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PubMed2003

Population dynamics of Lymnaea columella and its natural infection by Fasciola hepatica in the State of Minas Gerais, Brazil.

Studies on the population dynamics and natural infection of Lymnaea columella by Fasciola hepatica were carried out from September 1999 to December 2000 in a low-lying area near Itajubá in the Brazilian State of Minas Gerais. A total of 626 snails were collected monthly at nine different sites, counted, and dissected to search for larvae of F. hepatica. The highest populations of L. columella were reached in October of 1999 and August of 2000, and the highest natural infection rates of snails by F. hepatica were reached in September 1999 (5.2%) and July 2000 (3.9%). The removal by farmers of aquatic plants from the drainage furrows caused a drastic reduction in this snail population.

Animals↗
PubMed2001

Population dynamics of the white wax scale, Ceroplastes destructor (Hemiptera: Coccidae), on citrus in South Africa, with implications for biological control.

The population dynamics of the white wax scale, Ceroplastes destructor Newstead, was studied intensively in four easy-peel citrus orchards in the Western Cape Province of South Africa over three consecutive years (1997-1999). Key factor analysis was used to determine and quantify the contribution of individual mortality factors to the total generation mortality. Key stage mortality, determined from a cohort life table, was in the third instar and pre-ovipositing female stages. Mortality of C. destructor was caused primarily by parasitoids, predators and miscellaneous factors. Parasitoids and miscellaneous factors acted as density-dependent regulatory agents during the pre-ovipositional and first instar stages respectively. This has implications for biological control of C. destructor. Some of the mortality factors acted either randomly with no reference to the population densities or in an inverse density-dependent manner during the egg-crawler, second or third instar stages.

Animals↗
PubMed2000

A two-reservoir, hollow-fiber bioreactor for the study of mixed-population dynamics: design aspects and validation of the approach.

A two-reservoir, membrane bioreactor for carrying out studies of mixed-population dynamics in batch fermentations is presented. Mixing requirements and design aspects for the validity of the approach are given and discussed. Equations describing mixing times between the reservoirs are presented and compared to the experimental results. The validity of the approach is demonstrated by the study of an amensalistic-type interaction, the protein-mediated killer phenomenon between two Saccharomyces cerevisiae strains. The validation consisted in the comparison between the results obtained in actual mixed culture and the results obtained by keeping the strains separated. A good agreement was found which demonstrates the viability of the designed bioreactor.

Bioreactors↗
PubMed2005

Population dynamics of the 2 major mitochondrial DNA haplotypes in experimental populations of Drosophila subobscura.

The evolution of Drosophila subobscura mitochondrial DNA has been studied in experimental populations, founded with flies from a natural population from Calvià (Majorca, Balearic Islands, Spain). This population, like others founded in Europe, is characterized by the presence of 2 very common (>95%) mitochondrial haplotypes (named I and II) and rare and endemic haplotypes that appear at very low frequencies. Four experimental populations were established with flies having a heterogeneous nuclear genetic background, which was representative of the composition of the natural population. The populations were started with haplotypes I and II at an initial frequency of 50% each. After 33 generations, the 2 haplotypes coexisted. Random drift could be rejected as the only force responsible for the observed changes in haplotype frequencies. A slight but significant linear trend favouring a mtDNA (haploid) fitness effect has been detected, with a nonlinear deviation that could be due to a nuclear component. An analysis of chromosomal arrangements was made before the foundations of the cages and at generation 23. Our results indicated that the hypothesis that the maintenance of the frequencies of haplotypes I and II in natural populations could be due to their association with chromosomal arrangements remains controversial.

Animals↗
PubMed2006

Competition between plasmid-bearing and plasmid-free organisms in the host: population dynamics and antibiotic resistance.

OBJECTIVE: To clarify the effects of antibiotic exposure on bacterial antibiotic resistance. MATERIALS AND METHODS: A competitive population dynamics model for plasmid-bearing organisms and plasmid-free organisms in the host was established. The Poincaré-Bendixson theorem was used for analysis. RESULTS: All possible results of the competition dependent on biologically meaningful parameters were obtained, which can be classified into eight categories. With the outcomes of the plasmid model, we discussed the sterilizing effect if an antibiotic was added to the host. CONCLUSION: When antibiotic-resistant bacteria existed in a host, a higher dosage of antibiotics was needed with an increased risk of survival of plasmid-bearing organisms and greater danger of resistance to antibiotics.

