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PubMed2005

Concentration-dependent effects of waterborne zinc on population dynamics of Gyrodactylus turnbulli (Monogenea) on isolated guppies ( Poecilia reticulata ).

The effect of waterborne zinc (Zn) on Gyrodactylus population dynamics was studied on isolated guppies maintained at concentrations ranging from 0 to 240 microg Zn/l. After 1 week pre-exposure to Zn, each fish was experimentally infected with 3 gyrodactylids and parasite numbers were recorded daily on each fish until the fish either died or recovered from infection. Parasite establishment was most successful at 0 and 240 microg Zn/l (97%) compared with the intermediate Zn concentrations. Low to moderate concentrations of Zn were beneficial to the parasite, as evidenced by the concentration-dependent increase in peak parasite burden on recovered fish up to 120 microg Zn/l. In contrast, 240 microg Zn/l may have been toxic to the parasite, as both peak parasite burden (in fish that recovered from infection), and maximum rate of increase of the parasite population (in fish that died) declined at this concentration. The combined effect of infection and Zn is harmful to the fish, because mortality of infected fish (but not uninfected fish) increased with increasing Zn concentrations. We suggest that the observed mortality occurs because of the inability of fish to continuously produce mucous that is a key factor for protecting fish from both waterborne Zn and ectoparasites.

Analysis of Variance↗
PubMed1997

Population dynamics, demographic stochasticity, and the evolution of cooperation.

A basic evolutionary problem posed by the Iterated Prisoner's Dilemma game is to understand when the paradigmatic cooperative strategy Tit-for-Tat can invade a population of pure defectors. Deterministically, this is impossible. We consider the role of demographic stochasticity by embedding the Iterated Prisoner's Dilemma into a population dynamic framework. Tit-for-Tat can invade a population of defectors when their dynamics exhibit short episodes of high population densities with subsequent crashes and long low density periods with strong genetic drift. Such dynamics tend to have reddened power spectra and temporal distributions of population size that are asymmetric and skewed toward low densities. The results indicate that ecological dynamics are important for evolutionary shifts between adaptive peaks.

Biological Evolution↗
PubMed1997

End-Epi: an application for inferring phylogenetic and population dynamical processes from molecular sequences.

MOTIVATION: Phylogenetic trees constructed from molecular sequences contain information about the evolutionary or population dynamical processes that created them. Here we describe a computer package (End-Epi) that uses graphical methods to allow researchers to make inferences about these processes from their data. Statistical analyses can be performed to test the consistency of the data with various competing hypotheses. AVAILABILITY: End-Epi can be obtained by WWW from http://evolve.zoo.ox.ac.uk/ and by anonymous FTP from ftp://evolve.zoo.ox.ac.uk/packages/End-Epi10.hqx. This file contains the compiled application, the manual and a test tree.

Algorithms↗
PubMed1986

Long-term population dynamics of pinworms (Syphacia obvelata and Aspiculuris tetraptera) in mice.

The population dynamics of concurrent infections of Syphacia obvelata and Aspiculuris tetraptera (Nematoda) in laboratory mice were investigated under conditions of constant re-exposure over periods of 56 and 115 days. The results indicate that A. tetraptera burdens equilibrate at a higher level than S. obvelata burdens and that both parasites become aggregated in the mouse population. Parasite burdens were higher following short-term (7 day) exposure of uninfected tracer mice to both parasites when compared with parasite burdens attained over long-term exposure, indicating probable development of immunity. A significant positive correlation was detected between numbers of immature S. obvelata and immature A. tetraptera for both experimental and tracer mice.

Animals↗
PubMed1997

Simulation of blacklegged tick (Acari:Ixodidae) population dynamics and transmission of Borrelia burgdorferi.

