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PubMed1989

Effect of cage population density on plasma corticosterone and peripheral lymphocyte populations of laboratory mice.

The effect of different population densities of mice per cage on plasma corticosterone, peripheral lymphocytes and specific lymphocyte subpopulations was investigated. The animals were housed in groups of 2, 4 or 8 mice per cage and the blood samples were taken from each animal of these groups on days one, 7 and 14. A significant elevation (P less than 0.05) in plasma corticosterone concentration was observed in the group of 8 mice per cage on days one and 7 as compared with those of 2 or 4 mice per cage. The number of peripheral lymphocytes was significantly decreased in the groups of 2 (P less than 0.01) and 8 (P less than 0.05) mice per cage as compared with the group of 4 mice per cage on day one. A significantly decreased number of lymphocytes (P less than 0.01) in the group of 8 mice per cage continued to day 7. There were no significant differences in specific lymphocyte subpopulations observed among these groups. The results of this study suggest that a population density of 4 mice per cage induced minimal stress compared to that induced by the population densities of 2 or 8 mice per cage. Since stress is known to induce alteration in a variety of biological functions, the population density of mice per cage should be considered in the interpretation of research data.

Animals↗
PubMed1993

Population density effects on longevity.

Population density, or the number of adults in an environment relative to the limiting resources, may have important long and short term consequences for the longevity of organisms. In this paper we summarize the way in which crowding may have an immediate impact on longevity, either through the phenomenon known as dietary restriction or through alterations in the quality of the environment brought on by the presence of large numbers of individuals. We also consider the possible long term consequences of population density on longevity by the process of natural selection. There has been much theoretical speculation about the possible impact of population density on the evolution of longevity but little experimental evidence has been gathered to test these ideas. We discuss some of the theory and empirical evidence that exists and show that population density is an important factor in determining both the immediate chances of survival and the course of natural selection.

Animals↗
PubMed1999

Population density influences male-male competition in guppies.

This study tested the general prediction that population density affects male-male competition, female mate choice and the opportunity for sexual selection. By manipulating the density of guppies, Poecilia reticulata, while keeping the sex ratio constant, I found that male mating tactics were phenotypically plastic with respect to density. As density increased, males decreased their courtship displays. Male-male competition and mate searching were highest at intermediate densities. Population density had no significant effect on the total number of copulations, copulatory tactics or the percentage of postcopulatory guarding. Female preference for males with a higher percentage of orange coloration was similar at all density levels. The 'opportunity for sexual selection', which estimates the upper limit to which a selected trait can shift if directional selection is operating and was calculated as the variance in number of copulations per male divided by the square of the mean number of copulations, was negatively associated with population density. This may be due to the decrease in male-male competition at high density rather than female preference which was similar across density treatments. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2004

Population density and teen pregnancy.

OBJECTIVE: The relationship between population density and the percentage of teens who electively terminate their pregnancy was the focus of this study. METHODS: The United States population density was determined for each state and each district of the American College of Obstetricians and Gynecologists (ACOG) from the 2000 US Census. The United States teenage pregnancy statistics for females aged 15 to 19 years in 1999 and 2000 were obtained from the Alan Guttmacher Institute. The main measures were the correlation between population density and teen pregnancy rate or teen abortion rate by state and ACOG district. RESULTS: In 2000 there was no significant correlation between population density and the percentage of teenage females who conceived when analyzed by ACOG district (correlation coefficient r = 0.063, P =.87). In contrast, there was a significant correlation between population density and the percentage of pregnant teens who electively terminated their pregnancy when analyzed by ACOG district (r = 0.85, P =.003). In regions of greatest population density the percentage of pregnant teens who electively terminated was about 50%. In regions of least population density the percentage of pregnant teens who electively terminated was about 25%. Similar results were observed when teen pregnancy and abortion data from 1999 were analyzed. CONCLUSION: In the United States population density is not associated with the percentage of teenage females who become pregnant, but it is positively correlated with the percentage of pregnant teens that electively terminate their pregnancy. In areas of low population density teens who become pregnant may prefer birth to pregnancy termination. Alternatively, the access to pregnancy termination services may be suboptimal for teens in geographic areas with low population density. LEVEL OF EVIDENCE: II-2

Abortion, Induced↗
PubMed2006

[Mating behavior in mutant strains of Drosophila melanogaster at different population densities].