Anti-Bacterial Agents↗
PubMed2002

Population dynamics in an aerobic submerged fixed bed reactor (ASFBR) process.

In this study, an aerobic submerged fixed bed reactor's (ASFBR) population dynamics has been studied in order to know its behavior in different conditions of organic load and oxygen concentration. The reactor was fed with synthetic wastewater. Tested variables and applied values were: 1) Variations in organic load (OL): 16-65 g COD/m2/d. 2) Variations in influent's COD concentration: 40-400 g COD/m3. 3) Variations in specific air flow (SAF): 15-127 m3air/kgCOD. Biofilm samples were taken at the top of the reactor. This study showed important variations in the composition and abundance of the microfauna depending on the experimental conditions. Variations in influent concentration had no significant effect on the abundance of the studied groups. However, differences depending on organic load and aeration conditions were observed. Organic load influenced every group studied but with different results. Sessile cilliates, metazoa and flagellates were abundant in low load, while crawling ones were in high load. Aeration intensity influenced most of the groups except Peranema and Vorticella spp. Despite obtaining good yields, not many protozoa, typical of biofilms under conventional processes, were found. Thus, a great variety of microorganisms, such as many classes of sessile and crawling cilliates, were not found. Important nitrifying activity was obtained at 20 cm depth in a bed. From this point, the heterotrophic and nitrifying populations exist but are inactive.

Animals↗
PubMed2005

Population dynamics of Digitaria spp submitted to selection pressure by herbicides in sugarcane crop.

The objective of this research was to study population dynamics of the weed crabgrass, genus Digitaria, submitted to selection pressure by herbicides currently applied in sugarcane crops in Brazil. In the first experiment two crabgrass species (Digitaria nuda and Digitaria ciliaris) and eight herbicide treatments applied in preemergence were used, and control percentage was evaluated at 7, 14, and 21 days after herbicide application (DAA). In the second experiment the level of tolerance through dose-response curve was determined for the species D. nuda and D. ciliaris, to the herbicides imazapyr, tebuthiuron, ametryne, and metribuzin. All the herbicides studied were efficient in controlling D. ciliaris, however, for D. nuda the best results were obtained only with ametryne, metribuzin, and isoxaflutole. The relation (T/S) between the rate required to reduce plant dry biomass (GR50) at 21 DAA of D. nuda and D. ciliaris was 16 for imazapyr and 6.3 for tebuthiuron, showing differential susceptibility of species; however for ametryne the rate T/S of 1.1 showed that D. nuda was not tolerant to this herbicide. For metribuzin, at 1.92 kg a.i. ha(-1), reduction of dry biomass was 80 and 90% to D. nuda and D. ciliaris, respectively. Even being controlled by metribuzin, D. nuda presented a higher level of tolerance to this herbicide, what was confirmed by the relationship T/S 14.4. As general conclusion of the research, it can be stated that the species D. nuda is more tolerant to ALS inhibiting herbicides and substituted urea, when compared with D. ciliaris; probably, D. nuda was selected by repetitive use of these herbicides.

Biomass↗
PubMed1989

Erythrocyte sedimentation realizable in terms of population dynamics.

A phenomenological theory is formulated in analogy to the theory of population dynamics to account for the observed erythrocyte sedimentation-time and velocity-time curves. The least square fitting of experimental data to the derived equations is quite satisfactory. Several parameters in the proposed equations can be used to characterize these two curves of erythrocyte sedimentation: the biotic potential or intrinsic rate of decrease of the lacuna population, r; the total distance settled by the interface between plasma and red cell column, K.delta h; the maximal settling velocity of the interface, Vmax; the time when Vmax occurs, tmv; and the final position of the interface, Hf.

Blood Sedimentation↗
PubMed2003

[Population dynamics of Quercus variabilis on northern slope of Qinling mountains].

Studies on the population dynamics, age structure, spatial distribution pattern, life table, and survival curve of Quercus variabilis showed that the Q. variabilis population on the northern slope of Qinling mountains was increasing. The number of young-aged individuals was larger, and that of middle-aged and old individuals was smaller. The life tables for different age classes showed that the mortality at age classes I and II was the highest, and the mortality rate was decreased with increasing age. However, at age classes VII and VIII, the mortality rose again for their decrepitude. The expected life span of age classes III, IV and V was higher, and decreased gradually with increasing age. The survival curves were the type of Deevey III, and the distribution pattern of population was aggregative as a whole. As the age increased, the intensity of aggregation decreased, and tended to a random distribution at higher elevations. A wise management should accelerate the recovery of Q. variabilis population and the enhancement of its productivity. The altitude 800-1,100 m was the favorable habitat for Q. variabilis population. As for the Q. variabilis at lower altitude, its protection should be reinforced, and the disturbance from human beings should be reduced. Forest thinning and other fostering management at middle altitude should be given in time. The target trees at higher altitude should be fostered.

