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PubMed2003

Taking malaria transmission out of the bottle: implications of mosquito dispersal for vector-control interventions.

Most malaria transmission models assume enclosed systems of people, parasites, and vectors in which neither emigration nor immigration of mosquitoes is considered. This simplification has facilitated insightful analyses but has substantial limitations for evaluating control measures in the field. Here we show that mosquito dispersal can confound conventional approaches to evaluating malaria vector-control interventions, and explore this association with a model of two villages between which mosquito subpopulation exchange occurs. Exchange of mosquitoes between such subpopulations can readily explain the discrepancy between experimental efficacy measurements for insecticide-treated nets and their much lower apparent effectiveness when in use. Our results indicate that current approaches to assessing malaria interventions that confer community-level protection may be severely compromised by mosquito dispersal in many endemic settings. The true effectiveness of many vector-control methods may be much greater than previously appreciated and the application of such interventions should be consolidated into larger contiguous spatial units so that more effective local suppression of malaria can be achieved. Spatially explicit modelling formats that consider vector dispersal as a determinant of malaria transmission and control are needed urgently for rational planning and evaluation of efforts to roll back malaria.

Animals↗

PubMed2006

Diversity and dispersal interactively affect predictability of ecosystem function.

Theory and small-scale experiments predict that biodiversity losses can decrease the magnitude and stability of ecosystem services such as production and nutrient cycling. Most of this research, however, has been isolated from the immigration and emigration (dispersal) processes that create and maintain diversity in nature. As common anthropogenic drivers of biodiversity change--such as habitat fragmentation, species introductions and climate change--are mediated by these understudied processes, it is unclear how environmental degradation will affect ecosystem services. Here we tested the interactive effects of mobile grazer diversity and dispersal on the magnitude and stability of ecosystem properties in experimental seagrass communities that were either isolated or connected by dispersal corridors. We show that, contrary to theoretical predictions, increasing the number of mobile grazer species in these metacommunities increased the spatial and temporal variability of primary and secondary production. Moreover, allowing grazers to move among and select patches reduced diversity effects on production. Finally, effects of diversity on stability differed qualitatively between patch and metacommunity scales. Our results indicate that declining biodiversity and habitat fragmentation synergistically influence the predictability of ecosystem functioning.

Animal Migration↗

PubMed2003

Estimating tsetse population parameters: application of a mathematical model with density-dependence.

A density-dependent model is used to describe the dynamics of an open population of tsetse flies (Diptera: Glossinidae). Immigration (or emigration) takes place when the total population is below (or above) a biologically determined threshold value. The population is also subjected to birth and death rates, as well as to the risk of being trapped (continuously or intermittently). During trapping the population decreases toward a 'low' equilibrium population and when trapping ceases the population starts recovering and increases toward a 'high' equilibrium. The model is fitted using data collected on trapped flies in four experiments. The first one was conducted with 'intermittent trapping' (i.e. several trapping-recovery cycles) on Glossina fuscipes fuscipes Newstead in the Central African Republic (Bangui area). In the other experiments, trapping data on Glossina palpalis palpalis (Robineau-Desvoidy) was collected in 'aggregate' form over several days at a time. Two of these were in Congo-Brazzaville (Bouenza area) and one in the Ivory Coast (Vavoua focus). Estimates are derived for the low and high equilibrium values as well as the trapping rate. The estimated effect of sustained trapping is to reduce the population to low equilibrium values that are 85-87% lower than the levels without trapping. The effects of the natural intrinsic growth and of the migration flows cannot be estimated separately because in the model they are mathematically indistinguishable.

Animal Migration↗

PubMed1983

Marking snails with nail varnish as a field experimental technique.

The use of nail varnish to mark snails for release and recapture in aquatic habitats in the Gezira Irrigation Canals has been evaluated. The nail varnish withstood immersion in canal water and adhered to the snail shell. The recovery of marked snails from a backwater site in a slow moving canal was satisfactory and indicated the usefulness of the technique in predicting changing patterns of immigration and emigration of snails. The method may also indicate ecological changes which affect the stability and mobility of snail populations and yield data on growth rates and longevity.

Animal Identification Systems↗

PubMed2004

Dispersal, eviction, and conflict in meerkats (Suricata suricatta): an evolutionarily stable strategy model.

