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PubMed2004

On moment closures for population dynamics in continuous space.

A first-order moment closure, the mean-field assumption that organisms encounter one another in proportion to their spatial average densities, lies at the heart of much theoretical ecology. This assumption ignores all spatial information and, at the very least, needs to be replaced by a second-order closure to gain understanding of ecological dynamics in spatially structured populations. We describe a number of conditions that a second-order closure should satisfy and use these conditions to evaluate some closures currently available in the literature. Two conditions are particularly helpful in discriminating among the alternatives: that the closure should be positive, and that the dynamics should be unaltered when identical individuals are given different labels. On this basis, a class of closures we refer to as 'power-2' turns out to provide a good compromise between positivity and dynamical invariance under relabelling.

Animals↗
PubMed2001

Effects of Oxyrrhis marina (Dinoflagellata), bacteria and vitamin D(2) on population dynamics of Tisbe holothuriae (Copepoda).

Laboratory experiments were performed to determine which food combinations had the most favorable effect on population dynamics of the harpacticoid copepod Tisbe holothuriae. In addition to basic diets of TetraMin (T), rice (R) or a mixture of both (T+R), supplements consisting of the following were given: the heterotrophic dinoflagellate Oxyrrhis marina, a bacterial suspension and vitamin D(2). Results show a beneficial effect of bacteria at a given concentration on T. holothuriae, which is enhanced in combination with vitamin D(2). A higher concentration of bacteria together with vitamin D(2), however, has a reverse effect leading to greater mortality, lower sex ratio and number of ovigerous females, and a dramatic decrease in production of eggs, regardless of the basic diet. We conclude that different concentrations of a given bacterial community may have variable effects on the reproduction of harpacticoid copepods and that, in addition to the bacteria, vitamin D(2) may also play a role in invertebrate nutrition.

Journal Article↗
PubMed1992

Protein content of CBA/Ca mouse diet: relationship with host antibody responses and the population dynamics of Trichuris muris (Nematoda) in repeated infection.

The influence of host dietary protein on acquired immunity and intestinal helminth population dynamics during repeated infection was studied using the mouse-Trichuris muris experimental model. CBA/Ca mice fed a 2% (by mass) protein diet ad libitum maintained body weight during the experiment, but when fed diets containing either 4% or 16% (by mass) protein gained weight steadily. Infection with T. muris did not affect the growth of the latter mice but significantly reduced the growth of animals fed on the 2% protein diet. When repeatedly infected with either 5 or 50 eggs every 10 days, the mice fed the 2% or 4% protein diet accumulated adults in proportion to infection dose. The results show that this is due to both the establishment of larvae at each repeated infection and the survival of established adults. In contrast, very few worms were recovered from animals fed the 16% protein diet, principally as a result of the development of strong acquired immunity to reinfection. T. muris egg output/mouse increased with infection dose in animals fed the low protein diets, but no parasite eggs were detected in the faeces of hosts fed the 16% protein diet. Mouse antibody responses to adult worm excretory/secretory antigen were time- and infection dose-dependent in all 3 dietary groups. The major finding was that the specific antibody response was more intense, both quantitatively (serum OD levels) and qualitatively (antigen recognition by IgG1), in mice fed the low protein diets, even though they remained susceptible to infection. This study shows that host dietary protein deficiency, even at levels irrelevant to normal growth, can markedly potentiate the transmission of T. muris via alterations in host resistance. The high levels of antibody in susceptible animals suggest that this defect in resistance is unlikely to be due to nutrient deficiency-associated defects in humoral immunity.

Analysis of Variance↗
PubMed2001

Effect of host tree seasonal phenology on substrate suitability for the pine engraver (Coleoptera: Scolytidae): implications for population dynamics and enemy free space.

This study evaluated the effects of seasonal phenology on the substrate quality of susceptible hosts to the pine engraver, Ips pini (Say). We also determined the effects of the duration and method of storage on host quality for purposes of laboratory rearing. Live red pine trees were felled at various times during the season, and I. pini adults from a laboratory colony were established on the logs. Subsamples of logs were stored for various intervals, and then provided to beetles. Subsamples of stored logs were waxed at both ends to prevent water loss before being submitted to the same assays. Suitability of red pine phloem tissue in susceptible hosts declined for I. pini throughout the growing season. As the season progressed, the number of beetle progeny that emerged from colonized hosts dropped substantially. This decline was associated with simultaneous reductions in phloem moisture content. Reduction in host suitability may partially offset any advantage I. pini may gain from colonizing trees after the major predators have become less abundant. Bark beetle brood production decreased significantly with length of storage, regardless of the month of tree felling or the method of storing. Implications for bark beetle population dynamics and laboratory rearing systems are discussed.

