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PubMed1987

Multiregional two-sex population model.

"The theory of stable population has been developed quite thoroughly in the demographic literature, but it deals with single-region populations that are assumed to be undisturbed by migration. Rogers...proposed the stable population model for the case of a multiregional population that experiences internal migration for single-sex. In this paper, considering a birth-function dependent on both sexes, the multiregional stable population model is extended for two-sex population."

Demography↗
PubMed1986

The rare-disease assumption revisited. A critique of "estimators of relative risk for case-control studies".

The extension of case-control methods to the study of common outcomes has led to the development of several design and analysis techniques which do not employ the rare-disease assumption. Unfortunately, the principles underlying valid application of these techniques are more subtle than those first considered by Cornfield in the rare-disease setting, and appear to be easily misunderstood. We especially wish to caution that: The unrestricted inclusion of prevalent cases in the control group (as described by Hogue et al. for estimation of the risk ratio) will not make the odds ratio an unbiased estimate of the risk ratio (or anything else). In their response to our article, following, Hogue et al. describe restrictions on prevalence and duration necessary for the odds ratio from a case-exposure design to unbiasedly estimate the risk ratio in a stable population; these conditions were not mentioned in their original article, and in their new paper Hogue et al. do not provide mathematical proof that the conditions are sufficient to guarantee unbiasedness. Exclusion ("decontamination") of incident cases from the control group (as recommended by Hogue et al. for testing and test-based interval estimation) will result in improperly narrow risk-ratio confidence intervals whether or not the population is stable, and, in unstable populations, will generally lead to an invalid test. Methods that replace the rare-disease assumption with the stable-population assumption (such as case-exposure designs applied to open populations) will not yield unbiased results when the source population is a fixed cohort. (Of course, this will not be an issue for methods that are not based on either assumption, such as the case-base design applied to fixed cohorts, and the matched density design.) As each case-control design has certain practical implications for selection and interviewing, in choosing a design one should carefully consider practical issues (such as vulnerability to recall bias and ease of control selection) in addition to the statistical issues discussed here. In general, however, one should be wary of methods of studying incidence that involve the use of prevalent cases (such as the approach of Hogue et al.): prevalence is influenced by factors related to treatment, recovery, and fatality, and thus any etiologic study employing prevalent cases may be biased by such factors.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2005

Xanthomonas axonopodis pv. phaseoli var. fuscans is aggregated in stable biofilm population sizes in the phyllosphere of field-grown beans.

The occurrence of "Xanthomonas axonopodis pv. phaseoli var. fuscans" (proposed name) populations as biofilms on bean leaves was investigated during three field experiments on plots established with naturally contaminated bean seeds. Behavior of aggregated versus solitary populations was determined by quantification of culturable cells in different fractions of the epiphytic population separated by particle size. X. axonopodis pv. phaseoli var. fuscans population dynamic studies confirmed an asymptomatic and epiphytic colonization of the bean phyllosphere. For all years of experiment and cultivars tested, biofilms and solitary components of the populations were always detected. Biofilm population sizes remained stable throughout the growing season (around 10(5) CFU/g of fresh weight) while solitary population sizes were more abundant and varied with climate. According to enterobacterial repetitive intergenic consensus fingerprinting, aggregated bacterial isolates were not different from solitary isolates. In controlled conditions, application of a hydric stress resulted in a decrease of the solitary populations on the leaf surface while the biofilm fraction remained stable. Suppression of the hydric stress allowed solitary bacterial populations to increase again. Aggregation in biofilms on leaf surfaces provides protection to the bacterial cells against hydric stress.

Agriculture↗
PubMed1978

Effects of DDT on stable laboratory mouse populations.

Four stable laboratory mouse populations were established; each contained approximately 400 mice of both sexes and all ages postweaning living in a single cage, as well as neonates caged in separate nesting boxes with their dams. Two were used to determine the effects of continuous exposure to a dietary level of 100 ppm DDT while the other two served as controls. The results indicated a significant decrease (p less than or equal to 0.05) in neonatal survival (lactation index) within 20 wk after the beginning of exposure to the toxicant in one of the exposed populations and by 30 wk in the other. This deleterious effect of the DDT continued through each succeeding generation. On the other hand, improved postweaning survival in DDT-fed mice was noted. Histological examination showed no tumors in test or control animals; other pathology was seen more frequently in control than in test animals.

Animals↗
PubMed1989

Malaysian schistosomiasis: description of a population at risk.

