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PubMed1995

Effects of population density on layer performance.

Four experiments were conducted to study the effects of population density on layer performance. in each experiment, 20-wk--old White leghorn pullets were housed in 30.5 x 50.8 cm cages at the rate of one, two, three, and four birds per cage for Treatments 1, 2, 3, and 4, respectively. in Experiment 4, there were three additional treatments: for Treatments 5, 6, and 7, birds were placed into identical cages (30.5 x 50.8 cm) at the rate of three, two, and three birds per cage, respectively, at 20 wk of age. At 28 wk of age, one bird was removed from each cage in Treatment 5, and one bird was added to each cage in Treatments 6 and 7. In the first three experiments, all eggs that were collected for 2 consecutive d every 8 wk starting at 28 wk of age were used to measure egg traits. In Experiment 4, egg traits were determined once at 52 week of age. Birds at the highest population density had the lowest percentage hen-day egg production and had one of the poorest feed efficiencies. Egg production was negatively correlated (P < or = .01, Experiments 1, 2, 3; P < or = .05, Experiment 4) with population density. Feed required to produce a dozen eggs was positively correlated (P < or = .01, Experiments 1, 2; P < or = .05, Experiment 3) with population density in three out of the four experiments. The addition or removal of a cage mate to or from a multiple-bird cage in Experiment 4 did not (P > .05) affect egg production or feed efficiency. Final BW, mortality, and egg weight were not (P > .05) affected by population density. Only in one out of the four experiments was feed consumption (Experiment 1), eggshell thickness (Experiment 2), or albumen height (Experiment 3 lowered (P < or = .05) by having more than one bird per cage. This study showed that increasing population density decreased laying performance of the birds.

Animals↗
PubMed1997

Population density, automated external defibrillator use, and survival in rural cardiac arrest.

OBJECTIVE: To determine whether population density is an independent predictor of survival from out-of-hospital cardiac arrest managed by basic life support (BLS) services using automated external defibrillators (AEDs). METHODS: A retrospective, observational study in Kentucky of 34 BLS services covering 22 counties during the years 1992 to 1994 who used AEDs to treat patients who had out-of-hospital cardiac arrests. RESULTS: Of 311 patients who had out-of-hospital cardiac arrests, 110 (35%) were defibrillated, 46 (15%) were resuscitated to hospital admission, and 19 (6%) survived to hospital discharge. Univariate predictors for survival to hospital discharge were emergency medical services response interval (from call receipt to ambulance arrival) < 8 minutes, defibrillation by the AED, initial rhythm of ventricular fibrillation or ventricular tachycardia (VF/VT), and population density > 100/square mile (sq mi) for the BLS service area (p < 0.001). A forced logistic regression model of survival to hospital discharge, using these 4 factors plus the presence of a witnessed arrest or bystander CPR, demonstrated that population density > 100/sq mi was highly significant (OR 9.4, 95% CI: 1.7 to 51.4, p < 0.01). Stepwise logistic regression models with combinations of these 6 factors found that survival to hospital discharge was best predicted by an initial rhythm of VF/VT (p = 0.004) and population density > 100/sq mi (p = 0.011). CONCLUSIONS: Population density is strongly associated with survival from out-of-hospital cardiac arrest. BLS services within areas with population densities < or = 100/sq mi sustained little benefit from the addition of AEDs to their treatment of patients who had out-of-hospital cardiac arrests.

Aged↗
PubMed1989

[Tuberculosis morbidity in regions with a low population density].

Tuberculosis incidence was studied in the northern areas of Irkutsk Province with low population density. In the areas slower lowering of pulmonary tuberculosis incidence was noted. The main contingent of the new cases included persons with the disease detected during fluorographic examinations. In the areas with low population density, the percentage of the new cases with tubercle bacilli isolation and late diagnosis of tuberculosis was higher than in the areas with high population density. The influence of migration on the epidemiological status with respect to tuberculosis in the areas with low population density was less significant as compared to that in the areas with high population density.

Age Factors↗
PubMed1995

Neoplastic development: paradoxical relation between impaired cell growth at low population density and excessive growth at high density.

