Population Viability Analysis Models Research Articles

Viability analysis for population reinforcement of Grauer's gorillas at Mount Tshiaberimu, Democratic Republic of the Congo

AbstractReintroduction and translocation programs have been sparingly used for the management of endangered primate populations. Mount Tshiaberimu in eastern Democratic Republic of the Congo (DRC) contains 6 Grauer's gorillas (Gorilla beringei graueri) with only 2 adult females. Without intervention, this population is at high risk of extinction. We designed population viability analysis models to compare different release scenarios of wild‐born captive female gorillas housed at the Gorilla Rehabilitation and Conservation Education (GRACE) Center in the DRC. We identified the minimum number of females needed to maintain a viable population in this habitat. We used a stochastic Leslie matrix model and a more complex individual‐based model to project population growth. We used published demographic parameters for mountain gorillas (Gorilla b. beringei) corresponding to a 3.2% annual growth rate, and then applied a correction factor to female fertility to obtain parameters consistent with 1% and 2% growth rates. We ran each scenario over a 50‐year time period (1,000 simulations) to determine the final population size and risk of local extinction. Results from our optimistic (3.2% growth) and conservative (1% growth) individual‐based model projections indicated that the extinction risk dropped below 1% with the release of at least 2 or 3 females, respectively. Both approaches predicted similar extinction risks for all scenarios; however, the variance in final population size was higher with the individual‐based model. For long‐lived mammals like primates, we recommend the use of individual‐based models, which can incorporate life‐history parameters such as long gestation and nursing periods. Our analysis suggests a translocation of ≥3 females to rescue the Tshiaberimu gorilla population in the short term. Factors such as inbreeding depression, habitat quality, disease risks, and anthropogenic pressures will need to be evaluated in later stages of population reinforcement planning.

Assessing the Viability of the Sarasota Bay Community of Bottlenose Dolphins

Population models, such as those used for Population Viability Analysis (PVA), are valuable for projecting trends, assessing threats, guiding environmental resource management, and planning species conservation measures. However, rarely are the needed data on all aspects of the life history available for cetacean species, because they are long-lived and difficult to study in their aquatic habitats. We present a detailed assessment of population dynamics for the long-term resident Sarasota Bay common bottlenose dolphin (Tursiops truncatus) community. Model parameters were estimated from 27 years of nearly complete monitoring, allowing calculation of age-specific and sex-specific mortality and reproductive rates, uncertainty in parameter values, fluctuation in demographic rates over time, and intrinsic uncertainty in the population trajectory resulting from stochastic processes. Using the Vortex PVA model, we projected mean population growth and quantified causes of variation and uncertainty in growth. The ability of the model to simulate the dynamics of the population was confirmed by comparing model projections to observed census trends from 1993 to 2020. When the simulation treated all losses as deaths and included observed immigration, the model projects a long-term mean annual population growth of 2.1%. Variance in annual growth across years of the simulation (SD= 3.1%) was due more to environmental variation and intrinsic demographic stochasticity than to uncertainty in estimates of mean demographic rates. Population growth was most sensitive to uncertainty and annual variation in reproduction of peak breeding age females and in calf and juvenile mortality, while adult survival varied little over time. We examined potential threats to the population, including increased anthropogenic mortality and impacts of red tides, and tested resilience to catastrophic events. Due to its life history characteristics, the population was projected to be demographically stable at smaller sizes than commonly assumed for Minimum Viable Population of mammals, but it is expected to recover only slowly from any catastrophic events, such as disease outbreaks and spills of oil or other toxins. The analyses indicate that well-studied populations of small cetaceans might typically experience slower growth rates (about 2%) than has been assumed in calculations of Potential Biological Removal used by management agencies to determine limits to incidental take of marine mammals. The loss of an additional one dolphin per year was found to cause significant harm to this population of about 150 to 175 animals. Beyond the significance for the specific population, demographic analyses of the Sarasota Bay dolphins provide a template for examining viability of other populations of small cetaceans.

