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[Role of bacteriocinogeny in regulating the population dynamics of oral cavity lactobacilli].

Bacteriocinogenicity and bacteriocine sensitivity of Lactobacilli isolated from human saliva were studied. It was shown that bacteriocinogenic cultures of Lactobacilli resistant to bacteriocines produced by them probably may play some ecological role in regulation of the population dynamics because of growth inhibition of Lactobacillus sensitive cultures in the saliva, thus providing favourable selective conditions for the development of both the strains producing them and the strains resistant to bacteriocines. Bacteriocinogenic strains sensitive to bacteriocines produced by them probably played no significant role in regulation of the dynamics of Lactobacillus population in the oral cavity, since they did not inhibit the growth of half of the Lactobacillus cultures present in human saliva.

Bacteriocins↗

Population Dynamics of Soil Pseudomonads in the Rhizosphere of Potato (Solanum tuberosum L.).

Rhizosphere population dynamics of seven Pseudomonas fluorescens and Pseudomonas putida strains isolated from rhizospheres of various agricultural plants were studied on potato (Solanum tuberosum L.) in field soil under controlled environmental conditions. Rhizosphere populations of two strains (B10 and B4) were quantitatively related to initial seed piece inoculum levels when plants were grown at -0.3 bar matric potential. At a given inoculum level, rhizosphere populations of strain B4 were consistently greater than those of strain B10. In vivo growth curves on 4-cm root tip-proximal segments indicated that both strains grew at similar rates in the potato rhizosphere, but large populations of strain B10 were not maintained at 24 degrees C after 7 h, whereas those of strain B4 were maintained for at least 40 h. Although both strains grew more rapidly in the rhizosphere at 24 degrees C than at 12 degrees C, their rhizosphere populations after seed piece inoculation were generally greater at 12 or 18 degrees C, indicating that in vivo growth did not solely determine rhizosphere populations in these studies. In vitro osmotolerance of seven Pseudomonas strains (including strains B4 and B10) was correlated with their abilities to establish stable populations in the rhizosphere of potato. Stability of rhizosphere populations of the Pseudomonas strains studied here was maximized at low (i.e., 12 degrees C) soil temperatures. These results indicate that Pseudomonas strains differ in their capacity to maintain stable rhizosphere populations in association with potato. This capacity, distinct from the ability to grow in the rhizosphere, may limit the establishment of rhizosphere populations under some environmental conditions.

Journal Article↗

Transmission and population dynamics of HTLV-I infection.

We present a modelling approach for transmission and population dynamics of human T-cell lymphotropic-virus-type-I (HTLV-I) infection. A steady-state analysis of the model was used to estimate transmission rates for males and females. The rate of heterosexual transmission was 2.7 times higher if the carrier was male. A dynamic transmission model was developed and used to study the impact of different intervention measures in the Jamaican population. Interventions concerning horizontal (heterosexual) transmission exceeds the effect of breaking vertical (mother-to-child) transmission, although breast feeding also has an important impact on the total number of infected individuals.

Disease Transmission, Infectious↗

Population dynamics of the metacercarial stage of the bucephalid trematode, Labratrema minimus (Stossich, 1887) from Salses-Leucate lagoon (France) during the cercarial shedding period.

The population dynamics of Labratrema minimus (Stossich, 1887) metacercariae (Trematoda, Bucephalidae) were studied in its second intermediate fish host Atherina boyeri from Salses-Leucate lagoon (Northwest Mediterranean Sea, South of France), during the cercarial shedding period. The infection parameters (prevalence and mean abundance of infection) showed the high susceptibility of silversides (juveniles and adults) to infection. The observed variation in the mean abundance of infection with respect to time and host size was explained by (i) the susceptibility of A. boyeri to multiple successive infections (increase in abundance of infection with host length and raising of parasite burden until August) and (ii) the loss, probably by more rapid death, of heavily infected silversides from each host size group (decrease in abundance of infection in September within each host size group, stability of the parasite burden within the older class of hosts over the whole period, premature decrease in the condition factor in August). Finally, it was deduced that the infection pattern observed over the May-September period was a dynamic process controlled by: availability of infective cercariae, influx of newborn silversides free of metacercariae until September, high susceptibility of juvenile and adult A. boyeri to infection, metacercarial loss and probably by parasite-induced host mortality.

