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PubMed2004

Lost in time, lonely, and single: reproductive asynchrony and the Allee effect.

Identifying linkages between life-history traits and small population processes is essential to effective multispecies conservation. Reproductive asynchrony, which occurs when individuals are reproductively active for only a portion of the population-level breeding period, may provide one such link. Traditionally, reproductive asynchrony has been considered from evolutionary perspectives as an advantageous bet-hedging strategy in temporally unpredictable environments. Here, we explore the dynamic consequences of reproductive asynchrony as a density-dependent life-history trait. To examine how asynchrony affects population growth rate and extinction risk, we used a general model of reproductive timing to quantify the temporal overlap of opposite-sex individuals and to simulate population dynamics over a range of initial densities and empirical estimates of reproductive asynchrony. We also considered how protandry, a sexually selected life-history strategy that often accompanies asynchrony, modulates the population-level effects of reproductive asynchrony. We found that asynchrony decreases the number of males a female overlaps with, decreases the average probability of mating per male/female pair that does overlap, and leaves some females completely isolated in time. This loss of reproductive potential, which is exacerbated by protandry, reduces population growth rate at low density and can lead to extinction via an Allee effect. Thus reproductive asynchrony and protandry, both of which can be evolutionarily advantageous at higher population densities, may prove detrimental when population density declines.

Animals↗
PubMed2006

DHLAS: A web-based information system for statistical genetic analysis of HLA population data.

DHLAS (database HLA system) is a user-friendly, web-based information system for the analysis of human leukocyte antigens (HLA) data from population studies. DHLAS has been developed using JAVA and the R system, it runs on a Java Virtual Machine and its user-interface is web-based powered by the servlet engine TOMCAT. It utilizes STRUTS, a Model-View-Controller framework and uses several GNU packages to perform several of its tasks. The database engine it relies upon for fast access is MySQL, but others can be used a well. The system estimates metrics, performs statistical testing and produces graphs required for HLA population studies: (i) Hardy-Weinberg equilibrium (calculated using both asymptotic and exact tests), (ii) genetics distances (Euclidian or Nei), (iii) phylogenetic trees using the unweighted pair group method with averages and neigbor-joining method, (iv) linkage disequilibrium (pairwise and overall, including variance estimations), (v) haplotype frequencies (estimate using the expectation-maximization algorithm) and (vi) discriminant analysis. The main merit of DHLAS is the incorporation of a database, thus, the data can be stored and manipulated along with integrated genetic data analysis procedures. In addition, it has an open architecture allowing the inclusion of other functions and procedures.

Databases, Genetic↗
PubMed1994

[Demographic statistics after the GBA Law is passed].

"The Dutch Ministry of Internal Affairs plans to replace the old written population systems on paper with a new system of decentralized automated population registers (in Dutch this system is called: GBA) on 1 October 1994.... In the summer of 1993 Statistics Netherlands carried out a test to find out whether the GBA messages are appropriate for making population statistics. To do this such messages were forwarded to Statistics Netherlands by five municipalities for three months. The conclusion of the test results was that the GBA system is technically adequate for making population statistics." (SUMMARY IN ENG)

Data Collection↗
PubMed1987

Spontaneous and induced interferon production by peripheral blood leucocytes from control population and patients with herpes genitalis.

The spontaneous and PHA induced levels of interferon were measured in peripheral blood leucocyte cultures of twenty-eight individuals diagnosed as positive for herpes genitalis, and in a group of control subjects. As reported by Cunningham and Merigan [1983] for herpes labialis, leucocytes from individuals with herpes genitalis produced low levels of interferon spontaneously; however, similar results were found for individuals within the control population. No statistically significant difference could be found for PHA induced interferon levels, antigen induced interferon levels, or helper/suppressor cell ratios between the herpes genitalis population and control population. Our results indicate that interferon does not play a major role in the latency or recurrence of herpes genitalis.

Antigens, Viral↗
PubMed2001

Heterogeneity and its biodemographic implications for longevity and mortality.