Distribution range and population viability of Emys orbicularis in Slovakia: a review with conservation implications

The European pond turtle (Emys orbicularis) is the only native freshwater turtle species in Slovakia. Due to watercourse regulations in the middle of the 20th century, its range became fragmented and, currently, there are only two isolated populations. From a total of 1,236 historical records in Slovakia, most observations (782 records) came from the area of the Tajba National Nature Reserve (NNR). Three of the population viability analysis models (‘baseline’, ‘catastrophe’, ‘nest protection during a catastrophe’) indicated the extinction of the population in Tajba, with the highest probability of extinction occurring during a catastrophic event (probability of extinction 1.00). We also evaluated information about the activity patterns of seven radio-tracked individuals and about the number of destroyed nests from the area. During the period 2017–2021, we recorded only two turtles leaving the aquatic habitat of Tajba. An alarming fact is the massive number of destroyed nests found in the area during the study period (Tajba 524; Poľany 56). Our results indicate that the population in the Tajba NNR require immediate application of management steps to ensure its long-term survival.

Conservation of Northwestern and Southwestern Pond Turtles: Threats, Population Size Estimates, and Population Viability Analysis

Abstract Accurate status assessments of long-lived, widely distributed taxa depend on the availability of long-term monitoring data from multiple populations. However, monitoring populations across large temporal and spatial scales is often beyond the scope of any one researcher or research group. Consequently, wildlife managers may be tasked with utilizing limited information from different sources to detect range-wide evidence of population declines and their causes. When assessments need to be made under such constraints, the research and management communities must determine how to extrapolate from variable population data to species-level inferences. Here, using three different approaches, we integrate and analyze data from the peer-reviewed literature and government agency reports to inform conservation for northwestern pond turtles (NPT) Actinemys marmorata and southwestern pond turtles (SPT) Actinemys pallida. Both NPT and SPT are long-lived freshwater turtles distributed along the west coast of the United States and Mexico. Conservation concerns exist for both species; however, SPT may face more severe threats and are thought to exist at lower densities throughout their range than NPT. For each species, we ranked the impacts of 13 potential threats, estimated population sizes, and modeled population viability with and without long-term droughts. Our results suggest that predation of hatchlings by invasive predators, such as American bullfrogs Lithobates catesbeianus and Largemouth Bass Micropterus salmoides, is a high-ranking threat for NPT and SPT. Southwestern pond turtles may also face more severe impacts associated with natural disasters (droughts, wildfires, and floods) than do NPT. Population size estimates from trapping surveys indicate that SPT have smaller population sizes on average than do NPT (P = 0.0003), suggesting they may be at greater risk of local extirpation. Population viability analysis models revealed that long-term droughts are a key environmental parameter; as the frequency of severe droughts increases with climate change, the likelihood of population recovery decreases, especially when census sizes are low. Given current population trends and vulnerability to natural disasters throughout their range, we suggest that conservation and recovery actions first focus on SPT to prevent further population declines.

A cumulative effects model for population trajectories of resident killer whales in the Northeast Pacific

Like numerous species at risk, the resident killer whale populations of the Northeast Pacific are vulnerable to the cumulative effects of anthropogenic threats. A Pathways of Effects conceptual model summarised the current understanding of each threat (prey availability, acoustic and physical disturbance, and contaminants), threat interactions, and potential impacts to fecundity and mortality. A Population Viability Analysis utilised the most recent available data to quantify impacts of threats on population parameters. The impacts of individual and cumulative threat scenarios on modelled Southern and Northern Resident Killer Whale populations were compared to the observed population demographics to define a model that best captured the real world dynamics. Of the individual and combined threat models tested, the cumulative model incorporating all threats predicted demographic rates closest to those observed for both populations. Recent low Chinook salmon abundance and its interactions with vessel disturbance and contamination strongly influenced modelled killer whale population dynamics. The cumulative effects population viability analysis model projected a mean increase in the modelled Northern Resident Killer Whale population to the carrying capacity within 25 years. In contrast, the mean modelled Southern Resident Killer Whale population trajectory was projected to decline under current conditions, with a 26% probability of population extinction, and in those projections, extinction was estimated to occur after 86 (± 11) years. Our results highlight the importance of considering the collective impact of multiple threats to imperilled species and the necessity of testing management and mitigation measures aimed at recovery using a holistic, validated model.

