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PubMed1994

Clustering of human T lymphotropic virus type I seropositive in Montserrat, West Indies: evidence for an environmental factor in transmission of the virus.

A community survey of human T cell lymphotropic virus type I (HTLV-I) in Montserrat, West Indies, identified 22 instances in which 2 HTLV-I-seropositive adults lived within 60 m of each other (close pairs), compared with 7.8 expected (P < .001). Five of these close pairs were mother-offspring or husband-wife. The remaining 17 pairs were of unrelated members in separate households. The percentages of male-female (41%), female-female (41%), and male-male (18%) types in these 17 pairs were very similar to those among the 1377 similarly defined pairs in which neither or only 1 member was seropositive, affording no support for extramarital heterosexual activity as an explanation for the clustering observed. Thus, the demography of HTLV-I was not accounted for completely by sexual and mother-to-offspring transmission. The predominance of clustering of unrelated HTLV-I-seropositive individuals in locations with high mosquito infestation raised the possibility of sporadic transmission of HTLV-I by hematophagous insects.

Adolescent↗
PubMed2006

Estimation of effective population size for the long-lived darkblotched rockfish Sebastes crameri.

We report the variance effective population size (Ne) in darkblotched rockfish (Sebastes crameri) utilizing the temporal method for overlapping generations, which requires a combination of age-specific demography and genetic information from cohorts. Following calculations of age-specific survival and reproductive success from fishery data, we genotyped a sample (n = 1087) comprised by 6 cohorts (from 1995 to 2000) across 7 microsatellite loci. Our Ne estimate (Ne) plus 95% confidence interval was (Ne) = 9157 [6495-12 215], showing that the breeding population number could be 3-4 orders of magnitude smaller than the census population size (N) = 24 376 210). Our estimates resemble closely those found for fishes with similar life history, suggesting that the small (Ne)/(N) ratio for S. crameri is most likely explained by a combination of high variance in reproductive success among individuals, genetic structure, and demographic perturbations such as historical fishing. Because small (Ne)/(N) ratios have been commonly associated with potential loss of genetic variation, our estimates need careful consideration in rockfish management and conservation.

Animals↗
PubMed1993

Premature mortality related to AIDS among men and women in Catalonia.

OBJECTIVES: To evaluate the mortality pattern observed in relation to the AIDS epidemic, and to estimate the current and future demographic impact of AIDS among the population aged between 20 and 39 years in Catalonia, Spain. DESIGN: Spain has the highest cumulative incidence rate of AIDS in Europe. One-third of Spanish AIDS cases have been consistently reported from Catalonia, an autonomous region in northeastern Spain with a population of 6 million, and with Pattern I HIV transmission. In this study data from the population-based AIDS registry and death certificates in Catalonia were used. METHODS: Since 1981 AIDS data have been collected routinely from all hospitals using an active surveillance system. All causes of death are coded from death certificates (ICD-9). Mortality rates since 1981 were analysed by age and sex. To assess the relative importance of premature mortality due to AIDS, years of potential life lost (YPLL) before age 65 were used. RESULTS: Since 1982 there has been a continuous increase in crude mortality rates, particularly significant for men aged 20-39 years after 1986 (F < 0.001). While AIDS was the fourth most likely cause of death among people aged 20-39 years in 1988, by 1991 it was the second most likely. In 1990 AIDS contributed to 13,213 YPLL (8.7%) for men and 2579 YPLL (4%) for women. During the last few years AIDS-related deaths have had the highest mortality rate progression among young adults. CONCLUSION: According to the current available data, AIDS might become the leading cause of death for the population aged 20-39 years in the near future. AIDS is having an important impact on the demography of European countries with Pattern I transmission and high HIV prevalence rates.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Evans syndrome: results of a national survey.