In the visible world, heterogeneity typically refers to the differences that exist among individuals in a defined population. These differences can arise from a variety of sources--biological, behavioral and social. Ever since Darwin, scientists have argued over the biological significance of differences observed at the individual, morphological, physiological, genetic, molecular and structural levels. A general consensus has been reached. Heterogeneity is ubiquitous, it is important, and it increases as observations are made at finer levels of biological resolution. Debates over the significance of heterogeneity have emerged once again as biologists and demographers work together in order to create the emerging field of biodemography. For these scientists, the debates center around the relative impact that individual heterogeneity has on population level statistics. It is argued here that in a world where the mortality barriers to long life for individuals have been dramatically weakened, the population consequences of heterogeneity are already visible and will grow in importance as biomedical technologies continue to usher progressively more people into the post-reproductive period of the lifespan.

Animals↗
PubMed2005

An empirical comparison of case-control and trio based study designs in high throughput association mapping.

Motivated by high throughput genotyping technology, our aim in this study was to experimentally compare the power and accuracy of case-control and family trio based approaches for haplotype based, large scale, association gene mapping. We compared trio based and case-control study designs in different disease models, and partitioned the performance differences into separate components: those from the sample ascertainment, the effective sample size, and the haplotyping approaches. For systematic and controlled tests, we simulated a rapidly expanding and relatively young isolated population. The experiments were also replicated with real asthma data. We used computationally efficient methods that scale up to large amounts of both markers and individuals. Mapping is based on a haplotype association test for haplotypes of 1-10 markers. For population based haplotype reconstruction, we use HaploRec, and compare it to both a simple trio based inference and true haplotypes. Firstly and surprisingly, statistically inferred population based haplotypes can be equally powerful as true haplotypes. Secondly, as expected, the effective sample size has a clear effect on both gene detection power and mapping accuracy. Thirdly, the sample ascertainment method does not have much effect on mapping accuracy. Finally, an interesting side result is that the simple haplotype association test clearly outperformed exhaustive allelic transmission disequilibrium tests. The results suggest that the case-control design is a powerful alternative to the more laborious family based ascertainment approach, especially for large datasets, and wherever population stratification can be controlled.

Algorithms↗
PubMed2001

Vitamin D status of women in the Geelong Osteoporosis Study: association with diet and casual exposure to sunlight.

OBJECTIVE: To assess vitamin D intake and casual exposure to sunshine in relation to serum 25-hydroxyvitamin D (25OHD) levels. DESIGN: Cross-sectional study of a population-based, random sample of women aged 20-92 years, assessed between 1994 and 1997. SETTING AND PARTICIPANTS: 861 women from the Barwon Statistical Division (population, 218000), which includes the city of Geelong (latitude 38 degrees south) in Victoria. MAIN OUTCOME MEASURES: Vitamin D intake; serum 25OHD level; season of assessment; exposure to sunshine. RESULTS: Median intake of vitamin D was 1.2 microg/day (range, 0.0-11.4 microg/day). Vitamin D supplements, taken by 7.9% of participants, increased intake by 8.1% to 1.3 microg/day (range, 0.0-101.2 microg/day) (P< 0.001). A dose-response relationship in serum 25OHD levels was observed for sunbathing frequency before and after adjusting for age (P< 0.05). During winter (May-October), serum 25OHD levels were dependent on vitamin D intake (partial r2= 0.01; P<0.05) and were lower than during summer (November-April) (age-adjusted mean, 59nmol/L [95% Cl, 57-62] v 81 nmol/L [95% CI, 78-84]; P<0.05). No association was detected between serum 25OHD and vitamin D intake during summer. The prevalences of low concentrations of serum 25OHD were, for <28nmol/L, 7.2% and 11.3% overall and in winter, respectively; and, for <50 nmol/L, 30.0% and 43.2% overall and in winter, respectively. CONCLUSIONS: At latitude 38 degrees south, the contribution of vitamin D from dietary sources appears to be insignificant during summer. However, during winter vitamin D status is influenced by dietary intake. Australia has no recommended dietary intake (RDI) for vitamin D, in the belief that adequate vitamin D can be obtained from solar irradiation alone. Our results suggest that an RDI may be needed.

Adult↗
PubMed2001

[Mortality in patients with affective disorder who commenced treatment with lithium. A 16-year follow-up].

