Viable Population Size Research Articles

A population viability analysis of serendipity berry ( Dioscoreophyllum cumminsii) in a semi-deciduous forest in Nigeria

The search for natural sweeteners has prompted intensive research on plants with sweetening properties. Dioscoreophyllum cumminsii (Stapf) Diels is a dioecious, semelparous annual liana found as a late successional, understorey species in West African semi-deciduous forests. The fruits and subterranean tubers are intensely sweet and are both edible. The sweetening substance in D. cumminsii is a protein (monellin), which is 3000 times as sweet as sugar. Unfortunately, it is one of the threatened plant species in the country because of massive habitat loss and fragmentation. Conservation is now needed as a salvage programme. Population size is a major determinant of extinction risk. This has prompted the application of growth and population dynamics models to viability analysis of wild species. The aim of population viability analysis (PVA) is to determine the minimum viable population size (MVP) or area (MVA) of a particular species. In this paper, MVP was estimated for D. cumminsii using genetic models. The models simulated minimum effective population size of 6040 individuals ha −1 in the ratio of 5032 males to 1008 females. This suggests that to retain evolutionary potential, D. cumminsii requires an effective population size of more than the 500–5000 range considered adequate for many other species.

Estimating Minimum Area of Suitable Habitat and Viable Population Size for the Northern Muriqui (Brachyteles hypoxanthus)

A population viability analysis (PVA) using the computer package VORTEX was conducted to assess the minimum viable population (MVP) of the Atlantic Forest endemic primate Brachyteles hypoxanthus. The objectives were: (1) to estimate demographic and genetic MVPs that could be used as quasi-extinction thresholds for future modeling, and (2) to estimate the minimum area of suitable habitat (MASH). The model predicted that populations of 40 and 700 individuals were necessary to achieve demographic and genetic stability, respectively. The model was more sensitive to changes in inbreeding depression, sex ratio and reproduction (percentage of breeding females). MASH estimated to contain genetically viable populations reached 11,570 ha. Muriquis have managed to persist despite severe habitat disturbance, but the results suggest that although most of the extant populations are not threatened by extinction, they are too small to be genetically viable in the long-run, and will loose most of their heterozygosity.

Development of vaccination strategies for the management of rabies in African wild dogs

The standard objective of a vaccination strategy is to reduce the reproductive ratio, R 0, defined as the number of secondary host infections arising directly from introduction of a single infected individual into an otherwise fully susceptible population, to below 1. This ensures that only very small outbreaks are likely to arise. However, this objective usually requires a high level of vaccination coverage that is often expensive and logistically difficult to achieve. For the purposes of conserving rare species that are threatened by outbreaks of infectious disease, population persistence may be assured by a vaccination strategy designed to suppress only the largest outbreaks of disease that reduce the population to below a minimum viable population size. Such strategies targeting only a viable minimal ‘core’ of the population are likely to be logistically less demanding. Here we explore how these core vaccination strategies might be designed for African wild dogs ( Lycaon pictus), an endangered canid species whose remaining populations are threatened by rabies outbreaks. We develop and analyse a population viability model with an explicit epidemiological model embedded within it. The model predicts that core vaccination campaigns, using vaccines that provide two years of immunity, and targets 30–40% of individuals within a population every 1–2 years would be successful in ensuring persistence of small populations, and required coverage levels can be even lower in larger populations. This strategy appears robust to synchronized introduction of rabies into packs, possible Allee effects, and the use of vaccines providing only one year of immunity.

Evaluation of Minimum Viable Population Size and Conservation Status of the Long-furred Woolly Mouse Opossum Micoureus paraguayanus: An Endemic Marsupial of the Atlantic Forest

A population viability analysis (PVA) using the computer package VORTEX was conducted to assess the minimum viable population (MVP) of the Atlantic Forest endemic marsupial Micoureus paraguayanus. The objectives were: to estimate demographic and genetic MVPs that could be used as quasi-extinction thresholds for future modeling, to estimate the minimum area of suitable habitat (MASH), and to use these results to apply IUCN red list criteria so as to suggest its proper status classification. The model predicted that populations of 100 and 2000 individuals were necessary to achieve demographic and genetic stability, respectively, within a time frame of 100 years. The model was sensitive to changes in inbreeding depression, mortality and reproduction. MASH estimated to contain genetically viable populations reached 1300 ha. Fortunately, there still are quite a number of forest remnants equal to or larger than this. Isolation is suggested as the principal threat facing M. paraguayanus. Therefore, promoting conditions for dispersal together with efforts dealing with translocation, should prove to be the most appropriate management strategies for M. paraguayanus at this stage. A landscape pattern composed of large patches holding MVPs and sets of smaller patches harboring viable metapopulations that maximize probability of dispersal can provide a viable scenario for the conservation of M. paraguayanus.

