Variation In Population Size Research Articles

Phenotypic evolution in stochastic environments: The contribution of frequency- and density-dependent selection.

Understanding how environmental variation affects phenotypic evolution requires models based on ecologically realistic assumptions that include variation in population size and specific mechanisms by which environmental fluctuations affect selection. Here we generalize quantitative genetic theory for environmentally induced stochastic selection to include general forms of frequency- and density-dependent selection. We show how the relevant fitness measure under stochastic selection relates to Fisher's fundamental theorem of natural selection, and present a general class of models in which density regulation acts through total use of resources rather than just population size. In this model, there is a constant adaptive topography for expected evolution, and the function maximized in the long run is the expected factor restricting population growth. This allows us to generalize several previous results and to explain why apparently " -selected" species with slow life histories often have low carrying capacities. Our joint analysis of density- and frequency-dependent selection reveals more clearly the relationship between population dynamics and phenotypic evolution, enabling a broader range of eco-evolutionary analyses of some of the most interesting problems in evolution in the face of environmentalvariation.

Variable Population Memetic Search: A Case Study on the Critical Node Problem

Population-based memetic algorithms have been successfully applied to solve many difficult combinatorial problems. Often, a population of fixed size is used in such algorithms to record some best solutions sampled during the search. However, given the particular features of the problem instance under consideration, a population of variable size would be more suitable to ensure the best search performance possible. In this work, we propose a variable population memetic search (VPMS), where a strategic population sizing mechanism is used to dynamically adjust the population size during the search process. Our VPMS approach starts its search from a small population of only two solutions to focus on exploitation and then adapts the population size according to the search status to continuously influence the balancing between exploitation and exploration. We illustrate an application of the VPMS approach to solve the challenging critical node problem (CNP). We show that the VPMS algorithm integrating a variable population, an effective local optimization procedure, and a backbone-based crossover operator performs very well compared to state-of-the-art CNP algorithms. The algorithm is able to discover new upper bounds for 12 instances out of the 42 popular benchmark instances while matching 23 previous best-known upper bounds.

Global Stability of Epidemic Models With Imperfect Vaccination and Quarantine on Scale-Free Networks

Public health services are constantly searching for ways to reduce the spread of infectious diseases, such as public vaccination of asymptomatic individuals, quarantine and treatment of symptomatic individuals. In this paper, we introduce epidemic models including variable population size, degree-related imperfect vaccination and quarantine on scale-free networks. More specifically, the models are formulated both on the population with and without permanent natural immunity to infection, which corresponds respectively to the susceptible-vaccinated-infected-quarantined-recovered (SVIQR) model and the susceptible-vaccinated-infected-quarantined (SVIQS) model. We develop different mathematical methods to study the dynamics of two models, including the basic reproduction number, the global stability of disease-free and endemic equilibria. For the SVIQR model, we show that the system exhibits a forward bifurcation. Meanwhile, the disease-free and unique endemic equilibria are shown to be globally asymptotically stable by constructing suitable Lyapunov functions. For the SVIQS model, conditions ensuring the occurrence of multiple endemic equilibria are derived. Under certain conditions, this system cannot undergo a backward bifurcation. The global asymptotical stability of disease-free equilibrium, and the persistence of the disease are proved. The endemic equilibrium is shown to be globally attractive by using monotone iterative technique. Finally, stochastic network simulations yield quantitative agreement with the deterministic mean-field approach.

