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PubMedDate not supplied

[Population dynamics in Serbia--present status and problems at the end of the 20th century].

INTRODUCTION: Population changes in Serbia in the last hundred years were very intensive in all fields of demographic development. They were positive, because the movement trend was basically up-to-date and as such responded to the needs and requirements of the problems in regard to population time. However, what was the intensity of these changes? What kinds of problems does Serbia face at the end of the 20th century? Methodology In order to establish precise data and isolate basic problems the following components were analyzed: fertility, mortality and population growth, age and ethnic distribution, migrations and spatial distribution. Data were taken from official vital statistics, censuses, censuses of people from the territory of former Yugoslavia, population projections and secondary analysis of relevant scientific findings. RESULTS: Serbia is faced with a number of problems in almost all segments of demographic development at the end of the 20th century. This primarily includes dual types of reproduction, open depopulation and fast population growth, reversible mortality trends of certain age-sex groups, a large number of refugees, pronounced emigration, especially of young and educated people, and greater or smaller distortions in the territorial distribution and in the development of certain subpopulations. DISCUSSION: Changes in population of Serbia have been intensive in all areas of demographic development giving it to a lesser or greater extent characteristics of contemporary population of developed countries. These changes, however, were either slow or began later, or too intensive and elemental, causing a series of distortions in the population development. CONCLUSION: The existence of demographic problems poses numerous questions. The basic one is to what extent do demographic distortions slow down the development of a country as a whole; how may the extreme differences in the population fertility levels represent a source of conflict, crises and instability, to questions concerning solutions and probabilities of strong political response. However, there is no dilemma that a population policy is necessary.

Demography↗
PubMed2002

Population dynamics of untreated Plasmodium falciparum malaria within the adult human host during the expansion phase of the infection.

A retrospective analysis was performed of parasite count data recorded from the first 7 days of blood or mosquito transmitted Plasmodium falciparum infections given for the treatment of neurosyphilis in the USA before 1963. The objective of this study was to characterize initial growth dynamics before host defences have significant effects on the infecting parasite population. Of the 328 patients' data available for analysis, 83 were excluded because they had received anti-malarial treatment during the first 7 days of the patent infection. Nonlinear mixed effects modelling was performed to estimate the parameters of interest; 'parasite multiplication rate per 48 h' (PMR), and length of the parasite life-cycle (periodicity). The parasitaemia versus time profiles showed great variability between patients. The mean population estimate of 'PMR' was approximately 8, and was highly dependent on the P. falciparum 'strain'. PMR also varied significantly between patients with a 90% prediction interval varying from 5.5 to 12.3-fold. Both intrinsic parasite multiplication rate (an intrinsic virulence determinant), and host susceptibility and defence contribute to expansion of the parasite biomass and thus disease severity in falciparum malaria.

Animals↗
PubMed1989

Spatial and temporal heterogeneity in the population dynamics of Bulinus globosus and Biomphalaria pfeifferi and in the epidemiology of their infection with schistosomes.

Populations of Bulinus globosus and Biomphalaria pfeifferi were studied in a river habitat in Zimbabwe over a period of 12 months. Data were obtained on the prevalences of infections of Schistosoma haematobium (also S. mattheei) and S. mansoni respectively. Population parameters showed the following patterns for both snail species. (1) A patchy distribution correlated with the distributions of aquatic plants. (2) Life-expectancies of only a few weeks. (3) Recruitment rates correlated with water temperature and showing a distinct seasonal peak. (4) Spatial variation in recruitment. (5) A redistribution of snails during the rainy season. Epidemiological parameters showed the following patterns. (1) Large seasonal variations in the prevalence of patent infections. (2) Evidence from size-prevalence curves that suggests a variable force-of-infection from man to snail, correlated with water temperature. (3) Prevalences of infection that were higher in the vicinity of (+/- 60 m from) major water contact sites. Local prevalences of infection for B. globosus sometimes exceeded 50% and may have approached 100% if pre-patent infections are included. Snail numbers may limit transmission at these locations. Attention is drawn to the need to make field observations at an appropriate spatial scale and also to the implications for the effectiveness of focal snail control as a means of reducing transmission.

Animals↗
PubMed2001

Minimizing potential resistance: a population dynamics view.

I examine the results of studies that used mathematical models of the epidemiology and population genetics of antibiotic treatment and resistance in open communities and in hospitals to explore the following issues: the relationship between antibiotic consumption and the frequency of antibiotic resistance in bacterial populations in communities and in hospitals; methods of controlling the growth, dissemination, and persistence of antibiotic resistance in these settings; the extent to which resistance can be controlled; and the speed with which the effects of control measures will be realized. In open communities, it will take years or even decades to see substantial reductions in the frequency of antibiotic resistance solely as a result of more prudent (reduced) use of antibiotics. However, if we can restrict the input of resistant bacteria into hospitals, through the application of infection control and other measures, it should be possible to reduce the frequency of resistance and even eliminate resistant bacteria from these institutions in short order.

Anti-Bacterial Agents↗
PubMed2003

The impact of selective oviposition and infection with Plagiorchis elegans on Aedes aegypti pre-imago population dynamics at optimal food availability.

