Theoretical and empirical studies of metapopulations: population and genetic dynamics of the Silene–Ustilago system

1995 ◽  
Vol 73 (S1) ◽  
pp. 1249-1258 ◽  
Author(s):  
Peter H. Thrall ◽  
Janis Antonovics
Keyword(s):  
Population Dynamics ◽  
Empirical Studies ◽  
Previous History ◽  
High Rate ◽  
Disease Spread ◽  
Plant Host ◽  
Theoretical Approaches ◽  
Population Turnover ◽  
Host Pathogen ◽  
Anther Smut

Host–pathogen population dynamics may often only be understood by a multifaceted approach designed to understand processes at a regional as well as local scale. We have investigated the regional population dynamics of the anther-smut Ustilago violacea, a pollinator-transmitted fungal disease, and its plant host Silene alba, using descriptive, experimental, and theoretical approaches. A 7-year survey of multiple natural populations revealed persistence of host and pathogen despite a high rate of population turnover. In an experimental metapopulation, disease spread was greater and more rapid in populations that were relatively isolated or had a previous history of disease occurrence. A computer simulation showed that spatial substructuring can drastically alter expectations based on analytical results from single population models of host–pathogen systems. Moreover, the simulation reproduced many of the patterns detected in the long-term survey and predicted that healthy populations should be more resistant than diseased ones, as found experimentally. Key words: metapopulations, host–pathogen dynamics, spatial models, anther-smut diseases.

scholarly journals Systematic shifts in the variation among host individuals must be considered in climate-disease theory

2021 ◽  
Author(s):  
Joseph R Mihaljevic ◽  
David J Páez
Keyword(s):  
Climate Change ◽  
Population Dynamics ◽  
Disease Ecology ◽  
Host Population ◽  
Host Susceptibility ◽  
Disease Spread ◽  
Species Variation ◽  
Trait Variation ◽  
Host Pathogen ◽  
Population Sizes

To make more informed predictions of host-pathogen interactions under climate change, studies have incorporated the thermal performance of host, vector, and pathogen traits into disease models. However, this body of work has ignored the fact that disease spread and long-term patterns of host population dynamics are largely determined by the variation in susceptibility among individuals in the host population. Furthermore, and especially for ectothermic host species, variation in susceptibility is likely to be plastic, influenced by variables such as environmental temperature. Quantifying the relationship between temperature and among-host trait variation will therefore be critical for predicting how climate change and disease will interact to influence host-pathogen population dynamics. Here, we demonstrate how short-term effects of temperature on the variation of host susceptibility drive epidemic characteristics, fluctuations in host population sizes, and probabilities of host extinction. We use this quantitative analysis as a basic framework to suggest that more research is needed in disease ecology to understand the mechanisms that shape trait variation, not just trait averages.

Estimation of welfare costs of inflation: The case of Russia

2019 ◽  
pp. 55-69 ◽  
Author(s):  
Sergey M. Drobyshevskiy ◽  
Natalia V. Makeeva ◽  
Elena V. Sinelnikova-Muryleva ◽  
Pavel V. Trunin
Keyword(s):  
Inflation Targeting ◽  
Empirical Studies ◽  
Welfare Costs ◽  
Economic Agents ◽  
Academic Literature ◽  
Russian Economy ◽  
Theoretical Approaches ◽  
Real Gdp ◽  
Quantitative Estimates ◽  
Positive Effect

This paper is devoted to the estimation of welfare costs of inflation, taking into account the peculiarities of the Russian economy. Theoretical approaches that are used in the literature to analyze the costs of inflation are discussed in the paper. It also provides an overview of the empirical studies of this topic. Research found in academic literature shows that the results of quantitative estimates are extremely sensitive to the choice of the functional form of the money demand equation, as well as to assumptions that are made to simplify the analysis, some of which do not fit Russian data. As a result, we have modified the standard approaches to estimating welfare costs of inflation, taking into account the monetization growth in Russia, and provide quantitative estimates of the magnitude of welfare costs of inflation. The results indicate a significant gain for economic agents in terms of real GDP with a decrease in inflation, which is regarded as a positive effect from the inflation targeting policy.