A model (LYMESIM) was developed for computer simulation of blacklegged tick, Ixodes scapularis Say, population dynamics and transmission of the Lyme disease agent. Borrelia burgdorferi Johnson. Schmid, Hyde, Steigerwalt & Brenner, LYMESIM simulates the effects of ambient temperature, saturation deficit, precipitation, habitat type, and host type and density on tick populations. Epidemiological parameters including host infectivity, tick infectivity, transovarial transmission, and transstadial transmission are included in the model to simulate transmission of the Lyme disease spirochete between vector ticks and vertebrate hosts. Validity of LYMESIM was established by comparing simulated and observed populations of immature I. scapularis on white-footed mice. Peromyscus leucopus, (Rafinesque), at 2 locations in Massachusetts. Validity also was indicated by comparisons of simulated and observed seasonality of blacklegged ticks in New York, Massachusetts, Florida, and Oklahoma-Arkansas. Further model validity was shown by correlation between simulated and observed numbers of immature ticks engorging on white-footed mice at 3 sites in Massachusetts. The model produced acceptable values for initial population growth rate, generation time, and 20-yr population density when historical meteorological data for 16 locations in eastern North America were used. Realistic rates of infection in ticks were produced for locations in the northeastern and northcentral United States. LYMESIM was used to study the effect of white-footed mouse and white-tailed deer, Odocoileus virginianus (Zimmerman), densities on tick density and infection rates. The model was also used to estimate tick density thresholds for maintenance of B. burgdorferi.

Animals↗
PubMed2006

Qualitative and quantitative observations on the flea population dynamics of dogs and cats in several areas of Germany.

From an ongoing country-wide study on the spectrum, the epidemiology and the population dynamics of flea infestations in dogs and cats, important preliminary results from the three areas of Karlsruhe, Nuernberg and Leipzig are presented. A total of 1922 dogs and 1838 cats from 12 different veterinary practices or clinics in three areas of Germany were systematically examined between July 2003 and June 2004. All dogs and cats appearing for a clinical veterinary consultation on one regular working day per month, per practice, were clinically examined. Dogs and cats were examined irrespective of any kind of prior therapeutic or prophylactic insecticidal treatment. The results show that a total of 99 dogs (5.13%) and 263 cats (14.33%) were infested. Cats were more often flea-infested than dogs (p < 0.05). The highest infestation rates for dogs (x = 7.87%) were detected between July and October, and for cats (x = 21.14%) between July and September, the lowest infestation rates for dogs (x = 2.88%) were observed between November and May, and for cats (x = 12.16%) between November and April (p < 0.05). Although the prevalences were generally higher during the summer months, no statistical differences were detectable when looking at the pattern between the four seasons, neither for dogs, nor for cats. Interestingly, the highest prevalences in dogs (9.9%) were detected in June 2004 and comparatively, in cats (23.86%) in August. The lowest detection rates in dogs were seen (1.28%) in April and in cats (7.26%) in January. The preliminary results did not indicate any tendency for a relationship between climatic conditions and flea infestation rates. Similarly, no differences of the infestations rates were detectable between urban and rural areas, 56% (dogs) and 46% (cats) of the infested pets originated from urban habitats. The flea species collected include Ctenocephalides felis, Ctenocephalides canis, Archaeopsylla erinacei, Pulex irritans, Ceratophyllus gallinae, etc. The overall frequencies reveal that C. felis was the most prominent species (81.5%), followed by C. canis (12.5%), A. erinacei (2.7%) and P. irritans (1.7%).

Animals↗
PubMed1999

Population dynamics of nitrifying bacteria in an aquatic ecosystem.

In a space environment such as Space Shuttle or Space Station, animal experiments with aquatic species in a closed system pose a crucial problem in maintaining their water quality for a long term. In nature, ammonia as an animal wastes is converted by nitrifying bacteria to nitrite or nitrate compounds, which usually become nitrogen sources for plants. Thus an application of the biological reactor with such bacteria attached on some filters has been suggested and experimentally studied for efficient waste managements of ammonia. Although some successful results were reported (Kozu et al. 1995, Nagaoka et al. 1998, Nakamura et al. 1997, 1998) in the space applications, purely empirical approaches have so far been taken to develop a biological filter having a stable nitrifying activity. In this study, we constructed a mathematical model to deal with the dynamics of the ammonia nitrifying processes in a biological reactor. The model describes population dynamics of the ammonia-oxidizing bacteria and the nitrite-oxidizing bacteria cultivated on the same filter. We estimated parameters involved in the model using the experimental data. The result shows that these estimated parameters could be applied to general cases and that the two bacteria are in a symbiotic relationship; they can better perform when both coexist, as has been empirically recognized. Based on the model analysis, we discuss how to prepare a high performance biological filter.

