Rapid evolution of morphology and adaptive life history in the invasive California wild radish (Raphanus sativus) and the implications for management

Understanding the evolution and demography of invasive populations may be key for successful management. In this study, we test whether or not populations of the non-native, hybrid-derived California wild radish have regionally adapted to divergent climates over their 150-year history in California and determine if population demographic dynamics might warrant different region-specific strategies for control. Using a reciprocal transplant approach, we found evidence for genetically based differences both between and among northern, coastal and southern, inland populations of wild radish. Individual fitness was analyzed using a relatively new statistical method called ‘aster modeling’ which integrates temporally sequential fitness measurements. In their respective home environments, fitness differences strongly favored southern populations and only slightly favored northern populations. Demographic rates of transition and sensitivities also differed between regions of origin, suggesting that the most effective approach for reducing overall population growth rate would be to target different life-history stages in each region.

Multiple mild heat-shocks decrease the Gompertz component of mortality in Caenorhabditis elegans

Exposure to mild heat-stress (heat-shock) can significantly increase the life expectancy of the nematode Caenorhabditis elegans. A single heat-shock early in life extends longevity by 20% or more and affects life-long mortality by decreasing initial mortality only; the rate of increase in subsequent mortality (Gompertz component) is unchanged. Repeated mild heat-shocks throughout life have a larger effect on life span than does a single heat-shock early in life. Here, we ask how multiple heat-shocks affect the mortality trajectory in nematodes and find increases of life expectancy of close to 50% and of maximum longevity as well. We examined mortality using large numbers of animals and found that multiple heat-shocks not only decrease initial mortality, but also slow the Gompertz rate of increase in mortality. Thus, multiple heat-shocks have anti-aging hormetic effects and represent an effective approach for modulating aging.

Population density and youth antisocial behavior

Theoretical models concerning how neighborhood contexts adversely influence juvenile antisocial behavior frequently focus on urban neighborhoods; however, previous studies comparing urban and rural areas on the prevalence of youth antisocial behavior have yielded mixed results. The current study uses longitudinal data on the offspring of a nationally representative sample of mothers (N = 4,886) in the US. There was no relation between density and mother-reported child conduct problems across ages 4-13 years, but youth living in areas of greater population density exhibited more youth self-reported delinquency across 10-17 years. Families often moved to counties with greater or lesser population density, but longitudinal analyses treating population density as a time-varying covariate did not support the hypothesis that living in densely populated counties influenced youth delinquency. Rather, the association between population density and delinquency appears to be due to unmeasured selection variables that differ between families who live in more or less densely populated counties.

Dynamics of distribution and performance of ramets constructing genets: a demographic-genetic study in a clonal plant, Convallaria keiskei

BACKGROUND AND AIMS

In clonal plants producing vegetative offspring, performance at the genet level as well as at the ramet level should be investigated in order to understand the entire picture of the population dynamics and the life history characteristics. In this study, demography, including reproduction and survival, the growth patterns and the spatial distributions of ramets within genets of the clonal herb Convallaria keiskei were explored.

METHODS

Vegetative growth, flowering and survival of shoots whose genets were identified using microsatellite markers were monitored in four study plots for 3 years (2003-2005). The size structures of ramets in genets and their temporal shifts were then analysed. Their spatial distributions were also examined.

KEY RESULTS

During the census, 274 and 149 ramets were mapped in two 1 x 2 m plots, and 83 and 94 ramets in two 2 x 2 m quadrats. Thirty-eight genotypes were identified from 580 samples. Each plot included 5-18 genets, and most ramets belonged to the predominant genet(s) in each plot. Shoots foliated yearly for several years, but flowering ramets did not have an inflorescence the next year. A considerable number of new clonal offspring persistently appeared, forming a bell-shaped curve of the size structure of ramets in each genet. Comparing the structures modelled by the normal distributions suggested variation among ramets belonging to a single genet and variation among genets. Furthermore, spatial analyses revealed clumped and distant distributions of ramet pairs in a genet, in which the distant patterns corresponded to the linearly elongating clonal growth pattern of this species.

CONCLUSION

Characteristics of ramet performances such as flowering and recruitment of clonal offspring, in addition to growth, played a large part in the regulation of genet dynamics and distribution, which were different among the studied genets. These might be characteristics particularly relevant to clonal life histories.

Is segregation bad for your health?

For decades, racial residential segregation has been observed to vary with health outcomes for African Americans, although only recently has interest increased in the public health literature. Utilizing a systematic review of the health and social science literature, the authors consider the segregation-health association through the lens of 4 questions of interest to epidemiologists: How is segregation best measured? Is the segregation-health association socially or biologically plausible? What evidence is there of segregation-health associations? Is segregation a modifiable risk factor? Thirty-nine identified studies test an association between segregation and health outcomes. The health effects of segregation are relatively consistent, but complex. Isolation segregation is associated with poor pregnancy outcomes and increased mortality for blacks, but several studies report health-protective effects of living in clustered black neighborhoods net of social and economic isolation. The majority of reviewed studies are cross-sectional and use coarse measures of segregation. Future work should extend recent developments in measuring and conceptualizing segregation in a multilevel framework, build upon the findings and challenges in the neighborhood-effects literature, and utilize longitudinal data sources to illuminate opportunities for public health action to reduce racial disparities in disease.

Population dynamics along a primary succession gradient: do alpine species fit into demographic succession theory?

