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At least 505 records · Page 28Linked to original sources
PubMed1998

Estimating sequestered parasite population dynamics in cerebral malaria.

Clinical investigation of malaria is hampered by the lack of a method for estimating the number of parasites that are sequestered in the tissues, for it is these parasites that are thought to be crucial to the pathogenesis of life-threatening complications such as cerebral malaria. We present a method of estimating this hidden population by using clinical observations of peripheral parasitemia combined with an age-structured mathematical model of the parasite erythrocyte cycle. Applying the model to data from 217 Gambian children undergoing treatment for cerebral malaria we conclude that although artemether clears parasitemia more rapidly than quinine, the clearance of sequestered parasites is similar for the two drugs. The estimated sequestered mass was found to be a more direct predictor of fatal outcome than clinically observed parasitemia. This method allows a sequential analysis of sequestered parasite population dynamics in children suffering from cerebral malaria, and the results offer a possible explanation for why artemether provides less advantage than might have been expected over quinine in reducing mortality despite its rapid effect on circulating parasites.

Animals↗
PubMed2001

Why circadian rhythms are circadian: competitive population dynamics of biological oscillators.

Living creatures are under control of biological clocks with various periods near those of environmental cycles. Examples are circadian (about a day) and circannual (about a year) clocks. We may ask why their periods are not precisely one day or one year because adaptation to the environment should then be easier. Here, introducing a model of competitive population dynamics of biological species with clock dynamics incorporated, it is shown that periods equal or close to that of the environment do not always guarantee overwhelming superiority and can even lead to extinction. This result may provide a clue to solve the mystery.

Animals↗
PubMed2005

Population dynamics of nasal strains of methicillin-resistant Staphylococcus aureus--and their relation to community-associated disease activity.

BACKGROUND: Nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) plays a key role in the epidemiology and pathogenesis of disease. The purpose of this study was to determine the characteristics and dynamics of nasal strains of MRSA, as well as their relation to community-associated disease activity. METHODS: This study is a cross-sectional survey and molecular epidemiologic analysis of nasal colonization by S. aureus in homeless and runaway youths, an underserved population at high risk for staphylococcal disease. RESULTS: Of the 308 study participants, 27.6% carried S. aureus, and 6.2% carried MRSA. Subgroups of individuals with increased MRSA carriage rates were also at highest risk for community-associated MRSA infection; these subgroups included individuals with either HIV infection or AIDS, injection drug users, patients with abscesses, and those recently hospitalized. Multilocus sequence typing and pulsed-field gel electrophoresis identified 2 genotypes--ST59:P (USA1000) and ST8:S (USA300)--that accounted for 84.2% (16/19) of the MRSA isolates carried. The genotypes were distinct from nosocomial genotypes endemic in the hospital, although they originated from individuals with prior exposure to health care. CONCLUSIONS: Comparison of MRSA strains from asymptomatic carriers versus concurrently collected community-associated clinical strains from patients treated at local health-care facilities allowed for the identification of 3 population dynamics of nasal strains of MRSA: (1) endemic clones--for example, ST8:C and ST59:P--sustained asymptomatic carriage and infection over prolonged periods; (2) an epidemic clone, ST8:S, demonstrated enhanced capacity for rapid transmission and widespread infections; and (3) an outbreak clone, ST30:Z (USA1100), was highly infectious but exhibited poor asymptomatic transmission.

Adolescent↗
PubMed2001

Population dynamics advected by chaotic flows: A discrete-time map approach.

A discrete-time model of reacting evolving fields, transported by a bidimensional chaotic fluid flow, is studied. Our approach is based on the use of a Lagrangian scheme where fluid particles are advected by a two-dimensional symplectic map possibly yielding Lagrangian chaos. Each fluid particle carries concentrations of active substances which evolve according to its own reaction dynamics. This evolution is also modeled in terms of maps. Motivated by the question, of relevance in marine ecology, of how a localized distribution of nutrients or preys affects the spatial structure of predators transported by a fluid flow, we study a specific model in which the population dynamics is given by a logistic map with space-dependent coefficient, and advection is given by the standard map. Fractal and random patterns in the Eulerian spatial concentration of predators are obtained under different conditions. Exploiting the analogies of this coupled-map (advection plus reaction) system with a random map, some features of these patterns are discussed. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed2006

Effect of abiotic factors on seasonal population dynamics of Lutzomyia longipalpis (Diptera: Psychodidae) in northeastern Brazil.