A stable population at risk of Malaysian schistosomiasis was studied. Census results indicated that approximately one-fourth of the inhabitants used a stream where Schistosoma malayensis-infected snails were present as their principal source of water for bathing, drinking, and household tasks. The general population also contacted this stream when fording it or while fishing. Serological surveys using enzyme-linked immunosorbent assay (ELISA) and the circumoval precipitin (COP) test revealed six (9%) and three (4%) positives, respectively, among 67 persons examined. No schistosome ova were found in a general survey of 56 persons which included five ELISA positive and two COP test positive patients. ELISA and COP test prevalences among those dependent on the foci of transmission for water, 13 and 7% respectively, were only slightly higher than prevalences among the remainder of the population, 8 and 4% respectively. These results indicate that even among a stable population at risk of Malaysian schistosomiasis the prevalence is low. Our findings support the hypothesis that S. malayensis is a zoonotic infection in man and that it is unlikely to become a significant public health problem.

Adolescent↗
PubMed1973

Gastrointestinal nematode populations in stabled ewes of Rimouski region.

Nematode populations is stabled ewes of the Rimouski region were studied by means of fecal worm egg counts, fecal culture of larvae, and worm counts at necropsy. It was found that during the winter strongyle egg counts were low, Trichostrongylus eggs being most numerous, The stronglye egg counts increased following lambing and reached peak in June. Ostertagia spp was the principal contributor to this "spring-rise", with substantial contribution from Trichostrongylus and Haemonchus contortus. The bulk of adult worm populations in winter, however, was made up of Trichostrongylus, whereas the great majority of the populations of Ostertagia spp, H. contortus and Nematodirus spp were inhibited in development at the fourth larval stage. All the worms recovered at necropsy in spring were adults, coinciding with the "spring-rise".

Animals↗
PubMed1993

[Stable multiregional population as a tool for economic analysis. An application to Italy, 1977-1986].

"The intensity of short-term fluctuations in a population's demographic behaviour is often overshadowed by a force of inertia resulting from the structures inherited from past behaviour. Stable population theory produces an effective way to eliminate this 'weight of the past'. This article presents the results of an application of this approach in analyzing changes in the fertility, migration and mortality regime of the Italian population during the 1977-1986 period." (SUMMARY IN ENG AND SPA)

Demography↗
PubMed1998

Ontogenetic alteration in peptidergic expression within a stable neuronal population in lobster stomatogastric nervous system.

In the adult lobster, Homarus gammarus, the stomatogastric ganglion (STG) contains two well-defined motor pattern generating networks that receive numerous modulatory peptidergic inputs from anterior ganglia. We are studying the appearance of extrinsic peptidergic inputs to these networks during ontogenesis. Neuron counts indicate that as early as 20% of development (E20) the STG neuronal population is quantitatively established. By using immunocytochemical detection of 5-bromo-2'-deoxyuridine incorporation, we found no immunopositive cells in the STG by E70. We concluded that the STG neuronal population remains quantitatively stable from mid-embryonic life until adulthood. We then investigated the ontogeny of FLRFamide- and proctolin-like peptides in the stomatogastric nervous system, from their first appearance until adulthood by using whole mount immunocytochemistry. Numerous FLRFamide-like-immunoreactive STG neuropilar ramifications were observable as early as E45 and remain thereafter. From E50 to the first larval stage, one to three STG somata stained, while somatic staining was not observed in larval stage II and subsequent stages. From E50 and thereafter, the STG neuropilar area was immunopositive for proctolin. One to two proctolinergic somata were detected in the STG of the three larval stages but were not seen in embryos, the post-larval stage or in adults. Thus, peptidergic inputs to the STG are present from mid-embryonic life. Moreover, whereas in the adult, STG neurons only contain glutamate or acetylcholine, some neurons transiently express peptidergic phenotypes during development. Although this system expresses an ontogenetic peptidergic plasticity, the STG neurons produce a single stable embryonic-larval motor output (Casasnovas and Meyrand [1995] J. Neurosci. 15:5703-5718).

Animals↗
PubMed1996

The development and use of demographic models.

In this review, we first examine two classical demographic models - conventional life tables and stable populations - and a modern generalization of stable population theory; we then discuss mathematical models of conception and birth. These models involve purely mathematical relations in formal demography as opposed to empirical regularities. Next we consider model age schedules of mortality, nuptialitiy, marital fertility, fertility, and migration that are explicitly based on such empirical patterns. We close this empirical section with a discussion of model stable populations, which are based on model life tables. We next examine the use of demographic models in forecasting future mortality, nuptiality, and fertility and in population projection. Following a discussion of microsimulation models, which gives us the opportunity to mention model age schedules of post partum amenorrhoea and of sterility, we close with observations about the purposes and uses of demographic models.

Demography↗
PubMed1977

The stable equivalent population, age composition, and Fisher's reproductive value function.