Decisions regarding immigration and emigration are crucial to understanding group dynamics in social animals, but dispersal is rarely treated in models of optimal behavior. We developed a model of evolutionarily stable dispersal and eviction strategies for a cooperative mammal, the meerkat Suricata suricatta. Using rank and group size as state variables, we determined state-specific probabilities that subordinate females would disperse and contrasted these with probabilities of eviction by the dominant female, based on the long-term fitness consequences of these behaviors but incorporating the potential for error. We examined whether long-term fitness considerations explain group size regulation in meerkats; whether long-term fitness considerations can lead to conflict between dominant and subordinate female group members; and under what circumstances those conflicts were likely to lead to stability, dispersal, or eviction. Our results indicated that long-term fitness considerations can explain group size regulation in meerkats. Group size distributions expected from predicted dispersal and eviction strategies matched empirical distributions most closely when emigrant survival was approximately that determined from the field study. Long-term fitness considerations may lead to conflicts between dominant and subordinate female meerkats, and eviction is the most likely result of these conflicts. Our model is computationally intensive but provides a general framework for incorporating future changes in the size of multimember cooperative breeding groups.

Animal Migration↗

PubMed1997

The effective size of a subdivided population.

This paper derives the long-term effective size, Ne, for a general model of population subdivision, allowing for differential deme fitness, variable emigration and immigration rates, extinction, colonization, and correlations across generations in these processes. We show that various long-term measures of Ne are equivalent. The effective size of a metapopulation can be expressed in a variety of ways. At a demographic equilibrium, Ne can be derived from the demography by combining information about the ultimate contribution of each deme to the future genetic make-up of the population and Wright's FST's. The effective size is given by Ne = 1/(1 + var (upsilon) ((1 - FST)/Nin), where n is the number of demes, theta i is the eventual contribution of individuals in deme i to the whole population (scaled such that sigma theta i = n), and < > denotes an average weighted by theta i. This formula is applied to a catastrophic extinction model (where sites are either empty or at carrying capacity) and to a metapopulation model with explicit dynamics, where extinction is caused by demographic stochasticity and by chaos. Contrary to the expectation from the standard island model, the usual effect of population subdivision is to decrease the effective size relative to a panmictic population living on the same resource.

Models, Genetic↗

PubMed2006

Increasing geographical inequalities in health in New Zealand, 1980-2001.

BACKGROUND: Recent studies have noted widening health inequalities between rich and poor areas in a number of OECD countries. This paper examines whether health in New Zealand has become more geographically polarized during the period 1980-2001, a time of rapid social and economic changes in New Zealand society. METHODS: Mortality records for each year between 1980 and 2001 were extracted for consistent geographical areas: the 21 District Health Boards operating in New Zealand in 2001 and used to calculate male and female life expectancies for each area. The geographical inequalities in life expectancy were measured by calculating the slope index of inequality for each year between 1980 and 2001. RESULTS: Although overall life expectancy has increased during the period of study, New Zealand has experienced increased spatial polarization in health, with a particularly sharp rise in inequality during the late 1980s and early 1990s. Since the mid-1990s regional inequality has remained at stable but high levels. The polarization in mortality was mirrored by a growth in income inequality during the 1980s and 1990s. CONCLUSIONS: Health inequalities as expressed geographically in New Zealand have reached historically high levels and show little sign of abating. In order to tackle health inequalities, a greater commitment by the New Zealand government to a more redistributive social and economic agenda is required. Furthermore, issues of differentiated and health selective migration, emigration, and immigration need to be addressed as if these are important they should matter more for New Zealand than for almost any other developed nation-state.

Aged↗

PubMed1981

Predicting the need for primary care specialists: the example of a southwestern state.

Because of a need to project the requirements for the training of primary care practitioners in the state of New Mexico, we reviewed available means of determining health manpower needs. Combining several of these methods, we constructed a three-tiered model, taking into account different patterns of care-seeking in areas of various population densities. These methods may be applicable in other states like New Mexico where densely populated cities contrast with sparsely settled rural areas. All such methods, however, are confounded by the state of balance of many factors, including immigration and emigration of physicians, use of nonphysician providers, and patient movement across boundaries for care. This report contributes to the growing literature on health manpower needs by recognizing and attempting to account for differences between urban and rural patterns of care-seeking.