Rare, Fragile Species, Small Populations, and the Dilemma of Collections

Considerable sums of money are aimed at biodiversity conservation programs at present, and although collection of specimens is necessary for the advancement of taxonomy and systematics, we detected a dilemma between conservation and collection of rare species with small populations. Collecting may act synergistically with other factors to increase the risk of, or even drive species to extinction. We present some examples we believe show the conflict between collecting rare species with a small population and the conservation programs for those species. We also stress the need to review the Minimum Viable Population Size concept as it can be used as a justification for collecting small, rare, and declining population species.

Minimum viable population sizes and global extinction risk are unrelated

Theoretical and empirical work has shown that once reduced in size and geographical range, species face a considerably elevated risk of extinction. We predict minimum viable population sizes (MVP) for 1198 species based on long-term time-series data and model-averaged population dynamics simulations. The median MVP estimate was 1377 individuals (90% probability of persistence over 100 years) but the overall distribution was wide and strongly positively skewed. Factors commonly cited as correlating with extinction risk failed to predict MVP but were able to predict successfully the probability of World Conservation Union Listing. MVPs were most strongly related to local environmental variation rather than a species' intrinsic ecological and life history attributes. Further, the large variation in MVP across species is unrelated to (or at least dwarfed by) the anthropogenic threats that drive the global biodiversity crisis by causing once-abundant species to decline.

A diffusive SI model with Allee effect and application to FIV

A minimal reaction–diffusion model for the spatiotemporal spread of an infectious disease is considered. The model is motivated by the Feline Immunodeficiency Virus (FIV) which causes AIDS in cat populations. Because the infected period is long compared with the lifespan, the model incorporates the host population growth. Two different types are considered: logistic growth and growth with a strong Allee effect. In the model with logistic growth, the introduced disease propagates in form of a travelling infection wave with a constant asymptotic rate of spread. In the model with Allee effect the spatiotemporal dynamics are more complicated and the disease has considerable impact on the host population spread. Most importantly, there are waves of extinction, which arise when the disease is introduced in the wake of the invading host population. These waves of extinction destabilize locally stable endemic coexistence states. Moreover, spatially restricted epidemics are possible as well as travelling infection pulses that correspond either to fatal epidemics with succeeding host population extinction or to epidemics with recovery of the host population. Generally, the Allee effect induces minimum viable population sizes and critical spatial lengths of the initial distribution. The local stability analysis yields bistability and the phenomenon of transient epidemics within the regime of disease-induced extinction. Sustained oscillations do not exist.

MODELING THE ADAPTIVE POTENTIAL OF ISOLATED POPULATIONS: EXPERIMENTAL SIMULATIONS USING DROSOPHILA

The genetic variability underlying many morphological and stress resistance traits may largely depend on the effects of genetic drift balanced by polygenic mutation. This model of adaptive potential has played a central role in the minimum viable population size concept and has been used to predict the effective population size necessary to prevent extinction within changing environments. However, there have been few long-term experimental studies of adaptive potential within isolated populations, and no study has thus far provided an experimental test of the drift-mutation model of quantitative genetic variation. Using the sternopleural bristle number of Drosophila melanogaster as a model quantitative trait, we performed repeated measurements of adaptive potential on 15 replicate populations of two and 10 male-female pairs over 30 and 77 generations, respectively. Declines in adaptive potential were analyzed by comparing observed and expected changes in realized heritability over time. The only significant model deviation occurred immediately after bottlenecks of two pairs, in which greater than expected declines in realized heritability were observed. This result suggests that changes in allelic diversity during bottleneck events may be as important as changes in heterozygosity in determining adaptive potential. Drift-mutation model expectations were otherwise realized over all generations. Our results validate the use of the drift-mutation model as a tool for understanding the dynamics of adaptive potential for peripheral fitness characters, but suggest caution in applying this model to recently bottlenecked populations.