The role of heritable, population-wide cell damage in neoplastic development was studied in the 28 L subline of NIH 3T3 cells. These cells differ from the 17(3c) subline used previously for such studies in their lower frequency of "spontaneous" transformation at high population density and their greater capacity to produce large, dense transformed foci. Three cultures of the 28 L subline of NIH 3T3 cells were held under the constraint of confluence for 5 wk (5 wk 1 degree assay) and then assayed twice in succession (2 degrees and 3 degrees assays) for transformed foci and saturation density. After the 2 degrees assay, the cells were also passaged at low density to determine their exponential growth rates and cloned to determine the size and morphological features of the colonies. Concurrent measurements were made in each case with control cells that had been kept only in frequent low-density passages and cells that had been kept at confluence for only 2 wk (2 wk 1 degree). Two of the three cultures transferred from the 2 degrees assay of the 5 wk 1 degree cultures produced light transformed foci, and the third produced dense foci. The light focus-forming cultures grew to twice the control saturation density in their 2 degrees assay and 6-8 times the control density in the 3 degrees assay; saturation densities for the dense focus formers were about 10 times the control values in both assays. All three of the cultures transferred from the 2 degrees assay of the 5 wk 1 degree cultures multiplied at lower rates than controls at low densities, but the dense focus formers multiplied faster than the light focus formers. The reduced rates of multiplication of the light focus formers persisted for > 50 generations of exponential multiplication at low densities. Isolated colonies formed from single cells of the light focus formers were of a lower population density than controls; colonies formed by the dense focus formers were slightly denser than the controls but occupied only half the area. A much higher proportion of the colonies from the 5 wk 1 degree cultures than the controls consisted of giant cells or mixtures of giant and normal-appearing cells. The results reinforce the previous conclusion that the early increases in saturation density and light focus formation are associated with, and perhaps caused by, heritable, population-wide damage to cells that is essentially epigenetic in nature. The more advanced transformation characterized by large increases in saturation density and dense focus formation could have originated from rare genetic changes, such as chromosome rearrangements, known to occur at an elevated frequency in cells destabilized by antecedent cellular damage.

3T3 Cells↗
PubMed2005

Evolutionary feedback mediated through population density, illustrated with viruses in chemostats.

A cornerstone of evolutionary ecology is that population density affects adaptation: r and K selection is the obvious example. The reverse is also appreciated: adaptation impacts population density. Yet, empirically demonstrating a direct connection between population density and adaptation is challenging. Here, we address both evolution and ecology of population density in models of viral (bacteriophage) chemostats. Chemostats supply nutrients for host cell growth, and the hosts are prey for viral reproduction. Two different chemostat designs have profoundly different consequences for viral evolution. If host and virus are confined to the same chamber, as in a predator-prey system, viral regulation of hosts feeds back to maintain low viral density (measured as infections per cell). Viral adaptation impacts host density but has a small effect on equilibrium viral density. More interesting are chemostats that supply the viral population with hosts from a virus-free refuge. Here, a type of evolutionary succession operates: adaptation at low viral density leads to higher density, but high density then favors competitive ability. Experiments support these models with both phenotypic and molecular data. Parallels to these designs exist in many natural systems, so these experimental systems may yield insights to the evolution and regulation of natural populations.

Adaptation, Biological↗
PubMedDate not supplied

[Effect of the population density on growth and regeneration in the snail Achatina fulica].

In the laboratory, the growth rate of the giant African snail Achatina fulica, as estimated by the weight and shell length was shown to decrease when the population density increased from 10 to 60 snails/m2 of the total terrarium area for five months. In the second experiment, when the population density increased from 48 to 193 snails/m2, the growth rate had already decreased by six weeks. In the groups with a high population density the feeding behavior was weakened, expressed by a greater amount of nonconsumed food, according to visual observations, than in the groups with lower population densities. At the population density of 10 to 60 snails/m2, the proliferative activity in the course of the optic tentacle regeneration, as expressed by the mitotic index, did not differ reliably within five months. In the second experiment, the mitotic indices at the population densities of 96 and 193 snails/m2 within 1.5 months exceeded that of 48 snails/m2. Recommendations are given concerning the population density from the viewpoint of commercial growth of the snails. It was proposed that, based on the analysis of the mechanism underlying the inhibition of feeding behavior in populations with extra high densities, one may develop a new approach to the production of chemical agents to control land snails as agricultural pests.

Animals↗
PubMedDate not supplied

[Body mass, population density, and offspring number in mammals].

