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At least 19 recordsLinked to original sources
PubMed1995

A note on population dynamics.

Population dynamics is analyzed by means of the power series expansion of a decay ratio F(P) with respect to the continuation probability, P, of survival. The truncation of the higher terms of the series yields the Verhulst equation as a first approximation. The approximation for higher age yields a simple exponential decay law of population, while the younger-age approximation recovers Gompertz's empirical law of human mortality. It is shown that there exists a finite survival probability in the limit of t = infinity. The validity of the present result is examined with real population dynamics of centenarians. In order to construct a commensurable definition of aging, an aging phenomenon in decay process is considered on the assumption of an ideal society, from which a simple relationship is derived between the extent of advancement of aging and the continuation probability.

Aging↗
PubMedDate not supplied

[The relationship of the population dynamics of gamasid mites with the population dynamics of their murine rodent hosts in the Sikhote-Alin].

22,500 mites were collected from 4515 rodents over a period of 5 years in the Sikhote-Alin reserve. The abundance dynamics of 4, out of 5, most numerous species of mites (Laelaps pavlovskyi, L. clethrionomydis, Eulaelaps stabularis, Haemogamasus serdjukovae) depends on the cyclic fluctuations in the number of rodents. A direct connection between the annual and, to some extent, seasonal dynamics of the abundance of parasites and that of their hosts is most distinct in L. pavlovskyi, an epizoon parasite of the large Japanese field mouse. At the same time the abundance of Hg. ambulans, a multihost parasite of small mammals, does not depend on the number of animals. Certain regularities in the abundance dynamics of gamasid mites in connection with that of their hosts, rodents, is discussed on the basis of obtained material and literary data.

Altitude↗
PubMed1992

[Bionomic studies of Dipetalogaster maximus (Uhler, 1894) (Hemiptera, Reduviidae, Triatominae). III. Population dynamics].

A population dynamics study of D. maximus was carried out under laboratory conditions (28 degrees C e 65% +/- 5% U.R.), and the methodology was the same that has been used for rearing these insects. In order to evaluate the population growth rate of this species, during a 24 months period, five colonies started with a couple recently emerged were observed. Each couple (a male and a female) was maintained in a glass container measuring 20 cm of diameter and 20 cm in height with filter paper on the bottom. The insects were monthly feeding with normal mice blood, and at this day the number of eggs, nymphal stages and adults was registered. All graphical representations of the populations growth showed the same shape. It was found that the average of nymphal stage represented 64.3% of the holè population whereas the oviposition curve showed to be inverse to this one (28.57%) a small percentage of adults was found: males 3.85% and females 3.12%. In this study observations on the biological cycle, longevity and fertility rates were also carried out.

Animals↗
PubMed2000

Visibility of the environmental noise modulating population dynamics.

Characterizing population fluctuations and their causes is a major theme in population ecology. The debate is on the relative merits of density-dependent and density-independent effects. One paradigm (revived by the research on global warming and its relation to long-term population data) states that fluctuations in population densities can often be accounted for by external noise. Several empirical models have been suggested to support this view. We followed this by assuming a given population skeleton dynamics (Ricker dynamics and second-order autoregressive dynamics) topped off with noise composed of low- and high-frequency components. Our aim was to determine to what extent the modulated population dynamics correlate with the noise signal. High correlations (with time-lag -1) were observed with both model categories in the region of stable dynamics, but not in the region of periodic or complex dynamics. This finding is not very sensitive to low-frequency noise. High correlations throughout the entire range of dynamics are only achievable when the impact of the noise is very high. Fitted parameter values of skeleton dynamics modulated with noise are prone to err substantially. This casts doubt as to what degree the underlying dynamics are any more recognizable after being modulated by the external noise.

Animals↗
PubMed2001

Anaerobic codigestion of municipal solid waste and biosolids under various mixing conditions--II: Microbial population dynamics.

Microbial population dynamics were evaluated in anaerobic codigesters treating municipal solid waste and sewage sludge. Ribosomal RNA based oligonucleotide probes were used to characterize changes in population abundance of syntrophic volatile fatty acid degrading bacteria and methanogens. Changes in community structure were linked to traditional performance parameters during the recovery of previously unstable codigesters induced by a reduction in mixing levels. Methanosarcina spp. were the most abundant aceticlastic methanogens in unstable codigesters with high acetate concentrations, while Methanosaeta concilii was dominant in stable systems with low levels of acetate. Growth of Syntrophobacter wolinii was enhanced during stabilization of a codigester with a well-developed population of Methanobacteriaceae, possibly because the presence of adequate numbers of these hydrogenotrophic methanogens encouraged the syntrophic oxidation of propionate. Mesophilic saturated fatty acid beta-oxidizing syntrophs were most abundant in previously unstable codigesters. One minimally mixed reactor became unstable after switching to continuously mixed conditions. After the switch, total archaeal abundance decreased sharply, though Methanobacteriaceae and Methanosarcina spp. levels increased as the fermentation became unbalanced. Based on the results presented here, mixing appears to inhibit the syntrophic oxidation of volatile fatty acids, possibly by disrupting the spatial juxtaposition of syntrophic bacteria and their methanogenic partners.