Forecasting↗

PubMed2002

Volatiles from potato plants infected with potato leafroll virus attract and arrest the virus vector, Myzus persicae (Homoptera: Aphididae).

The influence of viral disease symptoms on the behaviour of virus vectors has implications for disease epidemiology. Here we show that previously reported preferential colonization of potatoes infected by potato leafroll virus (genus Polerovirus) (luteovirus) (PLRV) by alatae of Myzus persicae, the principal aphid vector of PLRV, is influenced by volatile emissions from PLRV-infected plants. First, in our bioassays both differential immigration and emigration were involved in preferential colonization by aphids of PLRV-infected plants. Second, M. persicae apterae aggregated preferentially, on screening above leaflets of PLRV-infected potatoes as compared with leaflets from uninfected plants, or from plants infected with potato virus X (PVX) or potato virus Y (PVY). Third, the aphids aggregated preferentially on screening over leaflet models treated with volatiles collected from PLRV-infected plants as compared with those collected from uninfected plants. The specific cues eliciting the aphid responses were not determined, but differences between headspace volatiles of infected and uninfected plants suggest possible ones.

Animals↗

PubMed2001

Gene expression profiling in human fetal liver and identification of tissue- and developmental-stage-specific genes through compiled expression profiles and efficient cloning of full-length cDNAs.

Fetal liver intriguingly consists of hepatic parenchymal cells and hematopoietic stem/progenitor cells. Human fetal liver aged 22 wk of gestation (HFL22w) corresponds to the turning point between immigration and emigration of the hematopoietic system. To gain further molecular insight into its developmental and functional characteristics, HFL22w was studied by generating expressed sequence tags (ESTs) and by analyzing the compiled expression profiles of liver at different developmental stages. A total of 13,077 ESTs were sequenced from a 3'-directed cDNA library of HFL22w, and classified as follows: 5819 (44.5%) matched to known genes; 5460 (41.8%) exhibited no significant homology to known genes; and the remaining 1798 (13.7%) were genomic sequences of unknown function, mitochondrial genomic sequences, or repetitive sequences. Integration of ESTs of known human genes generated a profile including 1660 genes that could be divided into 15 gene categories according to their functions. Genes related to general housekeeping, ESTs associated with hematopoiesis, and liver-specific genes were highly expressed. Genes for signal transduction and those associated with diseases, abnormalities, or transcription regulation were also noticeably active. By comparing the expression profiles, we identified six gene groups that were associated with different developmental stages of human fetal liver, tumorigenesis, different physiological functions of Itoh cells against the other types of hepatic cells, and fetal hematopoiesis. The gene expression profile therefore reflected the unique functional characteristics of HFL22w remarkably. Meanwhile, 110 full-length cDNAs of novel genes were cloned and sequenced. These novel genes might contribute to our understanding of the unique functional characteristics of the human fetal liver at 22 wk.

Cloning, Molecular↗

PubMed2007

Modelling population redistribution in a leaf beetle: an evaluation of alternative dispersal functions.

1. Dispersal is a fundamental ecological process, so spatial models require realistic dispersal kernels. We compare five different forms for the dispersal kernel of the tansy beetle Chrysolina graminis moving between patches of its host-plant (tansy Tanacetum vulgare) in a riparian landscape. 2. Multi-patch mark-recapture data were collected every 2 weeks over 2 years within a large network of patches and from 2226 beetles. Dispersal was common (28.4% of 880 recaptures after a fortnight) and was more likely over longer intervals, out of small patches, for females and during flooding. Interpatch movement rates did not differ between years and exhibited no density dependence. Dispersal distances were similar for males and females, in both years and over all intervals, with a median dispersal distance of just 9.8 m, although a maximum of 856 m was recorded. 3. A model of dispersal, where patches competed for dispersers based on their size and distance from the beetle's source patch (scaled by the dispersal kernel) was fitted to the field data with a maximum likelihood procedure and each of five alternative kernels. The best fitting had relatively extended tails of long-distance dispersal, while Gaussian and negative exponential kernels performed worst. 4. The model suggests that females disperse more commonly than males and that both are strongly attracted to large patches but do not differ between years, which are consistent with the empirical results. Model-predicted emigration and immigration rates and dispersal phenologies match those observed, suggesting that the model captured the major drivers of tansy beetle dispersal. 5. Although negative exponential and Gaussian kernels are widely used for their simplicity, we suggest that these should not be the models of automatic choice, and that fat-tailed kernels with relatively higher proportions of long-distance dispersal may be more realistic.

