Use Of Population Viability Analysis Research Articles

Population viability analysis informs Western Grasswren translocation: Multi-population sourcing of 112 founder individuals needed to meet success criteria

Abstract Conservation translocations have become an increasingly popular method to restore or secure vulnerable populations. However, translocations greatly vary in success. The use of population viability analysis (PVA) may increase the likelihood of meeting translocation goals. However, the quality of PVAs to inform translocations is dependent on the availability of ecological data and clear translocation objectives to guide them. Here, we used PVAs to inform the planned conservation translocation of the Western Grasswren (Amytornis textilis textilis) from mainland Shark Bay onto Dirk Hartog Island, Western Australia. A range of translocation scenarios were modelled and scored against success criteria as determined by translocation objectives. Simulations of 20-yr outcomes found that a minimum founder population of 112 individuals meet all success criteria. PVA supported sourcing individuals from 2 subpopulations to maximize genetic diversity. No impact to source populations was detected for the proposed harvest quantities despite conservative estimates of initial source population sizes. Here we demonstrate that creating clear, measurable objectives alongside a PVA lessens ambiguity about which translocation scenarios could be viable. In doing so, we have identified the minimum translocation sizes needed to maintain genetic diversity and population growth, thus increasing the likelihood of translocation success without impacting the source population.

Implicit decision framing as an unrecognized source of confusion in endangered species classification.

Legal classification of species requires scientific and values-based components, and how those components interact depends on how people frame the decision. Is classification a negotiation of trade-offs, a decision on how to allocate conservation efforts, or simply a comparison of the biological status of a species to a legal standard? The answers to problem-framing questions such as these influence decision making in species classifications. In our experience, however, decision makers, staff biologists, and stakeholders often have differing perspectives of the decision problem and assume different framings. In addition to differences between individuals, in some cases it appears individuals themselves are unclear about the decision process, which contributes to regulatory paralysis, litigation, and a loss of trust by agency staff and the public. We present 5 framings: putting species in the right bin, doing right by the species over time, saving the most species on a limited budget, weighing extinction risk against other objectives, and strategic classification to advance conservation. These framings are inspired by elements observed in current classification practices. Putting species in the right bin entails comparing a scientific status assessment with policy thresholds and accounting for potential misclassification costs. Doing right by the species adds a time dimension to the classification decision, and saving the most species on a limited budget classifies a suite of species simultaneously. Weighing extinction risk against other objectives would weigh ecological or socioeconomic concerns in classification decisions, and strategic classification to advance conservation would make negotiation a component of classification. We view these framings as a means to generate thought, discussion, and movement toward selection and application of explicit classification framings. Being explicit about the decision framing could lead decision makers toward more efficient and defensible decisions, reduce internal confusion and external conflict, and support better collaboration between scientists and policy makers.

Viability analysis for multiple populations

Many species of conservation interest exist solely or largely in isolated populations. Ideally, prioritization of management actions among such populations would be guided by quantitative estimates of extinction risk, but conventional methods of demographic population viability analysis (PVA) model each population separately and require temporally extensive datasets that are rarely available in practice. We introduce a general class of statistical PVA that can be applied to many populations at once, which we term multiple population viability analysis or MPVA. The approach combines models of abundance at multiple spatial locations with temporal models of population dynamics, effectively borrowing information from more data-rich populations to inform inferences for data-poor populations. Covariates are used to explain population variability in space and time. Using Bayesian analysis, we illustrate the method with a dataset of Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) observations that previously had been analyzed with conventional PVA. We find that MPVA predictions are similar in bias and higher in precision than predictions from simple PVA models that treat each population individually; moreover, the use of covariates in MPVA allows for predictions in minimally-sampled and unsampled populations. The basic MPVA model can be extended in multiple ways, such as by linking to a sampling and observation model to provide a full accounting of uncertainty. We conclude that the approach has great potential to expand the use of PVA for species that exist in multiple, isolated populations.

