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Results for “population dynamics”

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PubMed2002

Markets, population dynamics, and coastal ecosystems.

Our synthesis focuses on how markets influence the population and environment relationship within coastal ecosystems by considering the differential valuing of environmental resources and ecosystem services through 3 perspectives: livelihood, globalization, and public goods and externalities. These are not new perspectives when considering how markets shape demographic and environmental outcomes. However, we suggest that the insight offered by viewing coastal and marine health through these combined lenses brings into focus with renewed urgency the perils facing these vital ecosystems.

Animals↗
PubMedDate not supplied

[Population dynamics and structures of Streptomyces lanatus in 2 soil types].

The dynamics and structure(mycelium--spores) of a population of the soil actinomycete Streptomyces lanatus 21-5 were studied in two types of nonsterile soil using the technique of inoculation on solid growth media in combination with autofluorescence, heat treatment of the culture, and addition of antibiotics, when the population was introduced into soil at a level of density close to the natural one. The dynamics of the population was found to depend on the form (spores or mycelium) in which it was introduced into soil. The population was shown to be stabilized at different levels of density in various types of soil at an identical level of inoculation. The population was found to behave differently in various types of soil. The population was represented in soils preferentially by spores. The structural coefficient K changing from 0 (only mycelium) to 1 (only spores) was proposed in order to estimate quantitatively the structure of the population.

Soil Microbiology↗
PubMed1989

HUMTRN and EFFECTS: age and sex specific dosimetric and physiological human population dynamics models for dose assessment.

A human simulation model called HUMTRN and a population risk assessment model called EFFECTS were developed at Los Alamos National Laboratory as a major component of the BIOTRAN environmental risk assessment model. HUMTRN simulates growth using dietary and physiological characteristics and kinetics of radionuclides to predict radiation doses to selected organs of both sexes in different age groups. The model called EFFECTS was interfaced with output from HUMTRN to predict cancer risks in a dynamic human population. EFFECTS is based on the National Research Council Committee on the Biological Effects of Ionizing Radiation (BEIR)-III radiation cancer mortality estimates from the U.S. population mortality and natality estimates for both sexes between the ages of 1 and 70. These models track radiation intake from air, water, and food, calculate uptake in major growing organs, and estimate cancer mortality risks. This report documents the use of an IBM Personal Computer AT to run HUMTRN and EFFECTS. Air, water, and food contaminant concentrations are provided as input to HUMTRN, which then provides input for EFFECTS. The limitations of this approach are also discussed.

Age Factors↗
PubMed1992

Population dynamics in rural South Australia.

The authors examine recent trends in Australia in turnaround migration, or the movement of the population from urban to rural areas. "The paper assesses the major changes which have occurred in population trends within the non-metropolitan sector of the nation, South Australia and, in particular, a study area in the lower north region of South Australia. The analysis of the case study region draws upon a survey undertaken in 1968-1970 and partially replicated in 1980 and 1990. It appears that for Australia in general and for the study area the turnaround is continuing but at a slower pace and in a more spatially concentrated pattern."

Australia↗
PubMed2005

Populational dynamics of Stomoxys calcitrans (Linneaus) (Diptera: Muscidae) in three biocenosis, Minas Gerais, Brazil.

Populational flux of the adult phase of Stomoxys calcitrans was observed in the municipal district of Pedro Leopoldo, Minas Gerais, Brazil. Three biocenoses were selected for the study: stable agrobiocenosis, pastural agrobiocenosis and eubiocenosis. The occurrence and the populational flux of the insects, using the Magoon trap for their capture, were established. For each trap located in different biocenoses, a crossbred calf (Bos taurusxBos indicus) approximately 6-month-old was used as "live bait," exposed weekly for 48h in the traps. Of the three agrobiocenoses studied, the stable agrobiocenosis contributed the greatest number of specimens of. S. calcitrans captured, corresponding to 96.9% of the total flies of this species collected. S. calcitrans shows seasonal behavior for approximately 6 months (spring and summer being the rainiest months of the year). The population peaked during the months of November and December. During the months of July and August, there was no capture of flies.

Animals↗
PubMed1990

Population dynamics of Trichostrongylus colubriformis in sheep: model to predict the worm population over time as a function of infection rate and host age.

The developing immunity of sheep to Trichostrongylus colubriformis infections was described by a mathematical function. The rate of adult establishment was assumed to be a measure of the host's acquired immunity to this parasite. Prediction of establishment from infection rate and host age was used to estimate worm burden, worm rejection and arrested development.

Age Factors↗
PubMed1991

[Population dynamics of ethnic groups in Estonia in the twentieth century].

The author describes and analyzes changes in the ethnic composition of Estonia during the twentieth century. "The paper points out that ethnic composition of the urban population was changing in the period under consideration much more rapidly than the ethnic structure of the rural population." Data are from censuses conducted between 1897 and 1989. (SUMMARY IN ENG)

Culture↗
PubMed2006

Testing the role of parasites in driving the cyclic population dynamics of a gamebird.