The effects of mutations and genetic background on the mating activity of male and receptivity of female Drosophila melanogaster have been studied at different population densities. Population density, as well as its combinations with other factors, significantly affects mating behavior of D. melanogaster. There are two distinct trends in the effect of this factor on mating behavior: the maximum larval overpopulation may cause either a significant suppression of the behaviors studied or an increase in their expressivity. The mating behaviors of wa and cn mutants against a certain genetic background changed similarly in response to varying population density.

Animals↗
PubMed2004

The synergistic effects of stochasticity and dispersal on population densities.

Using laboratory experiments, simulation models, and analytical techniques, we examined the impact of dispersal on the mean densities of patchily distributed populations. Even when dispersal leads to no net additions or removals of individuals from a population, it may nonetheless increase mean population densities if the net immigration rate is positive when populations are growing and negative when they are declining. As a model system for exploring this phenomenon, we used the yeastlike fungus Aureobasidium pullulans. In a laboratory experiment, we showed that dispersal can both ensure persistence and increase mean population densities even when dispersal among populations causes no direct addition or loss of fungal cells. From the laboratory data, we constructed a plausible model of A. pullulans dynamics among apple leaves within an orchard. This simulation model demonstrated that the effect of dispersal on mean densities is enhanced by three factors: weak density dependence of the dynamics within populations, high environmental variability affecting population growth rates, and lack of synchrony among the fluctuations of populations. Using an analytical model, we showed that the underlying mechanisms for this phenomenon are general, suggesting that a large effect of dispersal on mean population densities is possible in many natural systems.

Emigration and Immigration↗
PubMed1992

Demography of the Hadza, an increasing and high density population of Savanna foragers.

This is a report on the demography of the Hadza, a population of East African hunter-gatherers. In it, we describe the results of a census, and our estimation of age structure, survivorship, mean age of women at childbearing, number of live children, total population size and density, and rate of change since 1967. We show that relevant measures fit closely the stable population model North 6 chosen by Dyson to represent Hadza demography in the 1960s. We compare aspects of Hadza demography with surrounding non-Hadza and with the !Kung. Among other things, we find that the Hadza have a higher population density, higher fertility, and a faster population growth rate than do the !Kung. These demographic differences are consistent with our expectations, which were based on differences in the costs and benefits of foraging in the two regions. We also show that Hadza demographic parameters display remarkable consistency over the past 20 years. Since neighboring populations have been encroaching on the area used by the Hadza, and Hadza foragers have been subject to interludes of externally imposed settlement, this consistency is surprising. We discuss some of the implications.

Adolescent↗
PubMed2000

On the comparative static properties of the expected population density in the presence of stochastic fluctuations.

We consider the impact of increased stochastic fluctuations on the expected density of an unstructured population evolving according to a regular diffusion process subject to a concave expected growth rate. By relying on the flow nature of the solutions of stochastic differential equations and Girsanov's theorem, we demonstrate that typically increased volatility decreases the expected future population density. As a consequence, we are able to characterize the sensitivity of the expected population density with respect to changes in the diffusion coefficient measuring the size of the stochastic fluctuations. We provide both qualitative and quantitative information about the consequences of a mis-specified volatility structure and, especially, of a deterministic approximation to stochastic population growth. We also consider the effect of uncertainty in the initial density and demonstrate that the sign of the relationship between the expected population density and initial uncertainty is unambiguosly negative.

Animals↗
PubMed1996

Fatal motor vehicle crashes: variations of crash characteristics within rural regions of different population densities.