Persistence of giants: population dynamics of the limpet Scutellastra laticostata on rocky shores in Western Australia

2020 ◽  
Vol 646 ◽  
pp. 79-92
Author(s):  
RE Scheibling ◽  
R Black
Keyword(s):  
Population Dynamics ◽  
Western Australia ◽  
Size Structure ◽  
Survival Rates ◽  
Maximum Size ◽  
High Rate ◽  
Adult Survival ◽  
Rocky Shores ◽  
Adult Size ◽  
Decadal Time Scale

Population dynamics and life history traits of the ‘giant’ limpet Scutellastra laticostata on intertidal limestone platforms at Rottnest Island, Western Australia, were recorded by interannual (January/February) monitoring of limpet density and size structure, and relocation of marked individuals, at 3 locations over periods of 13-16 yr between 1993 and 2020. Limpet densities ranged from 4 to 9 ind. m-2 on wave-swept seaward margins of platforms at 2 locations and on a rocky notch at the landward margin of the platform at a third. Juvenile recruits (25-55 mm shell length) were present each year, usually at low densities (<1 m-2), but localized pulses of recruitment occurred in some years. Annual survival rates of marked limpets varied among sites and cohorts, ranging from 0.42 yr-1 at the notch to 0.79 and 0.87 yr-1 on the platforms. A mass mortality of limpets on the platforms occurred in 2003, likely mediated by thermal stress during daytime low tides, coincident with high air temperatures and calm seas. Juveniles grew rapidly to adult size within 2 yr. Asymptotic size (L∞, von Bertalanffy growth model) ranged from 89 to 97 mm, and maximum size from 100 to 113 mm, on platforms. Growth rate and maximum size were lower on the notch. Our empirical observations and simulation models suggest that these populations are relatively stable on a decadal time scale. The frequency and magnitude of recruitment pulses and high rate of adult survival provide considerable inertia, enabling persistence of these populations in the face of sporadic climatic extremes.

scholarly journals Parasitism of Aedes albopictus by Ascogregarina taiwanensis lowers its competitive ability against Aedes triseriatus

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Emma Stump ◽  
Lauren M. Childs ◽  
Melody Walker
Keyword(s):  
Population Dynamics ◽  
Competitive Advantage ◽  
Aedes Albopictus ◽  
Abiotic Factors ◽  
Mosquito Species ◽  
Disease Spread ◽  
Aedes Triseriatus ◽  
La Crosse Virus ◽  
The Impact ◽  
Ascogregarina Taiwanensis

Abstract Background Mosquitoes are vectors for diseases such as dengue, malaria and La Crosse virus that significantly impact the human population. When multiple mosquito species are present, the competition between species may alter population dynamics as well as disease spread. Two mosquito species, Aedes albopictus and Aedes triseriatus, both inhabit areas where La Crosse virus is found. Infection of Aedes albopictus by the parasite Ascogregarina taiwanensis and Aedes triseriatus by the parasite Ascogregarina barretti can decrease a mosquito’s fitness, respectively. In particular, the decrease in fitness of Aedes albopictus occurs through the impact of Ascogregarina taiwanensis on female fecundity, larval development rate, and larval mortality and may impact its initial competitive advantage over Aedes triseriatus during invasion. Methods We examine the effects of parasitism of gregarine parasites on Aedes albopictus and triseriatus population dynamics and competition with a focus on when Aedes albopictus is new to an area. We build a compartmental model including competition between Aedes albopictus and triseriatus while under parasitism of the gregarine parasites. Using parameters based on the literature, we simulate the dynamics and analyze the equilibrium population proportion of the two species. We consider the presence of both parasites and potential dilution effects. Results We show that increased levels of parasitism in Aedes albopictus will decrease the initial competitive advantage of the species over Aedes triseriatus and increase the survivorship of Aedes triseriatus. We find Aedes albopictus is better able to invade when there is more extreme parasitism of Aedes triseriatus. Furthermore, although the transient dynamics differ, dilution of the parasite density through uptake by both species does not alter the equilibrium population sizes of either species. Conclusions Mosquito population dynamics are affected by many factors, such as abiotic factors (e.g. temperature and humidity) and competition between mosquito species. This is especially true when multiple mosquito species are vying to live in the same area. Knowledge of how population dynamics are affected by gregarine parasites among competing species can inform future mosquito control efforts and help prevent the spread of vector-borne disease.