Altitude↗
PubMed2006

Combining population-dynamic and ecophysiological models to predict climate-induced insect range shifts.

Hundreds of species are shifting their ranges in response to recent climate warming. To predict how continued climate warming will affect the potential, or “bioclimatic range,” of a skipper butterfly, we present a population‐dynamic model of range shift in which population growth is a function of temperature. We estimate the parameters of this model using previously published data for Atalopedes campestris. Summer and winter temperatures affect population growth rate independently in this species and therefore interact as potential range‐limiting factors. Our model predicts a two‐phase response to climate change; one range‐limiting factor gradually becomes dominant, even if warming occurs steadily along a thermally linear landscape. Whether the range shift accelerates or decelerates and whether the number of generations per year at the range edge increases or decreases depend on whether summer or winter warms faster. To estimate the uncertainty in our predictions of range shift, we use a parametric bootstrap of biological parameter values. Our results show that even modest amounts of data yield predictions with reasonably small confidence intervals, indicating that ecophysiological models can be useful in predicting range changes. Nevertheless, the confidence intervals are sensitive to regional differences in the underlying thermal landscape and the warming scenario.

Animals↗
PubMed2006

Microbial population dynamics associated with crude-oil biodegradation in diverse soils.

Soil bacterial population dynamics were examined in several crude-oil-contaminated soils to identify those organisms associated with alkane degradation and to assess patterns in microbial response across disparate soils. Seven soil types obtained from six geographically distinct areas of the United States (Arizona, Oregon, Indiana, Virginia, Oklahoma, and Montana) were used in controlled contamination experiments containing 2% (wt/wt) crude oil spiked with [1-(14)C]hexadecane. Microbial populations present during hydrocarbon degradation were analyzed using both 16S rRNA gene sequence analysis and by traditional methods for cultivating hydrocarbon-oxidizing bacteria. After a 50-day incubation, all seven soils showed comparable hydrocarbon depletion, where >80% of added crude oil was depleted and approximately 40 to 70% of added [(14)C]hexadecane was converted to (14)CO(2). However, the initial rates of hydrocarbon depletion differed up to 10-fold, and preferential utilization of shorter-chain-length n-alkanes relative to longer-chain-length n-alkanes was observed in some soils. Distinct microbial populations developed, concomitant with crude-oil depletion. Phylogenetically diverse bacterial populations were selected across different soils, many of which were identical to hydrocarbon-degrading isolates obtained from the same systems (e.g., Nocardioides albus, Collimonas sp., and Rhodococcus coprophilus). In several cases, soil type was shown to be an important determinant, defining specific microorganisms responding to hydrocarbon contamination. However, similar Rhodococcus erythropolis-like populations were observed in four of the seven soils and were the most common hydrocarbon-degrading organisms identified via cultivation.

Alkanes↗
PubMed2004

Clustering, advection, and patterns in a model of population dynamics with neighborhood-dependent rates.

We introduce a simple model of population dynamics which considers reproducing individuals or particles with birth and death rates depending on the number of other individuals in their neighborhood. The model shows an inhomogeneous quasistationary pattern with many different clusters of particles arranged periodically in space. We derive the equation for the macroscopic density of particles, perform a linear stability analysis on it, and show that there is a finite-wavelength instability leading to pattern formation. This is responsible for the approximate periodicity with which the clusters of particles arrange in the microscopic model. In addition, we consider the population when immersed in a fluid medium and analyze the influence of advection on global properties of the model, such as the average number of individuals.

Journal Article↗
PubMed1999

Population dynamics of ticks on indigenous cattle in a pastoral dry to semi-arid rangeland zone of Uganda.