OBJECTIVE: While it is known that motor vehicle crash (MVC) fatality rates are inversely related to population density, there has been no description of which crash variables are related to population density. The purpose of this study was to describe crash characteristics of fatal MVCs and to determine which crash characteristics are related to population density. DESIGN: This is a retrospective review of fatal accident reporting system (FARS) records. They represent four different population density regions over a 5-year period in a four-state midwest region. RESULTS: There were 10,932 people in 6,318 vehicles who were involved in 4,970 fatalities. Occupant fatality rates per 100,000 persons were inversely related to population density. The variables related to lower population density were more light and heavy truck types, more frequent alcohol use and higher levels of intoxication, more frequent crashes that are noncollisions on less heavily traveled roads, more frequent crashes on gravel surface types, more frequent occupant ejection, and delayed medical care. CONCLUSION: Rural areas are not homogenous in terms of fatal MVC crash characteristics. By analyzing fatal MVC crash characteristics in regions with different population densities, many crash variables were found to be related to population density. By understanding which characteristics about fatal MVCs are related to population densities, different interventions could be targeted to different rural populations.

Accidents, Traffic↗
PubMed1992

Population density and cancer incidence differentials in New York State, 1978-82.

Patterns of cancer incidence within five population density quintiles in New York State, exclusive of New York City, were investigated between 1978 and 1982. Sex-specific, standardized incidence ratios were calculated within each population density quintile for all cancer cases combined and for site-specific cancers based on cancer incidence patterns exhibited by the general population of New York State, exclusive of New York City. Areas with the highest population density demonstrated a 13 percent excess of cancer cases among males and a seven percent excess among females. In contrast, areas with the lowest population density exhibited lower cancer incidence, among both males (12 percent less) and females (12 percent less). Males demonstrated a significant, direct linear relationship between increasing population density and all cancer sites combined, and for cancers of the oral cavity and pharynx, esophagus, stomach, colon, rectum, liver, pancreas, larynx, lung, bladder, brain, and nervous system, and for Hodgkin's disease and multiple myelomas. Among females, a significant, direct linear relationship was observed between increasing population density and all cancer sites combined, and for cancers of the buccal cavity and pharynx, esophagus, stomach, lung, breast, and kidney. Malignant melanomas of the skin, and in situ and invasive cancers of the cervix exhibited unusual incidence patterns across the population density quintiles. These data are most useful in generating hypotheses for further studies to define specific etiologic factors operating within population density groupings. Population density, as measured in this investigation, may represent a surrogate measure for other factors which are related to cancer morbidity.

Female↗
PubMed1992

Broiler production under varying population densities.

The influence of population density on the growth performance and stress level of Hubbard x Hubbard chicks of equally mixed sex was studied. Six hundred and sixteen birds were housed under .05, .07, .09, or .11 m2 per bird (four replicates per density) from 0 to 7 wk. There were no treatment effects on feed conversion at 6 or 7 wk. Birds housed at .07, .09, and .11 m2 per bird had similar 7-wk BW and carcass weights, all significantly higher than birds housed at .05 m2 per bird. Under .05 m2 per bird, a higher percentage of breast blisters and ammonia burns (30%) was observed than at other densities. The 7-wk heterophil to lymphocyte ratios of birds raised at .09 and .11 m2 per bird (.42 and .45) were significantly higher than those at .05 and .07 m2 per bird (.28 and .30). Lowered BW and decreased carcass quality of birds raised at .05 m2 per bird suggested that these birds were stressed. However, decision analysis of economic potential indicated that the optimum profit potential per square meter was .05 m2 per bird for Maximax and Equally Likely decisions and .07 m2 per bird for the Maximin decision.

Animal Husbandry↗
PubMed1990

Population density and cancer mortality differentials in New York State, 1978-1982.