Effects of natural selection by fertility on the evolution of the dynamic modes of population number: bistability and multistability

A discrete-time model of a structured population dynamics considering both density-dependent regulation and natural selection is studied. In the model, the dynamics of two population groups corresponding to different development stages is described, and birth rate limitation is considered. Fertility is assumed to change during microevolution. The stability loss of nontrivial fixed points was shown to realise according to the Neimark–Sacker scenario and the Feigenbaum one. Bifurcations, dynamic modes and possible shifting for the proposed model are explored. Bistability and multistability are also revealed. The phase space structure of bistability and multistability areas in which a variation in population sizes or population genotype compositions can lead to shift in the dynamic modes is examined using attraction basins. The multistability of genetic structure dynamics is also investigated. The presence of multistability fundamentally increases the quantity and variety of possible evolutionary scenarios and makes them dependent on both parameter values and initial conditions. In particular, shifting dynamic mode in a population can occur because of an increase in an individual’s reproductive potential during natural evolution.

Spatial distribution of people diagnosed with tuberculosis through routine and active case finding: a community-based study in Kampala, Uganda

BackgroundRoutine tuberculosis (TB) notifications are geographically heterogeneous, but their utility in predicting the location of undiagnosed TB cases is unclear. We aimed to identify small-scale geographic areas with high TB notification rates based on routinely collected data and to evaluate whether these areas have a correspondingly high rate of undiagnosed prevalent TB.MethodsWe used routinely collected data to identify geographic areas with high TB notification rates and evaluated the extent to which these areas correlated with the location of undiagnosed cases during a subsequent community-wide active case finding intervention in Kampala, Uganda. We first enrolled all adults who lived within 35 contiguous zones and were diagnosed through routine care at four local TB Diagnosis and Treatment Units. We calculated average monthly TB notification rates in each zone and defined geographic areas of “high risk” as zones that constituted the 20% of the population with highest notification rates. We compared the observed proportion of TB notifications among residents of these high-risk zones to the expected proportion, using simulated estimates based on population size and random variation alone. We then evaluated the extent to which these high-risk zones identified areas with high burdens of undiagnosed TB during a subsequent community-based active case finding campaign using a chi-square test.ResultsWe enrolled 45 adults diagnosed with TB through routine practices and who lived within the study area (estimated population of 49 527). Eighteen zones reported no TB cases in the 9-month period; among the remaining zones, monthly TB notification rates ranged from 3.9 to 39.4 per 100 000 population. The five zones with the highest notification rates constituted 62% (95% CI: 47–75%) of TB cases and 22% of the population–significantly higher than would be expected if population size and random chance were the only determinants of zone-to-zone variation (48%, 95% simulation interval: 40–59%). These five high-risk zones accounted for 42% (95% CI: 34–51%) of the 128 cases detected during the subsequent community-based case finding intervention, which was significantly higher than the 22% expected by chance (P < 0.001) but lower than the 62% of cases notified from those zones during the pre-intervention period (P = 0.02).ConclusionsThere is substantial heterogeneity in routine TB notification rates at the zone level. Using facility-based TB notification rates to prioritize high-yield areas for active case finding could double the yield of such case-finding interventions.

Threshold harvesting as a conservation or exploitation strategy in population management

Threshold harvesting removes the surplus of a population above a set threshold and takes no harvest below the threshold. This harvesting strategy is known to prevent overexploitation while obtaining higher yields than other harvesting strategies. However, the harvest taken can vary over time, including seasons of no harvest at all. While this is undesirable in fisheries or other exploitation activities, it can be an attractive feature of management strategies where removal interventions are costly and desirable only occasionally. In the presence of population fluctuations, the issue of variable harvests and population sizes becomes even more notorious. Here, we investigate the impact of threshold harvesting on the dynamics of both population size and harvests, especially in the presence of population cycles. We take into account semelparous and iteroparous life cycles, Allee effects, observation uncertainty, and demographic as well as environmental stochasticity, using generic mathematical models in discrete time. Our results show that threshold harvesting enhances multiple forms of population stability, namely persistence, constancy, resilience, and dynamic stability. We discuss plausible choices of threshold values, depending on whether the aim is resource exploitation, pest control, or the stabilization of fluctuations.