INTRODUCTION: Lithium treatment is claimed to reduce mortality in patients with affective disorder, but the evidence is conflicting. The aim of this study was to estimate mortality rates from a cohort of such patients, who commenced treatment with lithium, over an observation period of 16 years. MATERIAL AND METHODS: The mortality rates of affectively ill patients, who commenced lithium treatment, were compared with the mortality rates in the general Danish population, standardised for age, sex, and a time to death from all causes, suicide, and cardiovascular death. Comparison of the time from a two-year follow-up to death from any cause between patients compliant and non-compliant with two years of lithium treatment was performed with the Cox regression analysis. RESULTS: Forty of the 133 patients who participated in the study died during the 16-year observational period; 11 from suicide. Mortality in the patients was twice that of the background population. This statistically significantly higher mortality was predominantly caused by the number of suicides, whereas mortality from all other causes was similar to the background population. Thirty-two patients died after the first two years of observation and were included in the analysis of association between death and two years of compliance with lithium. Suicide occurred more frequently in the lithium non-compliant patients than in the lithium compliant patients. DISCUSSION: Mortality, particularly death from suicide, was significantly increased in unselected affective disorder patients, who commenced lithium treatment, as compared with the background population.

Adolescent↗
PubMed1997

Chronic disability trends in elderly United States populations: 1982-1994.

Statistically significant declines in chronic disability prevalence rates were observed in the elderly United States population between the 1982 and 1989 National Long Term Care Surveys (NLTCS). The 1994 NLTCS was used to investigate whether disability rate declines continued to 1994. The 1982, 1984, 1989, and 1994 NLTCS employ the same sample design and instrumentation so that trends in disability can be estimated with minimal sampling and measurement bias. Age (5-year categories from 65 to >95)-specific rates were calculated for the 1982 NLTCS and applied to United States Census Bureau estimates of the 1994 population to calculate chronic disability prevalence rates adjusted for aging in the United States population aged > 65. The 1982 age standardized rates were compared with 1994 NLTCS estimates. The prevalence of disability estimated for 1994 (21.3%) was 3.6% lower than the 1982 age standardized rate (24.9%)-a highly significant reduction (t = -8.5; P << 0.0001). Of the 3.6 percentage point decline in prevalence, 1.7% occurred in the 5 years between 1989 and 1994-compared with the 1.9% decline in the 7 years between 1982 and 1989. Both declines are significant. Because of the shorter time period, the per year decline in disability prevalence from 1989 to 1994 was greater than that from 1982 to 1989. Given the higher acute and long-term care service needs of the disabled elderly population, Medicare, Medicaid, and private health expenditures may be dramatically lower than if declines had not occurred.

Activities of Daily Living↗
PubMed1998

Migration dynamics and development in rural South Africa: demographic and socioeconomic perspectives.

"This paper addresses five key questions related to migration dynamics and development in rural South Africa: (1) Which individual and household level factors are particularly important in understanding migration patterns? (2) Taken together, are sociodemographic or socioeconomic factors more influential? (3) Do present patterns of migration and remittance flows reflect strategies that connote survival, or do they represent household efforts to advance their well-being and their position in society? (4) Which segments of the population appear to gain or lose from contemporary patterns of migration and remittance flows? and (5) How might remittances shape trends in local level development and equality, or inequality?... The data source is the nationwide representative sample survey ¿Project for Statistics on Living Standards and Development' undertaken in the latter part of 1993."

Africa↗
PubMedDate not supplied

[Estimation of infant and child mortality in the eastern provinces of Cuba].

An estimate of infant and child mortality in the eastern provinces of Cuba is presented using the Brass method as adapted by Trussell. "Estimations by urban and rural zones are also performed within the provinces studied, and results are compared with those possible to obtain by continuous statistics. Results obtained show that in the eastern [part] of the country Holguin and Guantanamo are the provinces with highest infantile mortality rates, and the lowest rates correspond to Granma, followed by Santiago de Cuba." (SUMMARY IN ENG AND FRE)

Americas↗
PubMedDate not supplied

[Superoxide dismutase and catalase levels in diseases of the aged].