The resurgence of visceral leishmaniasis in Brazil increases the need for studies to elucidate the spatial and temporal dynamics of Lutzomyia longipalpis (Lutz and Neiva) (Diptera: Psychodidae), the vector of Leishmania infantum, the causative agent of visceral leishmaniasis in Brazil. Sand flies were captured in peridomestic habitats biweekly for 3 yr. Cross-correlation tests and spectral analysis were used to analyze the simultaneous and lag-time correlations between Lu. longipalpis population densities and abiotic factors of temperature, relative humidity, wind velocity, and rainfall. Distinct seasonal patterns were observed for males and females, with intervals of 6 mo between population peaks for males and 12 mo for females. Peak female population densities lagged 3 mo behind the maximum annual temperature. Female population density was negatively correlated with relative humidity. An increase in average wind velocity was followed by a decrease in the number of females for 2 wk. Understanding the relationship between the seasonal population dynamics of Lu. longipalpis and abiotic factors will contribute to the design of better control measures to decrease transmission of L. infantum and consequently the incidence of leishmaniasis.

Animals↗
PubMed2006

Stochastic and deterministic simulations of heterogeneous cell population dynamics.

A Monte Carlo algorithm, which can accurately simulate the dynamics of entire heterogeneous cell populations, was developed. The algorithm takes into account the random nature of cell division as well as unequal partitioning of cellular material at cell division. Moreover, it is general in the sense that it can accommodate a variety of single-cell, deterministic reaction kinetics as well as various stochastic division and partitioning mechanisms. The validity of the algorithm was assessed through comparison of its results with those of the corresponding deterministic cell population balance model in cases where stochastic behavior is expected to be quantitatively negligible. Both algorithms were applied to study: (a) linear intracellular kinetics and (b) the expression dynamics of a genetic network with positive feedback architecture, such as the lac operon. The effects of stochastic division as well as those of different division and partitioning mechanisms were assessed in these systems, while the comparison of the stochastic model with a continuum model elucidated the significance of cell population heterogeneity even in cases where only the prediction of average properties is of primary interest.

Algorithms↗
PubMed1984

Reproductive performance, population dynamics and anthropometrics of the free-ranging Cayo Santiago rhesus macaques.

This report summarizes demographic data collected on the Cayo Santiago colony of rhesus monkeys from 1976-1983 and compares the results with those from 1959-1964 [8,9]. For males and nonpregnant/nonlactating, pregnant, and lactating females mean (+/- 1 SD), body weights, crown-rump lengths, and ponderal indices are tabulated for each age on a large (n = 586) single sampling of this free-ranging population of macaques.

Animals↗
PubMed1993

Population dynamics of aberrant chromosome 1 in mice.

Natural populations of two semispecies of house mouse, Mus musculus domesticus and M.m. musculus, were found to be polymorphic for an aberrant chromosome 1 bearing a large inserted block of homogeneously staining heterochromatin. Strong meiotic drive for the aberrant chromosome from M.m. musculus was previously observed in heterozygous female mice. There are at least three meiotic drive levels determined by different allelic variants of distorter. Homozygotes had low viability and females showed low fertility. Both homo- and heterozygous males had normal fertility and their segregation patterns did not deviate from normal. Computer simulations were performed of the dynamics of aberrant chromosome 1 in demes and populations. The data demonstrate that a spontaneous mutation (inversion) of an aberrant chromosome 1, once arisen, has a high probability of spreading in a population at high coefficients of meiotic drive and migration. In the long-term, the population attains a stationary state which is determined by the drive level and migration intensity. The state of stable genotypic equilibrium is independent of deme and population size, as well as of the initial concentration of the aberrant chromosome. As populations initially polymorphic for the distorters approach the stationary state, the stronger distorter is eliminated. The frequencies of the aberrant chromosome determined by computer analysis agree well with those obtained for the studied Asian M.m. musculus populations. The evolutionary pathways for the origin and fixation of the aberrant chromosome in natural populations are considered.