Projecting long‐term impacts of a mortality event on vertebrates: incorporating stochasticity in population assessment

AbstractWildlife managers must be able to assess the long‐term, population‐wide impacts of mortality events on long lived vertebrates, taking into account the stochastic nature of population fluctuations. Here, we present a case study of the potential impacts on Western gulls (Larus occidentalis) of a single, non‐target mortality event, potentially resulting from exposure to rodenticide directed at eradicating house mice (Mus musculus) on the Farallon Islands National Wildlife Refuge. Firstly, we conducted a population viability analysis based on over 25 yr of Farallon Western gull demographic data to model future population trends under varying environmental conditions. Future population trends for Farallon Western gulls, independent of any potential mouse eradication‐related mortality, depend on the frequency of years with near‐failure in reproductive success, as was observed in 2009, 2010, and 2011. We modeled population trends under three environmental scenarios defined by the probability of near‐failure in future breeding: optimistic (probability of near‐failure = 0.0), realistic (probability = 0.115), or pessimistic (probability = 0.25). Secondly, we determined the maximum level of additional mortality, C, that would result in a population outcome distribution that cannot be effectively distinguished from a no additional mortality scenario after 20 yr (defined as 95% overlap in the two frequency distributions). We determined the threshold of detection to be an additional mortality of 3.3% beyond normally observed levels under the realistic scenario, 2.8% under the optimistic scenario, and 4.2% under the pessimistic scenario. Results demonstrate that the greater the background stochasticity, the greater C must be to be able to discriminate a long‐term effect of the mortality event against the backdrop of environmental variability. We demonstrate that incorporation of stochasticity is critical for evaluating one‐time mortality events given the high degree of variability characterizing many ecosystems; deterministic projections alone may provide poor guidance. While the need to account for stochasticity in Population Viability Analysis models is well established, this study is innovative in addressing how to evaluate a future or retrospective one‐time mortality event in the context of stochasticity. Our approach can help resource managers' plan for both best‐case and worst‐case scenarios when evaluating impacts of mortality events.

A hippo in the room: Predicting the persistence and dispersion of an invasive mega-vertebrate in Colombia, South America

Biological invasions are a big concern due to their potential to impact ecosystems, as well as local people. The hippo Hippopotamus amphibius, native to Africa, has invaded extensive areas of the Magdalena River basin (Colombia) over the past decades, and has been considered the largest invasive animal in the world. Here, we propose the use of two approaches of predictive modeling, in order to guide recommendations for the management of this biological invasion. First, we developed a population viability analysis (PVA) to simulate a hypothetical population growth under different management scenarios. Next, we explored the potential invasion area under future climate change scenarios throughout ecological niche modeling analyses. PVA models predicted that in the absence of an intense culling/hunting pressure, the population size will continue to steadily increase, which is consistent with the population growth observed during the last 20 years. Furthermore, our static and dynamic habitat suitability projections suggested that without dispersal limiting factors, potential colonization habitat for hippos may become very extensive across the landscape and can be favored by climate change in the future. Therefore, our findings show the urgent need of taking critical management decisions by the Colombian authorities, which should be focused on limiting the hippos' population growth and expansion. Ignoring cost-benefit considerations for the control of this invasive species may have unexpected and long-term social and ecological implications. However, the proposal of a course of action can become controversial when the species has a charismatic value for the society, regardless of its ecological or social impact.

Slow breeding rates and low population connectivity indicate Australian palm cockatoos are in severe decline

Dispersal dynamics can determine whether animal populations recover or become extinct following decline or disturbance, especially for species with slow life-histories that cannot replenish quickly. Palm cockatoos (Probosciger aterrimus) have one of the slowest known reproductive rates of any parrot, and they face steep decline in at least one of three populations comprising the meta-population for the species in Australia. Consequently, we estimated demographic rates and population connectivity using data from published field studies, population genetics, and vocal dialects. We then used these parameters in a population viability analysis (PVA) to predict the trajectories of the three regional populations, together with the trajectory of the meta-population. We incorporated dispersal between populations using genetic and vocal data modified by landscape permeability, whereby dispersal is limited by a major topographical barrier and non-uniform habitat. Our PVA models suggest that, while dispersal between palm cockatoo populations can reduce local population decline, this is not enough to buffer steep decline in one population with very low breeding success. The small population size and likely decrease in the meta-population of greater than 50% over three generations (49 years) supports a change of conservation status for Australian palm cockatoos from ‘Vulnerable’ to ‘Endangered’ under IUCN criteria. Our research provides an important demonstration of how PVA can be used to assess the influence of complex meta-population scale processes on the population trajectory of species that are challenging to monitor.

