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

1999 ◽  
Vol 5 (2) ◽  
pp. 144 ◽  
Author(s):  
Michael A. McCarthy ◽  
Alan Webster ◽  
Richard H. Loyn ◽  
Kim W. Lowe
Keyword(s):  
Management Strategies ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Large Field ◽  
Adult Survival ◽  
Metapopulation Dynamics ◽  
Viability Analysis ◽  
Term Monitoring ◽  
Predicted Risk

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.

scholarly journals Can we reestablish a self-sustaining population? A case study on reintroduced Crested Ibis with population viability analysis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yashuai Zhang ◽  
Fang Wang ◽  
Zhenxia Cui ◽  
Min Li ◽  
Xia Li ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Population Size ◽  
Carrying Capacity ◽  
Wild Population ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Viability Analysis ◽  
Crested Ibis ◽  
Reintroduced Population

Abstract Background One of the most challenging tasks in wildlife conservation and management is clarifying which and how external and intrinsic factors influence wildlife demography and long-term viability. The wild population of the Crested Ibis (Nipponia nippon) has recovered to approximately 4400, and several reintroduction programs have been carried out in China, Japan and Korea. Population viability analysis on this endangered species has been limited to the wild population, showing that the long-term population growth is restricted by the carrying capacity and inbreeding. However, gaps in knowledge of the viability of the reintroduced population and its drivers in the release environment impede the identification of the most effective population-level priorities for aiding in species recovery. Methods The field monitoring data were collected from a reintroduced Crested Ibis population in Ningshan, China from 2007 to 2018. An individual-based VORTEX model (Version 10.3.5.0) was used to predict the future viability of the reintroduced population by incorporating adaptive patterns of ibis movement in relation to catastrophe frequency, mortality and sex ratio. Results The reintroduced population in Ningshan County is unlikely to go extinct in the next 50 years. The population size was estimated to be 367, and the population genetic diversity was estimated to be 0.97. Sensitivity analysis showed that population size and extinction probability were dependent on the carrying capacity and sex ratio. The carrying capacity is the main factor accounting for the population size and genetic diversity, while the sex ratio is the primary factor responsible for the population growth trend. Conclusions A viable population of the Crested Ibis can be established according to population viability analysis. Based on our results, conservation management should prioritize a balanced sex ratio, high-quality habitat and low mortality.

Reproductive biology, post-fire succession dynamics and population viability analysis of the critically endangered Western Australian shrub Calytrix breviseta subsp. breviseta (Myrtaceae)

2009 ◽  
Vol 57 (6) ◽  
pp. 451 ◽  
Author(s):  
Andrew P. Nield ◽  
Philip G. Ladd ◽  
Colin J. Yates
Keyword(s):  
Reproductive Biology ◽  
Carrying Capacity ◽  
Seedling Recruitment ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Fire Return Interval ◽  
Viability Analysis ◽  
Return Interval ◽  
Western Australian

Calytrix breviseta Lindl. subsp. breviseta is a critically endangered, obligate-seeder shrub within fire-prone kwongan of south-west Western Australia. Little is known about the species’ reproductive biology and how threatening processes, particularly altered fire regimes and exotic species invasion, will impact the long-term viability of the species. This study aims to elucidate the species’ reproductive biology and patterns of seedling recruitment during succession after fire. The effects of changes to the fire return interval and exotic species invasion on the long-term viability of the species is also described. The species exhibits abundant recruitment following fire and the application of a smoke treatment significantly improves germination, similar to many other Western Australian shrubs. However, significant inter-fire recruitment was observed up to 10 years following fire, leading to the presence of multi-aged subpopulations, although seedling recruitment was negligible >20 years after fire. The juvenile period is short at 3–4 years to first flowering. Population viability analysis (PVA) predicted that the optimal fire return interval to maintain C. breviseta subsp. breviseta was dependent on the carrying capacity (K) of the community and the number of individuals present. Carrying capacity will be related to site quality and competition from invasive species. PVA showed that if K remains high, then the optimal fire return interval is ~15–20 years, but under lower carrying capacity, (i.e. weed competition) fires decrease the likelihood of population survival.

