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IntroductionNatural resource management uses expert judgement to estimate facts that inform important decisions. Unfortunately, expert judgement is often derived by informal and largely untested protocols, despite evidence that the quality of judgements can be improved with structured approaches. We attribute the lack of uptake of structured protocols to the dearth of illustrative examples that demonstrate how they can be applied within pressing time and resource constraints, while also improving judgements.Aims and methodsIn this paper, we demonstrate how the IDEA protocol for structured expert elicitation may be deployed to overcome operational challenges while improving the quality of judgements. The protocol was applied to the estimation of 14 future abiotic and biotic events on the Great Barrier Reef, Australia. Seventy-six participants with varying levels of expertise related to the Great Barrier Reef were recruited and allocated randomly to eight groups. Each participant provided their judgements using the four-step question format of the IDEA protocol (‘Investigate’, ‘Discuss’, ‘Estimate’, ‘Aggregate’) through remote elicitation. When the events were realised, the participant judgements were scored in terms of accuracy, calibration and informativeness.Results and conclusionsThe results demonstrate that the IDEA protocol provides a practical, cost-effective, and repeatable approach to the elicitation of quantitative estimates and uncertainty via remote elicitation. We emphasise that i) the aggregation of diverse individual judgements into pooled group judgments almost always outperformed individuals, and ii) use of a modified Delphi approach helped to remove linguistic ambiguity, and further improved individual and group judgements. Importantly, the protocol encourages review, critical appraisal and replication, each of which is required if judgements are to be used in place of data in a scientific context. The results add to the growing body of literature that demonstrates the merit of using structured elicitation protocols. We urge decision-makers and analysts to use insights and examples to improve the evidence base of expert judgement in natural resource management.

Aim Conservation practitioners use biological surveys to ascertain whether or not a site is occupied by a particular species. Widely used statistical methods estimate the probability that a species will be detected in a survey of an occupied site. However, these estimates of detection probability are alone not sufficient to calculate the probability that a species is present given that it was not detected. The aim of this paper is to demonstrate methods for correctly calculating (1) the probability a species occupies a site given one or more non-detections, and (2) the number of sequential non-detections necessary to assert, with a pre-specified confidence, that a species is absent from a site.Location Occupancy data for a tree frog in eastern Australia serve to illustrate methods that may be applied anywhere species' occupancy data are used and detection probabilities are < 1.Methods Building on Bayesian expressions for the probability that a site is occupied by a species when it is not detected, and the number of non-detections necessary to assert absence with a pre-specified confidence, we estimate occupancy probabilities across tree frog survey locations, drawing on information about where and when the species was detected during surveys. Results We show that the number of sequential non-detections necessary to assert that a species is absent increases nonlinearly with the prior probability of occupancy, the probability of detection if present, and the desired level of confidence about absence.Main conclusions If used more widely, the Bayesian analytical approaches illustrated here would improve collection and interpretation of biological survey data, providing a coherent way to incorporate detection probability estimates in the design of minimum survey requirements for monitoring, impact assessment and distribution modelling.

Biodiversity conservation decisions are difficult, especially when they involve differing values, complex multidimensional objectives, scarce resources, urgency, and considerable uncertainty. Decision science embodies a theory about how to make difficult decisions and an extensive array of frameworks and tools that make that theory practical. We sought to improve conceptual clarity and practical application of decision science to help decision makers apply decision science to conservation problems. We addressed barriers to the uptake of decision science, including a lack of training and awareness of decision science; confusion over common terminology and which tools and frameworks to apply; and the mistaken impression that applying decision science must be time consuming, expensive, and complex. To aid in navigating the extensive and disparate decision science literature, we clarify meaning of common terms: decision science, decision theory, decision analysis, structured decision-making, and decision-support tools. Applying decision science does not have to be complex or time consuming; rather, it begins with knowing how to think through the components of a decision utilizing decision analysis (i.e., define the problem, elicit objectives, develop alternatives, estimate consequences, and perform trade-offs). This is best achieved by applying a rapid-prototyping approach. At each step, decision-support tools can provide additional insight and clarity, whereas decision-support frameworks (e.g., priority threat management and systematic conservation planning) can aid navigation of multiple steps of a decision analysis for particular contexts. We summarize key decision-support frameworks and tools and describe to which step of a decision analysis, and to which contexts, each is most useful to apply. Our introduction to decision science will aid in contextualizing current approaches and new developments, and help decision makers begin to apply decision science to conservation problems.

Frameworks for analyzing the risks of emerging diseases and invasive species often have relied on unstructured estimates of likelihoods and consequences. We suggest a flexible alternative that offers more transparent analysis without need for additional data. Its strength lies in explicit and complementary treatment of technical and social judgments. We describe a system in which cognitive maps, Bayes nets, and multicriteria analysis can be used in tandem to structure a problem, identify exposure pathways, combine data and expert judgement to estimate the likelihoods, and assess consequences of alternative decisions. These tools may be employed in participatory settings or as part of standard regulatory practice. We illustrate this approach with an assessment of the management of an emerging disease that poses a hazard to Australia.