Ammonia↗
PubMed1988

Large time behavior in a nonlinear age-dependent population dynamics problem with spatial diffusion.

In this work we analyze the large time behavior in a nonlinear model of population dynamics with age-dependence and spatial diffusion. We show that when t----+ infinity either the solution of our problem goes to 0 or it stabilizes to a nontrivial stationary solution. We give two typical examples where the stationary solutions can be evaluated upon solving very simple partial differential equations. As a by-product of the extinction case we find a necessary condition for a nontrivial periodic solution to exist. Numerical computations not described below show a rapid stabilization.

Aging↗
PubMed2001

Quantifying Population Dynamics Based on Community Structure Fingerprints Extracted from Biosolids Samples.

This paper presents a standardized metric for quantifying the rate change in community structure of complex mixed microbial cultures such as those maintained in biological wastewater treatment systems. Quantifying the stability of microbial community structures is a first step toward more aggressive monitoring and control of biological systems for greater reliability in contaminant removal. Statistical analysis of compositions that uniquely specify the balance of populations of species in a mixed culture sample can be used to specify a biosolids community state as a unique position in an orthogonal coordinate system. Changes in biosolids state are observable as a trajectory within this coordinate space, and the rate of passage along this trajectory relates to the population dynamics. The geometric interpretation and the statistical analysis methods necessary for the proposed calculation methodology are introduced by way of simulated case studies with a simple model system. With the example of this model system, concepts of changing microbial community shape and size are contrasted. The rate change in community structure is defined geometrically in terms of a rate change in relative proportions of the characteristic community shape at constant biomass. A change in biomass is defined as the rate change in the quantity of biosolids at constant shape. The method robustness with respect to random measurement error was also demonstrated using the model system. The potential applications of the approach are presented with experimental data of microbial fatty acid compositions extracted from samples during the operation of bench-scale bioreactors degrading contaminants found in pulp mill wastewater. Scaling the level of population dynamics with a metric that is independent of chemotypic content presents a standard for direct comparisons of community responses between distinct cultures and experiments.

Journal Article↗
PubMed2000

Use of 16S-rRNA to investigate microbial population dynamics during biodegradation of toluene and phenol by a binary culture.

Interspecies interactions and changes in the rate and extent of biodegradation in mixed culture-mixed substrate studies were investigated. A binary mixed culture of Pseudomonas putida F1 and Burkholderia sp. JS150 degraded toluene, phenol, and their mixture. Both toluene and phenol can serve as sole sources of carbon and energy for both P. putida F1 and strain JS150. To investigate the population dynamics of this system, a fluorescent in-situ hybridization method was chosen because of its ability to produce quantitative data, its low standard error, and the ease of use of this method. When the binary mixed culture was grown on toluene or phenol alone, significant interactions between the species were observed. These interactions could not be explained by a pure-and-simple competition model and were substrate dependent. Strain JS150 growth was slightly inhibited when grown with P. putida F1 on phenol, and P. putida F1 grew more rapidly than expected. Conversely, when the two species were grown together on toluene alone, P. putida F1 was inhibited while strain JS150 was unaffected. During growth of the mixed culture on a combination of toluene and phenol, the interactions were similar to that observed during growth on phenol alone; P. putida F1 growth was enhanced while strain JS150 was unaffected. Because of the observed interspecies interactions, monoculture kinetic parameters were not sufficient to describe the mixed culture kinetics in any experiment. This is one of the first reports of microbial population dynamics in which molecular microbial ecology and mathematical modeling have been combined. The use of the 16S-rRNA-based method allowed for observation and understanding of interspecies interactions that were not observable with standard culture-based methods. These results suggest the need for more investigations that account for both substrate and microbial interactions when predicting the fate of organic pollutants in real systems.

Biodegradation, Environmental↗
PubMed1994

Population dynamics of Lutzomyia shannoni (Diptera: Psychodidae) in relation to the epizootiology of vesicular stomatitis virus on Ossabaw Island, Georgia.