Animals↗
PubMed2006

Dependent population dynamics between chironomids (nonbiting midges) and Vibrio cholerae.

Vibrio cholerae, the causative agent of cholera, is a natural inhabitant of the aquatic ecosystem. Chironomid (nonbiting midges) egg masses were recently found to harbour V. cholerae non-O1 and non-O139, providing a natural reservoir for the cholera bacterium. Chironomid populations and the presence of V. cholerae in chironomid egg masses were monitored. All V. cholerae isolates were able to degrade chironomid egg masses. The following virulence associated genes were detected in the bacterial isolates: hapA (100%), toxR (100%), hlyA (72%) and ompU (28%). The chironomid populations and the V. cholerae in their egg masses followed the phenological succession and interaction of host-pathogen population dynamics. A peak in the chironomid population was followed by a peak in the V. cholerae population. If such a connection is further substantiated for the pathogenic serogroups of V. cholerae in endemic areas of the disease, it may lead to a better understanding of the role of chironomids as a host for the cholera bacterium.

Adhesins, Bacterial↗
PubMedDate not supplied

Population dynamics and stock assessment for Octopus maya (Cephalopoda: Octopodidae) fishery in the Campeche Bank, Gulf of Mexico.

The octopus (Octopus maya) is one of the most important fish resources in the Mexican Gulf of Mexico with a mean annual yield of 9000 ton, and a reasonable number of jobs created; O. maya represents 80% of the total octopus catch, followed by Octopus vulgaris. There are two artisanal fleets based on Octopus maya and a middle-size fleet that covers both species. Catch-at-length structured data from the artisanal fleets, for the 1994 season (August 1st to December 15th) were used to analyze the O. maya population dynamics and stock and to estimate the current level of exploitation. Von Bertalanffy growth parameters were: L infinity = 252 mm, mantle length; K = 1.4 year-1; oscillation parameters C = 1.0, WP = 0.6; and tz = 0.842 years. A rough estimate of natural mortality was M = 2.2, total mortality from catch curve Z = 8.77, and exploitation rate F/Z = 0.75. This last value suggests an intensive exploitation, even when yield per recruit analysis indicates both fleets may increase the minimum legal size on about 10% to increase yields. The length-based VPA also shows that the stock is being exploited under its maximum acceptable biological limit. These apparently contradictory results are explained by biological and behavioral characteristics of this species. Because most females die after reproduction, a new gross estimation of natural mortality was computed as M = 3.3. The new estimate of exploitation rate was F/Z = 0.57. This new value coincides with results from the length-VPA and the Thompson and Bell methods, the former suggesting that a reduction of 20% in fishing mortality may provide larger yields. This fishery resource is fully exploited and current management measures must be revised to sustain and probably optimize yields.

Animals↗
PubMed1987

Population dynamics of Onchocerca volvulus after 7 to 8 years of vector control in West Africa.

In an attempt to describe the changing population dynamics of Onchocerca volvulus during a period of vector control, nodulectomies were undertaken in 256 patients from ten villages in the Onchocerciasis Control Programme (OCP) and in 74 patients from two villages in an area with ongoing transmission. A total of 1198 nodules were excised and 4350 adult worms were isolated and examined for viability and productivity. In the OCP villages, the worm population is ageing and dying without replacement by new generations of parasites and various findings signal a breakdown of the worm population after about 12 years interruption of transmission. The sexual activity of the worms was significantly reduced. A Productivity Index was developed to measure the microfilariae production at the nodule level. The reduction in this index for the OCP villages correlates closely with the decline over the control period in the community microfilarial loads in the skin. The results show that it is not only the longevity of the parasite which will determine the duration of vector control, but that the reduced productivity of the ageing parasite population is of equal importance.

Africa, Western↗
PubMed1997

Bacterial population dynamics in a meromictic lake.

Polyclonal antibodies against nine different bacteria isolated from Lake Saelenvannet in western Norway were produced, and the population dynamics of these strains in the lake were monitored through two spring seasons by immunofluorescence staining. The total counts of bacteria varied over time and space from 1.5 x 10(6) to 1.5 x 10(7) cells ml-1. The counts of specific bacteria were in the range of 10(3) to 10(4) cells ml-1 or less; in sum, they generally made up less than 1% of the bacterial community. Some populations showed significant changes in abundance, with blooms lasting 1 to 3 weeks. The rate of change (increase and decrease) in abundance during blooms was estimated to be 0.2 to 0.6 day-1. The average virus-to-bacteria ratio was 50, and there was a significant correlation between the abundances of virus and bacteria. Both protozoan grazing and lytic virus infection were assessed as possible mechanisms driving the variations in bacterial population density.