The role of parasites in regulating populations has been the subject of debate. We tested whether parasites caused population cycles in red grouse by manipulating parasite intensities in four, paired 1 km(2) study areas during cyclic population declines over 4 years. Parasite reductions led to (1) larger grouse broods, (2) higher population densities in both autumn and spring, (3) reduced autumn population declines in one of two regions, and (4) reduced spring declines, but only in the first year. We infer that a single trophic interaction between a parasite and its host does not explain cyclic dynamics in spring breeding density in this species, although it contributed to the start of a cyclic decline. Another process was operating to drive the populations down. Together with our other results these findings emphasize that both trophic and intrinsic processes may act within populations to cause unstable dynamics.

Animals↗
PubMed2000

Methods of aggregation of variables in population dynamics.

In ecology, we are faced with modelling complex systems involving many variables corresponding to interacting populations structured in different compartmental classes, ages and spatial patches. Models that incorporate such a variety of aspects would lead to systems of equations with many variables and parameters. Mathematical analysis of these models would, in general, be impossible. In many real cases, the dynamics of the system corresponds to two or more time scales. For example, individual decisions can be rapid in comparison to growth of the populations. In that case, it is possible to perform aggregation methods that allow one to build a reduced model that governs the dynamics of a lower dimensional system, at a slow time scale. In this article, we present a review of aggregation methods for time continuous systems as well as for discrete models. We also present applications in population dynamics. A first example concerns a continuous time model of a single population distributed on a system of two connected patches (a logistic source and a sink), by fast migration. It is shown that under a certain condition, the total equilibrium population can be larger than the carrying capacity of the logistic source. A second example concerns a discrete model of a population distributed on two patches, still a source and a sink, connected by fast migration. The use of aggregation methods permits us to conclude that density-dependent migration can stabilize the total population.

Animals↗
PubMed2001

Iteroparous reproduction strategies and population dynamics.

Asymptotic relationships between a class of continuous partial differential equation population models and a class of discrete matrix equations are derived for iteroparous populations. First, the governing equations are presented for the dynamics of an individual with juvenile and adult life stages. The organisms reproduce after maturation, as determined by the juvenile period, and at specific equidistant ages, which are determined by the iteroparous reproductive period. A discrete population matrix model is constructed that utilizes the reproductive information and a density-dependent mortality function. Mortality in the period between two reproductive events is assumed to be a continuous process where the death rate for the adults is a function of the number of adults and environmental conditions. The asymptotic dynamic behaviour of the discrete population model is related to the steady-state solution of the continuous-time formulation. Conclusions include that there can be a lack of convergence to the steady-state age distribution in discrete event reproduction models. The iteroparous vital ratio (the ratio between the maximal age and the reproductive period) is fundamental to determining this convergence. When the vital ratio is rational, an equivalent discrete-time model for the population can be derived whose asymptotic dynamics are periodic and when there are a finite number of founder cohorts, the number of cohorts remains finite. When the ratio is an irrational number, effectively there is convergence to the steady-state age distribution. With a finite number of founder cohorts, the number of cohorts becomes countably infinite. The matrix model is useful to clarify numerical results for population models with continuous densities as well as delta measure age distribution. The applicability in ecotoxicology of the population matrix model formulation for iteroparous populations is discussed.

Animals↗
PubMed2000

Population dynamics of Tetranychus kanzawai (Acari: Tetranychidae) on hydrangea.

The seasonal occurrence of Tetranychus kanzawai Kishida populations on hydrangea (Hydrangea macrophylla) was studied at two different localities in Ibaraki, Japan, during a three-year period. There were two types of seasonal population trends: one with a population peak from May to June, and the other with the spring peak in June and the autumn peak in September-October. Each year the populations on hydrangea plants abruptly declined just after the spring peak. Predators showed a delayed density-dependent numerical response. The population crashed even in the absence of predators, suggesting that the predators had nothing to do with the June decline. Furthermore, the rate of development from larva to adult and the fecundity in adult females on detached hydrangea leaves decreased markedly just prior to the abrupt decline in density in June. Consequently, seasonal changes in plant quality (perhaps influenced by secondary compounds) seem to contribute to the drastic decline of T. kanzawai density on hydrangea in June.

Animals↗
PubMed2003

Population dynamic of algae and bacteria in an oxidation channel.

A study on algae and bacteria population changes, as a function of time, was carried out in a pilot scale oxidation channel bioreactor using a carrousel system. Total Coliforms, Pseudomonas aeruginosa, and Streptococcus faecalis, the most common bacteria found in sewage, Scenedesmus obliquus and Chlorella vulgaris were the microalgae considered in this work. Physicochemical parameters such as COD, BOD, Chlorophyll a, nitrogen, and phosphorous compounds were studied and determined during the experiments. It was demonstrated that the level of wastewater contamination could be predicted based on the bacterial and algae composition. The relationships between the algae and bacteria population, and the variation of these microorganism populations as a measurement of the level of purification were established. The oxidation channel was able to remove a considerable amount of organic matter and pathogenic microorganisms in a relatively short time. The nitrification process could not be measured. The increase in the relative concentration of microalgae contributed toward improving the global efficiency of the system as well as reducing the pathogenic bacteria population.

Bacteria↗