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At least 37 records · Page 2Linked to original sources
PubMed1998

The dynamics of drug action on the within-host population growth of infectious agents: melding pharmacokinetics with pathogen population dynamics.

The use of simple mathematical models to study the kinetics of drug action and decay within vertebrate hosts has a long history with a major objective being to derive drug dosage regimens that optimize efficacy and minimize toxicity to the patient. Mathematical models of the relationship between dosage, route of delivery, drug concentration in defined sites and effect on a particular pathogen are widely used in the pharmacological literature. A more recent literature is that concerned with the population dynamics of pathogen replication within the host subjected to pressures exerted by the human immune system. In this paper we develop a theoretical framework to meld both approaches with the aim of identifying threshold criteria that dictate the optimum pattern of drug administration for pathogen clearance from the host. In particular we show how the percentage reduction in microparasite abundance is related to the pharmacokinetic parameter, AUC, recording the area under the drug concentration-time curve within the treated patient, in terms of the parameters that define the population dynamics of the pathogen and the properties of the drug. Two particular pathogens are examined to illustrate the principles underpinning the dynamics of the pharmacokinetic-population dynamic models, namely HIV and Plasmodium falciparum. Criteria for pathogen persistence or elimination are derived for these specific models based on the definition of a basic reproductive number, R0, which measures the average number of secondary infected target cells in a host generated by a single infected cell (CD4 lymphocyte for HIV, and erythrocyte for P. falciparum) within a population of susceptible cells. For the pathogen to invade the host and persist over time, R0</=1. Under chemotherapeutic regimens, expressions for R0 are derived allowing estimates to be made of the ideal treatment regime required to eliminate the pathogen, both for HIV and P. falciparum malaria.

Animals↗
PubMed2001

Egg size evolution and energetic constraints on population dynamics.

We use population models that are based on dynamic energy budget models for individuals in order to study the evolution of offspring size and its relationship to the evolution of population dynamics. We show the existence of alternative evolutionarily stable strategies for offspring investment strategy resulting from a trade off between offspring number and time-to-maturity. The model predicts egg energy in Daphnia magna well, and suggests that the observed egg energy in D. magna is the result of selection for minimal egg investment constrained by minimum viable egg energy, combined with selection for a juvenile energy reserve. The selection for minimal egg size pushes populations toward chaotic dynamics. However, the minimum viable egg size combined with low efficiency of conversion of energy to new biomass is sufficient to keep population dynamics out of chaos.

Animals↗
PubMed1998

An investigation into the interaction between drug efficacy and drug price of praziquantel in determining the cost-effectiveness of school-targeted treatment for Schistosoma mansoni using a population dynamic model.

A population dynamic model of schistosome transmission was used to investigate the interaction between drug efficacy and drug price of different brands of praziquantel in determining the cost-effectiveness of school-targeted treatment for Schistosoma mansoni. In this analysis, costs were affected by coverage, drug price and distance travelled, and effectiveness by coverage and drug efficacy. Four effectiveness measures were assessed: the number of infection case-years prevented, heavy infection case-years prevented, hepatomegaly case-years prevented and fibrosis case-years prevented. The interactions between drug efficacy and drug price were complex. In particular, there was a highly nonlinear relationship between drug efficacy and cost-effectiveness, with drugs of low efficacy producing high and variable cost-effectiveness ratios, particularly when other programme costs related to distance travelled were high. The results suggest that given the current price range of praziquantel, a drug with less than a 50% chance of killing the worms is not to be recommended. This has important practical implications for the widespread use of praziquantel, since most international agencies procure praziquantel purely on the basis of price. There is clearly a need for studies which evaluate the efficacy of new brands of praziquantel, and more credence should be given to the use of high efficacy brands, not only in terms of maximizing the cost-effectiveness of the intervention programme, but also in delaying the onset of drug resistance.

Adolescent↗
PubMed2004

Spatially structured population dynamics in feral oilseed rape.