BACKGROUND AND AIMS

Understanding processes and mechanisms governing changes in plant species along primary successions has been of major importance in ecology. However, to date hardly any studies have focused on the complete life cycle of species along a successional gradient, comparing pioneer, early and late-successional species. In this study it is hypothesized that pioneer species should initially have a population growth rate, lambda, greater than one with high fecundity rates, and declining growth rates when they are replaced by late-successional species. Populations of late-successional species should also start, at the mid-successional stage (when pioneer species are declining), with growth rates greater than one and arrive at rates equal to one at the late successional stage, mainly due to higher survival rates that allow these species to persist for a long time.

METHODS

The demography of pioneer- (Saxifraga aizoides), early (Artemisia genipi) and late-successional species (Anthyllis vulneraria ssp. alpicola) was investigated together with that of a ubiquitous species (Poa alpina) along the Rotmoos glacier foreland (2300-2400 m a.s.l., Central Alps, Austria) over 3 years. A matrix modelling approach was used to compare the main demographic parameters. Elasticity values were plotted in a demographic triangle using fecundity, individual growth and survival as vital rates contributing to the population growth rates.

KEY RESULTS

The results largely confirmed the predictions for population growth rates during succession. However, high survival rates of larger adults characterized all species, regardless of where they were growing along the succession. At the pioneer site, high mortality rates of seedlings, plantlets and young individuals were recorded. Fecundity was found to be of minor relevance everywhere, but it was nevertheless sufficient to increase or maintain the population sizes.

CONCLUSIONS

Demographically, all the species over all sites behaved like late-successional or climax species in secondary successions, mainly relying on survival of adult individuals. Survival serves as a buffer against temporal variation right from the beginning of the primary succession, indicating a major difference between primary and secondary succession.

Level of education and back pain in France: the role of demographic, lifestyle and physical work factors

PURPOSE

To investigate the pathways from level of education to low back pain (LBP) in the adult population, especially concerning the role of physical working constraints, and personal factors (overweight, tobacco consumption, and tallness).

METHODS

The study population consisted of 15,534 subjects from the National Health Survey, with data on LBP, level of education, personal factors, and physical working constraints. Logistic models for LBP (pain more than 30 days during the previous 12 months) were compared in order to check the consistency of the data with specific causal pathways.

RESULTS

Low back pain was strongly associated with level of education. This association was almost completely explained if present or past exposure to tiring work postures and handling of heavy loads were taken into account. For men, the OR for "no diploma", adjusted only for age, was 1.75; it was 1.02 after additional adjustment on physical work factors. Personal factors played also a role, especially overweight for women. Among them, the OR associated with a body mass index = 27 or more was 1.58 after adjustment on all the other factors.

CONCLUSIONS

In this national population the main pathways from education to LBP were through occupational exposure and lifestyle factors.

The most frequent psychiatric disorders registered at day hospital of psychiatric clinic in sarajevo during 2006-2007

CONFLICT OF INTEREST

NONE DECLARED Day Hospital is an alternative to inpatient treatment as a transition from hospital to outpatient type of treatment, especially for those patients who cannot quickly return to the family, and patients who are unable to leave the usual social contacts so to them the hospitalization will pose a great mental risk. The aim of the research is to determine the structure of psychiatric morbidity, as well as demographic features and duration of hospitalization in patients treated at a Day Hospital of Psychiatric Clinic in Sarajevo during the period 2006-2007. The survey is conducted at the Psychiatric Clinic, Clinical Center of Sarajevo University as retrospective, based on observations of certain variables (gender, age, hospitalization duration), and the number of diagnosis. The results of the research show that the total number of registered patients in the observed period is 400. During the two year study there were more female (61.3%) than male patients (38.7%). Also, during the two years of research, most of those were with one diagnosis. The average hospitalization duration was 45 days, and the most often hospitalization duration was from 1 to 3 months. During both years, mostly present was the population in age group 46 to 65 years, followed by age group 26 to 44 years. Leading diseases during both years of research were from the group F30-F39, and the most common co-morbid diseases from groups: F30-F39, F40-F49 and F60-F69. We can conclude that Day Hospital has great significance in the mental health prevention. Daily structured program provides hospital diagnosis, treatment and rehabilitation of persons of both genders from different age groups and with diverse psychopathology.

THE COST OF REPRODUCTION AND EXPERIENCE-DEPENDENT VITAL RATES IN A SMALL PETREL

Life history theory predicts that higher levels of reproductive investment entail higher reproductive costs especially among young and inexperienced individuals that might not optimize reproductive investment. Using a long-term individual and state-dependent capture-recapture data on Storm Petrels (Hydrobates pelagicus) we analyzed whether breeding experience and current breeding investment were associated with the expression of the cost of reproduction in terms of reduced survival and/or future breeding performance. We found a positive relationship between current breeding investment, breeding experience, and future survival and an improvement in breeding performance with individual experience independently of the previous breeding outcome. Our results suggest that the survival cost paid by first-time breeders and the positive correlation between reproduction and survival corresponds to selection against low quality birds unrelated to the breeding effort. Our work outlines the need to investigate the effect of multiple individual traits on different life history trade-offs simultaneously.

A latitudinal gradient in climate effects on seabird demography: results from interspecific analyses

For an understanding of the effect of climate change on animal population dynamics, it is crucial to be able to identify which climatologic parameters affect which demographic rate, and what the underlying mechanistic links are. An important reason for why the interactions between demography and climate still are poorly understood is that the effects of climate vary both geographically and taxonomically. Here, we analyse interspecifically how different climate variables affect the breeding success of North Atlantic seabird species along latitudinal and longitudinal gradients. By approaching the problem comparatively, we are able to generalize across populations and species. We find a strong interactive effect of climate and latitude on breeding success. Of the climatic variables considered, local sea surface temperatures during the breeding season tend to be more relevant than the North Atlantic Oscillation (NAO). However, the effect of NAO on breeding success shows a clear geographic pattern, changing in sign from positive in the south to negative in the north. If this interaction is taken account of, the model explains more variation than any model with sea surface temperature. This superiority of the NAO index is due to its ability to capture effects of more than one season in a single parameter. Mechanistically, however, several lines of evidence suggest that sea surface temperature is the biologically most relevant explanatory variable.