Patterns of cancer mortality within five population density quintiles in Upstate New York (New York State, exclusive of New York City), were investigated between 1978 and 1982. Sex-specific standardized mortality ratios (SMRs) were calculated within each population density quintile for all cancer deaths combined and for site-specific cancer deaths based on cancer mortality patterns exhibited by the general population of New York State, exclusive of New York City. Areas with the highest population density demonstrated a 12% excess of cancer deaths among males and a 6% excess among females. In contrast, areas with the lowest population density exhibited lower cancer mortality, among both males (9% less) and females (7% less). Males demonstrated a significant linear relationship between increasing population density and deaths for all cancer sites combined and for cancers of the oral cavity and pharynx, oesophagus, stomach, colon, gallbladder, pancreas, lung, prostate, and kidney. Among females, a significant linear relationship was observed between increasing population density and deaths for all cancer sites combined and for deaths due to cancers of the stomach, colon, liver and breast. Deaths due to cancers of the rectum, malignant melanomas of the skin, and cervix also exhibited unusual patterns of mortality across the population density quintiles. These data are most useful in generating hypotheses for further studies to define specific aetiological factors operating within population density groupings. Population density, as measured in this investigation, may represent a surrogate measure for other factors which are related to cancer morbidity and cancer mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed2004

Rural and urban traffic fatalities, vehicle miles, and population density.

The purpose of this study was to evaluate the effect of population density on the rates of motor vehicle mortality in rural and urban areas, while controlling for vehicle miles traveled (VMT). Rural and urban data for traffic mortality, VMT, and population were obtained for each state from the Federal Highway Administration for 1998-2000. Linear regression was used to estimate the effect of population density, VMT per capita, southern location, and presence of a trauma system on mortality. Variation in rural mortality rate (per 100,000 population) was proportional to rural VMT per capita, but population density and southern location were also independent predictors, together accounting for 91% of this variation. Variation in urban mortality rates was not affected by population density, but urban rates were also higher in the south. The exposure-based rural mortality rate (deaths per 100 million VMT) was inversely proportional to population density, which along with southern location explained 41% of the variation from state to state. The presence of a state trauma system did not measurably affect mortality. After controlling for VMT and southern location, state population density was a moderately strong predictor of rural but not urban traffic mortality rates.

Accidents, Traffic↗
PubMed2002

Dust mite, cockroach, cat, and dog allergen concentrations in homes of asthmatic children in the northeastern United States: impact of socioeconomic factors and population density.

Home exposures to aeroallergens are an important environmental factor in allergic sensitization and in the development and exacerbation of asthma. We assessed variations in home concentrations of dust mite, cockroach, cat, and dog allergens in dust collected in the main living areas of asthmatics' homes by family income, mother's education, dwelling type, population density, household population density, and ethnicity in Connecticut and south-central Massachusetts. Dust samples were collected at the time of home interview in 999 homes as part of an ongoing longitudinal birth cohort study of 1,002 infants and their asthmatic siblings. The analysis employed lower and upper cut points for group 1 dust mite (> or = 2.0 microg/g and > or = 10 microg/g), cockroach (> or = 1.0 U/g and > or = 4.0 U/g), cat (> or = 1.0 microg/g and > or = 8.0 ug/g), and dog (> or = 2.0 microg/g and > or = 10.0 microg/g) allergens. Subject residences were geocoded to assess population density from the U.S. Census, and multiple logistic regression was used to control for confounding. The portion of homes at the lower cut point for dust mite, cockroach, cat, and dog allergens were 46.9%, 24.9%, 42.2%, and 35.6%, respectively; the upper cut point for each of the allergens was reached in 22.4%, 13.4%, 21.0%, and 22.9% of the homes, respectively. In all, 86.0% of the homes had at least one allergen at the lower cut point, and 58.0% had at least one allergen at the upper cut point. Forty-nine percent of the homes had two or more allergens at the lower cut point, and 19.7% had two or more allergens at the upper cut point. Higher education of the mother, higher household income, living in a single-family home in a less densely populated area with fewer people per room, and being a white household were associated with elevated dust mite, cat, and dog allergens and low cockroach allergen. In contrast, low income, living in a multifamily home in a high population density area with a higher occupancy rate per room, and being a Hispanic or black household were associated with elevated cockroach allergens and low concentrations of dust mite, cat, and dog allergens. Although the presence of an individual allergen is more likely associated with one or more socioeconomic or ethnic factors, most homes typically have multiple allergen burdens in excess of concentrations thought to be associated with sensitization and exacerbation of asthma. Mite and cockroach allergens have distinct and opposite associations with socioeconomic factors and population density.