Effect of microplastics PAN polymer and/or Cu2+ pollution on the growth of Chlorella pyrenoidosa

Polyacrylonitrile polymer (PAN), a common representative textile material and a microplastic, has significant influence on phytoplankton algae, especially with co-exposure with other pollutants, e.g. Cu2+. In the present study, we carried out experiments to reveal the population size variation trends of Chlorella pyrenoidosa over time (during a whole growth cycle of 6 days) under PAN and/or Cu2+. The levels of pigments (chlorophyll a, b, total chlorophyll and carotenoids), chlorophyll a fluorescence parameters, and other physiological and biochemical indices, containing total protein measurements of H2O2, catalase (CAT), and malondialdehyde (MDA) under different treatment groups were measured to explain the physio-ecological mechanism of the effect of PAN and/or Cu2+ on the growth of C. pyrenoidosa. The results showed that PAN, Cu2+ and the combination of PAN and Cu2+ inhibited the growth of C. pyrenoidosa. Chlorophyll a and b decreased significantly with increasing levels of pollutants (PAN and/or Cu2+); however, the carotenoid levels increased with increasing levels of pollutants (PAN and/or Cu2+) for the first three cultivation days. The oxygen-evolving complexes (OECs) of C. pyrenoidosa had been damaged under Cu2+ pollution. The results also showed that CAT activity, MDA content and H2O2 activity of C. pyrenoidosa increased with increasing levels of pollutants (PAN and/or Cu2+); however, total protein content decreased with increasing levels of pollutants (PAN and/or Cu2+) at the first cultivation day. These results indicate that pollutants (PAN and/or Cu2+) are harmful to the growth of the C. pyrenoidosa population and negatively affect the levels and function of the pigments in C. pyrenoidosa by decreasing chlorophyll a and b levels, increasing carotenoid levels, and increasing antioxidant enzyme activity.

Evolutionary dynamics in fluctuating environment

This paper analyzes the effect of variations in population size and in selection on the fate of a mutant type. Using the diffusion approximation, the authors present simple analytic formulas for effective population size and effective selection, and use it to calculate the chance of ultimate fixation and the time scales.

Dynamic stability of an SIVS epidemic model with imperfect vaccination on scale-free networks and its control strategy

Vaccination is the most effective and extensive method to prevent and control the spread of infectious diseases. In this paper, we develop an SIVS epidemic model with demographics and variable population size on scale-free networks. Firstly, we derive two threshold parameters R0 and R˜0 with death rate, and present existence conditions of equilibria. Not only the global asymptotical stability of the disease-free equilibrium is obtained for R˜0<1, but also the global attractivity of the unique endemic equilibrium is proved for R0 > 1. Secondly, the effects of various immunization schemes including uniform immunization, targeted immunization and acquaintance immunization are compared, and the optimal vaccination strategy is analyzed by Pontryagin Maximum Principle. Finally, we perform numerical simulations to verify the correctness of the theoretical results.

A characterisation of the reconstructed birth–death process through time rescaling

The dynamics of a population exhibiting exponential growth can be modelled as a birth–death process, which naturally captures the stochastic variation in population size over time. In this article, we consider a supercritical birth–death process, started at a random time in the past, and conditioned to have n sampled individuals at the present. The genealogy of individuals sampled at the present time is then described by the reversed reconstructed process (RRP), which traces the ancestry of the sample backwards from the present. We show that a simple, analytic, time rescaling of the RRP provides a straightforward way to derive its inter-event times. The same rescaling characterises other distributions underlying this process, obtained elsewhere in the literature via more cumbersome calculations. We also consider the case of incomplete sampling of the population, in which each leaf of the genealogy is retained with an independent Bernoulli trial with probability ψ, and we show that corresponding results for Bernoulli-sampled RRPs can be derived using time rescaling, for any values of the underlying parameters. A central result is the derivation of a scaling limit as ψ approaches 0, corresponding to the underlying population growing to infinity, using the time rescaling formalism. We show that in this setting, after a linear time rescaling, the event times are the order statistics of n logistic random variables with mode log(1∕ψ); moreover, we show that the inter-event times are approximately exponentially distributed.