PURPOSE: Our goal was to improve the management of Evans Syndrome, an uncommon and frequently refractory condition. We conducted a retrospective survey to assess the demography, presentation, clinical course, and treatment response of affected children. PATIENTS AND METHODS: Information was analyzed from a detailed questionnaire completed by pediatric hematologists mainly in the U.S. and Canada. We sought information regarding demographics, findings at presentation, approach to diagnosis, treatments used (with specific reference to splenectomy, corticosteroids, and intravenous immunoglobulin (IVIG)), course of the disease with emphasis on recurrences, and status at last follow-up. RESULTS: Forty-two patients (22 male, 20 female) were included in the study. The median age was 7.7 years (range 0.2-26.6 years). At presentation, thrombocytopenia (32 patients) and anemia (28) were common; neutropenia occurred in 10 and pancytopenia in 6. Patients received a median of 5 (range 0-12) modalities of treatment. Courses of IVIG and corticosteroids were given to almost all patients; responses were varied but the effects lasted as long as 2 years. Splenectomy was performed for 15 patients but the median duration of response was only 1 month. Other treatments included cyclosporine, vincristine, danazol, azathioprine, cyclophosphamide, and plasmapheresis. The course of the disease was characterized by recurrent thrombocytopenia, hemolytic anemia, and neutropenia. After a median follow-up of 3 years, 3 patients had died, 20 had active disease on treatment, 5 had persistent disease (not on treatment), and 14 had no evidence of disease. CONCLUSION: Evans syndrome is a chronic and recurrent condition which is often refractory to IVIG, corticosteroids, and splenectomy. Responses to other agents have been anecdotal and inconclusive. A prospective study involving these agents is needed to determine optimal therapeutic combinations.

Adolescent↗
PubMed2004

Evolution of size-dependent flowering in a variable environment: partitioning the effects of fluctuating selection.

In a stochastic environment, two distinct processes, namely nonlinear averaging and non-equilibrium dynamics, influence fitness. We develop methods for decomposing the effects of temporal variation in demography into contributions from nonlinear averaging and non-equilibrium dynamics. We illustrate the approach using Carlina vulgaris, a monocarpic species in which recruitment, growth and survival all vary from year to year. In Carlina the absolute effect of temporal variation on the evolutionarily stable flowering strategy is substantial (ca. 50% of the evolutionarily stable flowering size) but the net effect is much smaller (ca. 10%) because the effects of temporal variation do not influence the evolutionarily stable strategy in the same direction.

Analysis of Variance↗
PubMed2005

Evidence of a shift in the cyclicity of Antarctic seabird dynamics linked to climate.

Ecosystems and populations are known to be influenced not only by long-term climatic trends, but also by other short-term climatic modes, such as interannual and decadal-scale variabilities. Because interactions between climatic forcing, biotic and abiotic components of ecosystems are subtle and complex, analysis of long-term series of both biological and physical factors is essential to understanding these interactions. Here, we apply a wavelet analysis simultaneously to long-term datasets on the environment and on the populations and breeding success of three Antarctic seabirds (southern fulmar, snow petrel, emperor penguin) breeding in Terre Adélie, to study the effects of climate fluctuations on Antarctic marine ecosystems. We show that over the past 40 years, populations and demographic parameters of the three species fluctuate with a periodicity of 3-5 years that was also detected in sea-ice extent and the Southern Oscillation Index. Although the major periodicity of these interannual fluctuations is not common to different species and environmental variables, their cyclic characteristics reveal a significant change since 1980. Moreover, sliding-correlation analysis highlighted the relationships between environmental variables and the demography of the three species, with important change of correlation occurring between the end of the 1970s and the beginning of the 1980s. These results suggest that a regime shift has probably occurred during this period, significantly affecting the Antarctic ecosystem, but with contrasted effects on the three species.

Animals↗
PubMed1986

Mitochondrial DNA and the evolutionary genetics of higher animals.

Mitochondrial DNA (mtDNA) in higher animals is rapidly becoming a well characterized genetic system at the molecular level. In this paper, I shift the focus to consider questions in organismal evolution that can be addressed by mtDNA assay. For the first time, it is possible to estimate empirically matriarchal phylogeny; to determine directionality in crosses producing hybrids; and to study the population genetic consequences of varying female demographies and life histories. The data obtainable from mtDNA may be especially well suited for studies of population genetic structure, dispersal, and historical zoogeography. The female-mediated, clonal transmission of mtDNA is also stimulating new ways of thinking about times to common ancestry of asexual lineages within otherwise sexually reproducing populations; about the possible relevance of mtDNA-nuclear DNA interactions to reproductive isolation; and about the very meaning of the phylogenetic status of related species with respect to particular kinds of genetic characters. These and other topics are reviewed.

Animals↗
PubMed1999

Population dynamics of scrapie in a sheep flock.