This paper deals with a further analysis of the stable equivalent population for human populations. It first shows that the arithmetic difference between the size of the stable equivalent population and the actual population captures the total prospective contribution of age composition to the growth of the present population" if fertility and mortality rates are held constant at their current levels. The second part of the paper examined Fisher's reproductive value function and investigates the location of maxima in relation to alternative values of the intrinsic growth rate. One conclusion which follows from this analysis is that, contrary to what has been discovered by others in specific examples, the reproductive value function can possess a global maximum in the first one or two years of life, provided the intrinsic rate of population growth is sufficiently negative. This principle is illustrated by reference to reproductive value functions calculated from the recent experience of U.S. females.

Adolescent↗
PubMed1997

Plasma haptoglobin levels in threatened Alaskan pinniped populations.

We evaluated the plasma concentration of the acute phase protein haptoglobin (Hp) from Steller sea lions (Eumetopias jubatus) and harbor seals (Phoca vitulina) in regions of Alaska (USA) where the populations of these pinnipeds were declining and compared the values with concentrations of Hp from the same species in areas where the populations were stable. Samples were collected from 1992 through 1994 at sites in Southeast Alaska, Prince William Sound, the Gulf of Alaska, and the Aleutian Islands. Significantly higher levels of Hp were found in the samples from the areas of decline compared to those from stable populations. Based on these findings, we propose that one may be able to distinguish these compromised pinniped populations using Hp as a biomedical indicator.

Alaska↗
PubMed1976

Influence of instantaneous fertility decline to replacement level on population growth: an alternative model.

If age-specific birth rate mx of a stable population drop abruptly to mx/Ro, where Ro is the net reproduction rate, then, according to Keyfitz, the size of the ultimate stationary population relative to that at the beginning of the process is given by I = beoo(Ro - 1)/(rmuRo), where b and r are the birth rate and the rate of growth, respectively, of the stable population, eoo the life expectancy at birth, and mu the average age at childbirth in resulting stationary population. Noting that the decline in mx need not necessarily be uniform, investigation has veen carried out to examine the effect on I when fertility decline is more rapid at higher ages. In particular, the effect of the reduced age-specific rates such as mxe-rx (which also produces a stationary population) has been analyzed, and simplifications of the results carried out separately for three different models of the net maternity function. It has also been shown the when mx drops abruptly to some m* x, where the form of m*x need not be specified except for the restriction that the resulting population will be stationary, the value of the index can be approximately obtained from I* = beoo (1 - rmu/2), where mu is the average age at childbearing of theinitial stable population.

Birth Rate↗
PubMed2000

High genetic variation in leopards indicates large and long-term stable effective population size.

In this paper we employ recently developed statistical and molecular tools to analyse the population history of the Tanzanian leopard (Panthera pardus), a large solitary felid. Because of their solitary lifestyle little is known of their past or present population dynamics. Eighty-one individuals were scored at 18 microsatellite loci. Overall, levels of heterozygosity were high (0.77 +/- 0.03), with a small heterozygote deficiency (0.06 +/- 0.03). Effective population size (Ne) was calculated to be 38 000-48 000. A Ne:N ratio of 0.42 (average from four cat studies) gives a present population size of about 100 000 leopards in Tanzania. Four different bottleneck tests indicated that this population has been large and stable for a minimum of several thousand years. FST values were low and no significant genetic structuring of the population could be detected. This concurs well with the large migration values (Nm) obtained (>3.3 individuals/generation). Our analysis reveals that ecological factors (e.g. disease), which are known to have had major impact on other carnivore populations, are unlikely to have impacted strongly on the population dynamics of Tanzanian leopards. The explanation may be found in their solitary life-style, their often nonconfrontational behaviour toward interspecific competitors, or that any bottlenecks have been of limited size, localized, or too short to have affected genetic variation to any measurable degree. Since the genetic structuring is weak, gene flow is not restricted to within protected areas. Local loss of genetic variation is therefore not of immediate concern.

Alleles↗
PubMed1998

Health status of young Alaska Steller sea lion pups (Eumetopias jubatus) as indicated by blood chemistry and hematology.

Blood chemistry and hematology were examined in 238 Steller sea lion pups (Eumetopias jubatus) to assess the health status of pups <1 month of age. Failure of juvenile recruitment (possibly due to nutritionally or physiologically compromised pups) into breeding populations has been proposed as a cause of recent declines of this endangered species in Alaska. To identify potential correlations with areas of high population decline, blood chemistry data were considered for three areas: eastern Aleutian Islands (low rates of population decline to stable populations), Gulf of Alaska (high rates of decline), and Southeast Alaska (stable to increasing population). Southeast Alaska pups showed elevated ketone body concentrations (beta-hydroxybutyrate,(beta-HBA)) and depressed glucose levels than pups in the Gulf of Alaska. Over 40% of the pups from Southeast Alaska had elevated beta-HBA concentrations suggesting they underwent longer periods of fasting than seen in pups from other areas. Hematocrit (Hct), hemoglobin concentration (Hb) and water content of the blood exhibited typical mammalian relationships. In summary, blood chemistry and hematology data showed no indication that Steller sea lion pups <1 month old from areas of population decline were nutritionally compromised.

