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Robert C Lacy - One of the best experts on this subject based on the ideXlab platform.

  • Biological and Sociopolitical Sources of Uncertainty in Population Viability Analysis for Endangered Species Recovery Planning.
    Scientific Reports, 2019
    Co-Authors: Carlos Carroll, Robert C Lacy, Richard J. Fredrickson, Daniel J. Rohlf, Sarah A. Hendricks, Michael K. Phillips
    Abstract:

    Although Population Viability Analysis (PVA) can be an important tool for strengthening endangered species recovery efforts, the extent to which such analyses remain embedded in the social process of recovery planning is often unrecognized. We analyzed two recovery plans for the Mexican wolf that were developed using similar data and methods but arrived at contrasting conclusions as to appropriate recovery goals or criteria. We found that approximately half of the contrast arose from uncertainty regarding biological data, with the remainder divided between policy-related decisions and mixed biological-policy factors. Contrasts arose from both differences in input parameter values and how parameter uncertainty informed the level of precaution embodied in resulting criteria. Policy-related uncertainty originated from contrasts in thresholds for acceptable risk and disagreement as to how to define endangered species recovery. Rather than turning to PVA to produce politically acceptable definitions of recovery that appear science-based, agencies should clarify the nexus between science and policy elements in their decision processes. The limitations we identify in endangered-species policy and how PVAs are conducted as part of recovery planning must be addressed if PVAs are to fulfill their potential to increase the odds of successful conservation outcomes.

  • lessons from 30 years of Population Viability Analysis of wildlife Populations
    Zoo Biology, 2019
    Co-Authors: Robert C Lacy
    Abstract:

    : Population Viability Analysis (PVA) has been used for three decades to assess threats and evaluate conservation options for wildlife Populations. What has been learned from PVA on in situ Populations are valuable lessons also for assessing and managing Viability and sustainability of ex situ Populations. The dynamics of individual Populations are unpredictable, due to limited knowledge about important factors, variability in the environment, and the probabilistic nature of demographic events. PVA considers such uncertainty within simulations that generate the distribution of likely fates for a Population; management of ex situ Populations should also take into consideration the uncertainty in our data and in the trajectories of Populations. The processes affecting wildlife Populations interact, with feedbacks often leading to amplified threats to Viability; projections of ex situ Populations should include such feedbacks to allow for management that foresees and responds to the cumulative and synergistic threats. PVA is useful for evaluating conservation options only if the goals for each Population and measures of success are first clearly identified; similarly, for ex situ Populations to contribute maximally to species conservation, the purposes for the Population and definitions of sustainability in terms of acceptable risk must be documented. PVA requires a lot of data, knowledge of many processes affecting the Populations, modeling expertize, and understanding of management goals and constraints. Therefore, to be useful in guiding conservation it must be a collaborative, trans-disciplinary, and social process. PVA can help integrate management of in situ and ex situ Populations within comprehensive species conservation plans.

  • testing a simulation model for Population Viability Analysis
    Ecological Applications, 2000
    Co-Authors: David B Lindenmayer, Robert C Lacy, M Pope
    Abstract:

    We conducted a field-based test of the widely available generic computer simulation model VORTEX for Population Viability Analysis (PVA). The model was used to predict the abundance of three species of arboreal marsupials in a system of 39 remnant patches of Eucalyptus forest embedded within a 5050-ha area of exotic radiata pine (Pinus radiata) forest in southeastern Australia. The marsupial species were: greater glider (Petauroides volans), mountain brushtail possum (Trichosurus caninus), and common ringtail possum (Pseudocheirus peregrinus). Predictions were generated for scenarios in which: (1) the rate of exchange of animals between patches was varied, (2) different models for the migration of animals between habitat patches were invoked, (3) different levels of immigration (or dispersal) from a large, neighboring source area were simulated, (4) variations in habitat quality between remnant patches were incorporated in the model, and (5) the influence of the pine matrix surrounding the remnant patches...