Predictions of the impacts of changes in population size and environmental variablitity on Leadbeater's possum, Gymnobelideus leadbeateri McCoy (Marsupialia: Petauridae) using population viability analysis: an application of the computer program VORTEX.

1993 ◽  
Vol 20 (1) ◽  
pp. 67 ◽  
Author(s):  
DB Lindenmayer ◽  
RC Lacy ◽  
VC Thomas ◽  
TW Clark
Keyword(s):  
Computer Program ◽  
Population Size ◽  
Carrying Capacity ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Suitable Habitat ◽  
Viability Analysis ◽  
Nest Sites ◽  
Leadbeater's Possum

Population Viability Analysis (PVA) uses computer modelling to simulate interacting deterministic and stochastic factors (e.g. demographic, genetic, spatial, environmental and catastrophic processes) that act on small populations and assess their long-term vulnerability to extinction. The computer program VORTEX was used in a PVA of Leadbeater's possum, Gymnobelideus leadbeateri McCoy, an endangered arboreal marsupial that is restricted to the montane ash forests of the central highlands of Victoria. PVA was used to examine the impacts of changes in the size of subpopulations and the effects of environmental variation. Our analyses demonstrated that an annual linear decline in the carrying capacity in all or parts of the habitat will lead to the extinction of G. leadbeateri in those areas. Mean time to extinction was related to the rate of annual decrease. This conclusion is of practical and management importance as there is presently a decline in suitable habitat because of an annual loss of more than 3.5% of trees with hollows, which provide nest sites for G. leadbeateri. Because nest sites are a factor that limits populations of G. leadbeateri, the species could be lost from large areas within the next 50 years. PVA was also used to determine the viability of populations in areas, such as oldgrowth forest, where there is not likely to be a steady decline in habitat carrying capacity resulting from the loss of trees with hollows. This allowed an analysis of the cumulative impacts of small population size, environmental variation and genetic factors, which showed that, for a 100-year projection, simulated populations of 200 animals or more remained demographically stable and experienced a less than 10% decline in predicted genetic variability. However, the relatively simplified nature of population modelling and the suite of assumptions that underpin VORTEX mean that the probability of extinction of populations of this size may be greater than determined in this study. As a result, it is possible that only populations of more than 200 animals may persist in the long term where suitable habitat can be conserved or established and subsequently maintained without a reduction in carrying capacity.

Population viability analysis of common marsupials, Didelphis marsupialis and Didelphis virginiana, in a scenario of constant loss of native vegetation

Mammalia ◽  
2020 ◽  
Vol 84 (5) ◽  
pp. 475-482
Author(s):  
Bárbara Cruz-Salazar ◽  
Lorena Ruiz-Montoya
Keyword(s):  
Genetic Diversity ◽  
Population Size ◽  
Forest Cover ◽  
Environmental Changes ◽  
Mammalian Species ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Didelphis Virginiana ◽  
Metapopulation Dynamics ◽  
Viability Analysis

AbstractWe studied the population viability of two common marsupials, Didelphis marsupialis and Didelphis virginiana, based on field data and published ecological and genetic information. Using the VORTEX v. 10. 2.6 program, a 100-year simulation was performed with 1000 iterations for five populations of D. marsupialis and six of D. virginiana. A low probability of extinction was observed in both species, particularly for D. virginiana (0.000–0.007). Population size is higher considering a metapopulation dynamics approach versus individual populations for the two marsupials: 498.25 individuals for D. marsupialis and 367.41 individuals for D. virginiana. The estimated mean genetic diversity was high for both D. marsupialis (He = 0.77–0.78) and D. virginiana (He = 0.79–0.82). The survival of both species over time could be expected to increase if a metapopulation dynamics is favored over the coming decades, despite a 1.3% loss rate of forest cover. The monitoring of population size and genetic diversity is highly recommended to validate the trends suggested by the model; this is especially true for D. marsupialis, a species associated with conserved areas that are becoming progressively less abundant. This research provides information on the responses of common mammalian species to environmental changes such as deforestation.