Age Distribution↗
PubMed1984

About Laplace transforms of the distribution of births in the initial population with unchanging net maternity rates.

"The solutions of the integral equation for the stable population by Laplace transform have been examined by shifting the origin from t=0 to other points in time. The relationship between the birth functions generated by the initial populations measured from different points of time has been found to be very simple and straight forward." The author also shows "that for a stable population, the total number of births in the next generation can be expressed as a simple function of the net reproduction rate, the intrinsic rate of growth and number of births at the beginning of the process. For the stationary population, the same relationship simplifies even further and is given in terms of the product of the number of births at the beginning of the process and the average age of motherhood."

Age Factors↗
PubMed1989

Lead concentrations in human bones from the Canadian population.

Stable lead was determined in post-mortem samples of human bones from three Canadian cities. All age groups and both sexes were represented. The cities selected for investigation were Winnipeg, Montreal and Charlottetown. No significant difference was found between the locations, although levels tended to be higher for Montreal. Mean lead concentrations (micrograms Pb/g ash) were 8.98 +/- 1.17, 11.11 +/- 1.74 and 8.47 +/- 1.06 for Winnipeg, Montreal and Charlottetown, respectively. Corresponding geometric means were 6.21, 7.88 and 6.71, respectively. Individual values ranged from 0.45 to 240.07 micrograms Pb/g ash. Concentrations were highest in the greater than 20-year age group, indicating increased body burden with age. An increase in lead concentration was observed for the ages 1-11 years with a decrease for the 12-19-year age group. Differences in concentrations between the sexes were not significant. Higher than average concentrations were observed in samples obtained from Winnipeg for the period 1976-1980, particularly in the 1-4-year age group. A similar pattern was observed in the air lead concentrations, suggesting a possible correlation between the concentrations of lead in the air and in bones at Winnipeg.

Age Factors↗
PubMed1996

Measuring population aging as a function of fertility, mortality, and migration.

Researchers often describe population aging with measures such as proportion of population under 15 years of age, proportion of population 65 years and over, the aged/child ratio (a ratio of the first two measures), median age, and mean age. Investigators of cross-cultural gerontology, too, use such measures to compare population aging between populations. While insights from comparing only the values of an aging measure between two populations may be helpful, results from such comparison can be misleading due to the influences of fertility, mortality, and migration. To show the effects of these demographic processes on measures of population aging, rates of change in five measures of population aging as a function of fertility, mortality, and migration are developed. These rates of change are estimated for various stable populations, for stable populations disequilibrated by fertility and mortality declines and by net migration, and for the population in Japan, 1988-1989. The findings demonstrate that the five aging measures, in general, do not give consistent rate-of-change estimates; they also suggest that directly comparing values of aging measures without considering the levels and patterns of fertility, mortality, and migration will lead to misleading conclusions.

Asia↗
PubMed1996

Localization of HIV-1 RNA in mammalian nuclei.

The Rev protein of human immunodeficiency virus type 1 (HIV-1) facilitates the nuclear export of unspliced and partially spliced viral RNAs. In the absence of Rev, these intron-containing HIV-1 RNAs are retained in the nucleus. The basis for nuclear retention is unclear and is an important aspect of Rev regulation. Here we use in situ hybridization and digital imaging microscopy to examine the intranuclear distributions of intron-containing HIV RNAs and to determine their spatial relationships to intranuclear structures. HeLa cells were transfected with an HIV-1 expression vector, and viral transcripts were localized using oligonucleotide probes specific for the unspliced or spliced forms of a particular viral RNA. In the absence of Rev, the unspliced viral RNAs were predominantly nuclear and had two distinct distributions. First, a population of viral transcripts was distributed as approximately 10-20 intranuclear punctate signals. Actinomycin D chase experiments indicate that these signals represent nascent transcripts. A second, stable population of viral transcripts was dispersed throughout the nucleoplasm excluding nucleoli. Rev promoted the export of this stable population of viral RNAs to the cytoplasm in a time-dependent fashion. Significantly, the distributions of neither the nascent nor the stable populations of viral RNAs coincided with intranuclear speckles in which splicing factors are enriched. Using splice-junction-specific probes, splicing of human beta-globin pre-mRNA occurred cotranscriptionally, whereas splicing of HIV-1 pre-mRNA did not. Taken together, our results indicate that the nucleolus and intranuclear speckles are not involved in Rev regulation, and provide further evidence that efficient splicing signals are critical for cotranscriptional splicing.

Biological Transport↗