Analysis of Variance↗

Forecasting cataract surgeries and intraocular lens implantation to 1990 using a model of population dynamics.

Extending the recently observed dramatic growth rates of cataract surgery and intraocular lens implantation into the future is not necessarily valid because of changes in population size, new incidence of cataracts, and rates of treatment for patients diagnosed in current as well as in previous years. Accelerated treatment of the pool of previously diagnosed patients caused a sharp growth in cataract surgery since 1980, but at the same time reduced patients and thus the potential for continued high growth rates. This paper describes a model that produces forecasts through explicit consideration of the many aspects of population dynamics. It provides an opportunity to examine how forecasts might vary under different assumptions about advances in medical technology.

Adult↗

Applicability of the Fisher equation to bacterial population dynamics.

The applicability of the Fisher equation, which combines diffusion with logistic nonlinearity, to population dynamics of bacterial colonies is studied with the help of explicit analytic solutions for the spatial distribution of a stationary bacterial population under a static mask. The mask protects bacteria from ultraviolet light. The solution, which is in terms of Jacobian elliptic functions, is used to provide a practical prescription to extract Fisher equation parameters from observations and to decide on the validity of the Fisher equation.

Bacteria↗

[Population dynamics of Bactrocera dorsalis (Diptera: Tephritidae) in Xishuangbanna of Southern Yunnan].

In the study, an all year round monitoring through lure-traps in 1997, 2000 and 2003 was conducted on the population dynamics of oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae) in Xishuangbanna of Southern Yunnan, and the factors in relation with its population fluctuation, including temperature, rainfall, and host species were analyzed. The fruit fly occurred year-round in Xishuangbanna, with a low population level from November to February, and increased steadily from March to July or August. An increasing peak appeared in July or August, depending on the rainfall amount in that year. Afterwards, the fly population declined markedly until to October. Temperature, rainfall, and host fruits were supposed to be the major factors affecting the population fluctuation. The monthly average temperature in Xishuangbanna was in the ranges suitable for the development and reproduction of the fly, but the monthly average minimum temperature from December to February appeared to be lower than the suitable temperature, which was suggested to be responsible for the low populations in the winter months. Rainfall was another essential factor affecting population fluctuation. The population was depressed when the monthly rainfall amount was lower than 50 mm, but increased when the amount ranged between 100 and 200 mm. Under conditions the monthly rainfall amount was higher than 250 mm, the fruit fly population was reduced markedly, which explained the decreasing population in July or August when the heavy rain occurred. Mango, orange, pear, longan, and peach were the main host species of the fly, among which, mango and longan were most preferred by the fly. Therefore, their planted area, fruiting period and productivity exerted essential effects on the fly population fluctuation, and regarded as another major factor affecting the fly population in this area.

Animals↗

The population dynamics of nematode parasites of sheep in northern England.

An investigation into the population dynamics of sheep nematodes was carried out between April 1970 and September 1971. Faecal egg counts were made from both ewes and lambs at weeks intervals while grass samples were taken fortnightly throughout the summer and monthly during the winter. From these results absolute numbers of nematode eggs and infective larvae were estimated and these figures used as a basis for determining the level of mortality occurring during development from egg to infective larva. The figures were also used to assess the relative importance of the ewe 'spring rise' and the egg output of the lambs in June while grazing contaminated pasture. These calculations suggest that larval mortality was very high and that it may vary considerably from year to year depending upon the climatic conditions prevailing. There was also an indication that the ewe 'spring rise' was the major source of the wave of infection which occurs in the lambs in late August and September.

Animals↗

Population dynamics of Toxocara canis in pigs receiving a single or multiple infection.