We studied the population dynamics of feral oilseed rape (Brassica napus) for 10 years (1993-2002) in 3658 adjacent permanent 100 m quadrats in the verges of the M25 motorway around London, UK. The aim was to determine the relative importance of different factors affecting the observed temporal patterns of population dynamics and their spatial correlations. A wide range of population dynamics was observed (downward or upward trends, cycles, local extinctions and recolonizations), but overall the populations were not self-replacing (lambda < 1). Many quadrats remained unoccupied throughout the study period, but a few were occupied at high densities for all 10 years. Most quadrats showed transient oilseed rape populations, lasting 1-4 years. There were strong spatial patterns in mean population density, associated with soil conditions and the successional age of the plant community dominating the verge, and these large-scale spatial patterns were highly consistent from year to year. The importance of seed spilled from trucks in transit to the processing plant at Erith in Kent was confirmed: rape populations were significantly higher on the 'to Erith' verge than the 'from Erith' verge (overall mean 2.83-fold greater stem density). Quadrats in which lambda > 1 were much more frequent in the 'to Erith' verge, indicating that seed immigration can give the spurious impression of self-replacing population dynamics in time-series analysis. There was little evidence of a pervasive Moran effect, and climatic forcing did not produce widespread large-scale synchrony in population dynamics for the motorway as a whole; just 23% of quadrats had significant rank correlations with the mean time-series. There was, however, significant local spatial synchrony of population dynamics, apparently associated with soil disturbance and seed input. This study draws attention to the possibility that different processes may impose population synchrony at different scales. We hypothesize that synchrony in this system is driven by at least three processes: small-scale, local forcing caused by soil disturbance, intermediate-scale forcing as a result of seed input, and large-scale climatic forcing (e.g. winter rainfall) that affects the motorway as a whole.

Brassica napus↗
PubMed2000

Effects of patch number and dispersal patterns on population dynamics and synchrony.

In this paper, we examine the effects of patch number and different dispersal patterns on dynamics of local populations and on the level of synchrony between them. Local population renewal is governed by the Ricker model and we also consider asymmetrical dispersal as well as the presence of environmental heterogeneity. Our results show that both population dynamics and the level of synchrony differ markedly between two and a larger number of local populations. For two patches different dispersal rules give very versatile dynamics. However, for a larger number of local populations the dynamics are similar irrespective of the dispersal rule. For example, for the parameter values yielding stable or periodic dynamics in a single population, the dynamics do not change when the patches are coupled with dispersal. High intensity of dispersal does not guarantee synchrony between local populations. The level of synchrony depends also on dispersal rule, the number of local populations, and the intrinsic rate of increase. In our study, the effects of density-independent and density-dependent dispersal rules do not show any consistent difference. The results call for caution when drawing general conclusions from models of only two interacting populations and question the applicability of a large number of theoretical papers dealing with two local populations.

Animals↗
PubMed1997

Microbial population dynamics on leaves.

Microbial population dynamics on leaves in time and space are a function of immigration, emigration, growth, and death. Insight into the relative significance of each population process to the generation of specific dynamics for individual microorganisms is necessary to understanding the ecology and life history strategy of the microorganism and to developing effective control strategies. Additionally, information on the significance of within-leaf versus extra-leaf processes to the generation of phyllosphere dynamics is important to determining the range of spatial scales over which a population should be studied. Unfortunately, such information is difficult to obtain due to the lack of effective methodologies for distinguishing these processes within phyllosphere populations. Future research efforts should focus on the quantification of immigration, emigration, growth, and death relative to the population dynamics of phyllosphere microorganisms.

Journal Article↗
PubMed1994

Spline models of biological population dynamics: how to estimate mortality rates for stage structured populations with dimorphic life histories.

Nonparametric spline based models of stage structured population dynamics provide an effective way of decomposing observed population dynamics into birth and death rate processes. Currently available methodology only considers simple life histories in which all individuals pass through the same sequence of stages in the same way. This paper presents techniques for obtaining birth and death rates from structured population time series of organisms with complex life histories. For example, in many species males and females develop at the same rate in early stages, but differently in late stages. The models are motivated by the need to obtain birth and death rates for a pest subject to biocontrol by a parasitoid.

Aging↗
PubMedDate not supplied

[Nonlinear effects on population dynamics related to age structure and fishery impact].