  • structure of the vortex simulation model for Population Viability Analysis
    2000
    Co-Authors: Robert C Lacy
    Abstract:

    The structure of the VORTEX computer simulation model for Population Viability Analysis is outlined. The program flow is described here in order to provide a detailed specification of the structure of a widely used Population Viability Analysis model. VORTEX is an individual-based simulation program that models the effects of mean demographic rates, demographic stochasticity, environmental variation in demographic rates, catastrophes, inbreeding depression, harvest and supplementation, and metapop ulation structure on the Viability of wildlife Populations. The model facilitates Analysis of density-dependent reproduction and changing habitat availability, and most demo graphic rates can optionally be specified as flexible functions of density, time, popula tion gene diversity, inbreeding, age, and sex. VORTEX projects changes in Population size, age and sex structure, and genetic variation, as well as estimating probabilities and times to extinction and recolonization.

  • Population Viability Analysis as a tool in wildlife conservation policy with reference to australia
    Environmental Management, 1993
    Co-Authors: David B Lindenmayer, Robert C Lacy, Tim W Clark, Virginia C Thomas
    Abstract:

    Wildlife conservation policy for endangered species restoration follows a six-phase process. Population Viability Analysis (PVA) can play a major contributing role in four of these. PVA, as discussed here, is a technique where extinction vulnerabilities of small Populations are estimated using computer simulation modeling. The benefits and limitations of using PVA in wildlife decision and policy processes are reviewed based on our direct experience. PVA permits decision makers to set time frames for management, estimate the required magnitude of restoration efforts, identify quantitative targets for species recovery, and select, implement, monitor, and evaluate management strategies. PVA is of greatest value for rare species policy and management. However, a limitation of PVA simulation models is that they are constrained by the amount of biological data available, and such data are difficult to obtain from small Populations that are at immediate risk of extinction. These problems may be overcome with improved models and more data. Our experience shows benefits of PVA far outweigh its limitations, and applications of the approach are most useful when integrated with decision Analysis and completed within an adaptive management philosophy. PVAs have been carried out for 14 Victorian species and less used elsewhere in Australia. Management and recovery plans are developed from these PVAs. We recommend that PVA be used to guide research programs, develop conservation strategies, and inform decision and policy making for both endangered and nonendangered species because it can significantly improve many aspects of natural resource policy and management.

Hugh P. Possingham - One of the best experts on this subject based on the ideXlab platform.

  • Application of Population Viability Analysis to Landscape Conservation Planning
    Models for Planning Wildlife Conservation in Large Landscapes, 2015
    Co-Authors: Steven R Beissinger, Emily Nicholson, Hugh P. Possingham
    Abstract:

    Large-scale landscape planning to maintain biodiversity usually integrates coarse-scale assessments of land use change with systematic evaluations of its effects on the likelihood of species becoming extinct years in the future, or their Population Viability. There are many methods for modeling Population Viability. They include demographic models that assess the impact of management on the rate of Population growth or risk of extinction, analyses of occupancy using presence-absence data, Population trend Analysis, and genetic models that assess the loss of genetic diversity. Demographic models explicitly incorporate birth and death rates, and to varying degrees the processes that affect them, and are often used to evaluate Population Viability. Demographic models vary in complexity from deterministic matrix models of a single Population to stochastic, spatially explicit individual-based models that keep track of each individual on specific landscapes. The Population Viability Analysis tools are used to provide information that can, in turn, be used in either systematic conservation planning or to design landscapes. The examples of such use include setting minimum Population or patch sizes for single species or multispecies systematic conservation planning, and parameterizing statistical approximation models.

  • Population Viability Analysis
    Reference Module in Life Sciences#R##N#Encyclopedia of Biodiversity (Second Edition), 2013
    Co-Authors: Hugh P. Possingham, Michael A. Mccarthy, David B Lindenmayer
    Abstract:

    Population Viability Analysis (PVA) is a process in which the extinction probability of a Population is assessed. This article discusses the processes that interact to cause extinction, and this discussion is then used to explain how the extinction process can be modeled. The authors emphasize recent attempts to provide quality control for PVA and the use of PVA models as a tool for making conservation decisions.