A detailed analysis of an outbreak of natural scrapie in a flock of Cheviot sheep is described. A total of 137 cases was reported over 13 years among 1307 sheep born into the flock. The epidemiology of scrapie can only be understood with reference to sheep demography, the population genetics of susceptibility to scrapie, pathogenesis during a long incubation period, and the rate of transmission (by both vertical and horizontal routes), all of which interact in complex ways. A mathematical model incorporating these features is described, parameter values and model inputs are derived from available information from the flock and from independent sources, and model outputs are compared with the field data. The model is able to reproduce key features of the outbreak, including its long duration and the ages of cases. The analysis supports earlier work suggesting that many infected sheep do not survive to show clinical signs, that most cases arise through horizontal transmission, and that there is strong selection against susceptible genotypes. However, important aspects of scrapie epidemiology remain poorly understood, including the possible role of carrier genotypes and of an environmental reservoir of infectivity, and the mechanisms maintaining alleles giving susceptibility to scrapie in the sheep population.

Alleles↗
PubMed2002

Population growth rate and its determinants: an overview.

We argue that population growth rate is the key unifying variable linking the various facets of population ecology. The importance of population growth rate lies partly in its central role in forecasting future population trends; indeed if the form of density dependence were constant and known, then the future population dynamics could to some degree be predicted. We argue that population growth rate is also central to our understanding of environmental stress: environmental stressors should be defined as factors which when first applied to a population reduce population growth rate. The joint action of such stressors determines an organism's ecological niche, which should be defined as the set of environmental conditions where population growth rate is greater than zero (where population growth rate = r = log(e)(N(t+1)/N(t))). While environmental stressors have negative effects on population growth rate, the same is true of population density, the case of negative linear effects corresponding to the well-known logistic equation. Following Sinclair, we recognize population regulation as occurring when population growth rate is negatively density dependent. Surprisingly, given its fundamental importance in population ecology, only 25 studies were discovered in the literature in which population growth rate has been plotted against population density. In 12 of these the effects of density were linear; in all but two of the remainder the relationship was concave viewed from above. Alternative approaches to establishing the determinants of population growth rate are reviewed, paying special attention to the demographic and mechanistic approaches. The effects of population density on population growth rate may act through their effects on food availability and associated effects on somatic growth, fecundity and survival, according to a 'numerical response', the evidence for which is briefly reviewed. Alternatively, there may be effects on population growth rate of population density in addition to those that arise through the partitioning of food between competitors; this is 'interference competition'. The distinction is illustrated using a replicated laboratory experiment on a marine copepod, Tisbe battagliae. Application of these approaches in conservation biology, ecotoxicology and human demography is briefly considered. We conclude that population regulation, density dependence, resource and interference competition, the effects of environmental stress and the form of the ecological niche, are all best defined and analysed in terms of population growth rate.

Conservation of Natural Resources↗
PubMed2005

The linkage disequilibrium maps of three human chromosomes across four populations reflect their demographic history and a common underlying recombination pattern.

The extent and patterns of linkage disequilibrium (LD) determine the feasibility of association studies to map genes that underlie complex traits. Here we present a comparison of the patterns of LD across four major human populations (African-American, Caucasian, Chinese, and Japanese) with a high-resolution single-nucleotide polymorphism (SNP) map covering almost the entire length of chromosomes 6, 21, and 22. We constructed metric LD maps formulated such that the units measure the extent of useful LD for association mapping. LD reaches almost twice as far in chromosome 6 as in chromosomes 21 or 22, in agreement with their differences in recombination rates. By all measures used, out-of-Africa populations showed over a third more LD than African-Americans, highlighting the role of the population's demography in shaping the patterns of LD. Despite those differences, the long-range contour of the LD maps is remarkably similar across the four populations, presumably reflecting common localization of recombination hot spots. Our results have practical implications for the rational design and selection of SNPs for disease association studies.

Black or African American↗
PubMed2004

Assessing the risk of invasive spread in fragmented landscapes.