The negative relationship between population density and body mass with the body mass exponent of -0.75 implies that the energy flow through populations of small- and large-bodied species is the same, for individual metabolism scales to body mass raised to the power of +0.75. This relationship called the energetic equivalence rule, has often been observed for mammal species assemblages studied at regional scales. Here we suggest a demography-based mechanism that may generate it. Having analyzed about 130 literature sources, mostly in Russian, we collected demography and body-mass data for 88 mammalian species from the territory and coastal waters of the former Soviet Union. The data were used to construct a number of interspecific relationships. It is shown that (1) the number of offspring per lifetime is approximately inversely proportional to the relative mass at birth (the exponent is not significantly different from -1), (2) the average lifespan is proportional to body mass to the 0.25 power, (3) body mass at birth is proportional to the adult body mass. We develop a simple theory to demonstrate that relations (1) to (3) entail the energetic equivalence rule. The theory also allows us to explain violation of this rule (in non-flying birds, for example), namely, to predict the exponent of relation (1) for any given exponent of the relation between population density and body mass. This is possible because relations (2) and (3) are likely to more universally hold than relation (1). Finally, since natural selection acts on individual traits rather than on population-level ones such as population density, the theory opens up the way to an evolutionary explanation for the energetic equivalence rule.

Algorithms↗
PubMed2000

[Effect of initial population density on resting egg formation of rotifer Brachionus calyciflorus].

With the method of population accumulative culture, the effect of initial population density on the formation of resting eggs of freshwater rotifer(Brachionus calyciflorus), and on the rates of mictic female and fertilization was studied. During 11 days culture, the productivity and the formation efficiency of resting eggs, and the mean rate of mictic female were the biggest when the initial population density was 1.0-10.0 ind.ml-1, second by the density of 20.0 ind.ml-1, and the lowest by the density of 50.0 ind.ml-1. There was no significant effect of initial population density on the fertilization rate. Statistical analysis on maximum formation efficiency of resting eggs, their emergence and productivity showed that when the production of resting eggs was large-scaled proceeded, the feasible initial population density should be 10.0 ind.ml-1, and the corresponding time should be 6 days to obtain a higher yield of resting eggs and a higher formation efficiency.

Animals↗
PubMed1991

Population density alters the responsiveness of GH4C1 pituitary tumor cells to 17 beta-estradiol.

In this study we have examined the effect of population density on the ability of 17 beta-estradiol (E2) to induce PRL mRNA, DNA synthesis, and progesterone receptor in GH4C1 pituitary tumor cells. These parameters were examined at three subconfluent population densities that varied over a 4-fold range. The culture medium was changed daily in these experiments to reduce the possibility of nutrient depletion, medium toxification, or E2 metabolism. At the low population density, a 5-day treatment with E2 at a concentration of 1.0 nM resulted in an 8.1-fold increase in the level of PRL mRNA, as measured by the cytosolic dot blot procedure. At the intermediate density, E2 induced PRL mRNA 2.4-fold. At the high density, the level of PRL mRNA was reduced by 50% in response to 5 days of treatment with E2. The cytosolic dot blot procedure would reflect changes in the level of PRL mRNA per cell as well as changes in the number of cells per culture. Therefore, the level of beta-actin mRNA was also measured, assuming that it would remain constant on a per cell basis. When the level of PRL mRNA was normalized to the level of beta-actin mRNA in the same cytosols, E2 increased PRL mRNA 2.6-fold in the low density cultures and 1.9-fold in the intermediate density cultures, and had no effect on the level of PRL mRNA in the high density cultures. The effect of population density on the induction of GH4C1 cell proliferation by E2 was examined directly by measuring cellular DNA, thymidine incorporation by whole cells, and deoxythymidine triphosphate (dTTP) incorporation by isolated nuclei. At the low density, E2 initially stimulated GH4C1 cell proliferation, as evidenced by an increased rate of dTTP incorporation. However, this stimulatory effect was lost by day 5 of treatment, as the population density of the E2-treated low density cultures increased. At the high density, the inhibitory effect of E2 on dTTP incorporation was observed by day 2 of treatment and thereafter become more pronounced. These stimulatory and inhibitory effects of E2 were also revealed when the level of cellular DNA was measured. In contrast to the effects of population density on the induction of PRL mRNA and cell proliferation, an increase in density had no observable effect on the induction of progesterone receptor by E2. These data illustrate the critical importance of the culture environment in studies examining estrogen action in vitro.