Animals↗
PubMed1994

Combining behaviour and population dynamics with applications for predicting consequences of habitat loss.

A population model for migratory vertebrates is developed by combining game theory models of foraging behaviour with population biology. Models of foraging behaviour which incorporate interference and resource depletion are developed to determine the density-dependent mortality occurring within sites. Population size can then be related to the strength of interference, the variance in competitive ability and the rate at which resources are depleted. The model is extended to predict evolutionarily stable migration strategies. This novel framework is then used to predict the population decline resulting from habitat loss.

Animals↗
PubMed2005

Ecological change, group territoriality, and population dynamics in Serengeti lions.

Territorial behavior is expected to buffer populations against short-term environmental perturbations, but we have found that group living in African lions causes a complex response to long-term ecological change. Despite numerous gradual changes in prey availability and vegetative cover, regional populations of Serengeti lions remained stable for 10- to 20-year periods and only shifted to new equilibria in sudden leaps. Although gradually improving environmental conditions provided sufficient resources to permit the subdivision of preexisting territories, regional lion populations did not expand until short-term conditions supplied enough prey to generate large cohorts of surviving young. The results of a simulation model show that the observed pattern of "saltatory equilibria" results from the lions' grouping behavior.

Algorithms↗
PubMed1982

Ecology and population dynamics of the pygmy marmoset, Cebuella pygmaea.

The pygmy marmoset population of a 3-km2 sample area of Amazonian lowland forest was censused and monitored intensively between September 1976 and January 1978. Floodplain forest constituted the habitat of Cebuella and supported a population density of 51.5 independently locomoting individuals (ILI) per square kilometer. The highest population concentration occurred along the edges of the river, where the density reached 274 ILI per km2. Adults comprised about one half of the total population. About 83% of the population lived in stable troops; the remaining 17% was made up by incipiently associated pairs and solitary individuals. Stable troops were made up of 1 breeding female, her mate, and her maturing offspring of up to four successive litters. Moreover, some troops contained 1-2 additional adult members. Troop size ranged from 2 to 9 ILI, with a modal size of 6 ILI. The births showed two annual peaks and the interbirth intervals ranged between 5 and 7 months. Infant survival was about 67%. Exudates (sap and gums) of trees and vines, insects and arachnids constituted the principal food resources of the population. The troops occupied exclusive home ranges of 0.2-0.4 ha. Several troops changed home range sites temporarily or permanently in the course of the study.

Animals↗
PubMed1999

Population dynamics of an introduced bacterium degrading chlorinated benzenes in a soil column and in sewage sludge.

The capacity of the beta-Proteobacterium Pseudomonas sp. strain P51, which degrades chlorinated benzenes, to metabolize 1,2,4-trichlorobenzene (TCB) under environmental conditions was tested by its release into two experimental systems. The first system consisted of laboratory scale microcosms which were operated with and without the addition of TCB and which were inoculated with sludge from a wastewater treatment plant. The second system consisted of a non sterile, water saturated soil column. We determined survival of strain P51 after its introduction and its ability to degrade TCB. The population dynamics was followed by selective plating and applying the polymerase chain reaction (PCR) to detect strain P51 and the chlorobenzene (tcb) genes on catabolic plasmid pP51. The results showed a completely different behaviour of strain P51 in the two habitats under the applied conditions. In the soil column the P51 bacteria inoculated the entire area and their population reached 2 x 10(6) cells/g soil. The population remained active since TCB was degraded to concentrations below the detection limit of 30 micrograms/l. In the sludge microcosms, the number of strain P51 cells immediately decreased from 4 x 10(7) cells/ml to 10(5) cells/ml over a period of 2 days after inoculation, and then the strain disappeared to levels below our detection limit (10(3)-10(4) cells/ml). In the reactor without TCB the population of P51 maintained a stable value of 10(5) cells/ml during 8 days but then also decreased to levels below the detection limit. In addition, no significant TCB degradation was found in the sludge reactors. The influence of presence of TCB on maintenance of strain P51 in the two habitats is discussed. This work demonstrates the possibility to successfully apply preselected strains to degrade otherwise poorly degradable substances in complex mixed microbial communities. However, survival and activity may depend strongly on the type of system into which the strain is introduced.

