PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “population dynamics”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
PubMed2002

Maintenance dialysis population dynamics: current trends and long-term implications.

Despite a general recognition that treatment of end-stage renal disease (ESRD) has become a large-scale undertaking, the size of the treated population and the associated costs are not well quantified. This report combines data available from a variety of sources and places the current (midyear 2001) estimated global maintenance dialysis population at just over 1.1 million patients. The size of this population has been expanding at a rate of 7% per year. Total therapy cost per patient per year in the United States is approximately 66,000 dollars. Assuming that this figure is a reasonable global average, the annual worldwide cost of maintenance ESRD therapy in the year 2001, excluding renal transplantation, will be between 70 and 75 billion US dollars. If current trends in ESRD prevalence continue, as seems probable, the ESRD population will exceed 2 million patients by the year 2010. The care of this group represents a major societal commitment: the aggregate cost of treating ESRD during the coming decade will exceed 1 trillion dollars, a thought-provoking sum by any economic metric.

Forecasting↗
PubMed2003

Influence of LAS on marine calanoid copepod population dynamics and potential reproduction.

The toxicity of linear alkyl benzene sulfonate (LAS) to marine invertebrates is well documented under laboratory conditions using single-species tests. It is less known how LAS affects natural populations of aquatic organisms. We hypothesised that LAS was more toxic to the calanoid copepod Acartia sp. under natural conditions than Acartia tonsa under cultured conditions in the laboratory. This hypothesis was checked by a direct comparison of LAS toxicity in single-species and model (mesocosm) studies. The acute and sublethal effects of LAS on the survival and egg production of laboratory reared A. tonsa were examined by standard test, i.e. incubation with LAS without food for 24-72 h. The LC(50) and EC(50) values averaged 1.23 and 0.74 mg l(-1) for survival and egg production, respectively. These values are comparable to previous reports. The effects of LAS on a natural copepod community were also investigated under in situ conditions. A series of seven mesocosms (holding approx. 3 m(3) of seawater each) was established with two mesocosms being controls without LAS and five mesocosms with increasing concentrations of LAS ranging from 0.1 to 6.5 mg l(-1) applied as a single dose. The indigenous copepod community, dominated by Acartia sp. and Centropages sp., responded clearly to LAS concentrations above 0.1 mg l(-1). The calculated no effect value was 0.14 mg LAS l(-1) (95% CI=0.08-1.82 mg LAS l(-1)) for the entire copepod community including all development stages after 24 h exposure. The increased sensitivity under in situ conditions was probably promoted by the suboptimal growth conditions, e.g. no saturated food concentration or inadequate nutritive values of the food. The amount of food expressed as chlorophyll concentration was low (around 2 microg chl. a l(-1)) but was not affected by LAS. It appeared that the naupliar stages of Acartia and Centropages were the least affected by LAS and that new cohorts were able to develop 15 days after the dosing with LAS.

Alkanesulfonic Acids↗
PubMed1984

Population dynamics across selected habitat variables of the helminth community in coyotes, Canis latrans, from south Texas.

The effects of selected intrinsic variables operating on host subpopulations and of extrinsic variables across the collective host population on the distributions of 10 common helminth species from coyotes in south Texas were compared. The intrinsic variables of host sex and presence and severity of sarcoptic mange had little effect on the distributions of most helminth species. The combined influences of (1) seasonal changes across the collective host population and (2) host subpopulations delineated by age were responsible for the overdispersed distributions of Oncicola canis, Physaloptera rara, and Protospirura numidica. Overdispersion in Ancylostoma caninum, Alaria marcianae, and Spirocerca lupi populations resulted almost exclusively from the heterogeneity of factors contributing to their rates of establishment, survival, and reproduction as generated across host age subpopulations. Aggregated abundances of A. caninum and A. marcianae occurred in young hosts, but were cumulative in older animals infected with S. lupi. The hypothesis that heterogeneity within the host population, rather than across the collective host population, is the main factor generating overdispersion in natural populations was confirmed for only 3 of 10 helminth species (A. caninum, A. marcianae, and S. lupi). The effects of extrinsic factors operating across the collective host population appeared to be equal to, or in some instances of greater importance than, these forces operating over host subpopulations in determining the dispersion patterns of some helminth species (O. canis, P. rara, and P. numidica). The distributions of Taenia pisiformis, Mesocestoides lineatus, Oslerus osleri, and Toxascaris leonina were not affected, or only minimally influenced, by these intrinsic or extrinsic variables. The effects of these habitat variables on dispersion patterns are highly correlated with the life cycle and mode of transmission of the respective helminth species.

Analysis of Variance↗
PubMed2002

Population dynamics during cell proliferation and neuronogenesis in the developing murine neocortex.

