocol to a DNA-based, mark-recapture approach on a large and tightly bounded sample frame to estimate brown bear abundance. We used lure to attract bears to barbed wire stations deployed in 145 9-km × 9-km cells systematically distributed across 10,200 km2 of available habitat on the Kenai National Wildlife Refuge and Chugach National Forest during 31 consecutive days in early summer 2010. Using 2 helicopters and 4 2-person field crews, we deployed the stations during a 6-day period and subsequently revisited these stations on 5 consecutive 5-day trap sessions. We extracted DNA to identify individual bears and developed capture histories as input to mark-recapture models. Combined with data from radio-telemetered bears, ≥243 brown bears were alive on the Kenai Peninsula in 2010, but we used only 99 females and 104 males in modeling. We used Akaike's Information Criterion selection and model averaging to estimate 428 (95% lognormal CI = 353–539) brown bears (including all age classes) on the study area. Despite low recaptures rates, we achieved reasonable precision by ensuring geographic and demographic population closure through a spatially comprehensive sample frame and very short sampling window. We reduced bias by including information from rub trees and telemetered females (i.e., occasion 0). Extrapolating the density estimate of 42 bears/1,000 km2 of available habitat on the study area to the Kenai Peninsula suggests a peninsula-wide population of582 brown bears (95% lognormal CI = 469–719). Despite a density estimate that is low compared to other coastal brown bear populations in Alaska and genetic evidence that suggests this peninsular population is insular, harvest management has been liberalized since 2012. We recommend this population estimate serve as the benchmark for future management. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
•We describe site occupancy dynamics for red squirrels in a subalpine forest.•Extinction rate was influenced by snag density up to 5 snags/0.04ha.•Colonization rate was associated with the basal area ...of live trees.•Harvested areas served as refugia for red squirrels after a bark beetle epidemic.
Extensive ecological disturbances can interact with spatial heterogeneity produced by previous disturbances, influencing responses of vertebrates to environmental change. Recent and ongoing outbreaks of bark beetles (including Dendroctonus spp. and Dryocoetes confuses) in the Rocky Mountains produced an opportunity to investigate effects of broad-scale tree mortality on an important seed predator in Nearctic coniferous forests, the red squirrel (Tamiasciurus hudsonicus), and to evaluate whether those effects interact with forest heterogeneity produced by previous timber harvest. Our study characterized site occupancy dynamics for red squirrels in relation to patch-cutting, a type of group-selection cut, and the bark-beetle outbreak, and evaluated whether patch cutting influenced subsequent effects of bark beetles on these squirrels. We used multi-season occupancy models and covariates for harvest- and outbreak-related habitat characteristics to describe extinction and colonization rates of red squirrels over a 27-yr period in Wyoming, USA. We observed effects of year, patch-cutting, and the bark beetle outbreak on the probability of detecting a red squirrel. We observed a negative association between local extinction rate and increasing snag density, but only to a threshold of 5 snags/0.04ha. Local colonization rate was positively associated with the basal area of live trees. Annual site occupancy varied across years (range pre-harvest: 0.76–0.89; post-harvest: 0.84–0.99), and was lowest (0.70–0.72) during the two years sampling occurred approximately 14years after the bark beetle outbreaks began. Tree mortality was lowest near patch cuts; this pattern was especially pronounced for mature trees (>30cm diameter at breast height), which tend to produce the most cones and would likely contribute the most to red squirrel survival. Strong habitat effects on occupancy dynamics suggest that previously-harvested areas may provide refugia for red squirrels in post-outbreak forests. Our results support managing for uneven-aged stands of mixed species composition in subalpine forests of the Rocky Mountains.
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