A severe predator-induced population decline predicted for endangered, migratory swift parrots (Lathamus discolor)

Identifying the impact of introduced predators on endangered prey populations is critical for conservation management. Population viability analysis (PVA) becomes a valuable tool for quantifying such impacts when high quality life history data are available but, surprisingly, predictions from PVA of future population decline have seldom been used directly to assess conservation status. Here we synthesise new research on the unusual life history of the endangered swift parrot Lathamus discolor, an austral migrant that breeds in Tasmania, Australia. Swift parrots are challenging to monitor because (1) spatio-temporal fluctuation in food availability causes them to select entirely different breeding sites each year over a 10,000km2 range, and (2) they suffer high but variable rates of predation from introduced sugar gliders Petaurus breviceps depending on where they breed. 50.9% of nesting females on the main island of Tasmania were killed by sugar gliders while incubating eggs, but there was no predation from this source on offshore islands. Over four years 16.5% (0–29%) of the population bred on offshore islands. We use PVAs to examine the likely extent of future population decrease due to sugar glider predation, and demonstrate that the remaining swift parrot population is likely to decrease by 78.8–94.7% (mean over four models=86.9%) over only three generations (12–18years). Our models offer a rare example of the use of PVAs for assessing impending population decline and conservation status in species that are challenging to monitor. In this case they support a change of status for swift parrots from “Endangered” to ‘Critically Endangered’ under IUCN criteria.

The use of population viability analysis to identify possible factors contributing to the decline of a rare ungulate population in south-eastern Zimbabwe

Populations that are vulnerable to decline are of particular concern to wildlife managers and uncovering the mechanisms responsible for downward trends is a crucial step towards developing future viable populations. The aims of this study were to better understand the mechanisms behind the historic decline of the sable antelope, Hippotragus niger, population at the Malilangwe Wildlife Reserve (MWR), to assess its future viability and to use this analysis to determine key areas of breakdown in population growth and link these to potential limiting factors. VORTEX, a population viability model was used to assess the future viability of the sable antelope population and a sensitivity analysis was applied to identify the key areas of breakdown in growth. The sable population is currently viable, but remains highly vulnerable to changes in adult female survival, a factor which had the greatest influence on overall population fitness. Lion predation, impacting on the adult segment of the population, appeared to be the main factor responsible for the historic decline at the MWR.Conservation implications: Sable generally occur at low densities in the lowveld region of Zimbabwe and, as such, populations are vulnerable to increases in mortality rates. The role of lions in driving the decline at the MWR suggests a need to control their numbers and develop prey refuges through improved management of artificial water.

Potential Use of Population Viability Analysis in Assessing Invasive Species Control

A significant proportion of effort in wildlife management and ecology is focused on assessing the future size, health, and risk of extinction for various populations of wild organisms (Menges 1990, Nantel et al. 1996, Haines et al. 2006). Although many methods have been developed to aid ecologists in this undertaking, one of the most powerful and pervasive of these has been population viability analysis (PVA; Possingham et al. 1993). Although commonly used to signify a specific analytical tool, the term “population viability analysis” actually refers to a wide variety of quantitative methods used to assess the likelihood that a population will become extinct within a certain amount of time under a specific set of conditions (Morris et al. 1999). These PVA methods have almost exclusively been employed by ecologists to assess the recovery of threatened populations of plants and animals by evaluating their risk of extinction under current and proposed management prescriptions.

Use of a population viability analysis to evaluate human-induced impacts and mitigation for the endangered Lower Keys marsh rabbit

Rapid development and urbanization of the lower Florida Keys in the last 30 years has fragmented the habitat of the Lower Keys marsh rabbit (Sylvilagus palustris hefneri), hereafter called marsh rabbit, and threatened it with extinction. On the Naval Air Station–Key West (NAS), Boca Chica Key, marsh rabbits exist as a meta-population of discrete habitat patches in a matrix of wetlands and airfield facilities. Airfield safety regulations require NAS to maintain vegetation below a minimum height on runway peripheries (clear zones). We developed a spatially-explicit, stage-structured, stochastic matrix model using the programs RAMAS-Metapop and ArcGIS. Model parameters were estimated using pellet counting (2001–2002), radio tracking (1991–1992 and 2001–2005, n = 75), and published literature. We compared a baseline no-action model to Alternative 1 that simulated impacts from the NAS airfield clearance project with no conservation measures for marsh rabbits and Alternative 2 that also simulated airfield clearance impacts. Alternative 2 included mitigation actions to offset impacts to marsh rabbits in the form of reduced mortality via free-roaming cat (Felis catus) control and creation of marsh rabbit habitat (e.g., salt marsh). Both alternatives increased the extinction risk (probability of extinction) from a baseline of 0.499 to 0.90 and 0.713 for Alternatives 1 and 2, respectively. Although airfield clearance with creation of marsh rabbit habitat (Alternative 2) increased extinction risk from the baseline scenario, reducing marsh rabbit mortality associated with control of free-roaming cats was an effective strategy to decrease this risk. Our research demonstrates the use of population viability analysis as a conservation planning tool for reducing human–wildlife conflicts.