Relationship between Population Size and Fitness

Abstract: Long‐term effective population size, which determines rates of inbreeding, is correlated with population fitness. Fitness, in turn, influences population persistence. I synthesized data from the literature concerning the effects of population size on population fitness in natural populations of plants to determine how large populations must be to maintain levels of fitness that will provide adequate protection against environmental perturbations that can cause extinction. Integral to this comment on what has been done and what needs to be done, sThe evidence suggests that there is a linear relationship between log population size and population fitness over the range of population sizes examined. More importantly, populations will have to be maintained at sizes of >2000 individuals to maintain population fitness at levels compatible with the conservation goal of long‐term persistence. This approach to estimating minimum viable population size provides estimates that are in general agreement with those from numerous other studies and strengthens the argument that conservation efforts should ultimately aim at maintaining populations of several thousand individuals to ensure long‐term persistence.

Deer Browsing and Population Viability of a Forest Understory Plant

American ginseng is the premier medicinal plant harvested from the wild in the United States. In this study, seven populations of ginseng plants were censused every 3 weeks during the growing season over 5 years to monitor deer browse and harvest and to project population growth and viability. The minimum viable population size was approximately 800 plants, a value greater than that of all populations currently being monitored. When simulated deer browsing rates were reduced 50% or more, population viability rose sharply. Without more effective deer population control, ginseng and many other valuable understory herbs are likely to become extinct in the coming century.

MODELING THE ADAPTIVE POTENTIAL OF ISOLATED POPULATIONS: EXPERIMENTAL SIMULATIONS USING DROSOPHILA

The genetic variability underlying many morphological and stress resistance traits may largely depend on the effects of genetic drift balanced by polygenic mutation. This model of adaptive potential has played a central role in the minimum viable population size concept and has been used to predict the effective population size necessary to prevent extinction within changing environments. However, there have been few long-term experimental studies of adaptive potential within isolated populations, and no study has thus far provided an experimental test of the drift-mutation model of quantitative genetic variation. Using the sternopleural bristle number of Drosophila melanogaster as a model quantitative trait, we performed repeated measurements of adaptive potential on 15 replicate populations of two and 10 male-female pairs over 30 and 77 generations, respectively. Declines in adaptive potential were analyzed by comparing observed and expected changes in realized heritability over time. The only significant model deviation occurred immediately after bottlenecks of two pairs, in which greater than expected declines in realized heritability were observed. This result suggests that changes in allelic diversity during bottleneck events may be as important as changes in heterozygosity in determining adaptive potential. Drift-mutation model expectations were otherwise realized over all generations. Our results validate the use of the drift-mutation model as a tool for understanding the dynamics of adaptive potential for peripheral fitness characters, but suggest caution in applying this model to recently bottlenecked populations.

Macroecology, geographic range size–body size relationship and minimum viable population analysis for new world carnivora

Abstract Macroecology deals with variation and covariation of complex variables, such as body size, population density and geographic range size (GRS), measured across species at broad spatial scales. Despite the increasing number of papers in this field, little attention has been given to the links between patterns at different scales. In this paper, we analysed the constraint envelope formed by the macroecological relationship between GRS and body size for 70 species of New World terrestrial Carnivora. The lower-right constraint line of this envelope is usually interpreted as the minimum viable GRS that keeps extinction risks relatively low across evolutionary time, and in this paper we fitted this line by multiplying average home range size (established by allometric equations) by different minimum viable population sizes, establishing a minimum viable GRS. Then we estimated the difference between actual geographical range size and minimum viable geographical range size, in log scale (Δ A ), which indicates how large is the geographic range of a species in relation to the minimum necessary to its long-term persistence. These Δ A values are significantly correlated with extinction risk defined by IUCN threat categories, even after keeping geographical range size constant and after taking into account phylogenetic structure in data. This gives support to the minimum viable population model explaining the relationship between GRS and body size and highlights a way to use constraint envelopes to evaluate the influence of complex variables to predict extinction risks.