Actins↗
PubMed2002

A two-component regulator mediates population-density-dependent expression of the Bradyrhizobium japonicum nodulation genes.

Bradyrhizobium japonicum nod gene expression was previously shown to be population density dependent. Induction of the nod genes is highest at low culture density and repressed at high population densities. This repression involves both NolA and NodD2 and is mediated by an extracellular factor found in B. japonicum conditioned medium. NolA and NodD2 expression is maximal at high population densities. We demonstrate here that a response regulator, encoded by nwsB, is required for the full expression of the B. japonicum nodYABC operon. In addition, NwsB is also required for the population-density-dependent expression of both nolA and nodD2. Expression of nolA and nodD2 in the nwsB mutant remained at a basal level, even at high culture densities. The nwsB defect could be complemented by overexpression of a second response regulator, NodW. Consistent with the fact that NolA and NodD2 repress nod gene expression, the expression of a nodY-lacZ fusion in the nwsB mutant was unaffected by culture density. In plant assays with GUS fusions, nodules infected with the wild type showed no nodY-GUS expression. In contrast, nodY-GUS expression was not repressed in nodules infected with the nwsB mutant. Nodule competition assays between the wild type and the nwsB mutant revealed that the addition of conditioned medium resulted in a competitive advantage for the nwsB mutant.

Bacterial Proteins↗
PubMed1997

Population density and spatial differentials in child mortality in Zimbabwe.

Large regional variations in under-five mortality exist within many sub-Saharan countries. Population density as a potential explanatory factor for these regional variations has seldom been considered despite it being implicated as a determinant of mortality at other spatial scales. In Zimbabwe, the "Ndebele provinces"-Matabeleland North and South-have significantly lower levels of under-five mortality than the other ("Shona") provinces. This regional differential is explored using the Zimbabwe Demographic and Health Survey and census data. Factors other than population density that may contribute to the differential are examined. After controlling for the effects of potentially confounding socio-economic, demographic and environmental variables using Cox regression models children aged 1-4 yr living in the Ndebele provinces continued to have a level of mortality 45% lower than their counterparts in the Shona provinces. The possibility that regional variations in health care provision and/or cultural factors contribute to the mortality differential is also examined and rejected. Population densities in the Ndebele provinces are of a far lower order than in the Shona provinces. The main causes of child mortality in Zimbabwe in the time period under consideration were diarrhoea, ALRI, measles and malaria. How population density may affect the transmission of these infections and, hence, mortality is discussed. It is suggested that population density may provide an explanation for the spatial variation in child mortality in Zimbabwe. The implications of changing population densities for child health in urban and rural sub-Saharan Africa are briefly considered.

Cause of Death↗
PubMedDate not supplied

[Effect of habitat type and population density on the stress level of midday gerbils (Meriones meridianus Pall.) in free-living populations].

New methods of noninvasive evaluation of the endocrine status of animals by the content of hormones in feces were used to study the relationship between the stress level and social (population density) and ecological (habitat integrity) indices in natural populations of midday gerbil in the Southern Kalmykia in 2000. Stress level proved to increase with habitat disturbance but did not depend on population density of animals. The obtained data are discussed in the context of species-specific ecology and social behavior of midday gerbils.

Animals↗
PubMed2006

Effect of population density on growth, biomass and nickel accumulation capacity of Lemna gibba (Lemnaceae).

The effect of population densities on the growth rate and metal (nickel) accumulation capacity of Lemna gibba (Lemnaceae) was studied under laboratory conditions. At high population densities (800 or 1600 seedling per pot), we observed decreasing growth rate with increasing L. gibba density. Especially, at a density of 1600 seedling a pot the net growth rate became negative. This lower growth rate may relate to lower local temperatures and nutrients within L. gibba mats. Biomass production was inhibited by an increase in plant density. Additionally, high population densities caused decreasing nickel accumulation by L. gibba. In this study, a simple model was created according to data obtained from this study. The model has suggested that crowding is an important factor in limitation of growth of L. gibba.

Araceae↗
PubMed1972

Relative population densities of Aedes albopictus and A. guamensis on Guam.