Anthropogenic Disturbance and Population Viability of Woodland Caribou in Ontario

ABSTRACTOne of the most challenging tasks in wildlife conservation and management is to clarify how spatial variation in land cover due to anthropogenic disturbance influences wildlife demography and long‐term viability. To evaluate this, we compared rates of survival and population growth by woodland caribou (Rangifer tarandus caribou) from 2 study sites in northern Ontario, Canada that differed in the degree of anthropogenic disturbance because of commercial logging and road development, resulting in differences in predation risk due to gray wolves (Canis lupus). We used an individual‐based model for population viability analysis (PVA) that incorporated adaptive patterns of caribou movement in relation to predation risk and food availability to predict stochastic variation in rates of caribou survival. Field estimates of annual survival rates for adult female caribou in the unlogged ( 0.90) and logged ( 0.76) study sites recorded during 2010–2014 did not differ significantly (P > 0.05) from values predicted by the individual‐based PVA model (unlogged:  = 0.87; logged:  0.79). Outcomes from the individual‐based PVA model and a simpler stage‐structured matrix model suggest that substantial differences in adult survival largely due to wolf predation are likely to lead to long‐term decline of woodland caribou in the commercially logged landscape, whereas the unlogged landscape should be considerably more capable of sustaining caribou. Estimates of population growth rates (λ) for the 2010–2014 period differed little between the matrix model and the individual‐based PVA model for the unlogged (matrix model  = 1.01; individual‐based model  = 0.98) and logged landscape (matrix model  = 0.88; individual‐based model  = 0.89). We applied the spatially explicit PVA model to assess the viability of woodland caribou across 14 woodland caribou ranges in Ontario. Outcomes of these simulations suggest that woodland caribou ranges that have experienced significant levels of commercial forestry activities in the past had annual growth rates <0.89, whereas caribou ranges that had not experienced commercial forestry operations had population growth rates >0.96. These differences were strongly related to regional variation in wolf densities. Our results suggest that increased wolf predation risk due to anthropogenic disturbance is of sufficient magnitude to cause appreciable risk of population decline in woodland caribou in Ontario. © 2020 The Authors. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

Combining modeling tools to identify conservation priority areas: A case study of the last large-bodied avian frugivore in the Atlantic Forest

Applicability of modeling tools to tackle conservation problems is key for conservation planning. However, modeling papers regarding real-world conservation issues are scarce. Here, we combined two modeling tools to identify priority areas in the Brazilian Atlantic Forest, focusing on the last large-bodied frugivorous bird in the region, the red-billed curassow (Crax blumenbachii). We used population viability analysis (PVA) to determine (1) the minimum viable population size under different hunting scenarios; and (2) the minimum critical forest patch size required to maintain viable populations. We used ecological niche modeling (ENM) to identify remnants that retain suitable environmental conditions to ensure the long-term persistence of this species. We overlapped the outputs from PVA and ENM models to identify priority areas for curassows. Under our best-case scenario, 56 individuals would suffice to maintain a viable population and 71 forest patches located within the species' known range are above the critical size of 3141 ha. In the worst-case scenario, at least 138 individuals would be required to maintain a viable population in forest patches larger than 9500 ha, corresponding to only 20 Atlantic Forest fragments within the species range. Among these, 17 presented median habitat suitability values higher than 0.70, eight of which were selected as priority areas for law enforcement and nine as priority areas for reintroduction. We encourage conservation biologists and land managers to combine modeling tools which can be guided by our conservation planning framework. This approach is promising to inform long-term conservation planning of a flagship species and its entire ecosystem.