Use of Population Viability Analysis to Evaluate CITES Trade‐Management Options for Threatened Marine Fishes

Achieving multiple conservation objectives can be challenging, particularly under high uncertainty. Having agreed to limit seahorse (Hippocampus) exports to sustainable levels, signatories to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) were offered the option of a single 10-cm minimum size limit (MSL) as an interim management measure for all Hippocampus species (> or =34). Although diverse stakeholders supported the recommended MSL, its biological and socioeconomic implications were not assessed quantitatively. We combined population viability analysis, model sensitivity analysis, and economic information to evaluate the trade-off between conservation threat to and long-term cumulative income from these exploited marine fishes of high conservation concern. We used the European long-snouted seahorse (Hippocampus guttulatus) as a representative species to compare the performance of MSLs set at alternative biological reference points. Our sensitivity analyses showed that in most of our scenarios, setting the MSL just above size at maturity (9.7 cm in H. guttulatus) would not prevent exploited populations from becoming listed as vulnerable. By contrast, the relative risk of decline and extinction were almost halved--at a cost of only a 5.6% reduction in long-term catches--by increasing the MSL to the size reached after at least one full reproductive season. On the basis of our analysis, a precautionary increase in the MSL could be compatible with sustaining fishers' livelihoods and international trade. Such management tactics that aid species conservation and have minimal effects on long term catch trends may help bolster the case for CITES trade management of other valuable marine fishes.

Flawed population viability analysis can result in misleading population assessment: A case study for wolves in Algonquin park, Canada

For many populations and species, population viability analysis (PVA) plays a critical role in developing defensible conservation strategies and recovery plans. Although technical aspects of PVA have been well scrutinized, misapplication of PVA and misinterpretation of its results have received less attention. To illustrate potential hazards of improper use of PVA we reanalyzed data from a recent study on viability of wolves in Algonquin Provincial Park (APP), Ontario, Canada. The original PVA predicted extirpation of wolves from APP and prompted both a ban on wolf harvesting in a 10–16km buffer zone surrounding the 7571km2 park and an intensive research program to evaluate efficacy of the ban. Our reanalysis showed that limited and imprecise wolf population density and demographic rate estimates, as well as flawed population assessment and reconstruction methods, led to overly pessimistic evaluation of wolf population status in APP. In fact, our analyses suggest that wolves in APP are unlikely to decline significantly over the next 20 years. Further, contrary to earlier conclusions we suggest that rapid wolf population recovery following protection from human exploitation would be likely and readily detectable. These findings highlight the need for adequate data, appropriate methodology, and proper analytical context when conducting PVA. Because the original PVA prompted substantial redirection of staff and financial resources from other significant conservation initiatives, we conclude that improper PVA may undermine execution of effective wildlife management and ultimately provide a disservice to conservation biology.

MANAGEMENT STRATEGIES FOR THE WOLVERINE IN SCANDINAVIA

Abstract The use of Population Viability Analysis has recently been criticized mainly because uncertainties in population predictions are often ignored. We analyzed the viability of Scandinavian wolverine Gulo gulo populations that allow for the inclusion of uncertainties in parameter estimates and stochastic effects on population dynamics. We used the insight gained from analyses of stochastic population models to quantitatively analyze different management options for the wolverine. These management options were based on data from an individual-based demographic study in the Sarek National Park, Sweden, and data from monitoring schemes in Norway and Sweden. Stochastic components in population dynamics of the wolverine were large. Strong density regulation occurred around the carrying capacity. According to the World Conservation Union (2001), the carrying capacity of populations must exceed 46 sexually mature (≥3-yr-old) females to be considered not vulnerable. Continuation of the current levels of offt...

POPULATION VIABILITY ANALYSIS IN ENDANGERED SPECIES RECOVERY PLANS: PAST USE AND FUTURE IMPROVEMENTS

Using the results of a survey of recovery plans for threatened and endangered species, we evaluated the role that Population Viability Analysis (PVA) has played in recovery planning and management of rare species in the United States. Although there was a significant increase over time in the percentage of plans presenting information on PVA and assigning recovery tasks to collect more such information, the use of PVA was still called for in less than half of the plans approved since 1991. Because scarcity of data for rare species may be limiting the application of PVA to endangered species, we also assessed how often recovery plans proposed to collect the full complement of data required to perform four general types of PVA. For most of the species in the database, proposed monitoring data would allow the simplest type of PVA method (i.e., analysis of total population counts) to be applied, but more complex PVAs would be possible for <25% of the species. We conclude with brief recommendations for how the use of PVA in endangered species recovery planning might be improved in the future.

Emerging Issues in Population Viability Analysis.