Biomass↗
PubMed2000

Environmental colour affects aspects of single-species population dynamics.

Single-species populations of ciliates (Colpidium and Paramecium) experienced constant temperature or white or reddened temperature fluctuations in aquatic microcosms in order to test three hypotheses about how environmental colour influences population dynamics. (i) Models predict that the colour of population dynamics is tinged by the colour of the environmental variability. However, environmental colour had no effect on the colour of population dynamics. All population dynamics in this experiment were reddened, regardless of environmental colour. (ii) Models predict that populations will track reddened environmental variability more closely than white environmental variability and that populations with a higher intrinsic growth rate (r) will track environmental variability more closely than populations with a low r. The experimental populations behaved as predicted. (iii) Models predict that population variability is determined by interaction between r and the environmental variability. The experimental populations behaved as predicted. These results show that (i) reddened population dynamics may need no special explanation, such as reddened environments, spatial subdivision or interspecific interactions, and (ii) and (iii) that population dynamics are sensitive to environmental colour, in agreement with population models. Correct specification of the colour of the environmental variability in models is required for accurate predictions. Further work is needed to study the effects of environmental colour on communities and ecosystems.

Animals↗
PubMed2002

DNA reveals high dispersal synchronizing the population dynamics of Canada lynx.

Population dynamics of Canada lynx (Lynx canadensis) have been of interest to ecologists for nearly sixty years. Two competing hypotheses concerning lynx population dynamics and large-scale spatial synchrony are currently debated. The first suggests that dispersal is substantial among lynx populations, and the second proposes that lynx at the periphery of their range exist in small, isolated patches that maintain cycle synchrony via correlation with extrinsic environmental factors. Resolving the nature of lynx population dynamics and dispersal is important both to ecological theory and to the conservation of threatened lynx populations: the lack of knowledge about connectivity between populations at the southern periphery of the lynx's geographic range delayed their legal listing in the United States. We test these competing hypotheses using microsatellite DNA markers and lynx samples from 17 collection sites in the core and periphery of the lynx's geographic range. Here we show high gene flow despite separation by distances greater than 3,100 km, supporting the dispersal hypothesis. We therefore suggest that management actions in the contiguous United States should focus on maintaining connectivity with the core of the lynx's geographic range.

Animals↗
PubMed2001

Investigating long-term ecological variability using the Global Population Dynamics Database.

The Global Population Dynamics Database (GPDD) is an important new source of information for ecologists, resource managers, and environmental scientists interested in the dynamics of natural populations. It comprises more than 4500 time series of population abundance for over 1800 animal species across many taxonomic groups and geographical locations. The GPDD offers great potential for asking comparative questions about the nature of population variability. We illustrate this by characterizing some critical features of ecological variability, variance growth, and spectral reddening.

Animals↗
PubMed2001

Stochastic dynamic population model for northern corn rootworm (Coleoptera: Chrysomelidae).

A stochastic dynamic population model for the complete life cycle of northern corn rootworm, Diabrotica barberi Smith & Lawrence, is described. Adult population dynamics from emergence to oviposition are based on a published single-season model for which temperature-dependent development and age-dependent advancement determine adult population dynamics and oviposition. Randomly generated daily temperatures make this model component stochastic. Stochastic hatch is 50+/-8%. A stochastic nonlinear density-dependent larval survival model is estimated using field data from artificial infestation experiments. A regional model of corn phenology is estimated to incorporate the effect of dispersal on adult mortality. Random daily weather is generated using parameters for Brookings, SD. Model performance is evaluated with deterministic simulations, which show that the population converges to zero unless adult mortality is reduced by the availability of corn pollen from the regional model of corn phenology. Stochastic model performance is evaluated with stochastic daily weather, egg hatch, and larval survival in various combinations. Sensitivity analysis is conducted to evaluate model responsiveness to each parameter. Model results are generally consistent with published data.

Animals↗
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↗
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↗
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↗