Sociodemographic and smoking behavioral predictors associated with smoking cessation according to follow-up periods: a randomized, double-blind, placebo-controlled trial of transdermal nicotine patches

This study investigated sociodemographic and smoking behavioral factors associated with smoking cessation according to follow-up periods. In this randomized, double-blind, placebo-controlled trial of transdermal nicotine patches, subjects were a total of 118 adult male smokers, who were followed up for 12 months. Univariable logistic regression analysis and stepwise multiple logistic regression analyses were performed to identify the predictors of smoking cessation. The overall self-reported point prevalence rates of abstinence were 20% (24/118) at 12 months follow-up, and there was no significant difference in abstinence rates between placebo and nicotine patch groups. In the univariable logistic regression analysis, predictors of successful smoking cessation were the low consumption of cigarettes per day and the low Fagerstrom Test for Nicotine Dependence (FTND) scores (p<0.05) at 3, 6, and 12 months follow-up. In the stepwise multiple logistic regression analyses, predictors of successful smoking cessation, which were different according to the follow- up periods, were found to be the low consumption of cigarettes per day at the short-term and midterm follow-up (< or =6 months), older age, and the low consumption of cigarettes per day at the long-term follow-up (12 months).

Use of the internet to communicate with health care providers in the United States: estimates from the 2003 and 2005 Health Information National Trends Surveys (HINTS)

BACKGROUND

Despite substantial evidence that the public wants access to Internet-based communication with health care providers, online patient-provider communication remains relatively uncommon, and few studies have examined sociodemographic and health-related factors associated with the use of online communication with health care providers at a population level.

OBJECTIVE

The aim of the study was to use nationally representative data to report on the prevalence of and changes in use of online patient-provider communication in 2003 and 2005 and to describe sociodemographic and health-related factors associated with its use.

METHODS

Data for this study are from two iterations of the Health Information National Trends Survey (HINTS 2003, HINTS 2005). In both years, respondents were asked whether they had ever used email or the Internet to communicate with a doctor or a doctor's office. Adult Internet users in 2003 (n = 3982) and 2005 (n = 3244) were included in the present study. Multivariate logistic regression analysis was conducted to identify predictors for electronic communication with health care providers.

RESULTS

In 2003, 7% of Internet users had communicated online with an health care provider; this prevalence significantly increased to 10% in 2005. In multivariate analyses, Internet users with more years of education, who lived in a metro area, who reported poorer health status or who had a personal history of cancer were more likely to have used online patient-provider communication.

CONCLUSIONS

Despite wide diffusion of the Internet, online patient-provider communication remains uncommon but is slowly increasing. Policy-level changes are needed to maximize the availability and effectiveness of online patient-provider communication for health care consumers and health care providers. Internet access remains a significant barrier to online patient-provider communication.

Lifespan modification by glucose and methionine in Drosophila melanogaster fed a chemically defined diet

Experimentally restricting dietary calories, while maintaining adequate dietary nutrient content, extends lifespan in phylogenetically diverse species; thus suggesting the existence of conserved pathways which can modify lifespan in response to energy intake. However, in some cases the impact on longevity may depend on the quality of the energy source. In Drosophila, restriction of dietary yeast yields considerable lifespan extension whereas isocaloric restriction of dietary sugar yields only modest extension, indicating that other diet-responsive pathways can modify lifespan in this species. In rodents, restricting intake of a single amino acid - methionine - extends lifespan. Here we show that dietary methionine can modify lifespan in adult female, non-virgin Oregon-R strain Drosophila fed a chemically defined media. Compared to a diet containing 0.135% methionine and 15% glucose, high dietary methionine (0.405%) shortened maximum lifespan by 2.33% from 86 to 84 days and mean lifespan by 9.55% from 71.7 to 64.9 days. Further restriction of methionine to 0.045% did not extend maximum lifespan and shortened mean lifespan by 1.95% from 71.1 to 70.3 days. Restricting glucose from 15% to 5% while holding methionine at a concentration of 0.135%, modestly extended maximum lifespan by 5.8% from 86 to 91 days, without extending mean lifespan. All these diet-induced changes were highly significant (log-rank p < 0.0001). Notably, all four diets resulted in considerably longer life spans than those typically reported for flies fed conventional yeast and sugar based diets. Such defined diets can be used to identify lifespan-modifying pathways and specific gene-nutrient interactions in Drosophila.

Demographic review of a captive colony of callitrichids (Callithrix kuhlii)

Although reports on colony demographics for a variety of callitrichid species are available in the literature, to date there has not been a detailed examination of Wied's black tufted-ear marmoset (Callithrix kuhlii). The purpose of this study is to present colony demographics for C. kuhlii from the University of Nebraska at Omaha's Callitrichid Research Center from 1991 to 2002. C. kuhlii are currently held in a number of zoological parks in the United States and abroad; however, the University of Nebraska at Omaha held the only breeding colony in North America. Here we report data on lifespan, sex ratio, litter size, and interbirth interval (IBI) for that captive breeding colony.

The boomers are coming: a total cost of care model of the impact of population aging on health care costs in the United States by Major Practice Category

OBJECTIVE

To project the impact of population aging on total U.S. health care per capita costs from 2000 to 2050 and for the range of clinical areas defined by Major Practice Categories (MPCs).