Assessing the effect of fungicide treatment on Cocoa black pod disease in Ghana: Insight from mathematical modeling

Black pod disease is caused by fungi of the species Phytophthora palmivora or Phytophthora megakarya. The disease causes darkening of affected areas of cocoa trees and/or fruits and leads to significant reduction in crop yields and decreases lifespan of the plant. This study presents a simple S_1S_2IT-type model with variable population size to assess the impact of fungicide treatment on the dynamics of the black pod disease. We do both theoretical studies and numerical simulations of the model. In particular, we analyze the existence of equilibrium points and their stability, simulate the model using data on reported black pod cases from Ghana. In addition, we perform sensitivity analysis of the basic reproduction number with respect to the model parameters. The results show that the top three parameters that govern the dynamics of the black pod disease are the treatment rate, transmission rate, and planting rate of new trees

Endoscopic Gluteus Medius Repair With an ITB-Sparing Versus ITB-Splitting Approach: A Systematic Review and Meta-analysis.

Background:During hip endoscopy, the iliotibial band (ITB) can be split or preserved to access the peritrochanteric workspace. To our knowledge, no comparative studies have been performed to analyze patient-reported outcomes (PROs) and surgical failure rates (gluteus medius retear and/or revision surgery rates) for ITB-sparing versus ITB-splitting approaches in endoscopic gluteus medius repairs.Purpose:To perform a systematic review and meta-analysis of the literature to evaluate PROs and failure rates of patients undergoing ITB-sparing versus ITB-splitting repairs of the gluteus medius.Study Design:Systematic review; Level of evidence, 4.Methods:A systematic review was performed by following PRISMA (Preferred Reporting Items for Systematic Meta-Analyses) guidelines and using the PubMed, Cochrane CENTRAL, and Embase databases. The quality of evidence was evaluated using the modified Coleman Methodology Score. Level 1-4 studies were evaluated for endoscopic abductor repair techniques on all types of gluteus medius tears. Given the small number of studies and varying population sizes, all quantitative data were adjusted for study population size.Results:A total of 13 studies met our inclusion criteria, while more granular data, including ITB approach, were available for 8 studies. Because of the paucity of literature on the subject, all included studies were of lower quality per the modified Coleman Methodology Score. The visual analog scale for pain, the modified Harris Hip Score (mHHS), and the surgical failure rates were compared between approaches. Patients who underwent ITB splitting had a significantly greater change in mHHS (45.5 ± 4.6 vs 27.3 ± 6.5; P < .001) and lower surgical failure rates (3.67 ± 2.33 vs 4.75 ± 2.54; P = .04). There was no significant difference in change in visual analog scale for splitting versus sparing (4.26 ± 0.41 vs 4.39 ± 0.14; P = .96). The results may have been biased by between-group differences, such as patients who undergo ITB sparing being significantly younger.Conclusion:Endoscopic gluteus medius repair is a reliable procedure to improve pain and function in appropriately selected patients. This study highlighted the lack of high-quality literature available regarding ITB approach. However, the evidence to date has suggested that ITB approach may influence hip-specific PROs. Splitting the ITB during abductor repair may be associated with a greater improvement in mHHS and lower surgical failure rates. Further prospective comparative studies are warranted to evaluate the effect of ITB approach.

Mathematical modeling of the transmission dynamics, control and vaccination of schistosomiasis with a variable population size

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Does China's carbon emission trading policy have an employment double dividend and a Porter effect?

