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At least 937 records · Page 52Linked to original sources
PubMed2001

Rationale, design, methods and baseline demography of participants of the Anglo-Scandinavian Cardiac Outcomes Trial. ASCOT investigators.

OBJECTIVE: To test the primary hypothesis that a newer antihypertensive treatment regimen (calcium channel blocker +/- an angiotensin converting enzyme inhibitor) is more effective than an older regimen (beta-blocker +/- a diuretic) in the primary prevention of coronary heart disease (CHD). To test a second primary hypothesis that a statin compared with placebo will further protect against CHD endpoints in hypertensive subjects with a total cholesterol < or = 6.5 mmol/l. DESIGN: Prospective, randomized, open, blinded endpoint trial with a double-blinded 2 x 2 factorial component. SETTING: Patients were recruited mainly from general practices. PATIENTS: Men and women aged 40-79 were eligible if their blood pressure was > or = 160 mmHg systolic or > or = 100 mmHg diastolic (untreated) or > or = 140 mmHg systolic or > or = 90 mmHg diastolic (treated) at randomization. INTERVENTIONS: Patients received either amlodipine (5/ 10 mg) +/- perindopril (4/8 mg) or atenolol (50/ 100 mg) +/- bendroflumethiazide (1.25/2.5 mg) +K+ with further therapy as required to reach a blood pressure of < or = 140 mmHg systolic and 90 mmHg diastolic. Patients with a total cholesterol of < or = 6.5 mmol/l were further randomized to receive either atorvastatin 10 mg or placebo daily. MAIN OUTCOME MEASURE: Non-fatal myocardial infarction (MI) and fatal coronary heart disease (CHD). RESULTS: 19 342 men and women were initially randomized, of these 10297 were also randomized into the lipid-lowering limb. All patients had three or more additional cardiovascular risk factors. CONCLUSIONS: The study has 80% power (at the 5% level) to detect a relative difference of 20% in CHD endpoints between the calcium channel blocker-based regimen and the beta-blocker-based regimen. The lipid-lowering limb of the study has 90% power at the 1% level to detect a relative difference of 30% in CHD endpoints between groups.

Adrenergic beta-Antagonists↗
PubMed2001

Human demography and reserve size predict wildlife extinction in West Africa.

Species-area models have become the primary tool used to predict baseline extinction rates for species in isolated habitats, and have influenced conservation and land-use planning worldwide. In particular, these models have been used to predict extinction rates following the loss or fragmentation of natural habitats in the absence of direct human influence on species persistence. Thus, where direct human influences, such as hunting, put added pressure on species in remnant habitat patches, we should expect to observe extinction rates higher than those predicted by simple species-area models. Here, we show that extinction rates for 41 species of large mammals in six nature reserves in West Africa are 14-307 times higher than those predicted by models based on reserve size alone. Human population and reserve size accounted for 98% of the observed variation in extinction rates between reserves. Extinction occurred at higher rates than predicted by species-area models for carnivores, primates and ungulates, and at the highest rates overall near reserve borders. Our results indicate that, where the harvest of wildlife is common, conservation plans should focus on increasing the size of reserves and reducing the rate of hunting.

Animals↗
PubMed2004

Influence of food availability on demography and local population dynamics in a long-lived seabird.

Few studies have addressed the effects of food availability as a proximate factor affecting local adult survival in long-lived organisms and their consequences at local population dynamics. We used capture-recapture analysis of resightings of 10 birth cohorts of ringed Audouin's gulls, Larus audouinii, to estimate adult survival and dispersal (both emigration and immigration). For the first time, permanent emigration (the transient effect in capture-recapture analysis) was modelled for the whole population and not only for the newly marked birds. Gulls exploit to a large extent fishes discarded from trawlers, and a trawling moratorium established since 1991 has decreased food supply for the colony. This was used as a natural experiment of food availability to assess its effects on adult survival and emigration. These and other demographic parameters were used in a projection modelling to assess the probabilities of extinction of the colony under two scenarios of lower and higher food availability. Food availability (together with the age of individuals) influenced emigration probabilities, but not adult survival, which was estimated at 0.91 (s.e. = 0.02). When food was in shorter supply during the chick-rearing period, emigration was very high (ca. 65%) for younger breeders, although this rate decreased sharply with age. Probabilities of extinction were very high when food availability was low, and when environmental stochasticity was introduced, and only stochastic immigration from the outside seemed to prevent extinction. The results highlight the importance of dispersal processes in the population dynamics of long-lived organisms.