Population dynamics of Lutzomyia shannoni Dyar were studied on Ossabaw Island, GA, to define further the role of this species in the epizootiology of the New Jersey serotype of vesicular stomatitis (VSNJ) virus. Bimonthly collections of sand flies egressing from hollow trees from April to November 1991 indicated that there were three generations of sand flies. Data from light trap collections from 1986 through 1989 indicated that similar seasonal cycles occurred during previous years. At this site, we hypothesize that L. shannoni undergoes facultative diapause. Two isolates of VSNJ virus were obtained from female sand flies collected in May and June of 1991. We believe that the virus overwinters in immature L. shannoni and that transovarially infected sand flies emerging each spring initiate a summer amplification cycle in swine on Ossabaw Island.

Animals↗
PubMed1995

Population dynamics of a meiotic/mitotic expansion model for the fragile X syndrome.

A model to explain the mutational process and population dynamics of the fragile X syndrome is presented. The mutational mechanism was assumed to be a multipathway, multistep process. Expansion of CGG repeats was based on an underlying biological process and was assumed to occur at two time points: meiosis and early embryonic development (mitosis). Meiotic expansion was assumed to occur equally in oogenesis and spermatogenesis, while mitotic expansion was restricted to somatic, or constitutional, alleles of maternal origin. Testable hypotheses were predicted by this meiotic/mitotic model. First, parental origin of mutation is predicted to be associated with the risk of a woman to have a full mutation child. Second, "contractions" seen in premutation male transmissions are predicted not to be true contractions in repeat size, but a consequence of the lack of mitotic expansion in paternally derived alleles. Third, a portion of full-mutation males should have full-mutation alleles in their sperm, due to the lack of complete selection against the full-mutation female. Fourth, a specific premutation-allele frequency distribution is predicted and differs from that based on models assuming only meiotic expansion. Last, it is predicted that approximately 65 generations are required to achieve equilibrium, but this depends greatly on the expansion probabilities.

Female↗
PubMed2004

Microbial population dynamics during start-up and overload conditions of anaerobic digesters treating municipal solid waste and sewage sludge.

Microbial population dynamics were investigated during start-up and during periods of overload conditions in anaerobic co-digesters treating municipal solid waste and sewage sludge. Changes in community structure were monitored using ribosomal RNA-based oligonucleotide probe hybridization to measure the abundance of syntrophic propionate-oxidizing bacteria (SPOB), saturated fatty acid-beta-oxidizing syntrophs (SFAS), and methanogens. These changes were linked to traditional performance parameters such as biogas production and volatile fatty acid (VFA) concentrations. Digesters with high levels of Archaea started up successfully. Methanosaeta concilii was the dominant aceticlastic methanogen in these systems. In contrast, digesters that experienced a difficult start-up period had lower levels of Archaea with proportionally more abundant Methanosarcina spp. Syntrophic propionate-oxidizing bacteria and saturated fatty acid-beta-oxidizing syntrophs were present at low levels in all digesters, and SPOB appeared to play a role in stabilizing propionate levels during start-up of one digester. Digesters with a history of poor performance tolerated a severe organic overload event better than digesters that had previously performed well. It is hypothesized that higher levels of SPOB and SFAS and their methanogenic partners in previously unstable digesters are responsible for this behavior.

Adaptation, Physiological↗
PubMed1998

A stochastic model for early HIV-1 population dynamics.