Population viability analysis ( PVA) has become a commonly used tool in endangered species management. There is no single process that constitutes PVA, but all approaches have in common an assessment of a population's risk of extinction (or quasi extinction) or its projected population growth either under current conditions or expected from proposed management. As model sophistication increases, and software programs that facilitate PVA without the need for modeling expertise become more available, there is greater potential for the misuse of models and increased confusion over interpreting their results. Consequently, we discuss the practical use and limitations of PVA in conservation planning, and we discuss some emerging issues of PVA. We review extant issues that have become prominent in PVA, including spatially explicit modeling, sensitivity analysis, incorporating genetics into PVA, PVA in plants, and PVA software packages, but our coverage of emerging issues is not comprehensive. We conclude that PVA is a powerful tool in conservation biology for comparing alternative research plans and relative extinction risks among species, but we suggest caution in its use: (1) because PVA is a model, its validity depends on the appropriateness of the model's structure and data quality; (2) results should be presented with appropriate assessment of confidence; (3) model construction and results should be subject to external review, and (4) model structure, input, and results should be treated as hypotheses to be tested. We also suggest (5) restricting the definition of PVA to development of a formal quantitative model, (6) focusing more research on determining how pervasive density-dependence feedback is across species, and (7) not using PVA to determine minimum population size or (8) the specific probability of reaching extinction. The most appropriate use of PVA may be for comparing the relative effects of potential management actions on population growth or persistence.

Testing the Accuracy of Population Viability Analysis

Abstract: Despite the growing use of population viability analysis ( PVA), the predictions of these models rarely have been tested with field data that were not used in initially developing the model. We review and discuss a suite of methods that may be used to test the predictive ability of models used in PVA. In addition to testing mean predictions, appropriate methods must analyze the probability distribution of the model predictions. The methods we discuss provide tests of the mean predictions, the predicted frequency of events such as extinction and colonization, and the predicted probability distribution of state variables. We discuss visual approaches based on plots of observations versus the predictions and statistical approaches based on determining significant differences between observations and predictions. The advantages and disadvantages of each method are identified. The best methods test the statistical distribution of the predictions; those that ignore variability are meaningless. Although we recognize that the quality of a model is not solely a function of its predictive abilities, tests help reduce inherent model uncertainty. The role of model testing is not to prove the truth of a model, which is impossible because models are never a perfect description of reality. Rather, testing should help identify the weakest aspects of models so they can be improved. We provide a framework for using model testing to improve the predictive performance of PVA models, through an iterative process of model development, testing, subsequent modification and re‐testing.

Use of Population Viability Analysis to Evaluate Management Options for the Endangered Lower Keys Marsh Rabbit

We conducted a population viability analysis (PVA) for the federally endangered Lower Keys marsh rabbit (Sylvilagus palustris hefucri). We estimated parameters via livetrapping, radiotelemetry, and fecal-pellet counting during a 2.5-year study. Historically, this subspecies ranged thronghout the Lower Keys of Florida. but today the marsh rabbit is limited to 41 subpopulations occurring in 3 distinct metapopulations. To evaluate this subspecies risk of extinction, we used VORTEX, a simulation modeling program, that combined deterministic and stochastic birth and death events, differing migration rates based on spatially explicit patch structure, and extinction and recolonization. Our simulation calculated, the chance that each metapopulation would go extinet imder current conditions and several management scenarios. Under current conditions, the model predicted there is a 100% chance that all metapopulations will go extinct. The metapopulation with many small patches went extinet faster that the metapopulations with fewer, larger patches The most effective strategy to decrease the risk of extinction of all 3 metapopulations was to increase the survival rate an several age and sex classes by eliminating predation by domestic cats.

Uncertainty in assessing the viability of the Powerful Owl Ninox strenua in Victoria, Australia

A model of the metapopulation dynamics of Powerful Owls Ninox strenua in Victoria, Australia is described, and its parameters were derived from available data. Sensitivity analysis indicates that the survival rate of adult owls is the most important parameter in the model. Because estimates of this parameter are uncertain, the predictions of the model are uncertain and unreliable. Using the best estimates of the parameters, the predicted risk of decline across Victoria is low, and local populations larger than 100 pairs have a low risk of extinction. If the lower estimates of adult and sub-adult survival are used, the abundance of Powerful Owls across Victoria is predicted to decline exponentially and faces extinction from deterministic forces. A prohibitively large field programme involving monitoring of individuallyrecognizable owls would be required to obtain an improved estimate of adult survival, and so further use of population viability analysis to assess the adequacy of particular management strategies is unlikely to be useful for this species. An alternative is to establish a long-term monitoring programme to document changes in abundance of the species in logged and unlogged landscapes.