The implementation of China's carbon emission trading policy has targeted achieving emission reduction and environmental protection as well as promoting economic development and technological innovation. The analysis is made through applying the Difference-in-Differences model and using the Ordinary Least Squares method and the Least Square Dummy Variable method in the paper. Results show that the pilot carbon emission trading policy leads to the expansion of employment scales and the reduction of carbon emissions after controlling for the environmental regulation, population size, economic level, and other important variables. Thus, it implies that an employment double dividend exists. For the Porter effect, it is found in the pilot carbon emission trading policy only without adding any control variable. The effect is further verified based on a robustness checks and a placebo test. Furthermore, from the perspective of market-oriented environmental regulation policy, this study explains that the carbon emission trading system launched in 2017 needs to be improved to spread both the employment double dividend and the Porter effect to the whole nation. China also needs to form a complete set of strict ecological environment protection policies and administrative measures to achieve sustainable development of the economy.

Resist or perish: Fate of a microbial population subjected to a periodic presence of antimicrobial.

The evolution of antimicrobial resistance can be strongly affected by variations of antimicrobial concentration. Here, we study the impact of periodic alternations of absence and presence of antimicrobial on resistance evolution in a microbial population, using a stochastic model that includes variations of both population composition and size, and fully incorporates stochastic population extinctions. We show that fast alternations of presence and absence of antimicrobial are inefficient to eradicate the microbial population and strongly favor the establishment of resistance, unless the antimicrobial increases enough the death rate. We further demonstrate that if the period of alternations is longer than a threshold value, the microbial population goes extinct upon the first addition of antimicrobial, if it is not rescued by resistance. We express the probability that the population is eradicated upon the first addition of antimicrobial, assuming rare mutations. Rescue by resistance can happen either if resistant mutants preexist, or if they appear after antimicrobial is added to the environment. Importantly, the latter case is fully prevented by perfect biostatic antimicrobials that completely stop division of sensitive microorganisms. By contrast, we show that the parameter regime where treatment is efficient is larger for biocidal drugs than for biostatic drugs. This sheds light on the respective merits of different antimicrobial modes of action.

Testing for population decline using maximal linkage disequilibrium blocks

Only 6% of known species have a conservation status. Methods that assess conservation statuses are often based on individual counts and are thus too laborious to be generalized to all species. Population genomics methods that infer past variations in population size are easy to use but limited to the relatively distant past. Here we propose a population genomics approach that tests for recent population decline and may be used to assess species conservation statuses. More specifically, we study Maximal Recombination Free (MRF) blocks, that are segments of a sequence alignment inherited from a common ancestor without recombination. MRF blocks are relatively longer in small than in large populations. We use the distribution of MRF block lengths rescaled by their mean to test for recent population decline. However, because MRF blocks are difficult to detect, we also consider Maximal Linkage Disequilibrium (MLD) blocks, which are runs of single nucleotide polymorphisms compatible with a single tree. We develop a new method capable of inferring a very recent decline (e.g. with a detection power of 50% for populations whose size was halved to N, 0.05 ×N generations ago) from rescaled MLD block lengths. Our framework could serve as a basis for quantitative tools to assess conservation status in a wide range of species.

Population Characteristics and Microhabitat Preference of Critically Endangered Kondana Soft-Furred Rat (Millardia kondana) in the Northern Western Ghats, India

Millardia kondana is a Critically Endangered species of rat, known only from four localities in India. All these sites were facing growing threats from grazing, fire, and infrastructure-, housing-, and tourism-development. Therefore, we conducted this study to examine the spatiotemporal variation in population density and size and habitat preference of M. kondana. We carried out live trapping of M. kondana at three sites and recorded microhabitat covariates which were likely to influence its abundance. Spatially explicit capture-recapture models (SECR) were used to estimate density of the species. In total, 210 individuals of M. kondana were captured for 301 times in 2700 trap night efforts with trapping success of 11.15 rats/100 trap nights. Density estimates (2.01–10.76 rats/ha) and population estimates (20.24–246.34 individuals) showed substantial spatiotemporal variation. M. kondana appeared to be fast breeding species with a short life span. Model predictions indicated that the species preferred open habitats. Its abundance was positively influenced by increasing perennial herb density (PHD) and herb height (HH). Thus, the conversion of open habitats into forested habitats or human settlements need to be stopped to conserve this species.