A simple stochastic mathematical model is developed and investigated for early human immunodeficiency virus type-1 (HIV-1) population dynamics. The model, which is a multi-dimensional diffusion process, includes activated uninfected CD4(+)T cells, latently and actively infected CD4(+)T cells and free virions occurring in plasma. Stochastic effects are assumed to arise in the process of infection of CD4(+)T cells and transitions may occur from uninfected to latently or actively infected cells by chance mechanisms. Using the best currently available parameter values, the intrinsic variability in response to a given initial infection is examined by solving the stochastic system numerically. We estimate the statistical distributions of the time of occurrence and the magnitude of the early peak in viral concentration. The maximum of the viral load has a value in the experimental range and its time of occurrence has a 95% confidence interval from 19.4 to 25.1 days. The stochastic nature of the growth of viral density is extremely pronounced in the first few days after initial infection. Threshold effects are noted at virion levels of about 3-5x10(-5) mm-3. In addition to modeling the intrinsic variability in HIV-1 growth, we have explored the effects of perturbations in the parameter values in order to assess the additional stochastic effects of between-patient variability. We found that changes in the initial number of virions or dose size, the rate at which latently infected CD4(+)T cells are converted to the actively infected form and the fraction of latent cells has only minor effects on the size, speed and variability of the response. In contrast, decreased speed and magnitude but greater variability in response were obtained when the death rate of uninfected CD4(+) T cells, the death rate of actively infected cells and the clearance rate of the virus were increased or when the appearance rate of uninfected CD4(+)T cells, the number of virions produced by infected cells, the infection rate of CD4(+)T cells and the initial number of uninfected activated CD4(+)T cells were decreased. We also determined the distribution of the time to reach a given virion density. From this distribution the probability of detection of the virus as a function of time can be estimated. The numerical results obtained are in the range of experimental values and are discussed in relation to recently proposed detection and testing procedures.

CD4-Positive T-Lymphocytes↗
PubMed1999

Simulation analysis of the population dynamics of the mite, Psoroptes ovis, infesting sheep.

The pattern of population growth of the ectoparasitic mite, Psoroptes ovis (Acari: Psoroptidae), on its ovine host is considered through the development of a Leslie matrix-based, simulation model. The model is parameterised using experimental data in conjunction with reanalysis of published data. The model shows that on sheep P. ovis populations grow at a rate of approximately 11% per day and the population doubles every 6.3 days. Additional rates of adult mortality, in excess of 50% per day, need to be imposed to prevent population growth. The predictions of the model are tested by comparison of the expected numbers of mites with the numbers recorded in lesions either on naturally infested sheep where the date of infestation can be estimated or on one artificially infested animal, where the initial number of mites and date of infestation are known precisely. In both cases the observed number of mites in lesions relate closely to the numbers expected from the simulations. The model simulations do not support the concept of a 'lag' phase as distinct from the 'growth' phase in the changing pattern of mite abundance on an infested sheep and suggests that the observed pattern of growth is a natural function of an exponential increase in numbers. The development of such models and their use in explaining the demographic processes which drive mite population dynamics are discussed.

Animals↗
PubMed2006

Within-host population dynamics of antibiotic-resistant M. tuberculosis.

Mathematical models for the population dynamics of de novo resistant Mycobacterium tuberculosis within individuals are studied. The models address the use of one or two antimicrobial drugs for treating latent tuberculosis (TB). They consider the effect of varying individual immune response strength on the dynamics for the appearance of resistant bacteria. From the analysis of the models, equilibria and local stabilities are determined. For assessing temporal dynamics and global stability for sensitive and drug-resistant bacteria, numerical simulations are used. Results indicate that for a low bacteria load that is characteristic of latent TB and for small reduction in an immune response, the use of a single drug is capable of curing the infection before the appearance of drug resistance. However, for severe immune deficiency, the use of two drugs will provide a larger time period before the emergence of resistance. Therefore, in this case, two-drugs treatment will be more efficient in controlling the infection.

Algorithms↗
PubMed1989

Stable controls in age-dependent population dynamics.

The classical age-dependent population model is considered, in which mortality depends on total population and fertility is age-dependent. It is shown that in general such systems are not completely controllable with respect to a control variable in the mortality function, but that in certain circumstances a suitable control can be found to hold the population at a specified level.

Age Factors↗
PubMed2006

Population dynamics of the water mite Unionicola arcuata (Unionicolidae) in the freshwater bivalve Cristaria plicata (Unionidae) in Poyang Lake, eastern China.

Population dynamics of the water mite Unionicola arcuata were investigated in the freshwater bivalve Cristaria plicata during the period from January to December 2002 in Poyang Lake, East China. A pattern of seasonal variation was observed, with prevalence and abundance peaking in early spring and autumn. The number of mites in individual hosts was significantly correlated with the size, but not with the sex, of bivalves. The change in infection level of mites on different infection sites in C. plicata was significant, with >58% of the mites found on the outer and inner gills, indicating that U. arcuata shows site preference.

Acari↗