scholarly journals Cirurgia no Aspergiloma Pulmonar: Experiência Mono-Institucional

2014 ◽  
Vol 27 (4) ◽  
pp. 417
Author(s):  
Silvia Da Silva Correia ◽  
Carlos Pinto ◽  
João Bernardo
Keyword(s):  
Postoperative Complications ◽  
Surgical Resection ◽  
Surgical Procedure ◽  
Lung Resection ◽  
Previous History ◽  
Term Treatment ◽  
High Rate ◽  
Long Term Treatment ◽  
Immunosuppressed Patients ◽  
Pulmonary Aspergilloma

<strong>Introduction:</strong> Pulmonary aspergiloma or mycetoma is a saprophytic colonization of a preexisting cavity by aspergilloma. Surgical resection is the only effective long-term treatment, but remains controversial because of the high rate of complications in the perioperative and postoperative time.<br /><strong>Objectives:</strong> Analysis of the experience of a Cardiothoracic Surgery Center for the treatment of pulmonary aspergilloma and evaluation of the prognostic factors after surgery.<br /><strong>Material and Methods:</strong> Retrospective analysis including all the patients with a diagnosis of pulmonary aspergilloma submitted to surgery for a 10 years period, in a single institution (June 2001-June 2011).<br /><strong>Results:</strong> The study included 22 patients (18 men) with a mean age of 51.0 + 17.4 years. Of them, 46% were smokers, 41% were alcoholic and 50% had a previous history of tuberculosis. Most of the patients had a complex aspergilloma (73%) and 17% a simple aspergilloma. The most common presentation was hemoptysis (50%). The common surgical procedure performed was atypical lung resection in 55%, lobectomy in 27% and pneumectomy in 9%. Two patients were submitted to thoracoplasty. There was one operative death (5%). Postoperative complications occurred in 36% and the most frequent were pneumothorax (18%) and empyema (18%). The mean follow-up period was 52 months (3 - 116) and the 5 years mortality rate of 35%. Of them, 4 patients died because of non- related causes and 3 were immunosuppressed patients. The mortality was 40% in the group of complex aspergilloma and 33% in the group of complex aspergilloma.<br /><strong>Discussion:</strong> The most common surgical procedure performed was atypical lung resection. The postoperative complications rate was similar to previous studies.<br /><strong>Conclusion:</strong> Surgical resection of aspergilloma presents a low morbidity and mortality. Therefore, for patients with lung function preserved, it is the preferred treatment.<br /><strong>Keywords:</strong> Aspergillus; Pulmonary Aspergillosis/surgery.

scholarly journals Conflicts in Family Firms in the International Context: A Literature Review

2018 ◽  
Vol 10 (1) ◽  
pp. 43-61
Author(s):  
Martin Jurek
Keyword(s):  
Family Business ◽  
Family Firms ◽  
Research Question ◽  
Empirical Studies ◽  
Value Added ◽  
Life Cycles ◽  
Generational Status ◽  
Business Research ◽  
Screening Criteria ◽  
Theoretical Approaches

Abstract Objective: This paper reviews the major family business research papers that address factors related to relationship and work-to-family conflicts. Methodology: The procedure this paper applies follows recommendations for literature reviews by Fink (2010) consisting of: (1) selecting a research question (2) selecting bibliographic or article databases, (3) choosing search terms, (4) applying practical screening criteria, (5) applying methodical screening criteria, (6) doing the review and (7) synthesizing the results. Findings: The article summarizes that, although family business research is progressing in terms of theory building, it continues to lack a systematic adoption of longitudinal, cross-national and multi-theoretical approaches. To date, research on conflict in family firms remains underdeveloped in the CEE. Value Added: Outlining the state of the art of theoretical and empirical studies by applying a resource-based view. Recommendations: Application of control variables, such as size of the business, business life cycles, generational status, type of industry and various cultural settings. Furthermore, the role of communication, sibling rivalry and perceived justice of family members could be investigated more thoroughly.