Viability analyses of an endangered donkey breed: the case of the Asinina de Miranda (Equus asinus)

2015 ◽  
Vol 55 (9) ◽  
pp. 1184 ◽  
Author(s):  
M. Quaresma ◽  
A. M. F. Martins ◽  
J. B. Rodrigues ◽  
J. Colaço ◽  
R. Payan-Carreira
Keyword(s):  
Neonatal Mortality ◽  
Management Strategies ◽  
Population Viability Analysis ◽  
Critical Factor ◽  
Mortality Rates ◽  
Population Viability ◽  
Analysis Program ◽  
Female Mortality ◽  
Viability Analysis ◽  
Equus Asinus

The donkey breed Asinina de Miranda, with fewer than 1000 breeding females, is in danger of extinction. The objectives of this study were to predict the progression of the breed under present management and identify determinants for survival, by means of a population viability analysis program, in order to suggest suitable management strategies. The simulation showed a high risk of extinction. The most critical factor for breed survival was the percentage of females breeding per year, but the actual percentage needed depended on the carrying capacity of the breed. Reducing female mortality and age at production of first offspring, assuring registration in the Studbook, and tracking the foals will significantly foster this donkey breed’s recovery and maintenance. The breed comprised a potentially reproductive population of 589 individuals; however, just 54.1% of the adult females registered in the Studbook ever foaled, and of these 62.7% foaled just once. The overall neonatal mortality for the first month of life was 8.92% and was lower in females (6.51%) than in males (12.0%) (P = 0.028). Neonatal mortality was unevenly distributed throughout the year, with lower mortality rates recorded in February–May and October–November, and higher mortality rates in June–September and again in December–January. The neonatal foal mortality rate was lower with females aged 5–15 years (8.06%) than those younger than 4 years (10.3%) or older than 16 years (14.1%) at foaling.

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

2021 ◽  
Author(s):  
Stephanie Manzo ◽  
E. Griffin Nicholson ◽  
Zachary Devereux ◽  
Robert N. Fisher ◽  
Chris W. Brown ◽  
...  
Keyword(s):  
Natural Disasters ◽  
Population Size ◽  
Population Viability Analysis ◽  
Population Viability ◽  
Population Declines ◽  
Viability Analysis ◽  
Population Size Estimates ◽  
Population Sizes ◽  
Size Estimates

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 NPT. Population size estimates from trapping surveys indicate that SPT have smaller population sizes on average than 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.

Population viability analysis shows spotted-tailed quolls may be vulnerable to competition

2013 ◽  
Vol 35 (2) ◽  
pp. 180 ◽  
Author(s):  
A. S. Glen ◽  
C. R. Dickman
Keyword(s):  
Population Viability Analysis ◽  
Population Viability ◽  
Case Scenario ◽  
Worst Case ◽  
Term Survival ◽  
Exploitation Competition ◽  
Viability Analysis ◽  
Probability Of Survival ◽  
Abundance And Distribution

Competition between carnivores can strongly affect their behaviour, abundance and distribution. Recent analyses suggest a strong likelihood of competition between eutherian predators and the endangered spotted-tailed quoll (Dasyurus maculatus), although experiments are required to confirm this. If competition does occur, what are its likely effects on the long-term survival of spotted-tailed quoll populations? We used population viability analysis (PVA) to predict the fate of a hypothetical quoll population under various scenarios of competition. PVA showed that spotted-tailed quoll populations may be susceptible to extinction when faced with high densities of competitors. Model scenarios simulating exploitation competition and/or intraguild killing greatly reduced the population’s probability of survival, leading in the worst-case scenario to almost certain extinction.

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