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At least 163 records · Page 9Linked to original sources
PubMed2001

[Relationship between growth potential of pine, population density of Monochamus alternatus and pathogenicity of Bursaphlenchus xyloophilus].

The results showed that the growth potential of pine (x) is negative related to the population density of Monochamus alternatus (y) and the pathoyenecity of Bursaphlenchus xyloophilus (z). But the population density of Monochamus alternatus is positively related to the pathogenicity of Bursaphlenchus xyloophilus. Three linear equations regression line were established as y = 1793.771 - 16404.47x, z = 31.80989 - 241.9274x, y = -407.611 + 70.51478z. Correlation coefficient is -0.8139, -0.8770 and +0.9864 respectively.

Animals↗
PubMedDate not supplied

[Oscillations in population densities of the bacterial prey-predator couple Escherichia coli-Bdellovibrio bacteriovorus: experimental study and theoretical model].

Oscillations in population densities in the bacterial predator-prey Bdellovibrio bacteriovorus-Escherichia coli system were investigated both experimentally and theoretically. Experimental conditions for observing (damped) oscillations were first determined in a closed system and then used in an open system, i.e. in a chemostat, when an adequate flux of nutritive medium was added. The experimentally observed oscillations were always unstable with poorly reproducible amplitude and period. A theoretical model was used in order to explain this behaviour. It was first presented and satisfactorily tested for the same bacterial couple operating in a closed system, and allowed an experimental determination of its kinetic parameters. When adapted to open system conditions, it yielded computer-simulations which showed oscillations of the population densities in good agreement with those experimentally observed. It also showed that stable oscillations were not possible, the only "focus" in the predator-prey-density plane being an unstable one with no surrounding limit cycle.

Bdellovibrio↗
PubMed2002

Distribution, population density, and status of sympatric cercopithecids in the Campo-Ma'an area, Southwestern Cameroon.

A study on species composition, distribution, and population density of cercopithecids in the Campo-Ma'an area, Southwestern Cameroon, was undertaken from December 1997 until August 2000. A total of 665.5 km of line transects was used for the census. Thirteen diurnal primate species including five endangered species (Gorilla g. gorilla, Pan troglodytes, Mandrillus sphinx, Colobus satanas, Cercocebus torquatus) were recorded in the Campo Forest, the greatest part of which is a logging concession. Cercopithecus nictitans (1.43 groups/km2), C. cephus (1.13 groups/km2), C. pogonias (0.81 groups/km2), and C. torquatus (0.51 groups/km2) occurred at medium frequencies compared to figures from other Central African study sites. Mandrill densities estimated (0.27 groups/km2) show that the area is very important for the conservation of this rare species. Guenon densities found inside areas with a high level of human activities did not differ significantly from densities estimated in areas with a lower level of human activities. C. torquatus densities were significantly higher in the areas with a low level of human disturbance and encounter rates with Lophocebus albigena also indicate a preference of less disturbed areas. Mangabeys are thus likely to be adversely affected by human activities in the area. In the Ma'an Forest, which has not been logged yet, ten species were confirmed. The population densities of two guenons (C. nictitans and C. cephus) were estimated to be twice as high in the unlogged forest area as compared to the logged forest of Campo. Other species are rarer in the Ma'an Forest than in the Campo Forest. Although mangabeys are adversely affected by human activities, the results still indicate that selective logging may be compatible with the conservation of cercopithecids, if a reduced damage logging concept and antipoaching measures are implemented. Increased hunting activities following logging operations will definitely have a negative longterm impact on primate populations in the Campo-Ma'an area if no further, more effective conservation measures will regulate wildlife use in future.

Animals↗
PubMed1999

Hypergastrinaemia, abomasal bacterial population densities and pH in sheep infected with Ostertagia circumcincta.

Serum gastrin and pepsinogen concentrations, food intake, abomasal pH and abomasal aerotolerant and anaerobic bacterial populations were measured in sheep infected with Ostertagia circumcincta to search for links between hypergastrinaemia, food intake and changes in the abomasal environment. Abomasal pH and serum gastrin and pepsinogen concentrations were elevated in each of five sheep infected via abomasal cannulae with 150000 exsheathed larval stage three, followed 11 days later by 100000 sheathed larvae given intraruminally. Unparasitised abomasa contained aerotolerant bacterial population densities of between 10(3) and 10(6) cells ml(-1) and these did not change significantly following parasitism. In contrast, anaerobic bacterial population densities increased markedly by about 10(4)-fold following parasitism. Anaerobic numbers changed rapidly when abomasal pH increased from 2.5 to 3.5. At pH 4 and above, anaerobic bacterial numbers approached levels expected in rumen contents but parameters other than pH did not relate to bacterial numbers. Brief periods when serum gastrin was lower than expected, coinciding with raised abomasal pH, were not explicable by increased bacterial numbers. Food intake, which decreased for a variable period from around Day 5 p.i., correlated poorly with serum gastrin concentration, suggesting hypergastrinaemia is not the sole cause of anorexia in parasitised animals. The survival of substantial numbers of rumen bacteria in the abomasum at only slightly raised pH may significantly lower the bacterial protein available to the sheep.