Animals↗

PubMed1991

Automatic recording of flea activity.

An Insect Activity Monitor was created to measure the behavioural responses of fleas (Siphonaptera). The apparatus allows for a range of visual, chemo- and mechanoreceptor cues to be presented. The jumping response is detected by counting amplified pulses produced as the fleas land on a stretched membrane held over a microphone. Horizontal movements are detected using a system of infra-red beams and phototransistors which, when broken, are counted as a measure of activity. The apparatus was tested using Ceratophyllus hirundinis (Curtis), Ceratophyllus farreni (Rothschild) and Ceratophyllus rusticus (Wagner), co-inhabiting species from the nests of the house martin (Delichon u.urbica L.). No unaided emigration or immigration has been demonstrated in these species (Clark, 1988) and much of their time is spent confined to the darkness of the nest. In addition to species contrasts, females were more active than males and fleas were more active at 25 degrees C than at 18 degrees C. The more active bird flea Ceratophyllus garei (Rothschild) from the nest of pheasant (Phasianus colchicus L), was tested for responses to light of varying intensity. Activity was stimulated by white light, but not proportional to light intensity.

Analysis of Variance↗

PubMed1988

The development of antisocial behaviour and sudden violent death.

In order to detect possible relationships between antisocial behaviour and the incidence of "sudden violent death" in young people, information relating to mortality in antisocial Swedish adolescents has been traced and compiled. A register was drawn up covering those young persons (1,056; 832 boys and 224 girls; mean age 16 years) who were admitted to Swedish probationary schools during the period 1 January - 31 December 1967. Using the registers of immigration and emigration, and causes of death kept by SCB (Statistiska Centralbyrån), mortality occurring between 1 January 1967 - 31 December 1985 was tabulated. One hundred and ten boys (13%) and 22 girls (10%) had died. The deaths had occurred at a rate of approximately seven new deaths per observation year, the youngest being still in their teens when they died. For comparison, the criteria set up by insurance companies for life insurance premiums are based on a death expectancy for healthy Swedish boys and girls in the age groups corresponding to the subjects under observation of 1.2-3.1% for boys and 1.1-2.6% for girls. Eighty-eight percent of the dead boys and 77% of the dead girls had died "sudden violent deaths" - accidents, suicides, death from uncertain causes, murder/manslaughter, or alcohol/drug abuse. For both sexes, death from uncertain causes and suicides were the most frequent single causes of death. Death as a direct result of alcohol/drug abuse occurred only in boys. The results give support to the assumption that a link exists between childhood environment, the development of antisocial behaviour/mental insufficiency and a "sudden violent death" at an early age.(ABSTRACT TRUNCATED AT 250 WORDS)

Accidents↗

PubMed2006

Death and suicide among former child and adolescent psychiatric patients.

BACKGROUND: Increased mortality rates among previous child and adolescent psychiatry (CAP) patients have been found in Scandinavian studies up to the 1980s. The suicide risk in this group has been estimated to be almost five times higher than expected. This article addresses two questions: Do Swedish CAP patients continue to risk premature death and what kind of information related to psychiatric symptoms and/or behavior problems can predict later suicide? METHODS: Hospital files, Sweden's census databases (including immigration and emigration) and administrative databases (including the Swedish Hospital Discharge register and the Persons Convicted of Offences register), and the Cause of Death register were examined to determine the mortality rate in a group of 1,400 former CAP inpatients and outpatients over a period of 12-33 years. Observed and expected numbers of deceased were calculated with the prospective method and the standardized mortality ratio (SMR) method. The relative risk or the risk ratio (RR) is presented with 95% confidence intervals (CIs). Significance level tests were made using two-by-two tables and chi-square tests. The Cox proportional-hazards regression model was used for survival analysis. RESULTS: Twenty-four males and 14 females died. Compared with the general population, the standardized mortality ratio in this group of CAP patients was significantly higher in both sexes. Behavioral problems, school problems, and co-morbid alcohol or drug abuse and criminality (including alcohol-related crimes) were found to be important predictors. Thirty-two deaths were attributed to suicide, intoxication, drug overdose, or accident; one patient died of an alcohol abuse-related disorder, and five patients died of natural causes. Suicide was the most common cause of death, but only 2 of these 19 cases were initially admitted for attempted suicide. CONCLUSION: We suggest that suicide and death prevention among CAP patients may not be a psychiatric issue per se but a future function of society's juvenile social-welfare investments and juvenile-delinquency prevention programs.