Delaying conservation actions matters for species vulnerable to climate change

Abstract Climate change vulnerability assessments are commonly used to identify species or populations at risk from global climate change, but few translate impact assessments to climate change adaptation actions. Furthermore, most climate change adaptation efforts emphasize where to implement management actions, whereas timing remains largely overlooked. The rate of modern climate change introduces urgency in evaluating whether delaying conservation actions compromises their efficacy for reaching important conservation targets. We evaluated the importance of multiple climate change adaptation strategies including timing of actions on preventing extinctions for a threatened climate‐sensitive species, the Eastern Massasauga rattlesnake (Sistrurus catenatus). We parameterized a range‐wide population viability analysis model that related demographic sensitivities to drought events and human‐modified land cover to assess vulnerability to future climate change. Using simulations, we assessed the efficacy and trade‐offs associated with alternative climate adaptation strategies aimed at maximizing the number of future populations including when to initiate conservation actions, duration of management, number of managed populations, and local management effectiveness. Population‐level projections under future climate change scenarios revealed a broad‐scale pattern of range contraction in the southwestern portion of the current range. Along the extinction gradient, we identified demographic strongholds and refugia critical for population persistence under climate change as well as populations at high risk of extinction and candidates for climate change adaptation actions. In the context of future climate change, the timing of conservation actions was crucial; acting earlier maximized chances of achieving conservation targets. Even considering uncertainty in climate change projections, delaying actions was less efficient and introduced undesirable trade‐offs including the need to implement conservation actions for longer or targeting more populations to achieve a similar conservation target. Synthesis and applications. Our findings highlight how acting quickly reduces risk and improves outcomes for a highly vulnerable species under future climate change. Climate change vulnerability assessments require translation of model‐based outputs into tractable information for climate change adaptation planning. Quantifying trade‐offs associated with the multidimensional decision space related to species conservation and recovery planning is a critical step in climate change adaptation.

Demographic and genetic viability of a medium-sized ground-dwelling mammal in a fire prone, rapidly urbanizing landscape.

The rapid and large-scale urbanization of peri-urban areas poses major and complex challenges for wildlife conservation. We used population viability analysis (PVA) to evaluate the influence of urban encroachment, fire, and fauna crossing structures, with and without accounting for inbreeding effects, on the metapopulation viability of a medium-sized ground-dwelling mammal, the southern brown bandicoot (Isoodon obesulus), in the rapidly expanding city of Perth, Australia. We surveyed two metapopulations over one and a half years, and parameterized the PVA models using largely field-collected data. The models revealed that spatial isolation imposed by housing and road encroachment has major impacts on I. obesulus. Although the species is known to persist in small metapopulations at moderate levels of habitat fragmentation, the models indicate that these populations become highly vulnerable to demographic decline, genetic deterioration, and local extinction under increasing habitat connectivity loss. Isolated metapopulations were also predicted to be highly sensitive to fire, with large-scale fires having greater negative impacts on population abundance than small-scale ones. To reduce the risk of decline and local extirpation of I. obesulus and other small- to medium-sized ground-dwelling mammals in urbanizing, fire prone landscapes, we recommend that remnant vegetation and vegetated, structurally-complex corridors between habitat patches be retained. Well-designed road underpasses can be effective to connect habitat patches and reduce the probability of inbreeding and genetic differentiation; however, adjustment of fire management practices to limit the size of unplanned fires and ensure the retention of long unburnt vegetation will also be required to ensure persistence. Our study supports the evidence that in rapidly urbanizing landscapes, a pro-active conservation approach is required that manages species at the metapopulation level and that prioritizes metapopulations and habitat with greater long-term probability of persistence and conservation capacity, respectively. This strategy may help us prevent future declines and local extirpations, and currently relatively common species from becoming rare.

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.

Predators and genetic fitness: key threatening factors for the conservation of a bettong species

Globally, many wildlife species are declining and an increasing number are threatened by extinction or are extinct. Active management is generally required to mitigate these trends and population viability analysis (PVA) enables different scenarios to be evaluated and informs management decisions. Based on population parameters obtained from a threatened bettong, the woylie (Bettongia penicillata ogilbyi), we developed and validated a PVA model. We identified the demographic and genetic responses to different threatening factors and developed a general framework that would facilitate similar work in other bettong species. The two main threatening processes are predation by introduced animals and its interaction with reduced fitness (e.g. due to inbreeding depression or a disease). Although predation alone can drive a decline in certain circumstances (e.g. when predation success is independent from prey population density), synergistically, predation and reduced fitness can be particularly relevant, especially for small populations. The minimum viable population size was estimated at 1000–2000 individuals. In addition, the models identified that research into age-specific mortality rates and predation rates by introduced animals should be the focus of future work. The PVA model created here provides a basis to investigate threatening processes and management strategies in woylie populations and other extant bettong species, given the ecological and physiological similarities among these threatened species.