Animal Nutritional Physiological Phenomena↗
PubMed2002

Genetic evidence on the demography of speciation in allopatric dolphin species.

Under a neutral model, the stochastic lineage sorting that leads to gene monophyly proceeds slowly in large populations. Therefore, in many recent species with large population size, the genome will have mixed support for monophyly unless historical bottlenecks have accelerated coalescence. We use genealogical patterns in mitochondrial DNA and in introns of four nuclear loci to test for historical bottlenecks during the speciation and divergence of two temperate Lagenorhynchus dolphin species isolated by tropical Pacific waters (an antitropical distribution). Despite distinct morphologies, foraging behaviors, and mitochondrial DNAs, these dolphin species are polyphyletic at all four nuclear loci. The abundance of shared polymorphisms between these sister taxa is most consistent with the maintenance of large effective population sizes (5.09 x 10(4) to 10.9 x 10(4)) during 0.74-1.05 million years of divergence. A variety of population size histories are possible, however. We used gene tree coalescent probabilities to explore the rejection region for historical bottlenecks of different intensity given best estimates of effective population size under a strict isolation model of divergence. In L. obliquidens the data are incompatible with a colonization propagule of an effective size of 10 or fewer individuals. Although the ability to reject less extreme historical bottlenecks will require data from additional loci, the intermixed genealogical patterns observed between these dolphin sister species are highly probable only under an extended history of large population size. If similar demographic histories are inferred for other marine antitropical taxa, a parsimonious model for the Pleistocene origin of these distributions would not involve rare breaches of a constant dispersal barrier by small colonization propagules. Instead, a history of large population size in L. obliquidens and L. obscurus contributes to growing biological and environmental evidence that the equatorial barrier became permeable during glacial/interglacial cycles, leading to vicariant isolation of antitropical populations.

Animals↗
PubMed2007

Environmental variation and experience-related differences in the demography of the long-lived black-browed albatross.

1. It has been largely demonstrated that demographic performances of animals increase with age or experience as a result of an improvement of foraging skills, an increasing reproductive effort or a selection process. However, little is known about the age or experience-related response of populations to environmental variations. Theoretical studies consider that age-related variations of the performances are greater under more restricting conditions, but this has rarely been tested. 2. We tested this hypothesis on a long-lived species, black browed albatross Thalassarche melanophrys Temminck, using a long-term capture-mark-recapture data set. We investigated the responses of a population to climate, by studying the effects of climatic factors and breeding experience on survival and breeding success. 3. First-time breeders appear to be poorer performers compared with experienced adults, with lower reproductive success and lower survival. In addition, interannual variations of demographic traits were partly explained by climatic indices, reflecting environmental variations. The survival probability of black-browed albatrosses varied with experience and climate, and differences being greater under harsh conditions. By contrast, the reproductive success of inexperienced individuals was affected by climatic fluctuations in the same way as the experienced ones. 4. First breeding event acts as a strong selective process on the highly heterogeneous class of inexperienced individuals, suggesting the increase in survival and breeding success with experience may mainly reflect a reduction in the heterogeneity among individual qualities.

Animals↗
PubMed2004

Genetic divergence, population structure and historical demography of rare springsnails (Pyrgulopsis) in the lower Colorado River basin.

Springsnails of the genus Pyrgulopsis are the most diverse group of freshwater gastropods in North America and current estimates show that Pyrgulopsis contains ~120 different species, many of which are at risk of extinction. Some factors contributing to their exceptional diversity include poor dispersal ability and extreme habitat specificity based on water availability, chemistry and depth. Most taxa exhibit high degrees of endemism, with many species occurring only in a single spring or seep, making springsnails ideal for studies of speciation and population structure. Here I present data from a survey of genetic variation at the mitochondrial gene cytochrome oxidase I from 37 populations and over 1000 individuals belonging to 16 species of Pyrgulopsis distributed throughout the lower Colorado River basin. High levels of interspecific sequence divergence indicate that Pyrgulopsis may have colonized this region multiple times beginning in the late Miocene (~6 Ma); earlier than previous estimates based on fossil evidence. Estimates of nucleotide diversity differ greatly among species and may reflect differences in demographic processes. These results are used to identify factors contributing to radiation of species in this region. The implications of this evolutionary history and genetic variation are discussed in relation to future management and conservation.