Aedes guamensis Farner & Bohart is indigenous to Guam but A. albopictus is known to have arrived in 1944. The larval ecology of the two species is very similar; both species breed in tree holes, coconut shells, and other natural and man-made water containers. The purpose of the study was to compare the relative densities of larval populations of the two species with those determined in a survey made in 1948-49. The results suggest that as the population density of A. albopictus increased, that of A. guamensis decreased by as much as about 95% in artificial containers, and by 30% or more in natural breeding habitats. Since there seems to be no environmental factor involved in rendering the breeding places unsuitable for A. guamensis, the reduction in A. guamensis populations may be, in part, the result of competition from A. albopictus.

Aedes↗
PubMed1993

Changes in population density elicit quantitative and qualitative changes in the estrogen receptor in intact GH4C1 pituitary tumor cells.

We have previously demonstrated that population density alters the responsiveness of GH4C1 pituitary tumor cells to 17 beta-estradiol (E2). At a low population density E2 was observed to increase prolactin mRNA and stimulate cell proliferation, whereas this estrogen was unable to elicit these responses when the cells were maintained at a 4-fold higher population density. In an attempt to determine the mechanism through which population density alters responsiveness to E2, the steady-state level of estrogen receptor (ER), the affinity of ER for E2, and ER down-regulation have been examined in both intact and fractionated cells using ligand binding and ligand exchange assays. Data presented herein demonstrate that (1) GH4C1 cells maintained at low density expressed fewer ER than cells cultured at high density; (2) ER in cells cultured at high density displayed a reduced affinity for E2; (3) ER down-regulation occurring within 1 h of E2 addition appeared to be more pronounced in high density cultures; and (4) steady-state levels of ER were similar in low and high density cells treated with E2 for 1 through 5 days. Although none of these observations appear to correlate with the previously observed effects of population density on the responsiveness of GH4C1 cells to E2, they further illustrate the potential of the culture environment to alter the responsiveness to estrogenic stimuli by altering the properties of the ER.

Cell Count↗
PubMed1983

The relation of the height of primary school children to population density.

The relation of the height of primary school children to population density, as measured at the 1971 census, was investigated for children in 21 study areas in England, using data from the 1972 survey of the National Study of Health and Growth. Shorter stature was found with increasing population density, and this relation remained after allowing for child's birthweight, mother's height, father's height, social class, number of siblings, and additionally a measure of home overcrowding. The results are in contrast to those found elsewhere, and are unlikely to indicate a cause-and-effect relationship between population density and height. The findings cannot be explained either by known differences between urban and rural areas in social characteristics or by plausible hypotheses of genetic heterogeneity.

Body Height↗
PubMed2006

A multivariate population density model of the dLGN/PGN relay.

Using a population density approach we study the dynamics of two interacting collections of integrate-and-fire-or-burst (IFB) neurons representing thalamocortical (TC) cells from the dorsal lateral geniculate nucleus (dLGN) and thalamic reticular (RE) cells from the perigeniculate nucleus (PGN). Each population of neurons is described by a multivariate probability density function that satisfies a conservation equation with appropriately defined probability fluxes and boundary conditions. The state variables of each neuron are the membrane potential and the inactivation gating variable of the low-threshold Ca2+ current I(T). The synaptic coupling of the populations and external excitatory drive are modeled by instantaneous jumps in the membrane potential of postsynaptic neurons. The population density model is validated by comparing its response to time-varying retinal input to Monte Carlo simulations of the corresponding IFB network composed of 100 to 1,000 cells per population. In the absence of retinal input, the population density model exhibits rhythmic bursting similar to the 7 to 14 Hz oscillations associated with slow wave sleep that require feedback inhibition from RE to TC cells. When the TC and RE cell potassium leakage conductances are adjusted to represent cholingergic neuromodulation and arousal of the network, rhythmic bursting of the probability density model may either persists or be eliminated depending on the number of excitatory (TC to RE) or inhibitory (RE to TC) connections made by each presynaptic cell. When the probability density model is stimulated with constant retinal input (10-100 spikes/sec), a wide range of responses are observed depending on cellular parameters and network connectivity. These include asynchronous burst and tonic spikes, sleep spindle-like rhythmic bursting, and oscillations in population firing rate that are distinguishable from sleep spindles due to their amplitude, frequency, or the presence of tonic spikes. In this context of dLGN/PGN network modeling, we find the population density approach using 2,500 mesh points and resolving membrane voltage to 0.7 mV is over 30 times more efficient than 1,000-cell Monte Carlo simulations.

Action Potentials↗