Adolescent↗
PubMedDate not supplied

Population density and occurrence of accidents in Finland.

INTRODUCTION: About one million accidents occur yearly in Finland (population 5.2 million), resulting in over 3,000 deaths, annually. The governmental and municipal authorities are responsible for the healthcare services that respond to these accidents. So far, resources for these services have been allocated according to regional equality, or in some cases, on the basis of population numbers. However, economical and effective resource allocation should be based on detailed risk analysis of the accidents. HYPOTHESIS: In areas with more dense populations, the level of social activity is greater, which leads to an increased risk for accidents (traffic, civil disturbance, etc.). METHODS: The number of accidents was estimated on the basis of registered emergency trauma patients using the Finnish healthcare statistics for the year 1999. The emergency visits were compared to the populations and populations' densities of the regional sub-units. The rate of emergency injuries was analysed by regression analysis according to varying population density in Finland. RESULTS: The number of accidents per inhabitants was related directly to population density. There was a correlation between emergency visits per inhabitant and population density (p < 0.0001). According to estimates, each 1% increase in population density is associated with a 0.4% increase in the risk of accidents. CONCLUSION: The relationship between population density and rate of emergency visits is decisive for the planning of emergency services. Services should be placed in areas of high population densities where there are more people with greater risk of accidents.

Accidents↗
PubMed2003

Influence of population density on antibiotic resistance.

Antibiotic consumption and population density as a measure of crowding in the community were related to the prevalence of antibiotic resistance of three cities in three different countries: St Johns in Newfoundland (Canada), Athens in Greece and Groningen in The Netherlands. Antibiotic consumption was expressed in DDD (defined daily dose), as DID (DDD/1000 inhabitants/day) and as DSD (DDD/km(2)). The prevalence of antibiotic-resistant Escherichia coli and enterococci was determined in faecal samples of healthy volunteers. In both Newfoundland (28 DID) and Greece (29 DID) the overall consumption of antibiotics was more than three times higher compared with that of The Netherlands (9 DID). The lowest prevalence of resistant E. coli against the majority of antibiotics tested was found for the samples from Newfoundland and was significant (P < 0.05) for cefazolin, oxytetracycline and trimethoprim. A poor correlation between the number of DID and the prevalence of resistance was observed [the Pearson correlation coefficient (Pcc) ranged between -0.93 and 0.87]. However, when population density was taken into consideration and antibiotic consumption was expressed in DSD, a strong correlation was observed (and Pcc ranged between 0.86 and 1.00). This study suggests that population density is an important factor in the development of antibiotic resistance and warrants special attention as a factor in resistance epidemiology.

Canada↗
PubMed1978

A graph analysis of the relationship between population density and social pathology.

This article deals with systematic variables--population density and pathological effects--at the level of a community or organizational system. Existing studies of the relationship between population density and social pathology (e.g., mortality, mental illness) in humans have failed to determine a strictly causal relationship between density and pathology in a linear model. They have not established a direct link between density and pathology in a simple two-variable, linear causal approach. Eliminating other variables by statistical control has obscured the conditions of a complex phenomenon. By incorporating socioeconomic variables into a general system model, this paper suggests that the total configuration of social organization, adaptation, previous group experience, and environment determine the effects of population density. Using a method of graph analysis, a model is presented of the relationship between population density and social pathology which has a high degree of isomorphism with the empirical situation.

Adrenocorticotropic Hormone↗