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PubMed1989

[Population density as a regulation factor of genetic structure and size of animal populations. Phenotypic variability of reaction to increase in density in Drosophila populations].

The presence of considerable level of phenotypic variability for the nature of fertility change in conditions of imago density increase has been shown in Drosophila natural populations. Genetic peculiarities of insects play the main role in its determination. The genotype groups sensitive and stable to density increase exist in the populations. The former have relatively high fertility at low density and low fertility at overcrowding. The latter are of contrary nature of fertility at given density conditions.

Analysis of Variance↗
PubMed1999

Population density and childhood leukaemia: results of the EUROCLUS Study.

The EUROCLUS study assembled incidence data for 13,551 cases of childhood leukaemia (CL) diagnosed between 1980 and 1989 in 17 countries (or regions of countries). These were referenced by location at diagnosis to small census areas of which there were 25,723 in the study area. Population counts, surface area and, hence, population density were available for all these small areas. Previous analyses have shown limited extra-Poisson variation (EPV) of case counts within small areas; this is most pronounced in areas of intermediate population density (150-499 persons/km2). In this study, the data set was examined in more detail for evidence that variations in incidence and EPV of CL are associated with population density. Incidence showed a curvilinear association with population density and was highest in areas which were somewhat more densely populated (500-750 persons/km2), where the incidence rate ratio relative to areas having > or = 1000 persons/km2 was 1.16 (95% confidence interval 1.07-1.26) and the P value for quadratic trend across eight strata of population density was 0.02. Incidence in these areas is uniformly elevated and showed no evidence of heterogeneity (i.e. EPV). Statistically significant evidence of EPV was evident amongst some of the areas previously classified as intermediate density areas (specifically, those with a density of 250-499 persons/km2, P < 0.001 for CL). These results were interpreted in terms of the current aetiological hypotheses for CL which propose that exposure to localised epidemics of one or more common infectious agent may contribute to the development of leukaemia. They suggest that such epidemics arise regularly in moderately densely populated areas and also sporadically in areas which are somewhat less densely populated. Although other interpretations are possible, these results may assist in the identification of characteristics which infectious agents must possess if direct or indirect causes of CL.

Child↗
PubMedDate not supplied

[Method of mathematical description of the dynamics of cell population density].

The paper presents a method of building a mathematical model of the time dynamics of the cell population density and mitotic index which allows the prediction of the population growth as related to the cultivation conditions. The process of mammalian cell division has been shown to delay noticeably with a decrease of the cultivation temperature from 36 to 30 degrees C and an increase of the initial population density. The curve of the population density has a typical sigmoidal pattern.

Cell Division↗
PubMed2006

Distribution-wide effects of climate on population densities of a declining migratory landbird.

1. Increases in global temperatures have created concern about effects of climatic variability on populations, and climate has been shown to affect population dynamics in an increasing number of species. Testing for effects of climate on population densities across a species' distribution allows for elucidation of effects of climate that would not be apparent at smaller spatial scales. 2. Using autoregressive population models, we tested for effects of the North Atlantic Oscillation (NAO) and the El Niño Southern Oscillation (ENSO) on annual population densities of a North American migratory landbird, the yellow-billed cuckoo Coccyzus americanus, across the species' breeding distribution over a 37-year period (1966-2002). 3. Our results indicate that both the NAO and ENSO have affected population densities of C. americanus across much of the species' breeding range, with the strongest effects of climate in regions in which these climate systems have the strongest effects on local temperatures. Analyses also indicate that the strength of the effect of local temperatures on C. americanus populations was predictive of long-term population decline, with populations that were more negatively affected by warm temperatures experiencing steeper declines. 4. Results of this study highlight the importance of distribution-wide analyses of climatic effects and demonstrate that increases in global temperatures have the potential to lead to additional population declines.

Animals↗
PubMed1976

[Effects of the population density on growth of SD-JCL rats (author's transl)].

The effects of the population density on growth and life span of 21 to 26 months in SD-JCL-rats were investigated. The mean life spans of males and females were 23 and 24 months, respectively. The population density had no definite influence on increase in body weight of females, whereas a most accelerated growth of males was seen with 2 rats per cage. The total amounts of food intake of each animal throughout its life were about 15 and 11 kg for males and females, respectively, and those of water intake were about twice the food. No correlation was observed between the population density and the weights of the liver, kidney, heart and femur, though mals reared at 5 animals per cage had lightest adrenals among all the animals.