scholarly journals The performance of corporate bond issuers in times of financial crisis: empirical evidence from Latin America

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Marc Berninger ◽  
Bruno Fiesenig ◽  
Dirk Schiereck
Keyword(s):  
Latin America ◽  
Latin American ◽  
Empirical Studies ◽  
Corporate Bond ◽  
Economic Conditions ◽  
Corporate Debt ◽  
Market Reactions ◽  
Content Type ◽  
Financing Decisions ◽  
Theoretical Approaches

PurposeThe fundamental theory of Modigliani and Miller (1958) states that a firm's financing decisions are independent from the firm's value. Nevertheless, several empirical studies as well as theoretical approaches from the past decade impugn this relation for real markets with their immanent inefficiencies. However, these questions are rather than academic in nature: Especially the influence of macroeconomic conditions on the market perception of debt issues is from high economic importance, since the need for new liquidity usually becomes even more urgent when the economic conditions worsen.Design/methodology/approachThis paper analyzes the reaction of shareholders to the issue of debt by Latin American firms under special consideration of the macroeconomic sentiment. To do so, a sample of debt issued by Latin American companies between 2003 and 2010 is empirically examined through an event study.FindingsThe authors empirically demonstrate that specifically in Latin America, debt issuing companies show a significant underperformance during recessionary periods and an overperformance during nonrecessionary periods. These findings differ from previous results for mature capital markets. The authors conclude that not only the overall economic conditions matter to explain stock market reactions on bond issues but also the maturity of the corporate debt market plays an important role.Originality/valueThe authors provide first evidence that the previously described changes in the returns on specific stocks depending on the economic sentiment (Baker and Wurgler, 2006) are under certain conditions also present in the market for corporate debt.

scholarly journals Atrial High-Rate Event Incidence and Predictors in Patients With Permanent Pacemaker Implantation

2021 ◽  
Vol 8 ◽  
Author(s):  
Jian Hua Chen ◽  
Guo Yao Chen ◽  
Hong Zheng ◽  
Quan He Chen ◽  
Fa Yuan Fu ◽  
...  
Keyword(s):  
Cox Regression ◽  
Previous History ◽  
Pacemaker Implantation ◽  
Permanent Pacemaker ◽  
High Rate ◽  
Atrial Pacing ◽  
Patient Age ◽  
Cox Regression Analysis ◽  
Patient Âgé

Objective: The present study aims to investigate the incidence and predictors of atrial high-rate events (AHREs) in patients with permanent pacemaker implants.Methods: A total of 289 patients who were implanted with a dual-chamber pacemaker due to complete atrioventricular block or symptomatic sick sinus syndrome (SSS) and had no previous history of atrial fibrillation were included in the present study. AHREs are defined as events with an atrial frequency of ≥175 bpm and a duration of ≥5 min. The patients were divided into two groups according to whether or not AHREs were detected during the follow-up: group A (AHRE+, n = 91) and group N (AHRE–, n = 198).Results: During the 12-month follow-up period, AHREs were detected in 91 patients (31.5%). The multivariate Cox regression analysis revealed that patient age [odds ratio [OR] = 1.041; 95% confidence interval [CI], 1.018–1.064; and P &lt; 0.001], pacemaker implantation due to symptomatic SSS (OR = 2.225; 95% CI, 1.227–4.036; and P = 0.008), and the percentage of atrial pacing after pacemaker implantation (OR = 1.010; 95% CI, 1.002–1.017; and P = 0.016) were independent AHRE predictors.Conclusion: The AHRE detection rate in patients with pacemaker implants was 31.5%. Patient age, pacemaker implantation due to symptomatic SSS, and the percentage of atrial pacing after pacemaker implantation were independent AHRE predictors.

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