Coping with wild boar in a conservation area: impacts of a 10-year management control program in north-eastern Argentina

Wild boar (Sus scrofa) are of serious concern in numerous conservation areas such as El Palmar National Park, Argentina, where their increasing abundance affected the iconic palm tree Butia yatay. We assessed the effectiveness of an innovative management control program on wild boar population dynamics and ground rooting area over 10 years. Park personnel recruited and supervised local recreational hunters who regularly conducted controlled still shooting from widely distributed watchtowers and used trained dogs mainly during the first 2 years post-intervention (YPI). We used the detailed records of harvest and hunting effort to estimate time- and stage-specific catch-per-unit-effort (CPUE) indices and stochastic population growth rates (μ). Catch was linearly related to hunting effort except at large effort levels. CPUE indices declined exponentially at 5–7 % month−1 over 0–1 YPI and thereafter stabilized with μ indistinguishable from 0. Relative to baseline levels, culling reduced annual pregnancy rates, the fraction of juveniles and older adults, and ground rooting area below target values (<1.3 %). Incipient population recovery followed one of two periods of marginal hunting effort. The program generated few undesirable collateral effects mainly related to dog-hunting. Mesopredator abundance (foxes) steadily increased following a large outbreak of canine distemper at baseline. The combined use of standardized CPUE indices, body-length data and simple population viability analysis models provided reliable metrics for wild boar trend analysis and management. Unlike a preceding plan, a highly structured multi-stakeholder program proved to be sustainable and brought wild boar abundance to a low-density, unstable equilibrium causing minimal damage.

Repeatability and Reproducibility of Population Viability Analysis (PVA) and the Implications for Threatened Species Management

Conservation triage focuses on prioritizing species, populations or habitats based on urgency, biodiversity benefits, recovery potential as well as cost. Population Viability Analysis (PVA) is frequently used in population focused conservation prioritizations. The critical nature of many of these management decisions requires that PVA models are repeatable and reproducible to reliably rank species and/or populations quantitatively. This paper assessed the repeatability and reproducibility of a subset of previously published PVA models. We attempted to rerun baseline models from 90 publicly available PVA studies published between 2000-2012 using the two most common PVA modelling software programs, VORTEX and RAMAS-GIS. Forty percent (n = 36) failed, 50% (45) were both repeatable and reproducible, and 10% (9) had missing baseline models. Repeatability was not linked to taxa, IUCN category, PVA program version used, year published or the quality of publication outlet, suggesting that the problem is systemic within the discipline. Complete and systematic presentation of PVA parameters and results are needed to ensure that the scientific input into conservation planning is both robust and reliable, thereby increasing the chances of making decisions that are both beneficial and defensible. The implications for conservation triage may be far reaching if population viability models cannot be reproduced with confidence, thus undermining their intended value.

Use of Simulation Modeling to Evaluate Management Strategies for Reintroduced Riparian Brush Rabbits in California

Abstract The riparian brush rabbit Sylvilagus bachmani riparius is restricted to areas of dense cover along rivers and tributaries in the Central Valley of California, USA, and is considered endangered under the U.S. Endangered Species Act. An approved recovery plan for this subspecies recommended establishment of three additional self-sustaining populations within its historical range. Concurrent with habitat restoration efforts that included revegetation of levees and provision of flood refugia, we reintroduced 325 captive-bred individuals to the San Joaquin River National Wildlife Refuge between July 2002 and July 2005, and monitored their survival with radiotelemetry. Using available survival estimates and estimated reproductive parameters, we developed a population viability analysis model to determine the risk of extinction of the reintroduced population under a series of alternate scenarios including different release strategies. All model scenarios resulted in high probabilities of extinction over 20 y in the absence of either ongoing supplementations or significant improvements to vital rates. Extinction risks over 20 y appeared independent of initial release strategies. The risk of extinction remained high (&amp;gt;99%) even when the initial founder population was supplemented with captive-bred brush rabbits for up to 10 y. Supplementing the population annually for the entire 20-y period would be required for the population to persist given current estimates of vital rates. These results suggest that the reintroduced population is not self-sustaining and continued releases will not provide the anticipated long-term benefits. Additionally, our understanding of the integral components of habitat and potential limiting factors should be refined to address their influence on demographics and the cause of brush rabbit declines at the release site in a comprehensive way. These results underscore the importance of viability analyses and developing testable hypotheses about potential limiting factors early in reintroduction efforts to more efficiently guide data-gathering and monitoring criteria, identify data deficiencies, and refine reintroduction techniques in the early stages of management.