Abomasum↗
PubMed1983

Correlation between population density and the frequency of Creutzfeldt-Jakob disease in France.

Epidemiologic studies of Creutzfeldt-Jakob disease (CJD) in countries throughout the world have consistently shown higher urban than national disease frequencies, but this finding has usually been ascribed to case-finding artefact. A detailed analysis has now been completed of annual mortality rates of CJD in France, based on a systematic study of 255 consecutive cases dying during the period 1968-1980, of whom 85 resided in the paris metropolitan area. In the country as a whole, the frequency of CJD increased from rural, through urban, to the Paris region; and in the Paris region, the frequency increased from the lowest to the highest density areas. The magnitude of this positive correlation between population density and the frequency of CJD is not explained by differences in age distribution of the various population groups, and suggests a role for random inter-human spread, either direct or indirect, in natural disease transmission.

Adult↗
PubMed2007

Resolving the tragedy of the commons: the feedback between intraspecific conflict and population density.

Competition and conflict among individuals can favour exploitative strategies that undermine the common good. Theory suggests that this can lead to a tragedy of the commons and ultimately population extinction, a phenomenon known as evolutionary suicide. Here, I present a model of the evolutionary tragedy of the commons that explicitly considers the population dynamics where individuals invest in individually costly competitive traits. In the simplest form, this supports the notion that selection for high levels of conflict can cause evolutionary suicide. However, as competition comes with survival and fecundity costs, a feedback between the investment in competition and population density can act to reduce the level of conflict and prevent the population from going extinct. This suggests that the interaction between population ecology and the evolution of competition and conflict among individuals may be an important mechanism in resolving the level of competition and conflict among individuals.

Biological Evolution↗
PubMed1994

Vintage growth and population density: an empirical investigation.

"This paper tests a central prediction of vintage growth models of urban structure: that there are discontinuities in the population density function. The data set covers quarter sections in Chicago in 1980. Using such highly disaggregated data is critical because discontinuities are less likely to be found the larger is the unit of observation. Both a switching regression model and a nonparametric estimator reveal discontinuities and upward-sloping segments in the function, which supports the vintage growth model."

Americas↗
PubMed2003

Small area variation in childhood diabetes mellitus in Austria: links to population density, 1989 to 1999.

We analyzed the associations of environmental factors with the regional distribution of Type 1 diabetes mellitus in Austria. All newly diagnosed cases (n=1449) from 1989 to 1999 were allocated to districts using the postal code. Nitrate content of the water was measured by the Austrian Federal Environmental Agency. Data on infant mortality, population density, and percentage of employment by industry were derived from Statistics Austria. An inverse effect was seen between the proportion of children younger than 15 years of age and the risk ratio (P<.01). Infant mortality, population density, and percentage of persons with employment in industry were not of significant influence. The mean nitrate level was positively associated (P=.07). In regions with a higher percentage of children younger than 15 years of age, fewer children developed diabetes, which is in agreement with the observation that early social mixing is a protective factor. Nitrate levels may have a confounding effect.

Adolescent↗
PubMed1970

Ecological consequences of island colonization by southwest Pacific birds. II. The effect of species diversity on total population density.

Among southwest Pacific birds colonizing a species-poor island from a species-rich island, spatial expansion of the niche to include a wider range of altitudes, habitats, or vertical strata is often an immediate response, while changes in foraging techniques and diet usually occur more slowly and require genotypic change. Despite occupation of spatially broader niches by some colonizing species and increases in abundance by others, the total population density of the whole avifauna is up to nine times lower on a species-poor island than in a comparable habitat on a species-rich island. Total population density varies among islands approximately linearly with the number of species in the lowlands, supralinearly at higher elevations. Part of the explanation is that many birds on small islands expand into niche space which is suboptimal for them and from which they would be excluded by species utilizing this niche space optimally on a species-rich island. The other suggested explanation is an intrinsic inefficiency or loss of fitness among populations on small Pacific islands compared to large-island populations, due to impoverished gene pools, reduced selection pressure, and low degree of endemism.

Animals↗
PubMed1978

In vivo development of Echinostoma malayanum Leiper, 1911 with notes on effects of population density, chemical composition and pathogenicity and in vitro excystment of the Metacercaria (Trematoda: Echinostomatidae).

In vivo development of Echinostoma malayanum Leiper, 1911 was studied in white rats and the developmental process was arbitrarily divided into four stages: organogeny, vitellogenesis, formation of Mehlis' gland complex and cirrus sac, and oviposition. The percentage of development was 86-94. Population density affected the prepatent period of flukes and the normal prepatent period of 13-16 days was altered to 18-23 days in infection with 500-800 flukes. The majority of flukes in heavy infection were undersized and in the immature stage of development at patency. Data from chemical analysis of flukes revealed that protein, lipids, calcium and ash decreased quantitatively in flukes from higher population densities but no such change was observed as regards glycogen. Pathological changes in the rat intestine included lysis and destruction of mucosa, increased activity of goblet cells, oedematous and reticulated appearance of lamina propria and slight to moderate hyperplasia of epithelial cells. The metacercariae excysted in the medium containing trypsin plus sodium cholate an pepsin, though not essential for a high percentage of excystment, affected the rate. The reductant sodium dithionite substantially enhanced the rate and percentage of excystment. Excystation was optimal at pH 8, and 42 degrees C was more effective than 39 degrees C.