Seasonal Population Fluctuations in Some Non-Passeriformes at Marala Head, Pakistan

Point count method was used to determine the relative abundance of non-passerine species at Marala wetlands (District Sialkot, Pakistan) during different calendar months between October, 2000 and September, 2001. Six species (Hoopoe, Lapwing, Spotted Owlet, Osprey, Indian Roller and Indian Nightjar) were recorded. Osprey and Spotted Owlet appearing in smaller numbers and Red Wattled Lapwing as a dominant resident. All the species were resident with some variation in population sizes during different seasons, though Osprey was a winter visitor.

Changes in &lt;i&gt;pmoA&lt;/i&gt; Gene Containing Methanotrophic Population and Methane Oxidation Potential of Dry Deciduous Tropical Forest Soils

In natural ecosystems such as forests topographical gradients, species composition variability and seasonality, are the potential drivers of methane (CH 4 ) metabolism, and thus, of the population size and activities of methane oxidizing bacteria (MOB). To test the hypothesis that topography, tree species and seasonal variability influence MOB population and soil methane oxidation potential (MOP), we conducted two consecutive years of study selecting three sites in a dry deciduous tropical forest in Chandauli district of eastern Uttar Pradesh, India. The qPCR results showed a large variation in MOB population size (copies g −1 dws), ranging from 1.0 × 10 6 to 2.1 × 10 7 and 9.0 × 10 5 to 2.2 × 10 7 during 2016 and 2017 respectively. The distribution of MOB population revealed the trend: hilltop > middle > hillbase with its maxima in the winter and minima in the rainy season. Laboratory incubation study revealed a similar trend in soil MOP (ng CH 4 g −1 h −1 dws), it varied from 10.6 to 20.6 and 10.5 to 20.7 during 2016 and 2017 respectively. The outer canopy soils showed lower MOB population and MOP compared to under canopy soils of tree species Butea monosperma, Madhuca indica and Tectona grandis during both years of study. The topography, season and tree species significantly influenced the MOB population size and MOP. Soil MOP showed a highly significant correlation (r = 0.89; p < 0.01) with MOB population, and a negative correlation was found with soil moisture (r = 0.76; p < 0.01). The results indicate that the dry deciduous tropical forest soils are potential sinks of atmospheric CH 4 wherein, the MOB population characteristically responds to topographical changes, tree species and seasonal shifts driving collectively the overall MOP of forest soils.

Genome Size Variation Between the Native and Invasive Ranges of Senecio madagascariensis (Asteraceae)

Abstract—Invasive species must colonize new habitats away from their native range; therefore, factors affecting plant dispersal play a key role in invasion. The ploidy level and genome size (or Cx value) can affect the dispersal traits, physiology, and ecology of invasive species over a few generations, generating individuals that can face fluctuating environments, exploit new ones, and compete with native species. Several studies have demonstrated that invasive species tend to have smaller genomes than their noninvasive congeners, which is explained by the role that the Cx value plays in phenotypic evolution and ecological tolerance. In order to test this hypothesis, we compare the genome size variation in Argentine populations (invasive range) vs. South African populations (native range) of S. madagascariensis. To meet our goals, we estimated the Cx value of invasive populations collected on field trips, while for native populations we considered available published data. We extracted the bioclimatic variables in order to establish the ecological amplitude in which the genome sizes may be distributed. Our results evidenced larger genomes in the invasive range than in the native one. Furthermore, we propose that large genomes of the invasive populations could be mainly explained by the founder genotypes effect and the anthropogenic introduction of this species to Argentina. In addition, we demonstrated that genotypes with big genomes can tolerate different environmental conditions from those of their native range. Therefore, they could present a greater ability for colonizing new environments. The implications and importance of ploidy level in the invasion of S. madagascariensis are discussed.