Population dynamics of commercial fish populations with an age structure was studied by the example of salmons. The relationship between the amount of catch on fishing efforts and total abundance of a stock fished is described by a nonlinear "trophic" function. Special attention is given to the analysis of population dynamics stability under conditions for maximum profit. Simulation results are compared to statistical data on the catch of Pacific salmon species in the Bering Sea.

Age Factors↗
PubMed2005

Monitoring coyote population dynamics by genotyping faeces.

Reliable population estimates are necessary for effective conservation and management, and faecal genotyping has been used successfully to estimate the population size of several elusive mammalian species. Information such as changes in population size over time and survival rates, however, are often more useful for conservation biology than single population estimates. We evaluated the use of faecal genotyping as a tool for monitoring long-term population dynamics, using coyotes (Canis latrans) in the Alaska Range as a case study. We obtained 544 genotypes from 56 coyotes over 3 years (2000-2002). Tissue samples from all 15 radio-collared coyotes in our study area had > or = 1 matching faecal genotypes. We used flexible maximum-likelihood models to study coyote population dynamics, and we tested model performance against radio telemetry data. The staple prey of coyotes, snowshoe hares (Lepus americanus), dramatically declined during this study, and the coyote population declined nearly two-fold with a 1(1/2)-year time lag. Survival rates declined the year after hares crashed but recovered the following year. We conclude that long-term monitoring of elusive species using faecal genotyping is feasible and can provide data that are useful for wildlife conservation and management. We highlight some drawbacks of standard open-population models, such as low precision and the requirement of discrete sampling intervals, and we suggest that the development of open models designed for continuously collected data would enhance the utility of faecal genotyping as a monitoring tool.

Alaska↗
PubMed2002

[Application of fuzzy cluster in analyzing population dynamics of Chorthippus fallax].

The population dynamics includes quantity dynamics, space dynamics and temporal dynamics. They are interdependent and mutually influential. Fuzzy cluster analysis was carried out with the data of mean densities, indices of patchiness and occupied plot rates of Chorthippus fallax(Zubovsky) on Ganjia High Mountain Grassland in Xia-he County, Gansu Province. The results showed that the population dynamics of this grasshopper could be divided into four distinct periods, i.e., the initial stage of hatching and the last stage of adult, the peak stage of nymph, the initial stage of adult, and the peak stage of first nymph and the adult. The peak period of nymph was in the middle ten days to the last ten days of July. In this period, the eggs were completely hatched, the population was mainly composed of nymphs of 2 and 3 instars, and the population size was related to the numbers and harmful levels of this grasshopper in the same year. Therefore, this period was the key time for population prediction and chemical control.

Animals↗
PubMed1996

A study (1977-1992) of population dynamics of endoparasites featuring benzimidazole-resistant small strongyles (population S) in Shetland ponies.

Critical tests (91) were done between 1977 and 1992 in Shetland ponies to evaluate drug susceptibility and population dynamics (present paper) of endoparasites. The test ponies, most less than 1 year old, were from a herd where older animals were treated every 8 weeks initially with cambendazole (CBZ) (1974-1978) and then with oxibendazole (OBZ) (1978-1992). Previous field test data (1974-1992) on older ponies in the breeding herd indicated the presence of benzimidazole (BZ) resistant small strongyles. Data on population dynamics from the present critical tests indicated that 28 species of small strongyles persisted over the study period in spite of initial susceptibility and later refractiveness of six species to both CBZ and OBZ. Changes in intensities and other aspects were observed for the six BZ-resistant species (Cyathostomum catinatium, Cyathostomum coronatum, Cylicocyclus nassatus, Cylicostephanus calicatus, Cylicostephanus goldi, and Cylicostephanus longibursatus). Variabilities, some striking, were found in prevalence and intensity in bots, stomach worms, ascarids, eyeworms, large strongyles, pinworms and tapeworms.

Animals↗
PubMed1999

Discrete event versus continuous approach to reproduction in structured population dynamics.