Animals↗
PubMed1982

Correlation of alkaline phosphatase activity with cell population density in tissue culture cells originated from rat liver.

Alkaline phosphatase (ALP) activity of cultured Li-10 cells obtained from rat liver was found to be a function of cell population density. After the cells grew to confluence, the enzyme activity per cell increased about 100 times that at a low population density. The increase of activity was inhibited by the addition of actinomycin D or cycloheximide to the culture medium. When the cells that had gained high ALP activity after confluency were subcultured, ALP activity decreased to a low basal level after about 48 h. Under cytochemical examination using an electron microscope, the induced ALP activity was seen exclusively at the apical surface region of the cells but scarcely at cell-cell and cell-substratum contact regions.

Alkaline Phosphatase↗
PubMed2000

Resource allocation modelling for home-based health and social care services in areas having differential population density levels: a case study in Northern Ireland.

This project arose from deliberations within the Department of Health and Social Services (DHSS) in Northern Ireland concerning the acceptability of the revenue resource allocation methodology they were using. One problem with the method being used had been the absence of a component that adequately reflected the relative costs associated with the differential population densities of the four health boards into which the Province is divided. This study investigates a particular element of this issue, viz differences in the travelling distances and times of those health and social service professionals who provide visiting services to patients in their own homes. A modelling approach has been developed and used in conjunction with a comprehensive spatial and geographical information system for Northern Ireland. An important outcome of the study has been estimates of the targets that should be set for the annual health and social care travelling distances and times per head of population in the boards, for a range of home-based services. Also, the project has contributed to decisions made by the DHSS in Northern Ireland concerning the annual financial compensations required by boards for costs associated with their relative population densities.

Catchment Area, Health↗
PubMed1993

Walking behaviour and population density of adult linyphiid spiders in relation to minimizing the plot size in short term pesticide studies with pyrethroid insecticides.

Temporal changes in spatial distribution and population density of linyphiid spiders were studied in relation to physical factors and deltamethrin spraying in the field. The results of the study have been used to set the conditions necessary when plot size is reduced in field trials. The results showed independence of observations at 7 m from an unsprayed reservoir, with respect to migration, in the week following pesticide application. Soil moisture had a positive effect on trapping success, without having apparent effect on trapping success, without having was found for deltamethrin spraying on wet and dry soil. Shifts in the spatial distribution of spider activity showed a close correlation with crop microclimatic conditions. The effect of trapping on population density was shown to be limited. The results suggest that small plots surrounded by a border of 7 m are appropriate for assessing short term pesticide effects on adult linyphiid spiders in winter wheat.

Journal Article↗
PubMed2002

A comparison of stream biological responses to discharge from wastewater treatment plants in high and low population density areas.

The ultimate purpose of this study was to identify broad relationships that may have relevance for the risk assessment of chemicals and materials that are discharged to receiving streams via municipal wastewater treatment plant (WWTP) effluents (e.g., consumer product ingredients). The effects of municipal wastewaters occurring in high population density (>500 persons per square mile, urban) and low population density (<500 persons per square mile, rural) environments were determined via analysis of biological, habitat, and water chemistry data collected both immediately upstream and downstream of 221 WWTPs in Ohio, USA. Several biological and chemistry indicators demonstrated poorer water quality in urban areas compared to rural areas. After considering the effect of river size, adverse effects downstream of WWTPs for both fish and macroinvertebrate communities were clearly identified for only urban areas. These data indicate that WWTP potency may be greater in urban areas compared to rural areas.

Animals↗
PubMed1984

Hyperthermic survival of Chinese hamster ovary cells as a function of cellular population density at the time of plating.

The survival of synchronous G1 or asynchronous Chinese hamster ovary cells in vitro to heat treatment may depend on the cellular population density at the time of heating and/or as the cells are cultured after heating. The addition of lethally irradiated feeder cells may increase survival at 10(-3) by as much as 10- to 100-fold for a variety of conditions when cells are heated either in suspension culture or as monolayers with or without trypsinization. The protective effect associated with feeder cells appears to be associated with close cell-to-cell proximity. However, when cells are heated without trypsinization about 24 hr or later after plating, when adaptation to monolayer has occurred, the protective effect is reduced; i.e., addition of feeder cells enhances survival much less, for example, about 2- to 3-fold at 10(-2)-10(-3) survival. Also, the survival of a cell to heat is independent of whether the neighboring cell in a microcolony is destined to live or die. Finally, if protective effects associated with cell density do occur and are not controlled, serious artifacts can result as the interaction of heat and radiation is studied; for example, survival curves can be moved upward, and thus changed in shape as the number of cells plated is increased with an increase in the hyperthermic treatment or radiation dose following hyperthermia. Therefore, to understand mechanisms and to obtain information relevant to populations of cells in close proximity, such as those in vivo, these cellular population density effects should be considered and understood.

Animals↗