The population dynamics of Toxocara canis in pigs, and their immune response to a primary and a challenge infection, were studied by parasitological, haematological and serological parameters. Seventy pigs were divided into 4 groups; 35 pigs received a primary infection (group A), 15 pigs received both a primary and a challenge infection (group B), 15 pigs received the challenge infection only (group C), and 5 pigs served as helminth-free controls (group NC). A dose of 50,000 eggs was administered for the primary infection (day 0) and a dose of 10,000 eggs was given for the challenge infection (day 28). On days 7, 14, 21 and 28 p.i., 5 pigs of group A, and on days 35, 42 and 49 p.i., 5 pigs from each of groups A, B and C were necropsied. Numbers of recovered larvae varied widely among the 5 pigs of each group on all days of necropsy. Toxocara canis larvae were recovered predominantly from the lungs; migration of larvae to other organs or tissues from the lungs was restricted. In group A, the larval burden in the lungs peaked on day 14 p.i., and the larval densities decreased significantly over time. Thereafter, the majority of larvae were recovered from the lungs until the end of the experiment (day 49 p.i.). A few larvae were found in the muscles and brain until day 42 p.i., and 2 larvae were found in the eyes of 2 pigs on day 35 p.i. There was little evidence of protective immunity to a challenge infection in this experiment. The eosinophil levels tended not to increase in pigs receiving a challenge infection, in contrast to the challenge control pigs. The fact that T. canis larvae migrate and persist in the tissues of pigs for more than 1 month suggests a zoonotic risk in infected pigs. The relevance of these data to the population biology and immunology of porcine and human toxocarosis is discussed.

Animals↗

Population dynamics of the house dust mites Dermatophagoides farinae, D. pteronyssinus, and Euroglyphus maynei (Acari: Pyroglyphidae) at specific relative humidities.

Experiments were conducted to determine the effects of relative humidity on the population dynamics of single and mixed species of Dermatophagoides farinae Hughes, D. pteronyssinus (Trouessart), and Euroglyphus maynei (Cooreman) at specific relative humidities maintained at 20 degrees C, with unlimited food. The population density of single and mixed species (D. farinae and D. pteronyssinus) increased exponentially when cultured at 65, 70, and 75% RH. The mean population growth rates were 17.3 +/- 4.4 SD and 32.5% +/- 4.7/wk for D. farinae and D. pteronyssinus, respectively. Mean population doubling times were 2.2 +/- 0.3 and 4.2 +/- 1.3 wk for D. pteronyssinus and D. farinae, respectively. Mixed species cultures, started with equal numbers of D. farinae and D. pteronyssinus, resulted in higher percentages of D. farinae than D. pteronyssinus. In cultures started with 75% of one species and 25% of the other, the more numerous species remained dominant and in similar ratios throughout the experiment. Both D. farinae and D. pteronyssinus population densities maintained at 85% RH declined over a 12-wk culture period because of mold growth. E. maynei were unable to survive at 65, 70, 75, and 85% RH, which indicated that their climatic requirements were different from those of D. farinae and D. pteronyssinus. Population densities of D. farinae and D. pteronyssinus cultures declined when held at 21-22 degrees C and relative humidities of < or = 50%; however, at 50% RH, significant proportions of the populations survived for 10 wk. Half-life for desiccation of D. farinae and D. pteronyssinus at 45% RH was 11.5 and 1.2 wk, respectively, but at 50% RH was 86.3 and 4.0 wk, respectively. The data indicated that a < or = 50% RH would have to be maintained for long periods to reduce both D. farinae and D. pteronyssinus by desiccation procedures. The results of this study show that D. farinae and D. pteronyssinus have high reproductive potentials and population growth rates, which indicate that mite reduction procedures must be thorough or mite densities will return to high levels quickly following remediation if adequate food and suitable microclimatic conditions exist.

Animals↗

Population dynamics of adult-formed granule neurons of the rat olfactory bulb.