Little theoretical work has investigated how landscape structure affects invasive spread, even though broad-scale disturbances caused by habitat loss and fragmentation are believed to facilitate the spread of exotic species. Neutral landscape models (NLMs), derived from percolation theory in the field of landscape ecology, provide a tool for assessing the risk of invasive spread in fragmented landscapes. A percolation-based analysis of the potential for invasive spread in fragmented landscapes predicts that invasive spread may be enormously enhanced beyond some threshold level of habitat loss, which depends upon the species' dispersal abilities and the degree of habitat fragmentation. Assuming that invasive species spread primarily through disturbed areas of the landscape, poor dispersers may spread better in landscapes in which disturbances are concentrated in space, whereas good dispersers are predicted to spread better in landscapes where disturbances are small and dispersed (i.e., fragmented landscape). Assessing the risk of invasive spread in fragmented landscapes ultimately requires understanding the relative effects of landscape structure on processes that contribute to invasive spread--dispersal (successful colonization) and demography (successful establishment). Colonization success is predicted to be highest when >20% of the landscape has been disturbed, particularly if disturbances are large or aggregated in space, because propagules are more likely to encounter sites suitable for colonization and establishment. However, landscape pattern becomes less important for predicting colonization success if species are capable of occasional long-distance dispersal events. Invasive species are also more likely to persist and achieve positive population growth rates (successful establishment) in landscapes with clumped disturbance patterns, which can then function as population sources that produce immigrants that invade other landscapes. Finally, the invasibility of communities may be greatest in landscapes with a concentrated pattern of disturbance, especially below some critical threshold of biodiversity. Below the critical biodiversity threshold, the introduction of a single species can trigger a cascade of extinctions among indigenous species. The application of NLMs may thus offer new insights and opportunities for the management and restoration of landscapes so as to slow the spread of invasive species.

Animals↗
PubMed2006

Gonochorism vs. hermaphroditism: relationship between life history and fitness in three species of Ophryotrocha (Polychaeta: Dorvilleidae) with different forms of sexuality.

1. The relationships between life history, fitness and sexuality, together with their ecological and evolutionary significance, has been analysed comparing the main life-history traits and demography in three closely related species belonging to the genus Ophryotrocha. The species are: the gonochoristic O. labronica, the simultaneous hermaphrodite O. diadema and the protandrous hermaphrodite O. puerilis. 2. Survivorship and reproductive data were collected weekly and were used to construct life tables and population projection matrices for each species and compare life-history characteristics. Elasticity, life-table response and decomposition analyses were performed to examine the relative contribution of fecundity and survivorship to differences in lamda between species. 3. The gonochoristic and hermaphroditic species differ in all the main life-history parameters and also in demographic characteristics. In particular the value of lamda, used commonly to express fitness, is markedly higher in the gonochoristic species while in terms of fitness simultaneous and sequential hermaphroditism are very similar. In the genus Ophryotrocha gonochorism currently represents the most widespread condition, being characteristic of the majority of the known species in the genus. 4. Given the demographic advantage ensured by gonochorism, it remains be understood why some species have retained simultaneous hermaphroditism and one has evolved a sequential type hermaphroditism; the most probable hypothesis is correlated with the density of the species in natural habitats.

Age Factors↗
PubMed2005

Demographic and clinical characteristics of patients admitted to medical departments.

INTRODUCTION: The significant changes, which have affected departments of medicine over the last two decades, have been much editorialized. Surprisingly few data have been published that document these changes. We describe the demographic and clinical characteristics of patients admitted to one hospital's departments of internal medicine. METHODS: During a 3 months prospective study, 1039 patients (46% of all 2277 new admissions to the departments of medicine, consisting of +/- 175 beds) were randomized for inclusion. Information was extracted from the medical records regarding demography; functional capacity; clinical data and outcome. RESULTS: The mean age of the patients was 72 +/- 16 years (mean +/- SD); 51% were male, 56% were married, and 83% lived at home. Although 293 patients (28%) were defined as dependent, the majority lived at home (170, 58%). Cognition was normal in only 74%. The four most common disease categories leading to admission were infections (383 patients, 37%), cardiovascular disorders (372, 36%), respiratory conditions (284, 27%) and genito-urinary problems (90, 9%). Overall, 98 persons died (9%). Independent risk factors for death were: mechanical ventilation; a 'do not resuscitate' order; a high APACHE-II score; a low serum albumin level; higher age; and not being married (P < 0.01). CONCLUSIONS: Geriatric patients occupy a central position in our medical wards. These data are relevant for allocation of special resources for departments with high proportions of geriatric patients; for the design of employment conditions that ascertains continuing job satisfaction; as well as for the planning of teaching opportunities for residents and students.

Age Factors↗
PubMed2006

A possible way out of poor healthcare resulting from demographic problems: need-orientated home-based-nursing-care and nursing-home-care.