Studies on seasonality and population dynamics of ticks on indigenous cattle and their crosses (calves) were carried out in Buruli Ranching Scheme, Nabiswera, Luwero district of Uganda on three treatment groups of animals: group 1 (twice a week dipping), group 2 (once a month dipping) and group 3 (no tick control). During this study, four major species of ticks of economic importance were recorded in decreasing order of abundance: Rhipicephalus appendiculatus, Rhipicephalus evertsi evertsi, Amblyomma variegatum and Boophilus decoloratus. Of these ticks, a seasonal pattern of activity was only observed in R. appendiculatus ticks, with peak activities occurring during rainy seasons. Greater numbers of ticks were recorded on cows than calves in the three treatment groups, with the exception of A. variegatum where the reverse occurred. The mean numbers of ticks per animal were highly significantly different (p < 0.01) when group 1 animals were compared with group 2 and 3 animals. However, no significant differences (p > 0.05) were observed in mean tick numbers between group 2 and 3 animals. Highly significant differences (p < 0.01) were observed in mean tick numbers on cows and calves (more than 12 months old) in different calving seasons. The state of lactation only affected tick counts on cows in group 1; significantly more ticks (p < 0.01) were observed in lactating than non-lactating cows. Furthermore, significantly greater (p < 0.05) numbers of ticks (with the exception of B. decoloratus) were recorded during the second year of study (March 1992-May 1993) than the first year (January 1991-February 1992), despite lower rainfall during the former period.

Animals↗
PubMed2001

Population dynamics of phytophagous and predatory mites (Acari: Tetranychidae, Eriophyidae, Phytoseiidae) on bamboo plants in Fujian, China.

The seasonal cycle and population dynamics of Schizotetranychus nanjingensis Ma and Yuan, Aponychus corpuzae Rimando (Tetranychidae), Aculus hambusae Kuang (Eriophyidae) and their natural enemy Tvphlodromus bambusae Ehara (Phytoseiidae) were studied during 1996-1998 in moso bamboo forests in Nanping, Fujian, China. Damage to bamboo leaves was often caused by mixed populations of the three phytophagous species, which displayed different seasonal dynamics: S. nanjingensis fed actively and reproduced in May and from late July to late October (aestivating from June to mid July), Ap. corpuzae was active and reproduced from mid July to late November, and Ac. bambusae from July to next February. During Spring S. nanjingensis was the dominant species with the greatest niche width, but in Summer Ac. bambusae and Ap. corpuzae became dominant and had greater niche widths. In Autumn, Ac. bambusae decreased but both S. nanjingensis and Ap. corpuzae mites increased and the latter became dominant. In winter all species decreased sharply in number. The two spider mite species (S. nanjingensis and Ap. corpuzae) had high niche overlaps in all four seasons. Niche overlaps between the eriophyid Ac. bambusae and the two spider mites were similarly high except during the spring when Ac. bambusae was absent. The predatory mite (T. bambusae) had higher niche overlap with Ap. corpuzae than with others during Autumn and Winter, but during Spring and Summer niche overlap was higher with S. nanjingensis.

Animals↗
PubMed1994

Description of a simulation model for the population dynamics of Eimeria acervulina infection in broilers.

A simulation model for the population dynamics of Eimeria acervulina infection in broilers is presented. The model describes the development of the numbers of parasites in the various life-stages during the growing period of broilers and the empty house period between grow-outs. The model includes assumptions with respect to development of immunity to E. acervulina infection and effects of application of anticoccidial drugs. The model consists of a set of difference equations that are solved numerically at 1 h intervals. Under constant conditions, an equilibrium level was reached after a few grow-outs during which infection always peaked around the 21st day in the growing period. Within a growing period, infection peaked earlier (later) than the 21st day in case initial numbers of sporulated oocysts were higher (lower) than the equilibrium number.

Animal Feed↗
PubMed1990

New approaches to the study of population dynamics in cities of Moscow Oblast.

New approaches to the study of population growth, spatial distribution, and urbanization in the USSR are presented. "Quantitative analysis of historical trends in city growth rates within Moscow Oblast (1926-1984) reveals two major components or city types: a group of cities with below-(oblast) average rates for each of five periods of analysis (1926-39, 1939-59, 1959-70, 1970-79, 1979-84) and a second category experiencing above-average growth until 1970, with subsequent reduction of rates below the oblast average."

Demography↗
PubMed2004

Evidence for the impact of global warming on the long-term population dynamics of common birds.

Taking the opportunity in 2003 of the exceptionally warm spring in France as a natural simulation of possible future climate, we analysed common bird productivity using the French long-term capture-recapture national monitoring scheme. Two-thirds of the 32 species studied had an above-average productivity in 2003. However, this gain in productivity was not consistent among species, with a relatively low productivity for species exhibiting a long-term decline and relatively high productivity for stable or increasing species. Such links between long-term and short-term dynamics suggest that the impact of increasingly warm springs on productivity is a major component of the recent population dynamics of a variety of common bird species.

Animals↗