Citation: Hemming, V., A. M. Hanea, T. Walshe, and M. A. Burgman. 2020. Weighting and aggregating expert ecological judgments. Ecological Applications 30(4):Abstract. Performance weighted aggregation of expert judgments, using calibration questions, has been advocated to improve pooled quantitative judgments for ecological questions. However, there is little discussion or practical advice in the ecological literature regarding the application, advantages or challenges of performance weighting. In this paper we (1) illustrate how the IDEA protocol with four-step question format can be extended to include performance weighted aggregation from the Classical Model, and (2) explore the extent to which this extension improves pooled judgments for a range of performance measures. Our case study demonstrates that performance weights can improve judgments derived from the IDEA protocol with four-step question format. However, there is no a-priori guarantee of improvement. We conclude that the merits of the method lie in demonstrating that the final aggregation of judgments provides the best representation of uncertainty (i.e., validation), whether that be via equally weighted or performance weighted aggregation. Whether the time and effort entailed in performance weights can be justified is a matter for decision-makers. Our case study outlines the rationale, challenges, and benefits of performance weighted aggregations. It will help to inform decisions about the deployment of performance weighting and avoid common pitfalls in its application.

Australian state and federal agencies use a broad range of methods for setting conservation priorities for species at risk. Some of these are based on rule sets developed by the International Union for the Conservation of Nature, while others use point scoring protocols to assess threat. All of them ignore uncertainty in the data. In this study, we assessed the conservation status of 29 threatened vascular plants from Tasmania and New South Wales using a variety of methods including point scoring and rule-based approaches. In addition, several methods for dealing with uncertainty in the data were applied to each of the prioritysetting schemes. The results indicate that the choice of a protocol for setting priorities and the choice of the way in which uncertainty is treated may make important differences to the resulting assessments of risk. The choice among methods needs to be rationalized within the management context in which it is to be applied. These methods are not a substitute for more formal risk assessment.

Changes in vegetation, pathogen population and distribution were monitored periodically in both defined infested quadrats and similar pathogen-free quadrats at six sites representing major types of forest and woodland. Assessments were recorded in May 1977, 1979, 1981, 1983–1984, 1995 and 2000. The susceptible eucalypts in the overstorey of infested sites, such as Eucalyptus obliqua, E. baxteri, E. willisii and E. macroryncha, showed severe dieback, loss of crown or deaths. All the trees died on some sites, others presented dead leaders with epicormic growth on lower branches. Dieback followed by death occurred in 54% of the understorey species, including the dominant Xanthorrhoea australis, thereby changing community structure and species composition. At the time of its greatest prevalence, the pathogen’s activity resulted in a decline in species richness in infested quadrats to a mean of 25.6 species compared with a mean of 39.2 for pathogen-free quadrats. Percentage cover and percentage contribution to the community by susceptible species were negligible. On steep sites, 65% of the ground remained bare, but on other sites the susceptible flora was replaced by field-resistant species of sedges and rushes, such as Lepidosperma semiteres and Hypolaena fastigiata, and by partly resistant tea-trees Leptospermum myrsinoides, L. continentis and L. scoparium. The dense, field-resistant understorey consisted of the ground cover of H. fastigiata, scattered clumps of various sedges and above this a mass of tea-tree scrub, approximately 1 m in height, with moderately severe dieback of the branches. From 1976 to 1984, the pathogen was isolated from 100% of the 345 root and soil samples and from all of the infested quadrats, but then gradually declined. In 2000, Phytophthora cinnamomi Rands was rare at four sites and was not isolated from two sites. Regeneration of 30 susceptible species, previously eliminated, was recorded from infested sites and 21 of these species were growing in more than one quadrat. Vigorous regeneration of the previously dominant but highly susceptible X. australis occurred at two sites and was similar to that recorded from some recovering infested sites in the Brisbane Ranges, Victoria. The decline of the pathogen and the regeneration of susceptible species may be associated with low spring rainfall from 1995 to 2000 and the consequent reduction in zoospore production, enabling a partial recovery from dieback. The disease cycle from invasion and destruction of a susceptible indigenous flora by this virulent pathogen to the decline of the pathogen and the regeneration of that same susceptible indigenous flora was almost complete on sections of two of the six sites studied. In other areas, the post-infection colonising flora of field-resistant species remained dominant, except at one steep site where the ground remained uncolonised and subsequently eroded following the death of susceptible flora. Extinction following infection by P. cinnamomi, however, remains a grave threat to endangered, endemic species if susceptible.