  • Encyclopedia of Environmetrics - Population Viability Analysis
    Encyclopedia of Biodiversity, 2013
    Co-Authors: Hugh P. Possingham, Michael A. Mccarthy, David B Lindenmayer
    Abstract:

    Population Viability Analysis (PVA) is a process in which the extinction probability of a Population is assessed. This article discusses the processes that interact to cause extinction, and this discussion is then used to explain how the extinction process can be modeled. The authors emphasize recent attempts to provide quality control for PVA and the use of PVA models as a tool for making conservation decisions.

  • Population Viability Analysis
    Wiley StatsRef: Statistics Reference Online, 2013
    Co-Authors: Michael A. Mccarthy, Hugh P. Possingham
    Abstract:

    Population Viability Analysis (PVA) assesses risks of Population decline of species, and how those risks can be managed. Typically, stochastic Population models are used to characterize the deterministic and stochastic components that govern changes in Population size. Sources of stochasticity include demographic stochasticity due to the chance birth and death of individuals, stochasticity in the environment that is common to all individuals, chance variation in genetic composition, and spatial structure. These factors can interact to create extinction vortices that drive Population decline. Predicted risks of Population decline from PVA models are usually uncertain due to imprecise parameter estimates, imperfect knowledge about factors that influence dynamics, and uncertainty about future conditions. Despite these sources of uncertainty, changes in risks due to management can be predicted more reliably. Using these changes in risk, PVA can help determine efficient management strategies for reducing high contemporary rates of extinction. Keywords: biodiversity; extinction; Population dynamics; risk; stochasticity; uncertainty

  • Reliability of Relative Predictions in Population Viability Analysis
    Conservation Biology, 2003
    Co-Authors: Michael A. Mccarthy, Sandy J. Andelman, Hugh P. Possingham
    Abstract:

    Despite numerous claims that Population Viability Analysis (PYA) makes reliable predictions of the relative risks of extinction, there is little evidence to support this assertion. To assess the veracity of the claim, we investigated uncertainty in the relative predictions of a PVA model with simulation experiments. We used a stochastic Ricker model to investigate the reliability of predicted changes in risks of decline in response to changes in parameters, the reliability of ranking species in terms of their relative threat, and the reliability of choosing the better of two management decisions. The predicted changes in risks of decline within 100 years were more reliable than absolute predictions. We made useful predictions of relative risks using only 10 years of data. Across 160 different parameter combinations, the rank correlation between the true risks of extinction within 100 years and predicted risks was 0.59 with 10 years of data, increasing to 0.89 with 100 years of data. We identified the better of two management strategies 67-74% of the time using 10 years of data, increasing to 92-93% of the time with 100 years of data. Our results demonstrate that, despite considerable uncertainty in the predicted risks of decline, PVA may reliably contribute to the management of threatened species

Eric S Menges - One of the best experts on this subject based on the ideXlab platform.

  • Population Viability Analysis and fire return intervals for an endemic florida scrub mint
    Biological Conservation, 2006
    Co-Authors: Eric S Menges, Pedro F. Quintana Ascencio, Carl W. Weekley, Orou G. Gaoue
    Abstract:

    We use Population Viability Analysis of an endangered Florida scrub mint, Dicerandra frutescens, to specify the optimal fire return intervals for its long-term persistence and for its specific habitat. We derived 83 Population projection matrices from 13 years of demographic data from eight Populations, 59 matrices from scrub Populations and 24 from firelane or yard edges. Seed dormancy and germination transitions were inferred based on experimental data and verified by comparing modeled vs. observed Population trajectories. Finite rates of increase in scrub sites were highest shortly after fire and declined steeply through 10 years postfire. The break-even value of k = 1 was passed quickly, in about six years, suggesting that Populations >6 years postfire were already facing decline. The decline is probably related to the rapid growth of competing shrubs in the habitat of D. frutescens. In long-unburned sites, finite rates of increase were nearly always 1 and <1, with no temporal trend. Stochastic simulations in scrub sites suggested an optimal regular fire return interval of about 6‐12 years. Regular fires at this interval were more favorable than stochastic fire regimes, but stochasticity reduced extinction percentages at longer fire return intervals. Stochastic fire return intervals implied a wider optimal fire return interval of 6‐21 years. We suggest that prescribed fire in Florida scrub on yellow sand has occurred (and needs to occur) more frequently than previously recommended.