AIM: The aim of is this paper is to present a study in which a system to classify different levels of home-based-nursing and nursing-home care for groups with differing care need is developed. BACKGROUND: Changes in demography, social conditions and medical development are leading to the fact that in the future more people will need specialized nursing care which today's services of home-based-care and nursing-homes cannot provide. METHOD: On the basis of a literature research, the service-structure and the care need of defined groups of patients were analysed and categorized. The resulting grid was used in an Internet-based standardized survey among 144 experts. RESULTS: The results of this study encompass the experts' views and the prognoses on developments in the design of care and service structures for each of the defined groups of patients in North-Rhine-Westphalia, Germany. CONCLUSION: The study reveals the areas and the patient groups with the most significant future needs. Thus, demands and recommendations concerning the prospective design and structure of care and nursing services for home-based nursing and care in nursing-homes can be formulated.

Aged↗
PubMed2004

Spatial genetic structure in a metapopulation of the land snail Cepaea nemoralis (Gastropoda: Helicidae).

Habitat fragmentation is a major force affecting demography and genetic structure of wild populations, especially in agricultural landscapes. The land snail Cepaea nemoralis (L.) was selected to investigate the impact of habitat fragmentation on the spatial genetic structure of an organism with limited dispersal ability. Genetic and morphological patterns were investigated at a local scale of a 500 m transect and a mesoscale of 4 x 4 km in a fragmented agricultural landscape while accounting for variation in the landscape using least-cost models. Analysis of microsatellite loci using expected heterozygosity (HE), pairwise genetic distance (FST/1-FST) and spatial autocorrelograms (Moran's I) as well as shell characteristics revealed spatial structuring at both scales and provided evidence for a metapopulation structure. Genetic diversity was related to morphological diversity regardless of landscape properties. This pointed to bottlenecks caused by founder effects after (re)colonization. Our study suggests that metapopulation structure depended on both landscape features and the shape of the dispersal function. A range of genetic spatial autocorrelation up to 80 m at the local scale and up to 800 m at the mesoscale indicated leptokurtic dispersal patterns. The metapopulation dynamics of C. nemoralis resulted in a patchwork of interconnected, spatially structured subpopulations. They were shaped by gene flow which was affected by landscape features, the dispersal function and an increasing role of genetic drift with distance.

Animals↗
PubMed1996

County wide employment and population growth: an analysis of the 1980s.

"Regional scientists remain interested in studying interregional differences in the growth rates of population and employment. Following the earlier work of Carlino and Mills, this paper examines growth trends at the county level in the U.S. during the period 1981-1989. Five major sectors of employment are examined. A partial adjustment model is developed that captures intercounty differences in amenities, business and fiscal conditions, demography, employment structure, and relative location. Some evidence is given that population and employment growth was simultaneous, although feedback effects apparently were not strong."

Americas↗
PubMed1991

The greying of the baby boom in the United States: framing the policy debate.

"Issues surrounding the retirement of the large post-World War II 'baby boom' generation in the United States are often framed either in terms of impending intergenerational crisis or as an event to which the United States can gradually adjust. This paper examines these two perspectives as they compete to define U.S. social security policy. It suggests that the intergenerational crisis perspective functions primarily as an ideological argument and strategy for de-structuring social welfare policy. In contrast, the gradual adjustment perspective provides a stronger basis for planning social security and other policy responses to the ageing of the baby boom. However, it is not informed by a clear social vision and has not, as yet, responded sufficiently to the potential divisiveness which may accompany changing demography. Also, to date, relatively little attention has been paid to the diverse social and economic circumstances of baby boomers and the implications of this diversity for retirement planning."

Americas↗
PubMed2004

Demographic window to aging in the wild: constructing life tables and estimating survival functions from marked individuals of unknown age.

Summary We address the problem of establishing a survival schedule for wild populations. A demographic key identity is established, leading to a method whereby age-specific survival and mortality can be deduced from a marked cohort life table established for individuals that are randomly sampled at unknown age and marked, with subsequent recording of time-to-death. This identity permits the construction of life tables from data where the birth date of subjects is unknown. An analogous key identity is established for the continuous case in which the survival schedule of the wild population is related to the density of the survival distribution in the marked cohort. These identities are explored for both life tables and continuous lifetime data. For the continuous case, they are implemented with statistical methods using non-parametric density estimation methods to obtain flexible estimates for the unknown survival distribution of the wild population. The analytical model provided here serves as a starting point to develop more complex models for residual demography, i.e. models for estimating survival of wild populations in which age-at-entry is unknown and using remaining information in randomly encountered individuals. This is a first step towards a broad new concept of 'expressed demographic information content of marked or captured individuals'.

Age Factors↗