DATA SOURCES

Secondary data: HealthPartners health plan administrative data; U.S. Census Bureau population projections 2000-2050; and MEPS 2001 health care annual per capita costs.

STUDY DESIGN

We calculate MPC-specific age and gender per capita cost rates using cross-sectional data for 2002-2003 and project U.S. changes by MPC due to aging from 2000 to 2050.

DATA COLLECTION METHODS

HealthPartners data were grouped using purchased software. We developed and validated a method to include pharmacy costs for the uncovered.

PRINCIPAL FINDINGS

While total U.S. per capita costs due to aging from 2000 to 2050 are projected to increase 18 percent (0.3 percent annually), the impact by MPC ranges from a 55 percent increase in kidney disorders to a 12 percent decrease in pregnancy and infertility care. Over 80 percent of the increase in total per capita cost will result from just seven of the 22 total MPCs.

CONCLUSIONS

Understanding the differential impact of aging on costs at clinically specific levels is important for resource planning, to effectively address future medical needs of the aging U.S. population.

Climate change and the demographic demise of a hoarding bird living on the edge

Population declines along the lower-latitude edge of a species' range may be diagnostic of climate change. We report evidence that climate change has contributed to deteriorating reproductive success in a rapidly declining population of the grey jay (Perisoreus canadensis) at the southern edge of its range. This non-migratory bird of boreal and subalpine forest lives on permanent territories, where it hoards enormous amounts of food for winter and then breeds very early, under still-wintry conditions. We hypothesized that warmer autumns have increased the perishability of hoards and compromised subsequent breeding attempts. Our analysis confirmed that warm autumns, especially when followed by cold late winters, have led to delayed breeding and reduced reproductive success. Our findings uniquely show that weather months before the breeding season impact the timing and success of breeding. Warm autumns apparently represent hostile conditions for this species, because it relies on cold storage. Our study population may be especially vulnerable, because it is situated at the southern edge of the range, where the potential for hoard rot is most pronounced. This population's demise may signal a climate-driven range contraction through local extinctions along the trailing edge.

Migration, social structure and old-age support networks: a comparison of three Indonesian communities

Contemporary trends in population ageing and urbanisation in the developing world imply that the extensive out-migration of young people from rural areas coincides with, and is likely to exacerbate, a rise in the older share of the rural population. This paper examines the impact of migration on vulnerability at older ages by drawing on the results of anthropological and demographic field studies in three Indonesian communities. The methodology for identifying vulnerable older people has a progressively sharper focus, beginning first with important differences between the communities, then examining variations by socio-economic strata, and finally the variability of older people's family networks. Comparative analysis indicates considerable heterogeneity in past and present migration patterns, both within and between villages. The migrants' contributions are a normal and important component of older people's support, often in combination with those of local family members. Higher status families are commonly able to reinforce their position by making better use of migration opportunities than the less advantaged. Although family networks in the poorer strata may effect some redistribution of the children's incomes, their social networks are smaller and insufficient to overcome their marked disadvantages. Vulnerability thus arises where several factors, including migration histories, result in unusually small networks, and when the migrations are within rural areas.

Impact of severe acute respiratory syndrome (SARS) outbreaks on the use of emergency department medical resources

BACKGROUND

The impact of the severe acute respiratory syndrome (SARS) outbreak in 2003 on the emergency department (ED) medical needs of adult patients has not been elucidated. The purpose of this study was to investigate the demographic and clinical characteristics of ED adult patients before, during and after the SARS epidemic in a SARS-dedicated hospital.

METHODS

A retrospective, ED chart review was conducted, and demographic data were obtained from a computer database, for a total of 17,586 patients. Patient information, including age, gender, mode of arrival, triage category, time of visit, main diagnosis, use of ED services, and status after the ED visit, were collected and compared for pre-, early-, peak-, late-, and post-SARS epidemic stages.

RESULTS

Demographic data demonstrated a significant decrease in patient attendances per day, with a mean reduction of 92.5 +/- 8.3 patients (43.7 +/- 3.9% reduction in rate; p < 0.01) during peak- versus pre-epidemic stages, but revealed no differences in patient age and gender. The numbers of patients with ambulance transport, inter-hospital referral, and critical illnesses, including DOA, categorized as triage 1, or admitted to a ward or intensive care unit after the ED visit, were not influenced by the SARS epidemic. The number of patients with upper airway infections and suicide attempts from drug overdoses increased, but not statistically significantly. The number of patients with other diagnoses decreased progressively from early- to peak-epidemic stages, but returned to their earlier levels at the post-epidemic stage. Statistically significant decreases (p < 0.05) were noted in mean attendance at peak-versus pre- and early-epidemic stages for patients with cardiovascular disease, inflammatory or functional bowel disease, endocrine disease, dizziness or vertigo, or trauma.

CONCLUSION

The SARS outbreak did not eliminate the need of critically ill patients for advanced medical support. However, besides an overall decrease in patient numbers, the SARS epidemic markedly altered demographic information, clinical characteristics, and the use of medical services by adult patients in the ED of a SARS-dedicated hospital.

Diabcare Asia 2001--Korea country report on outcome data and analysis

BACKGROUND

The Diabcare-Asia study was designed for the purpose of describing diabetes control and management, and late complication status in the diabetic population.

METHODS

From the 1st of July 2001 to the 1st of September 2001, data from 1170 diabetic patients were collected in 21 centers (one university hospital and 20 clinics located in Seoul and in Gyeonggi, Korea), and blood samples were collected for centralized HbAtc measurements.