During the development of the neocortex, cell proliferation occurs in two specialized zones adjacent to the lateral ventricle. One of these zones, the ventricular zone, produces most of the neurons of the neocortex. The proliferating population that resides in the ventricular zone is a pseudostratified ventricular epithelium (PVE) that looks uniform in routine histological preparations, but is, in fact, an active and dynamically changing population. In the mouse, over the course of a 6-day period, the PVE produces approximately 95% of the neurons of the adult neocortex. During this time, the cell cycle of the PVE population lengthens from about 8 h to over 18 h and the progenitor population passes through a total of 11 cell cycles. This 6-day, 11-cell cycle period comprises the "neuronogenetic interval" (NI). At each passage through the cell cycle, the proportion of daughter cells that exit the cell cycle (Q cells) increases from 0 at the onset of the NI to 1 at the end of the NI. The proportion of daughter cells that re-enter the cell cycle (P cells) changes in a complementary fashion from 1 at the onset of the NI to 0 at the end of the NI. This set of systematic changes in the cell cycle and the output from the proliferative population of the PVE allows a quantitative and mathematical treatment of the expansion of the PVE and the growth of the cortical plate that nicely accounts for the observed expansion and growth of the developing neocortex. In addition, we show that the cells produced during a 2-h window of development during specific cell cycles reside in a specific set of laminae in the adult cortex, but that the distributions of the output from consecutive cell cycles overlap. These dynamic events occur in all areas of the PVE underlying the neocortex, but there is a gradient of maturation that begins in the rostrolateral neocortex near the striatotelencephalic junction and which spreads across the surface of the neocortex over a period of 24-36 h. The presence of the gradient across the hemisphere is a possible source of positional information that could be exploited during development to establish the areal borders that characterize the adult neocortex.

Animals↗
PubMed2002

Fitness versus longevity in age-structured population dynamics.

We examine the dynamics of an age-structured population model in which the life expectancy of an offspring may be mutated with respect to that of the parent. While the total population of the system always reaches a steady state, the fitness and age characteristics exhibit counter-intuitive behavior as a function of the mutational bias. By analytical and numerical study of the underlying rate equations, we show that if deleterious mutations are favored, the average fitness of the population reaches a steady state, while the average population age is a decreasing function of the average fitness. When advantageous mutations are favored, the average population fitness grows linearly with time t, while the average age is independent of the average fitness. For no mutational bias, the average fitness grows as t2/3.

Life Expectancy↗
PubMed2004

Replicator-mutator equation, universality property and population dynamics of learning.

Replicator-mutator equation is used to describe the dynamics of complex adaptive systems in population genetics, biochemistry and models of language learning. We study "localized", or "coherent", solutions, which are especially relevant in the context of learning and correspond to the existence of a predominant language in the population. There is a coherence threshold for learning fidelity, above which coherent communication can be maintained. We prove the following surprising universality property of coherence threshold: for typical realizations of random coefficients in the fitness matrix, the value of the coherence threshold does not depend on the size of the system.

Biological Evolution↗
PubMed2001

Population dynamics of an Ac-like transposable element in self- and cross-pollinating arabidopsis.

Theoretical models predict that the mating system should be an important factor driving the dynamics of transposable elements in natural populations due to differences in selective pressure on both element and host. We used a PCR-based approach to examine the abundance and levels of insertion polymorphism of Ac-III, a recently identified Ac-like transposon family, in natural populations of the selfing plant Arabidopsis thaliana and its close outcrossing relative, Arabidopsis lyrata. Although several insertions appeared to be ancient and shared between species, there is strong evidence for recent activity of this element family in both species. Sequences of the regions flanking insertions indicate that all Ac-III transposons segregating in natural populations are in noncoding regions and provide no evidence for local transposition events. Transposon display analysis suggests the presence of slightly higher numbers of insertion sites per individual but fewer total polymorphic insertions in the self-pollinating A. thaliana than A. lyrata. Element insertions appear to be segregating at significantly lower frequencies in A. lyrata than A. thaliana, which is consistent with a reduction in transposition rate, reduction in effective population size, or reduced efficacy of natural selection against element insertions in selfing populations.

Arabidopsis↗
PubMed2004

Life cycle and population dynamic of Armadillidium pelagicum Arcangeli, 1955 (Isopoda, Oniscidea) at Aouina.

Armadillidium pelagicum Arcangeli, 1955 is a terrestrial isopod endemic to the circum-Sicilian islands and the North of Tunisia. The life cycle and the population structure of this species were studied on a natural population at Aouina, in the surroundings of Tunis, over 16 months from, January 2000 to April 2001, by monthly or semi-monthly samplings. The ovigerous females were present from March/April to the end of August and absent from September to February/March. These observations indicate that A. pelagicum at Aouina has a seasonal reproduction, followed by a sexual rest. The recruitment period is spread from April/May to mid-September. The fecundity, estimated by the number of eggs in the marsupium of ovigerous females, exhibited a great variability, which is related to the weight of these females. The sex ratio underwent fluctuations throughout the sampling period. It was female-biased in most samplings. Mass frequency distribution was analysed and nine cohorts were identified during the sampling period. The field growth rates are high in the first life phase, decrease during winter and increase during spring. The characteristics of the life cycle of A. pelagicum at Aouina may be summarized as follows: (i) Semi-annual species, since females appear to produce up to five broods per year, (ii) iteroparous females, since females seem to reproduce twice or more in life; (iii) bivoltine life cycle, since the population produces two generations per year; (iv) variability of cohorts' life span.