Animals↗
PubMed2004

Breeding system and demography shape population genetic structure across ecological and climatic zones in the African freshwater snail, Bulinus forskalii (Gastropoda, Pulmonata), intermediate host for schistosomes.

The role of breeding system and population bottlenecks in shaping the distribution of neutral genetic variation among populations inhabiting patchily distributed, ephemeral water bodies was examined for the hermaphroditic freshwater snail Bulinus forskalii, intermediate host for the medically important trematode Schistosoma guineensis. Levels of genetic variation at 11 microsatellite loci were assessed for 600 individuals sampled from 19 populations that span three ecological and climatic zones (ecozones) in Cameroon, West Africa. Significant heterozygote deficiencies and linkage disequilibria indicated very high selfing rates in these populations. Despite this and the large genetic differentiation detected between populations, high levels of genetic variation were harboured within these populations. The high level of gene flow inferred from assignment tests may be responsible for this pattern. Indeed, metapopulation dynamics, including high levels of gene flow as well as extinction/contraction and recolonization events, are invoked to account for the observed population structuring, which was not a consequence of isolation-by-distance. Because B. forskalii populations inhabiting the northern, Sahelian area are subject to more pronounced annual cycles of drought and flood than the southern equatorial ones, they were expected to be subject to population bottlenecks of increased frequency and severity and, therefore, show reduced genetic variability and elevated population differentiation. Contrary to predictions, the populations inhabiting the most northerly ecozone exhibited higher genetic diversity and lower genetic differentiation than those in the most southerly one, suggesting that elevated gene flow in this region is counteracting genetic drift.

Africa↗
PubMed2005

Phylogeography and demography of Guianan harlequin toads (Atelopus): diversification within a refuge.

We investigated the genetic structure of populations of Guianan harlequin toads (genus Atelopus) and their evolutionary affinities to extra-Guianan congeners. Phylogenetic analysis of mitochondrial cytochrome b (cyt b) and NADH dehydrogenase subunit 2 (ND2) gene sequences produced well-supported clades largely corresponding to the four recognized taxa in the Guianas (Atelopus spumarius hoogmoedi, Atelopus spumarius barbotini, Atelopus franciscus, and Atelopus flavescens). Our findings suggest that the Guianan A. spumarius represent distinct evolutionary lineages that merit distinction from Amazonian conspecifics, and that the status of A. flavescens and A. franciscus is somewhat less clear. Approximately 69% of the observed genetic variation is accounted for by differences between these four recognized taxa. Coalescent-based estimates of gene flow between taxa suggest that these lineages are largely isolated from one another. Negligible rates of migration between populations and significant divergence within such close proximity suggests that although the region inhabited by these taxa is almost entirely undisturbed, significant habitat heterogeneity exists as to have produced a remarkable diversification of Atelopus within the eastern Guiana Shield. These results contradict the commonly held view of the Guiana Shield as a 'refuge' whose stability during late Tertiary and Quaternary climatic fluctuations served as a biotic reservoir. Instead, we provide evidence that climatic fluctuations during this time had a diversifying effect within the Guianan region.

Animals↗
PubMed2006

History vs. current demography: explaining the genetic population structure of the common frog (Rana temporaria).

The amount of genetic variability at neutral marker loci is expected to decrease, and the degree of genetic differentiation among populations to increase, as a negative function of effective population size. We assessed the patterns of genetic variability and differentiation at seven microsatellite loci in the common frog (Rana temporaria) in a hierarchical sampling scheme involving three regions (208-885 km apart), three subregions within regions and nine populations (5-20 km apart) within subregions, and related the variability and differentiation estimates to variation in local population size estimates. Genetic variability within local populations decreased significantly with increasing latitude, as well as with decreasing population size and regional site occupancy (proportion of censured localities occupied). The positive relationship between population size and genetic variability estimates was evident also when the effect of latitude (cf. colonization history) was accounted for. Significant genetic differentiation was found at all hierarchical levels, and the degree of population differentiation tended to increase with increasing latitude. Isolation by distance was evident especially at the regional sampling level, and its strength increased significantly towards the north in concordance with decreasing census and marker-based neighbourhood size estimates. These results are in line with the conjecture that the influence of current demographic factors can override the influence of historical factors on species population genetic structure. Further, the observed reductions in genetic variability and increased degree of population differentiation towards the north are in line with theoretical and empirical treatments suggesting that effective population sizes decline towards the periphery of a species' range.