Adolescent↗

PubMed2006

Do top-down or bottom-up forces determine Stephanitis pyrioides abundance in urban landscapes?

This study examined the influence of habitat structural complexity on the collective effects of top-down and bottom-up forces on herbivore abundance in urban landscapes. The persistence and varying complexity of urban landscapes set them apart from ephemeral agroecosystems and natural habitats where the majority of studies have been conducted. Using surveys and manipulative experiments. We explicitly tested the effect of natural enemies (enemies hypothesis), host plant quality, and herbivore movement on the abundance of the specialist insect herbivore, Stephanitis pyrioides, in landscapes of varying structural complexity. This herbivore was extremely abundant in simple landscapes and rare in complex ones. Natural enemies were the major force influencing abundance of S. pyrioides across habitat types. Generalist predators, particularly the spider Anyphaena celer, were more abundant in complex landscapes. Predator abundance was related to greater abundance of alternative prey in those landscapes. Stephanitis pyrioides survival was lower in complex habitats when exposed to endemic natural enemy populations. Laboratory feeding trials confirmed the more abundant predators consumed S. pyrioides. Host plant quality was not a strong force influencing patterns of S. pyrioides abundance. When predators were excluded, adult S. pyrioides survival was greater on azaleas grown in complex habitats, in opposition to the observed pattern of abundance. Similarly, complexity did not affect S. pyrioides immigration and emigration rates. The complexity of urban landscapes affects the strength of top-down forces on herbivorous insect populations by influencing alternative prey and generalist predator abundance. It is possible that habitats can be manipulated to promote the suppressive effects of generalist predators.

Animals↗

PubMed1985

[Predictability of demographic changes in the short run].

The author discusses the value of univariate time series models to assess the accuracy of official short-term population forecasts in the Netherlands. "Three time series methods (exponential smoothing, ARIMA-model and structural time series model) are applied to Dutch data on live births, deaths, marriages, immigrants and emigrants." The data concern the period 1979-1984. The methods are also applied to data for the period 1970-1975 for comparative purposes. (summary in ENG)

Demography↗

PubMed1991

Functional anatomy of the thymic microenvironment.

This paper presents a review of our current understanding of the nature of the thymic microenvironment, after briefly considering the major role of the gland. The epithelial cells and their products are of fundamental importance, and other cells of the macrophage series are implicated in most functional events. The embryological origin of the epithelium is still not clear, although disease conditions would suggest a single origin. Immigration and emigration of thymocytes is considered, and also the passage of antigens into the gland. The events within the thymus are under the control of the CNS acting through the innervation or via hormonal pathways. Both of these areas are considered in detail, especially thymic hormone origins, functions and interactions.

Animals↗

PubMedDate not supplied

[Demography and cause of death in a Local Health Unit in Lombardy].

We studied demography from 1980 to 1987 and death causes in the population of the USSL 12 of LombardY in 1986-1987. The USSL includes 63,255 inhabitants on a surface of 60 km2. BIRTH and mortality rates. We collected data about births, deaths, immigration and emigration in every municipality of USSL 12 from 1980 to 1987. In those years the birth rates was constant about 10% and mortality rate was about 8%. We did not find significant phenomena of migration. The fertility rate in 1987 shows two peaks: the first at the age of 26-27 years, the second at the age of 31 years. Population distribution in age classes. We compared the population distribution in 1971 to the distribution in 1981. We found a decrease of 20% in population under 20 and an increase of 24% in population over 65 years. These increase is higher in females (relative increase of 62%) then in males (relative increase of 28%). Ages and death causes. The death age average in 1986-1987 is 67 years for males and 73 years for females. Under 65 years the more frequent and important death causes are neoplastic diseases (breast, lungs, alimentary tract), cardiovascular diseases, traffic accidents. We registered only 6% of deaths under 40 years of age.

Adolescent↗