The population dynamics of internal granule cells in the rat olfactory bulb during adult life were analyzed in histological sections and in autoradiograms with (1) counts of granule cells, (2) counts of labeled granule cells 1 month after injection of 3H-thymidine at various ages, and (3) counts of labeled granule cells at varying survival times (up to 18 months) after injection at 3 months and 24 months. The total number of granule cells increases linearly throughout life, approximately doubling between 3 and 31 months. Autoradiographic studies show that the rate of production of new granule cells decreases from 3 to 12 months and then is approximately constant during the rest of the life span. The number of labeled cells found 6 months after injection at 3 and 24 months is about one-fourth and one-half, respectively, that of the number at a 1-month survival, suggesting that many of the cells produced to do not survive. However, at least some granule cells labeled at 3 months survive for 18 months. A model is suggested in which granule cells are produced continuously throughout life and control of the total number of granule cells is effected chiefly through the rate of cell death.

Age Factors↗

Borrelia burgdorferi population dynamics and prototype gene expression during infection of immunocompetent and immunodeficient mice.

The population dynamics of Borrelia burgdorferi were quantified by real-time PCR targeting the flaB gene in skin (inoculation site, noninoculation site, and ear), heart (heart base and ventricle), quadriceps muscle, and the tibiotarsal joint at 1, 2, 4, 6, and 8 weeks after intradermal inoculation in C3H and C3H-scid mice. In addition, RNA transcription was assessed for several prototype genes, including flaB, ospA, ospC, dbpA, arp, vlsE, fbp, oppA-2, and p37-42. Spirochete numbers were equivalent in C3H and C3H-scid mice at 1 or 2 weeks and then declined in C3H mice, but they continued to rise and then plateaued in C3H-scid mice. Gene transcription was likewise higher in C3H-scid mice than in C3H mice, particularly at 4 or more weeks of infection. Gene transcription showed variation among tissues, with the highest levels of transcription in heart and joint tissue, which are sites of inflammation.

Animals↗

Yeast population dynamics of industrial fuel-ethanol fermentation process assessed by PCR-fingerprinting.

Yeast population used in industrial production of fuel-ethanol may vary according to the plant process condition and to the environmental stresses imposed to yeast cells. Therefore, yeast strains isolated from a particular industrial process may be adapted to such conditions and should be used as starter strain instead of less adapted commercial strains. This work reports the use of PCR-fingerprinting method based on microsatellite primer (GTG)5 to characterize the yeast population dynamics along the fermentation period in six distilleries. The results show that indigenous fermenting strains present in the crude substrate can be more adapted to the industrial process than commercial strains. We also identified new strains that dominate the yeast population and were more present either in molasses or sugar cane fermenting distilleries. Those strains were proposed to be used as starters in those industrial processes. This is the first report on the use of molecular markers to discriminate Saccharomyces cerevisiae strains from fuel-ethanol producing process.

Biomarkers↗

Scaling up population dynamics: integrating theory and data.

How to scale up from local-scale interactions to regional-scale dynamics is a critical issue in field ecology. We show how to implement a systematic approach to the problem of scaling up, using scale transition theory. Scale transition theory shows that dynamics on larger spatial scales differ from predictions based on the local dynamics alone because of an interaction between local-scale nonlinear dynamics and spatial variation in density or the environment. Based on this theory, a systematic approach to scaling up has four steps: (1) derive a model to translate the effects of local dynamics to the regional scale, and to identify key interactions between nonlinearity and spatial variation, (2) measure local-scale model parameters to determine nonlinearities at local scales, (3) measure spatial variation, and (4) combine nonlinearity and variation measures to obtain the scale transition. We illustrate the approach, with an example from benthic stream ecology of caddisflies living in riffles. By sampling from a simulated system, we show how collecting the appropriate data at local (riffle) scales to measure nonlinearities, combined with measures of spatial variation, leads to the correct inference for dynamics at the larger scale of the stream. The approach provides a way to investigate the mechanisms and consequences of changes in population dynamics with spatial scale using a relatively small amount of field data.

Animals↗

Population dynamics and effects of Oebalus ornatus (Hemiptera: Pentatomidae) on rice yield and quality in southwestern Colombia.