RESULTS

Only 16.8% of patients at the clinics reported self-monitoring their blood glucose. The mean HbA(1c) was 7.3 +/- 1.4% at the hospital and 7.5 +/- 1.5% at the clinics, and the mean fasting plasma glucose (FPG) levels were 7.0 +/- 3.3 mmol/L at the hospital and 7.9 +/- 2.5 mmol/L at the clinics. About 40% of patients had a HbA(1c) and FPG above the normal upper limits. Screening for microalbuminuria was rarely performed. The available data represents only about 0.9% of the patients at the hospital and 12.3% of the patients at the clinics. Nephropathy (serum creatinine >2 mg/dL) was found in 0.8% of the patients at the hospital and in 3.4% of the patients at the clinics. Retinopathy and neuropathy were commonly reported diabetic complications. The prevalence of other severe late complications was relatively low.

CONCLUSION

The data revealed suboptimal glycemic control in about 40% of patients.

Demographic dynamics and kinship in anthropological populations

Changes in fertility and mortality affect the size of surviving sibling sets and thus numbers of surviving kin. Because the genealogical generations specifying kinship relations are not temporal cohorts and most plausible demographic changes in anthropological populations are period shocks, the effect of such shocks on kin counts are complex. Shocks increasing fertility or decreasing mortality produce larger numbers of kin per ego and decrease the inequality of the distribution of kin and vice versa. Effects are more diffuse at more distant collateral ranges. Effects are stronger the more intense the shock and the longer its duration. Kinship distributions return to their initial state after the shock and as the original age structure of the population is ergodically reattained. Alternating shocks produce more complex patterns. Implications of these outcomes are that opportunities for political networking and consolidation by means of kinship are altered by demographic instabilities, as are the dynamics of kin selection. This analysis is limited for simplicity to unilineal agnatic reckoning of kin.

Population Dynamics and Tropical Deforestation: State of the Debate and Conceptual Challenges

What is the role of population in driving deforestation? This question was put forth as a discussion topic in the cyberseminar hosted by Population Environment Research Network (PERN) in Spring, 2003. Contributors from diverse backgrounds weighed in on the discussion, citing key factors in the population-deforestation nexus and suggesting further courses of action and research. Participants explored themes of their own choosing, with many coming to the forefront. Scale, time, and place-based effects were cited as areas in need of particular attention. Consumption patterns as the mechanism for spurring deforestation were discussed, drawing attention to the differential patterns associated with urban vs. rural demands on forest resources and land. The applicability of the IPAT formula and the influence of its component parts, affluence and technology, when operating in tandem with population, was debated. The relation of demographic factors to these pathways was critically examined. Institutional and governmental influence, such as infrastructure and policies affecting access and incentives, the valuation of resources, and institutional failures such as mismanagement and corruption emerged as a crucial set of factors. This article synthesizes the critical debates in the population-deforestation literature, makes suggestions for future paths of research, and discussed possible policy and direct action initiatives.

How risky is risk assessment: the role that life history strategies play in susceptibility of species to stress

Measurements of toxicity based on individuals, such as the LC(50) (concentration that kills 50% of a population), and effects on reproduction are used extensively in determining ecological risk, in particular, for endangered or threatened species. An underlying assumption is that individual-based toxicity metrics for one species can be directly compared with that for another species. However, this assumption overlooks the fact that different species have different life-history strategies and variables, such as lifespan, time to first reproduction, and number of offspring produced over a lifetime. Using a simple model and laboratory-derived parameter values, we tested the impact of differences in life-history traits on predicted responses to stress. The model predicts the delay in population growth. We compared seven invertebrate species by imposing 50% chronic mortality, 50% reduction of offspring, and both of these effects. The model predicted substantial differences in population delay among all of the species. Furthermore, the intrinsic rate of increase of each population was negatively correlated with the delay in population growth; species with high intrinsic rates of increase were less susceptible to equal levels of stress than species with lower intrinsic rates of increase. These results suggest that the susceptibility of species to pollutants is more complicated than previously thought and that differences in life-history variables must be considered in analyses of population persistence for threatened and endangered species.

Spanish flu and early 20th-century expansion of a coronary heart disease-prone subpopulation

According to Stephen Jay Gould, "we have a strong preference for seeing trends as entities moving somewhere." However, trends may instead be the product of relative expansions and contractions of different subpopulations constituting the system. Variation in attributes of coronary heart disease cases during the decline in coronary heart disease mortality suggests a change in the primary source-subpopulation of cases over time. It is proposed that an early 20th-century expansion of a coronary heart disease-prone subpopulation, characterized by high serum-cholesterol phenotype and high case-fatality--which contributed to most of the coronary heart disease cases and deaths during the 1960s--may have been a late result of the 1918 influenza pandemic. The same unusual immune response to infection that in 1918 killed preferentially men, whites, and those born from 1880 to 1900 (20-40 years old) may have "primed" survivors of those birth cohorts to late coronary heart disease mortality. Ecologic evidence in favor of a birth cohort and geographic association between both epidemics is presented. Cross-reactive auto-immune response upon reinfection could explain the excess coronary heart disease deaths reported during influenza epidemics from the late 1920s onward. Mimicry between the viral hemagglutinin and the apolipoprotein B or the low-density lipoprotein receptor could be the link between infection and hypercholesterolemia. The extinction of those birth cohorts would result in a relative increase in cases coming from a 2nd subpopulation, which was characterized by insulin resistance and chronic expression of low-grade inflammation markers and was comparatively less vulnerable to die acutely from coronary heart disease.

Variation in the ecology of medical care

BACKGROUND

We wanted to quantify how the location in which medical care is delivered in the United States varies with the sociodemographic characteristics and health care arrangements of the individual person.