Alleles↗
PubMed2006

Demography, altruism, and the benefits of budding.

It is now widely appreciated that competition between kin inhibits the evolution of altruism. In standard population genetics models, it is difficult for indiscriminate altruism towards social partners to be favoured at all. The reason is that while limited dispersal increases the kinship of social partners it also intensifies local competition. One solution that has received very little attention is if individuals disperse as groups (budding dispersal), as this relaxes local competition without reducing kinship. Budding behaviour is widespread through all levels of biological organization, from early protocellular life to cooperatively breeding vertebrates. We model the effects of individual dispersal, budding dispersal, soft selection and hard selection to examine the conditions under which altruism is favoured. More generally, we examine how these various demographic details feed into relatedness and scale of competition parameters that can be included into Hamilton's rule.

Altruism↗
PubMed1981

Demography of arterial surgery in New South Wales.

IN New South Wales in 1978, 2545 patients received arterial reconstructions excluding procedures which were primarily intrathoracic. Seventy-one per cent of these involved the abdominal aorta and lower limb arteries, 22 per cent were associated with renal transplantation and angioaccess, while only seven per cent involved the extracranial arteries. Fifty-two surgeons regularly practised arterial surgery of whom 39 worked in the metropolitan health regions and 13 in country areas. The optimum number required for the whole state probably lies between 30 and 50. On a population basis the number of aortic and lower limb reconstruction seems appropriate to the projected need based on clinical indications, but the number of carotid reconstructions was less than 10 per cent of the projected need.

Australia↗
PubMed1993

Projecting the need for physicians to care for older persons: effects of changes in demography, utilization patterns, and physician productivity.

OBJECTIVE: To determine the influence of differing assumptions of population growth, visit rates, prevalence of functional impairment, physician productivity, and hospitalization rates on projected need for physicians to provide medical care for older persons. DESIGN: Sensitivity analysis of a manpower model. MAIN RESULTS: The factors that appear to have the most impact on projections of physician need are related to physician productivity, especially delegation to mid-level providers, and case-mix. Other factors, such as the variability of census projections and per capita visit rates, are likely to have less effect on overall physician supply needs. CONCLUSIONS: Although case mix and delegation to mid-level providers may both substantially affect the need for physician supply to care for older persons, only the latter can be directly affected by health policy decisions. Consideration should be given to increasing the supply of mid-level providers and providing incentives for patients and physicians to receive and provide care in delivery systems that utilize mid-level providers extensively.

Activities of Daily Living↗
PubMed1999

Demography and seasonal variation of acute necrotising gingivitis in Nairobi, Kenya.

The objectives of this study were to determine the frequency of Acute Necrotising Gingivitis (ANG), its sex and age distribution, ethnicity and seasonal variation amongst patients at the Dental Unit of Kenyatta National Hospital (KNH) in Nairobi, Kenya. Cards of patients who were seen in the Dental Unit of KNH in 1992/1993, were scrutinised for positive diagnosis of ANG, age, sex, presenting signs and symptoms and treatment that was given. Of the 53,572 patients who were treated, (0.15 per cent) had ANG. Their age range was 1.5-46 years (Mean = 14.5 years), with 58.5 per cent being below 11 years and 32.9 per cent being between 21 and 40 years. The most affected ethnic groups were the Luos and Kikuyus, while 72 per cent of the patients were seen in March and April, and between September and December. It is concluded that the frequency of ANG was low, ANG affected children and adults, and that ANG varied seasonally.

Acute Disease↗
PubMed2005

How science survived: medieval manuscripts' "demography" and classic texts' extinction.

Determining what fraction of texts and manuscripts have survived from Antiquity and the Middle Ages has been highly problematic. Analyzing the transmission of texts as the "paleodemography" of their manuscripts yields definite and surprisingly high estimates. Parchment copies of the foremost medieval textbooks on arithmetical and calendrical calculation closely fit age distributions expected for populations with logistic growth and manuscripts with exponential survivorship. The estimated half-lives of copies agree with Bischoff's paleographically based suggestion that roughly one in seven manuscripts survive in some form from ninth-century Carolingian workshops. On this basis, many if not most of the leading technical titles circulating in Latin probably survived, even from late Antiquity.

History, 15th Century↗