Antibodies, Bacterial↗
PubMed1991

Diplectanidae (Monogenea) infestations of sea bass, Dicentrarchus labrax (L.), from the Spanish Mediterranean area. Histopathology and population dynamics under culture conditions.

In the present study, Diplectanum laubieri was redescribed from material obtained from wild and cultured fish. The population dynamics of D. aequans and D. laubieri under culture conditions was studied. The prevalence and mean intensity (average number of worms per parasitized fish) were 80.64% and 112 for D. aequans and 67.74% and 59.61 for D. laubieri, respectively. Both Diplectanidae exhibited seasonal variations, with maximal infection levels occurring in winter, suggesting continuous parasites recruitment, and infection levels tended to increase with host age. Male hosts were more heavily infested than females. The apparent positive association between D. aequans and D. laubieri was not confirmed statistically. The Diplectanidae showed definite and different patterns of gill distribution. Histopathological gill damage mainly consisted of hyperplasia of the epithelium, fusion of branchial lamellae and the presence of hemorrhagic and inflammatory foci with leucocytic infiltration. The results demonstrated the pathological importance of both Diplectanidae for the cultivation of sea bass.

Age Factors↗
PubMed2002

Population dynamics of free-floating and attached bacteria in a styrene-degrading biotrickling filter analyzed by denaturing gradient gel electrophoresis.

Population dynamics was studied in a 52-l biotrickling filter (BTF) operated for 182 days and used to clean air contaminated with styrene vapors. In the BTF, biomass grew either as free-floating (planktonic) or attached (sessile) microorganisms. PCR-amplified 16S rDNA fragments from planktonic and sessile cells within the bioreactor were analyzed using denaturing gradient gel electrophoresis (DGGE). The results indicated that the complexity of biofilm community was always more pronounced than the complexity of the planktonic cell community. Notably, Rhodococcus erythropolis was identified, based on DNA sequence analysis, as one of the biofilm-specific strains. It was also shown that the inoculum, even when enriched with styrene-degrading bacteria, was not adapted to the growth conditions imposed by the BTF. After a 35-day microbial acclimation period, the DGGE analysis also showed less variation in the banding pattern representing the microbial complexity of the biofilm. In addition, the phylogenic fingerprinting method used demonstrated similar banding profiles in the biofilm along the filter bed.

Animals↗
PubMed1986

Some features of the ecology of fleas inhabiting the nests of the suslik (Citellus citellus (L.)). I: Population dynamics, sex ratio, feeding, reproduction.

While studying the suslik fleas in artificial nests planted in free nature, significant changes in the population dynamics of N. setosa, C. simplex and C. orientalis (from the spring build up to the autumnal peak and the decrease of flea number until the next spring) were noted. The predominance of females in the spring period was recorded in N. setosa. Significant seasonal changes in the number of engorged females of N. setosa and C. simplex and of C. orientalis males (the increase of engorged specimens in the spring and summer) were demonstrated. A significant predominance of females with mature eggs in the spring and summer and their negligible number in the autumn were found in N. setosa and C. simplex.

Animals↗
PubMed1980

[Planktonic and bacterial population dynamics during experimental production of natural marine phytoplankton. II. Structure and physiology of populations and their interactions].