Large Estimates of Minimum Viable Population Sizes

Large Estimates of Minimum Viable Population Sizes

Large Estimates of Minimum Viable Population Sizes

Large Estimates of Minimum Viable Population Sizes

Macroecology and the hierarchical expansion of evolutionary theory

ABSTRACTThe constraint envelope describing the relationship between geographical range size and body size has usually been explained by a minimum viable population size model, furnishing a strong argument for species selection if geographical range size turns out to be ‘heritable’. Recent papers have questioned this assumption of nonzero geographical range heritability at a phylogenetic level, meaning that the logic that constraint envelopes provide support for higher‐level selection fails. However, I believe that analysis of constraint envelopes can still furnish insights for the hierarchical expansion of evolutionary theory because the fitness furnished by variation in body size, which is frequently measured as a highly ‘heritable’ trait at the species level, can be partitioned into anagenetic and cladogenetic components. The constraint envelope furnishes an explicit mechanism for large‐body biased extinction rates influencing the distribution of body size. More importantly, it is possible to envisage a scenario in which anagenetic trends driving an increase in body size in higher latitudes within species (Bergmann's rule) are counteracted by available habitat area or continental edges constraining overall species distribution in these higher latitudes, increasing the probability of extinction. Under this combined model, faunas at higher latitudes and under habitat constraints may reach equilibrium points between these opposing hierarchical adaptive forces at smaller body size than faunas with less intense higher‐level constraints and will tend to be more right‐skewed.

Effects of heavy metal contamination and remediation on soil microbial communities in the vicinity of a zinc smelter as indicated by analysis of microbial community phospholipid fatty acid profiles

Heavy metal contamination in an area immediately surrounding a zinc smelter has resulted in destruction of over 485 hectares of forest. The elevated levels of heavy metals in these soils have had significant impacts on the population size and overall activity of the soil microbial communities. Remediation of these soils has resulted in increases in indicators of biological activity and viable population size, which suggest recovery of the microbial populations. Questions remain as to how the metal contamination and subsequent remediation at this site have impacted the population structure of the soil microbial communities. In the current study, microbial communities from this site were analyzed by the phospholipid fatty acid (PLFA) procedure. Principal component analysis of the PLFA profiles indicated that there were differences in the profiles for soils with different levels of metal contamination, and that soils with higher levels of metal contamination showed decreases in indicator PLFAs for mycorrhizal fungi, Gram-positive bacteria, fungi, and actinomycetes. PLFA profiles for remediated sites indicated that remediated soils showed increases in indicator PLFAs for fungi, actinomycetes, and Gram-positive bacteria, compared to unremediated metal contaminated soils. These data suggest a change in the population structure of the soil microbial communities resulting from metal contamination and a recovery of several microbial populations resulting from remediation.

Estimates of minimum viable population sizes for vertebrates and factors influencing those estimates

Population size is a major determinant of extinction risk. However, controversy remains as to how large populations need to be to ensure persistence. It is generally believed that minimum viable population sizes (MVPs) would be highly specific, depending on the environmental and life history characteristics of the species. We used population viability analysis to estimate MVPs for 102 species. We define a minimum viable population size as one with a 99% probability of persistence for 40 generations. The models are comprehensive and include age-structure, catastrophes, demographic stochasticity, environmental stochasticity, and inbreeding depression. The mean and median estimates of MVP were 7316 and 5816 adults, respectively. This is slightly larger than, but in general agreement with, previous estimates of MVP. MVPs did not differ significantly among major taxa, or with latitude or trophic level, but were negatively correlated with population growth rate and positively correlated with the length of the study used to parameterize the model. A doubling of study duration increased the estimated MVP by approximately 67%. The increase in extinction risk is associated with greater temporal variation in population size for models built from longer data sets. Short-term studies consistently underestimate the true variances for demographic parameters in populations. Thus, the lack of long-term studies for endangered species leads to widespread underestimation of extinction risk. The results of our simulations suggest that conservation programs, for wild populations, need to be designed to conserve habitat capable of supporting approximately 7000 adult vertebrates in order to ensure long-term persistence.