Adrenal Glands↗
PubMed1973

Cross-national comparison of population density.

The unresolved difficulties associated with defining and measuring population density strictly circumscribe the scope and nature of the conclusions that can be properly derived from differentials in man:land ratios. Any conclusions about human density will have meaning only to the extent that they are based on a recognition that this density must be viewed in both static and dynamic terms and that it cannot be isolated in analysis, from either the social and cultural setting, the demographic characteristics of the population, or the broader processes of social change within the society. In and of itself, the familiar man:land ratio says more about area than it does about either the human experience of density or the relation of population to resources. This ratio is therefore essentially meaningless as an indicator of comparative conditions of life among different countries and different geographic regions. The mere fact of having a relatively low average population density thus, does not automatically entitle a nation to complacency about its ability to adjust readily to future population change, either in terms of growth in numbers or in the geographic location of its people.

Environmental Pollution↗
PubMed2006

Disentangling contextual effects on cause-specific mortality in a longitudinal 23-year follow-up study: impact of population density or socioeconomic environment?

BACKGROUND: Various studies have investigated urban/rural differences in cause-specific mortality. A separate body of literature has analysed effects of socioeconomic environment on mortality. Almost no studies have attempted to disentangle effects of population density and socioeconomic environment on mortality, beyond the effects of individual characteristics. METHODS: Considering all individuals living in the region of Scania, Sweden, from 1970-93, we performed 10 year mortality follow-ups on (i) individuals aged 55, (ii) individuals aged 65, and (iii) individuals aged 75 years at baseline. Cox multilevel models adjusted for individual factors allowed us to investigate the independent effects of population density and median income in the parish of residence on mortality from ischaemic heart disease (IHD), lung cancer, and chronic obstructive pulmonary disease (COPD) among individuals who had lived in the same parish for at least 10 years prior to mortality follow-up. RESULTS: In females, as in males, after adjustment for individual and contextual socioeconomic status, we found a dose-response association between population density and mortality from lung cancer and COPD in all age groups investigated, and from IHD especially in the youngest age group. Overall, the population density effect was the strongest on lung cancer mortality. Median income had an additional impact only in 2 out of 16 subgroups of age x gender x cause of death. CONCLUSIONS: In our region-wide study conducted at the parish level, contextual disparities in mortality were dominated by the population density effect. However, it may be unwise to conclude that truly contextual effects exist on mortality, before identification of plausible mediating processes through which urbanicity may influence mortality risk.

Aged↗
PubMed1983

Effect of population density on the results of the study of water supplies in five California counties.

Two previous studies (1969-1971 and 1969-1974) examined the association between cancer incidence and chrysotile asbestos ingested through drinking water in the San Francisco-Oakland Standard Metropolitan Statistical Area (SMSA). Population density, an important covariable in the association between cancer and environmental agents, was not included in the analyses of these studies. The present work determines the effect of this covariable on the results of the second San Francisco-Oakland SMSA study. The original and reanalyzed results are compared to reassess the association between cancer and asbestos. The only change in the regression procedures of the original studies was the addition of population density as an independent variable in the reanalysis. The results of the reanalysis showed that population density had little effect on the results of the second study. Slightly more significance was found for asbestos regression coefficients in the reanalysis, including population density, than in the original analysis. These regression coefficients for asbestos indicated a positive association between ingested chrysotile asbestos and some cancer body sites. The conclusion of the reanalysis was that population density was distributed across the San Francisco-Oakland SMSA in such a way that it had little effect on the observation of an association between ingested asbestos and cancer.

Asbestos↗
PubMed1999

Allee effects can both conserve and create spatial heterogeneity in population densities.

In order to determine conditions which allow the Allee effect (caused by biparental reproduction) to conserve and create spatial heterogeneity in population densities, we studied a deterministic model of a symmetric two-patch metapopulation. We proved that under certain conditions there exist stable equilibria with unequal population densities in the two patches, a situation which can be interpreted as conserved heterogeneity. Furthermore, the Allee effect can lead to instability of the equilibrium with equal population densities if some degree of competition is assumed to occur between the subpopulations (non-local competition). This indicates the potential of the Allee effect to create spatial heterogeneity. Neither of these effects appear under biologically realistic parameter values in a model where uniparental reproduction is assumed. We proved that both the between-patch migration intensity and the degree of non-local competition are decisive in determining boundaries between these types of behaviour of the spatial system with Allee effect. Therefore, we propose that the Allee effect, migration intensity, and non-local competition should be considered jointly in studies focusing on problems like pattern formation in space and invasions of spreading species.