METHODS

Data from the 1996 Medical Expenditures Panel Survey (MEPS) were used to estimate the number of persons per 1,000 per month in 1996 who had at least 1 contact with physicians' offices, hospital outpatient departments, or emergency departments, hospitals, or home care. These data were stratified by age, sex, race, ethnicity, household income, education of head of household, residence in or out of metropolitan statistical areas, having health insurance, and having a usual source of care.

RESULTS

Physicians' offices were overwhelmingly the most common site of health care for all subgroups studied. Lacking a usual source of care was the only variable independently associated with a decreased likelihood of care in all 5 settings, and lack of insurance was associated with lower rates of care in all settings but emergency departments. Generally, more complicated patterns emerged for most sociodemographic characteristics. The combination of having a usual source of care and health insurance was especially related to higher rates of care in all settings except the emergency department.

CONCLUSION

Frequency and location of health care delivery varies substantially with sociodemographic characteristics, insurance, and having a usual source of care. Understanding this variation can inform public consideration of policy related to access to care.

Sexual differences in reproductive phenology and their consequences for the demography of Baccharis dracunculifolia (Asteraceae), a dioecious tropical shrub

Patterns of phenological variation and reproductive investment were studied in the dioecious shrub Baccharis dracunculifolia DC (Asteraceae), and possible consequences on survivorship were evaluated. The sex ratio was determined in a natural field population (n = 921) of B. dracunculifolia in Belo Horizonte, Brazil. Fifty-two males and 56 females were sampled at random from this population. During the reproductive season of 1999, inflorescence production, shoot growth and mortality, and xylem water potential were recorded for each individual. The population sex ratio was male-biased (1.27 : 1, P < 0.05), and was associated with a higher mortality of female shoots (38.4 vs. 23.1 %, P < 0.05), and individuals (17.8 vs. 11.5 %, P < 0.1), despite lower water stress in female plants. Flowering phenology also differed between the sexes, with males producing more inflorescences, and earlier, than females. Owing to fruit maturation, the number of inflorescences supported by females was higher than that supported by males later in the reproductive season. This occurred during the dry season, and drought stress may have been responsible for the greater female mortality. Thus, the male-biased sex ratio in this population of B. dracunculifolia is probably due to different reproductive functions of males and females. Intersexual differences in reproductive phenology had consequences for plant demography.

Congenital transmission of Trypanosoma cruzi infection in Argentina

Trypanosoma cruzi, the causative agent of Chagas disease, infects 10-18 million people and may be transmitted to the newborn. Using various data sources, we estimated that nearly 850 congenital cases occurred in Argentina in 1993, or 6.3 expected cases per each reported case in 1994 and in 1994-2001. The congenital transmission of T. cruzi constitutes a sizeable public health problem in the region.

An approach to forecasting health expenditures, with application to the U.S. Medicare system

OBJECTIVE

To quantify uncertainty in forecasts of health expenditures.

STUDY DESIGN

Stochastic time series models are estimated for historical variations in fertility, mortality, and health spending per capita in the United States, and used to generate stochastic simulations of the growth of Medicare expenditures. Individual health spending is modeled to depend on the number of years until death.

DATA SOURCES/STUDY SETTING

A simple accounting model is developed for forecasting health expenditures, using the U.S. Medicare system as an example.

PRINCIPAL FINDINGS

Medicare expenditures are projected to rise from 2.2 percent of GDP (gross domestic product) to about 8 percent of GDP by 2075. This increase is due in equal measure to increasing health spending per beneficiary and to population aging. The traditional projection method constructs high, medium, and low scenarios to assess uncertainty, an approach that has many problems. Using stochastic forecasting, we find a 95 percent probability that Medicare spending in 2075 will fall between 4 percent and 18 percent of GDP, indicating a wide band of uncertainty. Although there is substantial uncertainty about future mortality decline, it contributed little to uncertainty about future Medicare spending, since lower mortality both raises the number of elderly, tending to raise spending, and is associated with improved health of the elderly, tending to reduce spending. Uncertainty about fertility, by contrast, leads to great uncertainty about the future size of the labor force, and therefore adds importantly to uncertainty about the health-share of GDP. In the shorter term, the major source of uncertainty is health spending per capita.

CONCLUSIONS

History is a valuable guide for quantifying our uncertainty about future health expenditures. The probabilistic model we present has several advantages over the high-low scenario approach to forecasting. It indicates great uncertainty about future Medicare expenditures relative to GDP.

Changing patterns of strabismus: a decade of experience in Hong Kong

BACKGROUND/AIMS

Racial variation in the pattern of strabismus is known, but few large scale studies on non-white populations are available. Furthermore, longitudinal change in this pattern within a local setting has not been well documented in the past. This study aims to support the clinical impression that exotropia is more common in Chinese patients, and that the proportion of patients with exotropia has been increasing in the past decade.

METHODS

A total of 2704 consecutive patients with the diagnosis of primary horizontal strabismus, seen in the strabismus clinic of the Hong Kong Eye Hospital, were retrospectively analysed to determine the relative prevalence of esotropia and exotropia. Characteristics recorded include patient demographics, type of strabismus, and whether the nature of the squint was constant or intermittent.

RESULTS

742 (27.4%) patients were found to have esotropia, 548 (20.3%) had constant exotropia, 1213 (44.9%) had intermittent exotropia, and 201 (7.4%) had microtropia. The proportion of exotropic to esotropic patients was shown to increase steadily throughout the past decade (p<0.0001). This was mainly accounted for by an increase in the number of patients with intermittent exotropia, and a corresponding decrease in the number of patients with esotropia.