Human-induced alteration of two boreal forest landscapes in central Norway, and some possible consequences for avian fauna

Exploitation over the last 50 years has altered the Fennoscandian boreal forest landscapes quite considerably. The situation in our two study areas in Lierne (Berglia and Raudberga) in central Norway in three periods, the 1950s, the 1970s and 1999, exemplifies this development. The ecological consequences of the landscape alterations identified during this period are illustrated by tracing the trend of the bird guild associated with old-growth forest. We have used existing and estimated density data for this guild, theories on landscape ecology and Geographical Information System (GIS) analyses. At Berglia, the area covered with old-growth forest was reduced by a further 19% in 1999 compared with the “pristine” situation where 65% of the landscape was forested. At Raudberga there has been a further 36% reduction from the original 72% coverage, leaving just 36% of this area covered by old growth. Given our assumptions (e.g. a 100-metre edge effect), the old-growth bird guild has been declining at ratios of 1.23–1.49 at Raudberga and 1.60–1.93 at Berglia relative to the reduction in the proportion of areas covered by old-growth forest stands, a significantly higher rate of decline than the one-to-one relationship expected if the loss of habitat areas had been the only effect. The difference in the spatial habitat configuration between these two areas can explain some of the variation as Raudberga shows a more coarse-grained fragmentation pattern. If the current trends, according to our best-fit models, are allowed to continue until 2050, only 30–44% of the population sizes at the “pristine” state will survive at Berglia and 22–32% at Raudberga. For some of the species involved, this certainly implies that the critical threshold value for maintaining viable population sizes will be exceeded, not least because the long-established practice of clear-felling will lead to a lack of important habitat features such as dead wood and large trees in the landscape. The boreal forest is, however, a natural, dynamic system whose resilience should be quite good and, as shown by our best possible scenario, a significantly improved situation can be achieved by 2050. However, this presupposes that the current alarming trends are taken seriously by the management authorities, and that the multi-professional knowledge available is applied in future planning processes for our rural areas.

Empirical estimates of minimum viable population sizes for primates: tens to tens of thousands?

AbstractTheoretical estimates of long‐term minimum viable population (MVP) sizes for mammals indicate MVPs of tens of thousands, even a million. However, data to test the theoretical estimates are effectively non‐existent. I here use information on distributions of primates on islands of southeast Asia to provide empirical estimates of the size of multi‐millennial MVPs following the post‐Pleistocene insularization in the Sunda region. Small Sunda region islands have fewer taxa than do large ones. Assuming extinction on the small islands, the MVP size is somewhere between the population size on the smallest island on which the taxon is extant and that on the largest island on which the taxon no longer exists (population size calculated as density of taxon by area of land available). Results for eight to ten genera (depending on the taxonomy) on 35 islands indicate MVPs of perhaps a few score for Nycticebus (loris) and Macaca (macaque) to several thousands, or scores of thousands, for Pongo (orang‐utan) and Symphalangus (siamang). Large‐bodied taxa have significantly larger MVPs than do small‐bodied taxa. Only four protected areas in southeast Asia are large enough to conserve the smaller MVPs of the siamang and orang‐utan.

Bird diversity and selection of protected areas in a large neotropical forest tract

The unbroken primary rain forest currently covering the interior ofFrench Guiana still offers a unique opportunity to establish a network of largeprotected areas. Bird species richness was surveyed within 20 study areasspreadover the country to assess the relative abundance and frequency of occurrenceofforest interior and natural gap taxa (391 species, excluding raptors andnon-resident birds). Richness, rarity, restricted range, hot spot andconservation value algorithms were used to rank sites in decreasing orders ofimportance and draw sets of survey sites likely to maximize bird diversity. Inmost sets from different methodological approaches, the southern regionconsistently emerged as a priority area for conservation, with the centralmountain range contributing some specialized taxa and the northern regionincorporating additional species, mostly from marginal habitats and moretypicalof the nearby coastal zone. Estimates of areas likely to preserve an almostcomplete sample of the regional biodiversity amounted to about 1–2millionhectares, either in one large area (national park) or divided into 2–3reserves overlapping regional hot spots. However, representation of all speciesand habitats in a protected area system is not an assurance of long-termviability when minimum viable population sizes and demographic patterns arelittle known, and when the risks and impacts of persistent human disturbancessuch as mining, logging and hunting are growing.