The governing equations are derived for the dynamics of a population consisting of organisms which reproduce by laying one egg at the time, on the basis of a simple physiological model for the uptake and use of energy. Two life stages are assumed, the egg and the adult stage where the adults do not grow. These assumptions hold true, for instance, for rotifers. From the model for the life history of the individuals, a physiologically structured population model for a rotifer population is derived. On the basis of this discrete event reproduction population model a continuous reproduction population model is proposed. The population model together with the equation for the food result in chemostat equations which are solved numerically. We show that for the calculation of the transient population dynamic behaviour after a step-wise change of the dilution rate, an age structure suffices, despite the size and energy structure used to describe the dynamics of the individuals. Aggregation of the continuous reproduction population model yields an approximate lumped parameter model in terms of delay differential equations. In order to assess the performance of the models, experimental data from the literature are fitted. The main purpose of this paper is to discuss the consequences of discrete event versus continuous reproduction. In both population models death by starvation is taken into account. Unlike the continuous reproduction model, the discrete model captures the experimentally observed lack of egg production shortly after the step change in the dilution rate of the chemostat.

Age Factors↗
PubMed2005

Density-dependent dispersal and spatial population dynamics.

The synchronization of the dynamics of spatially subdivided populations is of both fundamental and applied interest in population biology. Based on theoretical studies, dispersal movements have been inferred to be one of the most general causes of population synchrony, yet no empirical study has mapped distance-dependent estimates of movement rates on the actual pattern of synchrony in species that are known to exhibit population synchrony. Northern vole and lemming species are particularly well-known for their spatially synchronized population dynamics. Here, we use results from an experimental study to demonstrate that tundra vole dispersal movements did not act to synchronize population dynamics in fragmented habitats. In contrast to the constant dispersal rate assumed in earlier theoretical studies, the tundra vole, and many other species, exhibit negative density-dependent dispersal. Simulations of a simple mathematical model, parametrized on the basis of our experimental data, verify the empirical results, namely that the observed negative density-dependent dispersal did not have a significant synchronizing effect.

Animals↗
PubMed1997

Population dynamics and the colour of environmental noise.

The effect of red, white and blue environmental noise on discrete-time population dynamics is analyzed. The coloured noise is superimposed on Moran-Ricker and Maynard Smith dynamics, the resulting power spectra are less than examined. Time series dominated by short- and long-term fluctuations are said to be blue and red, respectively. In the stable range of the Moran-Ricker dynamics, environmental noise of any colour will make population dynamics red or blue depending the intrinsic growth rate. Thus, telling apart the colour of the noise from the colour of the population dynamics may not be possible. Population dynamics subjected to red and blue environmental noises show, respectively, more red or blue power spectra than those subjected to white noise. The sensitivity to differences in the noise colours decreases with increasing complexity and ultimately disappears in the chaotic range of the population dynamics. These findings are duplicated with the Maynard Smith model for high growth rates when the strength of density dependence changes. However, for low growth rates the power spectra of the population dynamics with noise are red in stable, periodic and aperiodic ranges irrespective of the noise colour. Since chaotic population fluctuations may show blue spectra in the deterministic case, this implies that blue deterministic chaos may become red under any colour of the noise.

Acoustics↗
PubMed2005

A direct approach to control short term population dynamics in time series studies.

BACKGROUND: Short term population dynamics is an important issue in several epidemiological studies. Usually, calendar time or dummy variables are used to control indirectly for this confounding. This study tested a direct method. METHODS: The study compared as proxy variables of population dynamics the summer 2003 data of cooking gas consumptions, solid urban waste production, and television access for the municipality of Bologna (Italy). RESULTS: Solid urban waste production and television access data showed similar trends. Considerably different were the >65 year olds estimates with respect to total population based on television access. CONCLUSIONS: Television access data are probably the best indicator in the estimates of population dynamics in large or densely populated areas, especially because of the possibility of stratifications with respect to age.

Aged↗
PubMed2005

Link between population dynamics and dynamics of Darwinian evolution.

We provide the link between population dynamics and the dynamics of Darwinian evolution via studying the joint population dynamics of similar populations. Similarity implies that the relative dynamics of the populations is slow compared to, and decoupled from, their aggregated dynamics. The relative dynamics is simple, and captured by a Taylor expansion in the difference between the populations. The emerging evolution is directional, except at the singular points of the evolutionary state space. Here "evolutionary branching" may occur. The diversification of life forms thus is demonstrated to be a natural consequence of the Darwinian process.

Biodiversity↗