CONCLUSION

Exotropia was shown to be more prevalent than esotropia in a Hong Kong Chinese population. Furthermore, the proportion of patients with intermittent exotropia appears to be increasing, in contrast with esotropic patients. The exact nature of this trend, and possible aetiological factors will require further study.

Population Dynamic and Genetic Consequences of Spatial Density-Dependent Dispersal in Patchy Populations

Predictions about sex-specific, spatial density-dependent dispersal and their demographic and genetic consequences were tested in experimental populations of root voles (Microtus oeconomus). Each population consisted of two demes inhabiting equal-sized habitat patches imbedded in a barren matrix area. We used a neutral two-allele allozyme marker to monitor gene flow. Initially, the two demes were genetically distinct and had different densities so that the size of a high-density deme (genotype bb) was four times larger than that of a low-density deme (genotype aa). The sex-specific dispersal pattern was in accordance with our prediction. Male dispersal was unconditional on deme-specific densities, and the majority of the first-generation males became dispersed from both demes, whereas female dispersal was strongly density dependent, so that dispersal took place exclusively from the high-density to the low-density deme. The demographic implication of this dispersal pattern was that the initial density difference between the demes was quickly canceled out. We built a mathematical model that predicted that the initially rare allele (a) would increase in frequency given the dispersal pattern, and this was supported by our experimental data. This result relies mostly on the density-independent male-dispersal strategy, which presumably stems from inbreeding avoidance. Our study highlights the importance of incorporating sex-specific dispersal strategies in population genetic models. Sex-biased dispersal may act as a deterministic force counteracting the tendency for stochastic loss of alleles in small and fragmented populations.

Self-reported legal needs of women with or at risk for HIV infection. The Her Study Group

Women at risk for human immunodeficiency virus (HIV) infection are often poor and members of racial or ethnic minorities. In addition to legal concerns that might be common among persons with similar sociodemographic characteristics, HIV infection adds the potential of possible stigma and discrimination, as well as the prospect of illness and increased mortality. To determine women's perceptions of need for and access to legal services and whether such perceptions are affected by HIV infection, from November 1993 through September 1995 we interviewed 509 women with or at risk for HIV infection by virtue of injection drug use or high-risk sexual behaviors in New York and Baltimore, Maryland. A majority of women, regardless of HIV serostatus, reported current or future needs for legal assistance with government benefits. More than 25% reported needing current or future legal help with housing, debts, arrangements for care of children, a will, and advance directives. Substantial minorities of women reported other legal needs. HIV-positive women were significantly more likely to report anticipated future need for help with paternal custody or visitation, current need in making a will, and anticipated future assistance with advance directives. For most items, a majority of women thought they knew where to receive help. However, among women reporting a current need, only a minority actually were receiving legal assistance. This study suggests that the extent of legal needs among women with or at risk for HIV infection is substantial, and that few receive legal assistance. With few exceptions, at least for women early in the course of illness, HIV infection does not appear to alter the pattern or extent of legal needs. There are dramatic differences, regardless of HIV status, between expectation and reality in women's access to legal services.

Effects of the spatial arrangement of aerial stems and current-year shoots on the demography and growth of Hydrangea hirta in a light-limited environment

This study investigates the effects of the spatial arrangement of aerial stems and current-year shoots on patterns of herbivory, competition and on the requirements for mechanical support in Hydrangea hirta Sieb. et Zucc. growing in a light-limited environment. Stem demography was followed for three consecutive growing seasons. Stem mortality rates decreased with increasing stem age. Age-specific mortality rate was highest for new stems owing to the high incidence of herbivory. Mortality due to herbivory was low in older stems and was attributed to the dispersion of the risk of herbivore attack as a result of the increase in number of current-year shoots per stem. Clumping of stems led to intense intra-clonal competition as inferred from size-dependent mortality and density-dependent turnover of stems, and higher maximum stem length in clumps with higher stem density. Analysis of the spatial distribution of current-year shoots within the stem crown revealed a uniform, mono-layered crown architecture. The horizontal distribution of buds within the mono-layer was aggregated as a result of their opposite position, but as current-year shoots grew, their apices became uniformly distributed, resulting in efficient leaf display for light capture and shading out competing stems. However, limits on stem growth were observed in crown expansion, shoot production rate and current-year shoot size. Crown width increased with increasing basal diameter to reach a maximum. Both shoot production rate and current-year shoot size decreased with stem growth and a minimum current-year shoot size was defined. These limits on stem growth were attributed to suppression from intra-clonal competition and to the requirements for mechanical support of the mono-layered crown.

Evolutionary theory predicts late-life mortality plateaus

Most demographic data indicate a roughly exponential increase in adult mortality with age, a phenomenon that has been explained in terms of a decline in the force of natural selection acting on age-specific mortality. Scattered demographic findings suggest the existence of a late-life mortality plateau in both humans and dipteran insects, seemingly at odds with both prior data and evolutionary theory. Extensions to the evolutionary theory of aging are developed which indicate that such late-life mortality plateaus are to be expected when enough late-life data are collected. This expanded theory predicts late-life mortality plateaus, with both antagonistic pleiotropy and mutation accumulation as driving population genetic mechanisms.