Field experiments were conducted from 1989 to 1992 to determine the effects of Oebalus ornatus (Sailer) on Cica 8 rice, Oryza sativa L., yield and to study the population dynamics of the insect. The effect of O. ornatus was measured for seven population levels (0, 2, 3, 4, 8, 12, and 24 sexed pairs per 20 panicles) at three stages of grain development (flowering, milk, and soft dough stage). Insect feeding during the flowering and milk stages of grain development caused more damage than feeding during the soft dough stage. The action threshold was calculated to be 14 O. ornatus adults per square meter for the flowering and milk stages and 67 for the soft dough stage of grain maturity. Population densities that would reduce rice yield in southwestern Colombia were not observed during the 3 yr of the study.

Animals↗

Alfalfa leafcutting bee population dynamics, flower availability, and pollination rates in two Oregon alfalfa fields.

Since the 1970s, it has become increasingly difficult for U.S. alfalfa seed producers to maintain Megachile rotundata (F.) populations used for alfalfa, Medicago sativa L., pollination. In 1998, we monitored M. rotundata population dynamics and foraging behavior, as well as alfalfa bloom and pollination rates in two fields in eastern Oregon. Despite marked differences in bee management, establishment was very similar in the two fields (approximately 0.5 females per nesting cavity) and lagged peak bloom by approximately 2 wk. Pollination rates increased from 0-10% in the first 3 wk to 80-90% in week 4-5. By then, M. rotundata females had difficulty finding untripped (nonpollinated) flowers and visited large numbers of already tripped or not fully matured flowers. M. rotundata progeny mortality was very high (54-78%). Estimated seed yields were similar in both fields. We contend similar seed yields, and improved bee production, could be accomplished with smaller bee populations, better timed with alfalfa bloom.

Animals↗

[Population dynamics of endangered plant species Abies chensiensis].

In order to know the endangered status and causes of Abies chensiensis in Qinlin Mountains, a field investigation on 18 plots was conducted on its age structure, life table and fecundity, and its population dynamics were predicted by time sequence model. The analysis on the age structure of Abies chensiensis populations showed that there were fewer young individuals, but middle-aged and old individuals were relatively rich. The population D in Abies chensiensis-Indigofera amblyantha-Carex lanceolata association showed a relatively stable development tendency, while other four populations (A, B, C and E) in Abies chensiensis-Pinus tabulaeformis-Sinarundinaria nitida-Carex lanceolata association, Abies chensiensis-Quercus aliena var. acutserrata-Litsea pungens-Carex lanceolata association, Abies chensiensis-Betula albo-sinensis-Sinarundinaria nitida-Duchesnea indica association, and Abies chensiensis-Pinus tabulaeformis-Smilax stans-Carex lanceolata association all showed an obviously declining tendency. The analysis on the life tables and survival curves showed that the survival curve of Abies chensiensis populations belonged to Deevey III, and the death peak of different populations was in the period of 60--100 years old. The number difference among populations reflected the population habitat. Time sequence prediction indicated the numbers of old individuals would be increased at the beginning, and decreased finally in 20, 40, and 80 years. It was difficult to maintain the population stability. Analysis on 10 ecological factors showed that tree coverage, soil organisms and air humidity influenced population positively, and human disturbance and sunlight influenced population negatively. In situ conservation should be taken as the most important management countermeasure, and natural regeneration should be promoted. At the same time, artificial population should be expanded.

Abies↗

Population dynamics of Pseudomonas sp. along a spatial gradient of phosphate: an experimental approach for spatial ecology.

Many theoretical models have been proposed to study the effect of space on population dynamics and interactions, but most of them are difficult to translate into experimental setups due to their abstract nature. Here we defend the gradostat as a valuable experimental tool for testing such theories. The gradostat is a culture system with bi-directional flow that forms nutrient gradients at steady state. In this study, we use a 3-vessel gradostat with a phosphate gradient to study the effect of spatial heterogeneity on the spatial distribution of Pseudomonas sp., an heterotrophic aquatic bacterium. The observed distributions partially agree with theoretical predictions, obtained from a mathematical model.

Ecology↗