  • Population Viability Analysis and fire return intervals for an endemic Florida scrub mint
    Biological Conservation, 2005
    Co-Authors: Eric S Menges, Pedro F. Quintana Ascencio, Carl W. Weekley, Orou G. Gaoue
    Abstract:

    We use Population Viability Analysis of an endangered Florida scrub mint, Dicerandra frutescens, to specify the optimal fire return intervals for its long-term persistence and for its specific habitat. We derived 83 Population projection matrices from 13 years of demographic data from eight Populations, 59 matrices from scrub Populations and 24 from firelane or yard edges. Seed dormancy and germination transitions were inferred based on experimental data and verified by comparing modeled vs. observed Population trajectories. Finite rates of increase in scrub sites were highest shortly after fire and declined steeply through 10 years postfire. The break-even value of k = 1 was passed quickly, in about six years, suggesting that Populations >6 years postfire were already facing decline. The decline is probably related to the rapid growth of competing shrubs in the habitat of D. frutescens. In long-unburned sites, finite rates of increase were nearly always 1 and

  • emerging issues in Population Viability Analysis
    Conservation Biology, 2002
    Co-Authors: Michael J Reed, Steven R Beissinger, Scott L Mills, John B Dunning, Eric S Menges, Kevin S Mckelvey, Robert J Frye, Mariecharlotte Anstett, Philip Miller
    Abstract:

    Population Viability Analysis (PVA) has become a commonly used tool in endangered species man- agement. 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 cur- rent conditions or expected from proposed management. As model sophistication increases, and software pro- grams that facilitate PVA without the need for modeling expertise become more available, there is greater po- tential 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 is- sues of PVA. We review extant issues that have become prominent in PVA, including spatially explicit model- ing, 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 re- sults should be treated as hypotheses to be tested. We also suggest (5) restricting the definition of PVA to devel- opment 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 rel- ative effects of potential management actions on Population growth or persistence.

Mirjana Lenhardt - One of the best experts on this subject based on the ideXlab platform.

  • Population Viability Analysis and Potential of its aPPlication to danube sturgeons
    Archives of Biological Sciences, 2020
    Co-Authors: Ivan Jarić, Mirjana Lenhardt, G. Cvijanović, Torbjorn Ebenhard
    Abstract:

    Sturgeon species in the Danube River basin have experienced severe decline. Besides overexploitation, habitat loss, and pollution, they are further endangered by lack of efficient policy and management, as well as by serious lack of knowledge about their life history. Although Population Viability Analysis (PVA) could represent an extremely valuable tool to cope with these problems, it has not so far been applied to Danube Populations. This paper represents an assess� ment of different PVA methods and models developed for sturgeon species. It analyzes their results, main advantages, drawbacks, and problems, and discusses the possibility of applying PVA to sturgeon Populations in the Danube River basin.

  • Population Viability Analysis of the European Sturgeon ( Acipenser sturio L.) from the Gironde Estuary System
    Biology and Conservation of the European Sturgeon Acipenser sturio L. 1758, 2011
    Co-Authors: Ivan Jarić, G. Cvijanović, Jelena Knežević-jarić, Mirjana Lenhardt
    Abstract:

    This study presents a Population Viability Analysis (PVA) conducted on the Gironde Population of Acipenser sturio using the Vortex software package. As identified by the model, the most important objects of the future research efforts related to A. sturio life history should be the determination of the mean fecundity, age at which females reach maturity, female spawning frequency and Population sex ratio, as well as the intrinsic Population growth rate and the age-specific natural mortality, especially of the youngest age classes. The model has confirmed a high Population susceptibility to unsustainable fishery, and a slow recovery potential that can span over a number of decades. The detected lag between the stocking activities and the initiation of the actual Population recovery should be taken into account in the planning of restoration projects. PVA should be recognized as an important tool, and integrated within future research, management and policy development efforts.