Base Sequence↗
PubMed2005

Population dynamics of Oenococcus oeni strains in a new winery and the effect of SO2 and yeast strain.

The effects of different yeast starters and SO(2) addition on malolactic fermentation in a new winery were evaluated by a molecular approach in three vintages. Alcoholic fermentations with 40 and 100mgl(-1) SO(2) were carried out, followed by uninoculated malolactic fermentations. Isolated colonies of Oenococcus oeni obtained from samples throughout the vinification were identified and typified by multiplex RAPD-PCR. This made it possible to monitor the population dynamics and follow the proportion of as many as 29 different indigenous strains. In one of the vintages, O. oeni strains were more inhibited when a specific yeast starter was used.

DNA Fingerprinting↗
PubMed2004

Genetic structure and population dynamics of Xanthomonas axonopodis pv. manihotis in Colombia from 1995 to 1999.

Restriction fragment length polymorphisms (RFLPs) were used to study the population genetics and temporal dynamics of the cassava bacterial pathogen Xanthomonas axonopodis pv. manihotis. The population dynamics were addressed by comparing samples collected from 1995 to 1999 from six locations, spanning four different edaphoclimatic zones (ECZs). Forty-five different X. axonopodis pv. manihotis RFLP types or haplotypes were identified between 1995 and 1999. High genetic diversity of the X. axonopodis pv. manihotis strains was evident within most of the fields sampled. In all but one site, diversity decreased over time within fields. Haplotype frequencies significantly differed over the years in all but one location. Studies of the rate of change of X. axonopodis pv. manihotis populations during the cropping cycle in two sites showed significant changes in the haplotype frequencies but not composition. However, variations in pathotype composition were observed from one year to the next at a single site in ECZs 1 and 2 and new pathotypes were described after 1997 in these ECZs, thus revealing the dramatic change in the pathogen population structure of X. axonopodis pv. manihotis. Disease incidence was used to show the progress of cassava bacterial blight in Colombia during the 5-year period in different ecosystems. Low disease incidence values were correlated with low rainfall in 1997 in ECZ 1.

Bacterial Proteins↗
PubMed2006

Methanogenic population dynamics and performance of an anaerobic membrane bioreactor (AnMBR) treating swine manure under high shear conditions.

A 6-L, completely mixed anaerobic bioreactor with an external ultrafiltration membrane module was operated for 300 days to evaluate the startup and performance of an anaerobic membrane bioreactor (AnMBR) treating swine manure. The reactor had a successful startup at the initial loading rate of 1g volatile solids (VS)/L/day. After a two-fold increase in loading rate followed by a sudden, two-fold increase in flow velocity through the membrane module on day 75, the performance of the AnMBR deteriorated as measured by volatile fatty acid (VFA) accumulation, decrease in pH, and decrease in biogas production. The methanogenic population dynamics in the reactor were monitored with terminal restriction fragment length polymorphism (T-RFLP). Changes in the relative levels of Methanosarcinaceae and Methanosaetaceae were consistent with changes in VFA concentrations, i.e., high and low levels of acetate corresponded to a high abundance of Methanosarcinaceae and Methanosaetaceae, respectively. The levels of hydrogenotrophic methanogens of the order of Methanomicrobiales increased during decreased reactor performance suggesting that syntrophic interactions involving hydrogenotrophic methanogens remained intact regardless of the degree of shear in the AnMBR.

Anaerobiosis↗
PubMed1976

Female dominant age-dependent deterministic population dynamics.

In this paper the study of a nonlinear deterministic model of an age/sex differentiated population is started with a proof of existence and uniqueness of solution of the governing equation. We also obtain time dependent upper bounds to the male and female populations as well as necessary and sufficient conditions for equilibrium.

Age Factors↗