Animals↗
PubMed2004

Fertilization in an egg-brooding colonial ascidian does not vary with population density.

The possibility that free-spawning marine organisms may be subject to fertilization failure at low population density (due to the effects of sperm dilution) has sparked much interest, but these effects have been demonstrated only in a few species that broadcast their eggs. Some egg-brooding species may overcome dilution effects by filtering low concentrations of sperm from seawater and fertilizing eggs throughout an extended period of time. We examined the effects of population density and size on fertilization in Botryllus schlosseri, a hermaphroditic colonial ascidian that free-spawns sperm, but broods eggs. We experimentally manipulated the size and density of mating groups and surveyed fertilization levels in natural populations that varied in density. Fertilization was not affected by variation in population size or density in either the experimental or natural populations. Near the end of the reproductive season, some eggs may have been fertilized too late to complete development, suggesting a temporal form of sperm limitation that has not been considered in other systems. We also detected greater variability in fertilization levels at lower population density. Nevertheless, these results suggest that caution must be used in extrapolating reported density effects on fertilization to all taxa of free-spawners; density effects may be reduced in brooders that have efficient sperm collection mechanisms.

Analysis of Variance↗
PubMed2003

Effect of population density on mortality after motor vehicle collisions.

The objective of this study was to evaluate the effect of population density on mortality after traffic crashes. Subjects were the drivers of vehicles requiring towing after collisions, sampled by NASS-GES during 1994-1998. Cases were classified by population of crash location (greater or lesser than 25,000) and by population density of the driver's county of residence (using ZIP code and Census data). Cases were also categorized by age, belt use and vehicle speed. Analytic methods for weighted, stratified survey data were used to estimate effects on mortality. A total of 190,721 cases with a specified crash location were identified in the sample, of which 93.7% had a specified population at the crash location, and 94.1% could be linked to the driver's county data. Mortality was higher in locations with populations less than 25,000 and was inversely proportional to the driver's county population density. Age, belt use, and vehicle speed also affected mortality significantly, but the effect of rural location remained after controlling for these factors (O.R. 2.10, 95% C.I. 1.62-2.73). The excess risk for residents of rural areas to die in traffic crashes can be attributed in part to post-crash factors.

Accidents, Traffic↗
PubMed1977

The association of population density, reduced space, and uncomfortable temperatures with misconduct in a prison community.

This study investigated the relation of population size, amount of personal space, and population density to the incidence of disruptive behavior over a 3-year period in a correctional institution for male youthful offenders. Population size was significantly correlated with the number but not the rate of disciplinary violations. The total amount of personal space and the index of population density were significantly correlated with both the number and the rate of violations. A post hoc analysis showed that the incidence of uncomfortably hot days had no relation to disruptive behavior. These results are contrasted with laboratory data on human crowding reporting no relation between population density and behavior pathology. It is suggested that the chronic high density explored in the present field study differs from temporarily crowded conditions produced in laboratory research on human crowding.

Adolescent↗
PubMed1992

Study on the physico-chemical characteristics of breeding grounds in relation to the population density of Anopheles stephensi.

The present study which was based on the quarterly sampling and estimation of various physico-chemical factors throw light on the three significant points with regard to the population build up of Anopheles stephensi. Slightly alkaline pH is essential for higher population density, lower the salinity, higher the population density and higher amount of free ammonia in the water is accounted for the higher population density of A. stephensi.

Ammonia↗
PubMed1983

A graphical analysis of the interrelationships among waterborne asbestos, digestive system cancer and population density.

Five statistical procedures were used to partial the correlation between waterborne asbestos and digestive site cancer for the putative effects of population density. These include: analysis based on a data subset with roughly homogeneous population density; standard residual analysis (partial correlation); conditional probability integral transformation; analysis based upon ranked data, and use of logarithmic transformation. Nonparametric regression graphical techniques are applied to examine the nature or shape of the asbestos-cancer dose-response curve. Evidence is presented that suggests that there is considerable difference between analyses involving nonhigh-density tracts and non-San Francisco tracts. Evidence is also presented that the modal-type nonparametric regression curve forks or bifurcates when adjustment is made for population density.

Asbestos↗
PubMed1995

Crystallization and preliminary X-ray analysis of two density populations of feline calicivirus.