Progressive changes in the attraction of waters harboring pre-imago populations of Aedes aegypti exposed to different levels of the entomopathogenic digenean Plagiorchis elegans to ovipositing conspecific females were assessed under conditions of optimal food availability. The impact of ovipositional preference and parasitic infection on population structure and development was investigated. Probabilities that larvae progress from one stage to the next or die within 24 h were calculated for all life stages. Exposure to P. elegans cercariae did not significantly affect the attractiveness of larval-holding waters. Ovipositional preference increased significantly with growing bio-mass of the larval population, with the event of pupation and, in some cases, with late instar mortality. Exposure to various levels of the parasite significantly increased mortality of all instars, but most of the damage caused by the parasite occurred in the form of increased pupal mortality and decreased adult emergence. Exposure to the parasite significantly reduced the number of adults produced yet did not impair larval development. Thus, larval recruitment into environments containing P. elegans remains high, the structure of larval populations remains relatively normal, but few adults are produced.

Analysis of Variance↗
PubMedDate not supplied

[Bacterial population dynamics in a soil--plant system].

The dynamics of Rhizobium leguminosarum and Arthrobacter crystallopoietes populations introduced into soil at different levels of density was studied in a zone near barley roots. Microbial life with a high rate of growth was found only at the root surface. For A. crystallopoietes, the ultimate bacterial incidence at the root surface was found to depend on the original level of population density. For Rh. leguminosarum, the ultimate incidence was shown to reach an identical level irrespective of the original population density. Apparently, the identical level of stabilization in Rh. leguminosarum and the dependence of the ultimate incidence of A. crystallopoietes on the original population density reflect the peculiarities of ecological strategies displayed by these microorganisms. The introduction of A. crystallopoietes and Rh. leguminosarum into soil had no effect on the dynamics of soil bacteria assayed by the inoculation method.

Arthrobacter↗
PubMed2006

Transient population dynamics in periodic matrix models: methodology and effects of cyclic permutations.

Many biological populations are subject to periodically changing environments such as years with or without fire, or rotation of crop types. The dynamics and management options for such populations are frequently investigated using periodic matrix models. However the analysis is usually limited to long-term results (asymptotic population growth rate and its sensitivity to perturbations of vital rates). In non-periodic matrix models it has been shown that long-term results may be misleading as populations are rarely in their stable structure. We therefore develop methods to analyze transient dynamics of periodic matrix models. In particular, we show how to calculate the effects of perturbations on population size within and at the end of environmental cycles. Using a model of a weed population subject to a crop rotation, we show that different cyclic permutations produce different patterns of sensitivity of population size and different population sizes. By examining how the starting environment interacts with the initial conditions, we explain how different patterns arise. Such understanding is critical to developing effective management and monitoring strategies for populations subject to periodically recurring environments.

Daucus carota↗
PubMed1999

Diffusion models for population dynamics incorporating individual behavior at boundaries: applications to refuge design.

We construct models for dispersal of a population which incorporate the response of individuals to interfaces between habitat types. The models are based on random walks where there may be a bias in the direction an individual moves when it encounters an interface. This sort of dispersal process is called skew Brownian motion. Our models take the form of diffusion equations with matching conditions across the interface between regions for population densities and fluxes. We combine the dispersal models with linear population growth models which assume that the population growth rate differs between regions of different habitat types. We use those models to study issues of refuge design. We specifically consider how the effectiveness of buffer zones depends on their size, quality, and the population's response to the interface between the buffer zone and the refuge.

Animals↗
PubMed2001

Population dynamic of Aedes vexans and Ochlerotatus sticticus in flooded areas of the River Drava in Osijek, Croatia.

Populations of adult mosquitoes occurring in the Osijek area in eastern Croatia were monitored from May 1995 to September 2000 with Centers for Disease Control-style traps baited with dry ice. A total of 106,663 adults was caught, ranging from 0 (several times) to 21,120 in May 1995. The mosquitoes captured represented 18 species. Aedes vexans was the most abundant, followed by Ochlerotatus sticticus. Both of these species have breeding sites in flooded areas in the areas surrounding Osijek. Furthermore, these 2 species comprised 86% of total adult mosquitoes collected. The life cycles of these species and their abundances were positively correlated with water level. The peak occurrence of these species was in late spring to early summer. During 6 years, adult mosquito populations were significantly correlated with the water level of the Drava River.

Aedes↗
PubMed2000

Population Dynamic and Genetic Consequences of Spatial Density-Dependent Dispersal in Patchy Populations.

Predictions about sex-specific, spatial density-dependent dispersal and their demographic and genetic consequences were tested in experimental populations of root voles (Microtus oeconomus). Each population consisted of two demes inhabiting equal-sized habitat patches imbedded in a barren matrix area. We used a neutral two-allele allozyme marker to monitor gene flow. Initially, the two demes were genetically distinct and had different densities so that the size of a high-density deme (genotype bb) was four times larger than that of a low-density deme (genotype aa). The sex-specific dispersal pattern was in accordance with our prediction. Male dispersal was unconditional on deme-specific densities, and the majority of the first-generation males became dispersed from both demes, whereas female dispersal was strongly density dependent, so that dispersal took place exclusively from the high-density to the low-density deme. The demographic implication of this dispersal pattern was that the initial density difference between the demes was quickly canceled out. We built a mathematical model that predicted that the initially rare allele (a) would increase in frequency given the dispersal pattern, and this was supported by our experimental data. This result relies mostly on the density-independent male-dispersal strategy, which presumably stems from inbreeding avoidance. Our study highlights the importance of incorporating sex-specific dispersal strategies in population genetic models. Sex-biased dispersal may act as a deterministic force counteracting the tendency for stochastic loss of alleles in small and fragmented populations.

conditional dispersal↗