The U.S.-Japan Cooperative Cancer Research Program: some highlights of seminars, interdisciplinary program area, 1981-1996

Thirty-one seminars have been held in the 16 years since 1981. A principal interest from the beginning was the genetics of cancer, well before this subject became widely popular. This interest arose in part because of marked binational differences in type-specific cancer rates, such as the very low rates among Japanese for Hodgkin's disease in the young, testicular cancer, Ewing's sarcoma, superficial spreading melanoma, chronic lymphocytic leukemia, and Wilms' tumor (half the U.S. frequency). Three seminars were devoted to the seeming reciprocal relationship between B-cell lymphoma (low in Japan) and certain autoimmune diseases (high in Japan), which is perhaps similar in origin to the male/female differences in the rates for these diseases. A seminar on Li-Fraumeni syndrome led to the recognition of cases among Japanese pedigrees brought to the meeting, and generated a study of its occurrence in Japanese families with adrenocortical carcinoma in a child. Another seminar revealed a marked clustering of rare cancers in Werner's (premature aging) syndrome in Japan, and led to a binational study and analysis of case-reports worldwide. Three seminars on pathology heightened appreciation of the importance of subclassifying cancer by subsite and subtype for racial and other comparisons. Four seminars on biostatistics in cancer research generated a substantial exchange of specialists and trainees in this field.

The influenza pandemic of 1918-1919 in the British Caribbean

The influenza pandemic swept through the Caribbean during the period October 1918 to March 1919 and resulted in c.100,000 deaths. This article focuses on the British possessions and is based principally on official reports and the local press. It looks at how the virus entered and spread through the region, the possible reasons for variations in levels of morbidity and mortality between islands, popular responses to the infection, and the mainly fruitless official attempts to arrest and deal with the disease. Jamaica was the first island to be affected, and along with Belize and Guyana, suffered most severely. A number of islands, particularly those in the eastern Caribbean, appear to have escaped relatively lightly. Although all sections of the population were vulnerable, the heaviest mortality rates were among the very poor, East Indian immigrant labourers, and native Americans. There was also a high toll among males aged 15-40. Altogether the death rate from influenza in the British Caribbean was c.30,000. In London influenza was added to the official list of British 'imperial diseases', and although it was recognized that poverty provided the conditions for the spread of disease, the resources in the Caribbean were barely used to improve standards of living and nutrition.

Enzymatic Digestion of Roots for Recovery of Root-knot Nematode Developmental Stages

Developmental stages of Meloidogyne javanica were successfully released from roots by treatment with commercially available cellulase and pectinase. The average percentage recovery of nematode developmental stages from Dolichos lablab, Elymus glaucus, and Lycopersicon esculentum were as follows: eggs = 526%, J2 = 272%, J3 = 783%, J4 = 549%, adult females = 285%, and total = 425%, expressed as percentages of the counts obtained from stained roots spread on glass plates. Root digestion was more accurate and sensitive in detecting low numbers of nematodes in roots than was the glass plate method. No simple linear, quadratic, or cubic relationship was found between the two methods that would allow a conversion factor to be developed.

The demography of fine roots in response to patches of water and nitrogen

Fine root demography was quantified in response to patches of increased water and nitrogen availability in a natural, second-growth, mixed hardwood forest in northern Michigan, USA. As expected, the addition of water and water plus nitrogen resulted in a significant overall increase in the production of new fine roots. New root production was much greater in response to water plus nitrogen when compared with water alone, and the duration of new root production was related to the length of resource addition in the water plus nitrogen treatments; the average difference in new root length between the 20 vs. 40 d additions of water plus nitrogen amounted to almost 600%. Roots produced in response to the additions of water and water plus nitrogen lived longer than roots in the control treatments. Thus, additions of water and water plus nitrogen influenced both the proliferation of new roots and their longevity, with both proliferation and longevity related to the type and duration of resource supply. Results suggest that root longevity and mortality may be plastic in response to changes in soil resource availability, as is well known for root proliferation.

Shigella dysenteriae type 1 infections in US travellers to Mexico, 1988

In 1825, the actuary Benjamin Gompertz read a paper, ‘On the nature of the function expressive of the law of human mortality, and on a new mode of determining the value of life contingencies’, to the Royal Society in which he showed that over much of the adult human lifespan, age-specific mortality rates increased in an exponential manner. Gompertz's work played an important role in shaping the emerging statistical science that underpins the pricing of life insurance and annuities. Latterly, as the subject of ageing itself became the focus of scientific study, the Gompertz model provided a powerful stimulus to examine the patterns of death across the life course not only in humans but also in a wide range of other organisms. The idea that the Gompertz model might constitute a fundamental ‘law of mortality’ has given way to the recognition that other patterns exist, not only across the species range but also in advanced old age. Nevertheless, Gompertz's way of representing the function expressive of the pattern of much of adult mortality retains considerable relevance for studying the factors that influence the intrinsic biology of ageing. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

A demographic analysis of the Wisconsin Regional Primate Center rhesus colony, 1962-1982

A detailed demographic analysis was made of the Wisconsin Regional Primate Research Center rhesus colony from vital statistics recorded over a 20-year period. Techniques used were based on demographic and epidemiological methods developed for human populations, which provide the potential for making standardized measurements within captive primate colonies. A life table based on 1,086 deaths showed an abnormally high survivorship at the older ages, probably caused by a tendency to retain especially robust animals for breeding purposes. During the period of study, 2,194 animals were removed for sale or research. Removal rates were relatively uniform across ages. Age-specific fertility rates based on 1,616 births occurring during the second decade showed a relatively rapid increase in births from about age 2 through age 12, with peak fertility persisting until about age 20. Vital events showed significant seasonality, with a birth peak in April and May. Analysis of the stable age structure (excluding removal) showed an intrinsic growth rate of 6.3%. With removal rates added, the growth rate dropped to -0.3%. Although the use of these methods is probably warranted onlyby the level of detail found in captive colony records, analysis of captive colonies can provide information relevant to the demography of wild primates.