Two density populations of full-size feline calicivirus (FCV), the intact infectious particles (P(H)) and the empty capsids (P(L)), have been crystallized using the hanging-drop method. Exposed to high-intensity synchrotron radiation, P(H) and P(L) crystals were shown to diffract X-rays to about 3.0 and 5.5 A resolution, respectively. The P(H) crystal belongs to an orthorhombic crystal system with unit-cell dimensions a = 889.0, b = 995.0, c = 436.6 A. Based on the V(M) value (3.4 A(3) Da(-l)), it was estimated that one crystallographic asymmetric unit of P(H) crystals contains the unique content of an entire virus particle, not necessarily from the same particle. This implies the presence of 60-fold non-crystallographic redundancy. The particle orientation was obtained from a locked rotation function.

Journal Article↗
PubMed1982

beta-Adrenergic receptors and cyclic AMP responses to epinephrine in cultured human fibroblasts at various population densities.

The beta-adrenergic receptors of the intact human lung diploid fibroblast line Wl-38 and an SV-40 transformed clone of Wl-38, Wl-38-VA-13-2RA (VA13), were estimated in experiments utilizing the beta-adrenergic ligand, 125l-hydroxybenzylpindolol (125IHYP). When specific 125IHYP binding was measured in cells grown to relatively low population densities (0.15x10(6)cells/35mm dish), both Wl-38 and VA13 cells had approximately 40,000 beta-adrenergic receptors per cell. Wl-38 cells, when cultured to a high population density (0.5x10(6) cells/35/mm dish) had clearly diminished numbers of beta-adrenergic receptors and greatly decreased cAMP responses to epinephrine stimulation. On the other hand, in VA13 cells, neither the receptor number nor the beta-adrenergic response was affected by cell population density. In Wl-38 cells, the diminished cAMP response to epinephrine paralleled the decrease in number of beta-adrenergic receptors. Prostaglandin E1 (PGE1) stimulation of cAMP levels was unaffected by cell population density in either Wl-38 or VA13 cells. Thus, increased cell population density, perhaps related to density dependent inhibition of growth, caused a specific diminution in 125IHYP binding concomitant with decreased cAMP responses to epinephrine.

Cell Count↗
PubMed1998

Population densities of Sulawesi crested black macaques (Macaca nigra) on Bacan and Sulawesi, Indonesia: effects of habitat disturbance and hunting.

Population surveys of Sulawesi crested black macaques (Macaca nigra) were conducted on the Indonesian islands of Sulawesi and Bacan in 1992-1994 to assess the status of natural populations and determine habitat and anthropogenic factors affecting their population densities. We surveyed five sites for primates, including undisturbed and disturbed habitats. Data were collected on habitat structure and composition at two undisturbed and one disturbed forest site in which the primates were surveyed. The highest density of macaques was found in primary forest at Gunung Sibela Nature Reserve on Bacan (170.3 individuals/km2). Population density in logged forest on Bacan was high but significantly less than primary forest (133.4 individuals/km2). The high density of crested black macaques in primary forest on Bacan is best explained by the high carrying capacity found in primary forest. The lower food quantity and quality of food resources found in logged forest correlated with lower primate densities compared to primary forest. However, the large population of macaques in logged forest demonstrates the conservation value of such forest. Densities on Sulawesi at Tangkoko-Batuangas-DuaSudara Nature Reserve (TBDS) showed a continuing decline since earlier surveys. Primate densities were highest near the protected center of Tangkoko Reserve (66.7 individuals/km2). The peripheral areas of Batuangas and DuaSudara, even though adjacent and continuous, showed lower population densities of 46.4 and 23.5 individuals/km2, respectively. The best explanation for the continued decline of Macaca nigra populations at TBDS is hunting. Unless conservation measures are implemented immediately, M. nigra on Sulawesi risks extinction in the near future.

Animals↗
PubMed1993

The link between population density and welfare participation.

This article explores a neglected topic in the social welfare, poverty, and demographic literatures--the link between population density and welfare participation in the United States. Longitudinal data from the Panel Study of Income Dynamics are used to meet two objectives: first, to test whether a relationship exists between population density and use of the food stamp program among eligible households; second, to explore the potential reasons for such a relationship. Our findings show that population density has a strong, positive impact on the likelihood of participating in the food stamp program. Low-income respondents in urban areas are significantly more likely to use food stamps in both an aggregate and a multivariate context. In analyzing the dynamic underlying such an effect, we find that those in urban areas are more likely to possess accurate eligibility information and to hold less adverse attitudes toward the use of welfare. These factors in turn increase the likelihood of food stamp participation.

Adult↗