Extinction probabilities of Hassawi cattle from Saudi Arabia using population viability analysis

The sharp reduction in population size (N) of Hassawi cattle alarmed to estimate the possibility of extinction over a defined future time horizon. Two Hassawi cattle populations were considered for population viability analysis (PVA) in order to provide estimates of extinction probabilities (EPs). The EPs were estimated using Vortex® modeling program. The estimates of 2013 census and records on previous numbers were utilized in PVA models for two separated populations and their meta-population. The results of EPs and evolutionary growth rate were simulated for past and future, utilizing their demographic parameters and catastrophic events; like, feed scarcity, low production capability, crossbreeding and epidemic diseases. The simulated model concludes that the Hassawi cattle is facing extinction as the population size (N) and effective population size (Ne) were much less than those recommended to save endangerment. Therefore, the mimicked dynamic history of real Hassawi cattle population suggests that the assumed model was reasonable to mimic the likely fate faced by the Hassawi cattle population in the past. The future model concluded that the Hassawi cattle are indeed facing extinction after 21years if assumptions of past model existed because both N and Ne were much lower than those recommended for escaping endangerment. Furthermore, PE increased with availability and severity of catastrophe events. The results of PVA and PEs should be considered into account to draw inferences about the expected future the Hassawi cattle dynamic because they are accurate data than those might extract from historical records. It is recommended that PVA may be considered in developing conservation strategy for the Hassawi cattle in order to conserve their valuable genetic resources, while the climate change is alarming.

Simple or complex: Relative impact of data availability and model purpose on the choice of model types for population viability analyses

Population viability analysis (PVA) models are used to estimate population extinction risk under different scenarios. Both simple and complex PVA models are developed and have their specific pros and cons; the question therefore arises whether we always use the most appropriate model type. Generally, the specific purpose of a model and the availability of data are listed as determining the choice of model type, but this has not been formally tested yet. We quantified the relative importance of model purpose and nine metrics of data availability and resolution for the choice of a PVA model type, while controlling for effects of the different life histories of the modelled species. We evaluated 37 model pairs: each consisting of a generally simpler, population-based model (PBM) and a more complex, individual-based model (IBM) developed for the same species. The choice of model type was primarily affected by the availability and resolution of demographic, dispersal and spatial data. Low-resolution data resulted in the development of less complex models. Model purpose did not affect the choice of the model type. We confirm the general assumption that poor data availability is the main reason for the wide use of simpler models, which may have limited predictive power for population responses to changing environmental conditions. Conservation biology is a crisis discipline where researchers learned to work with the data at hand. However, for threatened and poorly-known species, there is no short-cut when developing either a PBM or an IBM: investments to collect appropriately detailed data are required to ensure PVA models can assess extinction risk under complex environmental conditions.

Combined Influences of Model Choice, Data Quality, and Data Quantity When Estimating Population Trends.

Estimating and projecting population trends using population viability analysis (PVA) are central to identifying species at risk of extinction and for informing conservation management strategies. Models for PVA generally fall within two categories, scalar (count-based) or matrix (demographic). Model structure, process error, measurement error, and time series length all have known impacts in population risk assessments, but their combined impact has not been thoroughly investigated. We tested the ability of scalar and matrix PVA models to predict percent decline over a ten-year interval, selected to coincide with the IUCN Red List criterion A.3, using data simulated for a hypothetical, short-lived organism with a simple life-history and for a threatened snail, Tasmaphena lamproides. PVA performance was assessed across different time series lengths, population growth rates, and levels of process and measurement error. We found that the magnitude of effects of measurement error, process error, and time series length, and interactions between these, depended on context. We found that high process and measurement error reduced the reliability of both models in predicted percent decline. Both sources of error contributed strongly to biased predictions, with process error tending to contribute to the spread of predictions more than measurement error. Increasing time series length improved precision and reduced bias of predicted population trends, but gains substantially diminished for time series lengths greater than 10–15 years. The simple parameterization scheme we employed contributed strongly to bias in matrix model predictions when both process and measurement error were high, causing scalar models to exhibit similar or greater precision and lower bias than matrix models. Our study provides evidence that, for short-lived species with structured but simple life histories, short time series and simple models can be sufficient for reasonably reliable conservation decision-making, and may be preferable for population projections when unbiased estimates of vital rates cannot be obtained.