UNLABELLED: Superoxide dismutase (SOD) and catalase (CAT) activities were measured in blood from 420 individuals: control population 126, males and females, age between 50 to 93 years of age without any relevant pathology. Pathological population: 294 patients, males and females, age between 50 to 93 years of age, with some disease in the cardiovascular system and in the osteoarticular system, myoma, prostatic pathologies, Chronic Obstructive Pulmonary Disease (EPOC), and Acute Cerebral Vascular Accident (ACVA). The method of Minami and Yoshikawa (SOD) and the method of Aebi (CAT) were judged the techniques of choice for a population study. STATISTICAL METHODS: ANOVA and Student's "t". 1) The results were that levels of activity for SOD and CAT were increased for women in control population, and 2) the level of activity for CAT decreases with aging. In the pathological population, we detected: 3) increased activity for SOD in cardiovascular diseases, myomas, EPOC and ACVA. 4) for CAT the level of activity decreases in cardiovascular and prostatic diseases, EPOC and ACVA. 5) while in osteoarticular diseases levels of activity for SOD and CAT were standard, but SOD level decreases with aging, for CAT in cardiovascular diseases and EPOC, too. Both enzymes work to balance the antioxidant system.

Age Factors↗
PubMed1989

Successful invasion of a food web in a chemostat.

A food web in a chemostat is considered in which an arbitrary number of competitor populations compete for a single, essential, nonreproducing, growth-limiting substrate, and an arbitrary number of predator populations prey on some or all of the competitor populations. Although any number of predator populations may prey on the same competitor population, each predator population preys on only one competitor population. The dynamics of substrate uptake is modeled by Lotka-Volterra or Michaelis-Menten (Holling type I or II), but the dynamics of competitor uptake is restricted to Lotka-Volterra. Based on certain parameters, the model predicts the asymptotic survival or extinction of each of the different populations and suggests how competitor and/or predator populations could successfully invade the chemostat with or without causing a diverse ecosystem to crash. Similarly, it suggests how the elimination of certain populations could result in a more diverse or less diverse system.

Bacteria↗
PubMed1994

Some discrete-time SI, SIR, and SIS epidemic models.

Discrete-time models, or difference equations, of some well-known SI, SIR, and SIS epidemic models are considered. The discrete-time SI and SIR models give rise to systems of nonlinear difference equations that are similar in behavior to their continuous analogues under the natural restriction that solutions to the discrete-time models be positive. It is important that the entire system be considered since the difference equation for infectives I in an SI model has a logistic form which can exhibit period-doubling and chaos for certain parameter values. Under the restriction that S and I be positive, these parameter values are excluded. In the case of a discrete SIS model, positivity of solutions is not enough to guarantee asymptotic convergence to an equilibrium value (as in the case of the continuous model). The positive feedback from the infective class to the susceptible class allows for more diverse behavior in the discrete model. Period-doubling and chaotic behavior is possible for some parameter values. In addition, if births and deaths are included in the SI and SIR models (positive feedback due to births) the discrete models exhibit periodicity and chaos for some parameter values. Single-population and multi-population, discrete-time epidemic models are analyzed.

Epidemiologic Methods↗
PubMed1990

Controlling for time-varying population distributions in disease clustering studies.

Both the Knox test and the Mantel test for the presence of disease clustering have previously been shown to be sensitive to changes that occur in the relative geographic population distribution during the time period of study. Although these procedures do not require knowledge of the underlying population density, they implicitly assume it is constant with time. If this is not the case, one may detect clustering which is completely independent of the disease process and simply reflects time-space clustering of the population. Modified procedures are presented which incorporate information from appropriately selected controls to adjust for the effect of a shifting population. Results of a computer simulation study demonstrating the stability of the modified tests in the face of an expanding population are reported.

Cluster Analysis↗
PubMed2006

Measurement error in a random walk model with applications to population dynamics.

Population abundances are rarely, if ever, known. Instead, they are estimated with some amount of uncertainty. The resulting measurement error has its consequences on subsequent analyses that model population dynamics and estimate probabilities about abundances at future points in time. This article addresses some outstanding questions on the consequences of measurement error in one such dynamic model, the random walk with drift model, and proposes some new ways to correct for measurement error. We present a broad and realistic class of measurement error models that allows both heteroskedasticity and possible correlation in the measurement errors, and we provide analytical results about the biases of estimators that ignore the measurement error. Our new estimators include both method of moments estimators and "pseudo"-estimators that proceed from both observed estimates of population abundance and estimates of parameters in the measurement error model. We derive the asymptotic properties of our methods and existing methods, and we compare their finite-sample performance with a simulation experiment. We also examine the practical implications of the methods by using them to analyze two existing population dynamics data sets.

Animals↗