  • Population Viability Analysis of the danube sturgeon Populations in a vortex simulation model
    Reviews in Fish Biology and Fisheries, 2010
    Co-Authors: Ivan Jaric, Torbjorn Ebenhard, Mirjana Lenhardt
    Abstract:

    Populations of six sturgeon species in the Danube River (beluga, Russian sturgeon, stellate sturgeon, sterlet, ship sturgeon and Atlantic sturgeon) have experienced severe decline during the last several decades, mostly due to the unsustainable fishery, river fragmentation and water pollution. Present lack of knowledge on basic sturgeon demography, life history and relative effects of different negative factors is further hindering implementation of efficient policy and management measures. In the present study, Population Viability Analysis in a Vortex simulation model has been conducted in order to assess the state of the six Danube sturgeon species, their future risk of extinction and to determine the most suitable conservation and management measures. Population Viability Analysis has revealed a large sensitivity of the Danube sturgeon Populations to changes in the natural mortality, fecundity, age at maturity and spawning frequency. It was also confirmed that the sturgeons are highly susceptible to even moderate levels of commercial fishery, and that their recovery is a multi-decadal affair. Stocking with adult individuals was shown to produce considerably greater effect on Population persistence than stocking with juveniles, but the latter approach is probably still preferable since it avoids many inherent problems of aquaculture cultivation. This study represents the first Population Viability Analysis of the Danube sturgeons.

Orou G. Gaoue - One of the best experts on this subject based on the ideXlab platform.

  • Population Viability Analysis and fire return intervals for an endemic florida scrub mint
    Biological Conservation, 2006
    Co-Authors: Eric S Menges, Pedro F. Quintana Ascencio, Carl W. Weekley, Orou G. Gaoue
    Abstract:

    We use Population Viability Analysis of an endangered Florida scrub mint, Dicerandra frutescens, to specify the optimal fire return intervals for its long-term persistence and for its specific habitat. We derived 83 Population projection matrices from 13 years of demographic data from eight Populations, 59 matrices from scrub Populations and 24 from firelane or yard edges. Seed dormancy and germination transitions were inferred based on experimental data and verified by comparing modeled vs. observed Population trajectories. Finite rates of increase in scrub sites were highest shortly after fire and declined steeply through 10 years postfire. The break-even value of k = 1 was passed quickly, in about six years, suggesting that Populations >6 years postfire were already facing decline. The decline is probably related to the rapid growth of competing shrubs in the habitat of D. frutescens. In long-unburned sites, finite rates of increase were nearly always 1 and <1, with no temporal trend. Stochastic simulations in scrub sites suggested an optimal regular fire return interval of about 6‐12 years. Regular fires at this interval were more favorable than stochastic fire regimes, but stochasticity reduced extinction percentages at longer fire return intervals. Stochastic fire return intervals implied a wider optimal fire return interval of 6‐21 years. We suggest that prescribed fire in Florida scrub on yellow sand has occurred (and needs to occur) more frequently than previously recommended.

  • Population Viability Analysis and fire return intervals for an endemic Florida scrub mint
    Biological Conservation, 2005
    Co-Authors: Eric S Menges, Pedro F. Quintana Ascencio, Carl W. Weekley, Orou G. Gaoue
    Abstract:

    We use Population Viability Analysis of an endangered Florida scrub mint, Dicerandra frutescens, to specify the optimal fire return intervals for its long-term persistence and for its specific habitat. We derived 83 Population projection matrices from 13 years of demographic data from eight Populations, 59 matrices from scrub Populations and 24 from firelane or yard edges. Seed dormancy and germination transitions were inferred based on experimental data and verified by comparing modeled vs. observed Population trajectories. Finite rates of increase in scrub sites were highest shortly after fire and declined steeply through 10 years postfire. The break-even value of k = 1 was passed quickly, in about six years, suggesting that Populations >6 years postfire were already facing decline. The decline is probably related to the rapid growth of competing shrubs in the habitat of D. frutescens. In long-unburned sites, finite rates of increase were nearly always 1 and