Animals↗
PubMed1992

Population dynamics of Loa loa and Mansonella perstans infections in individuals living in an endemic area of the Congo.

A follow-up of Loa loa and Mansonella perstans microfilaremia was carried out in an adult population living in a highly endemic area of the Congo. Infection rates and parasite loads were found to be stable in the general population, both in the short-term (two months) and long-term (3-4 years) followup. The microfilarial status of most of the subjects examined did not change between tests. At the individual level, the microfilarial densities of L. loa and M. perstans also remained remarkably constant over time. This results in a qualitative and quantitative stability of the parasitic material available for the vectors.

Animals↗
PubMedDate not supplied

[Population dynamics of Donax dentifer (Veneroida: Donacidae) in Bay of Bahía Málaga, Colombian Pacific during the "El Niño" 1997/1998].

Donax dentifer is a dominant member of the sandy beach communities of the Colombian Pacific coast. A population of this bivalve was monthly sampled in Playa Chucheros at the Bay of Málaga, Colombian Pacific, between August 1997 and July 1998, during the "El Niño 1997/1998" phenomenon. Quantitative samples were taken in perpendicular and parallel to the coastal line transects to determine the population density and a length-frequency distribution. Qualitative samples were taken to study the reproduction and monthly length weight relationship. Sea surface temperature, dissolved oxygen, salinity and pH in the water was monthly registered in the sampling station. Additionally, a tagging-recapture experiment was performed to growth estimations. Results indicate a continuous reproduction cycle with two annual spawning seasons in December and March. The growth parameters of the non-oscillating von Bertalanffy growth function were K = 0.62 yr-1 and L infinity = 29.3 mm. Mortality (Z) was higher (2.65 yr-1) for small individuals (between 2 mm and 5 mm) while a lower Z value (1.71 yr-1) were obtained for larger ones (between 19 mm and 25 mm). An annual mean biomass value of B = 1.229 g ash-free dry weight m-2 and an annual somatic production of Psom = 1.215 g ash-free dry weight m-2 were estimated, which correspond to a Psom/B value of 0.988. Population density increased in November and April, but any population density pattern related with "El Niño" was evident. Low body weight during November-December seems to show a relation between reproductive cycle in D. dentifer and El Niño 97/98 event. The fluctuation in dissolved oxygen show a high correlation with parameters of the reproductive cycle, which could be related to assimilation process and body weight cycle. Growth in D. dentifer in the Colombian Pacific coast was faster than other Donax species, as can be expected for tropical bivalves mollusks in comparison whit high latitude bivalves. The mortality pattern suggest that the population was selectively affected by El Niño 97/98, due to smaller individuals are living in the lowest areas of the beach, where they are exposed to abnormal seawater conditions for a longer time. Individual and population production was higher for medium-size animals than each for small-size ones, which were the most abundant in the population.

Animals↗
PubMed2004

[Effects of different vegetation restoration of degraded red soil on earthworm population dynamics].

This study was conducted at the long-term experimental plots in Ecological Experimental Station of Red Soil in Yujiang County (28 degrees 15'30''N, 116 degrees 55'30''E ), Jiangxi Province, subtropical China. Earthworm population was investigated seasonally from May 1999 to February 2000, under different vegetations including four artificial woodlands [deciduous broadleaf woodland (Quercus chenii, Qc), evergreen broadleaf woodland (Schima superba, Ss), coniferous woodland (Pinus massonina, Pm) and mixed woodland (Schima superba-Pinus massonina, Sm)], two grasslands [gently-disturbed grassland (G1), undisturbed grassland (G2)] and control wasteland (CK). The results indicated that the population structure was very simple. Only Drawinda gisti characterized by pioneer was found. The seasonal averages of density and biomass were in the order of G2 > G1 > Qc > Ss > Pm > Sm > CK, and those of G2, G1 and Qc were significantly higher than those of the latters (P < 0.05). Seasonal fluctuations were obvious with dry-hot summer depressing the earthworm population sharply, leading to the aestivation of earthworm. Based on the variation coefficients of density and biomass, Qc had the highest ecosystem stability, followed by Sm and Ss, and G1, G2, and Pm had the lowest stability. The overall differentiation of earthworm population could be drawn through canonical discriminant analysis. There were significant correlations between earthworms and some soil properties (P < 0.01). Overall, the differentiation of earthworm population was driven by the quantity and quality of soil organic matter returned by the vegetations. Additionally, based on earthworm population, the importance of selecting appropriate vegetation types during the restoration of degraded red soil was emphasized.

Animals↗