During the spring, an experiment was conducted on the production of natural phytoplankton in a continuous flow layout of large capacity, and an analysis was made of the simultaneous evolution of microplanktonic populations (taxonomic composition, diversity, class ranges, and energetic charge) and of bacterial populations (structure, diversity, dominances, and cetabolic potentialities). Oligotrophic initial conditions were charcterized by a poor (0.22 umg of chlorphyll a/L) and diversified (pigment diversity = 4.5) phytoplankton with nanoplanktonic dominance associated with several benthic type diatoms. Bacterial flora, in which pseudomonads were dominant (54.5%), were also diversified (Shannon index H = 3.57). Metabolic potentialities of these bacterial communities were several. Enrichment of the milieu caused the selection and development of a small number of algal species dominated by the diatoms skeletonema costatum (64 x 106/L) and Chaetoceros (3.2 x 106/L) leading to a paucispecific population with a large biomass, a pigment diversity of 1.97, and a chlorophyll a concentration of 25.08 mu/L. The bacterial community then because diversified (H = 4.12) and, although pseudomonads remained dominant (62%), a larger use of organic micromolecules was noted. The establishment of this phytoplanktonic community was followed by a zooplanktonic development in which larger species succeeded smaller ones (ciliates, tintinnides, rotifers, and copepods) corresponding to the global increase of the phytobiomass. Although this system appeared to be in a phase of relative stability, a decease in the energetic charge showed a disturbance in the physiological state of the planktonic populations. These phenomena led to the vanishing of the diatom's dominance (Chaetoceros, and then S. costatum) and its replacement by nanoplankton (123 x 106 cells/L) and dinoflagellates (300000 cells/L). A modification in the organic wealth of the milieu with the addition of particular complex material that was not or little degraded caused deep disturbances in the bacterial populations. Their diversity reached a very low level (H = 1.56 to 2.25) with a proliferation of vibrions (up to 74%) well equipped with exoenzymes, but more restricted in their nutritional versatility (marked preference for organic macromolecules). During the final phase of experimentation, despite a change in qualitative composition and a more important biomass, microplanktonic and bacterial populations returned to a diversified state nearing that of the initial conditions (pigment diversity = 3.2; H = 3.37).

Adenosine Triphosphate↗
PubMed2005

Cell population dynamics modulate the rates of tissue growth processes.

The development and testing of a discrete model describing the dynamic process of tissue growth in three-dimensional scaffolds is presented. The model considers populations of cells that execute persistent random walks on the computational grid, collide, and proliferate until they reach confluence. To isolate the effect of population dynamics on tissue growth, the model assumes that nutrient and growth factor concentrations remain constant in space and time. Simulations start either by distributing the seed cells uniformly and randomly throughout the scaffold, or from an initial condition designed to simulate the migration and cell proliferation phase of wound healing. Simulations with uniform seeding show that cell migration enhances tissue growth by counterbalancing the adverse effects of contact inhibition. This beneficial effect, however, diminishes and disappears completely for large migration speeds. By contrast, simulations with the "wound" seeding mode show a continual enhancement of tissue regeneration rates with increasing cell migration speeds. We conclude that cell locomotory parameters and the spatial distribution of seed cells can have profound effects on the dynamics of the process and, consequently, on the pattern and rates of tissue growth. These results can guide the design of experiments for testing the effectiveness of biomimetic modifications for stimulating tissue growth.

Algorithms↗
PubMed2004

The effect of seasonal host birth rates on population dynamics: the importance of resonance.

Many of the simple mathematical models currently in use often fail to capture important biological factors. Here we extend current models of insect-pathogen interactions to include seasonality in the birth rate. In particular, we consider the SIR model with self-regulation when applied to specific cases--rabbit haemorrhagic disease and fox rabies. In this paper, we briefly summarize the results of the model with a constant time-independent birth rate, a, which we then replace with the time dependent birth rate a(t), to investigate how this effects the dynamics of the host population. We can split parameter space into an area in which the model without seasonality has no oscillations, in which case a simple averaging rule predicts the behaviour. Alternatively, in the area where oscillations to the equilibrium do occur in the non-seasonal model, disease persistence is more complicated and we get more complex dynamical behaviour in this case. We apply resonance techniques to discover the structure of the subharmonic modes of the SIR model with self-regulation. We then look at whether many biological systems are likely to display these "resonant" dynamics and find that we would expect them to be widespread.

Animals↗
PubMed2004

Species of ticks on camels and their seasonal population dynamics in Eastern Ethiopia.

A study was conducted to identify the species of ticks found on camels (Camelus dromedarius) and their seasonal population dynamics in Eastern Ethiopia. Collection and identification of the ticks were undertaken at 2-month intervals from December 1997 to August 1999. On each occasion, all the visible adult ticks were collected from one side of the body of each of the same 17 camels. The most abundant species of ticks on the camels were Rhipiephalus pulchellus (85.2%), Hyalomma dromedarii (5.9%), Amblyomma gemma (4.0%) and Amblyomma variegatum (1.8%). The average tick load per camel was higher during rainy months than during dry months. The smallest number of ticks per camel was observed during the driest month (December), whereas the highest was recorded in the wettest month (August). Any strategy intended to mitigate problems of tick infestation of camels in this area should take into account the identified tick species and their season of abundance.

Animals↗
PubMed2004

Community-adapted methicillin-resistant Staphylococcus aureus (MRSA): population dynamics of an expanding community reservoir of MRSA.

To define methicillin-resistant Staphylococcus aureus (MRSA) reservoirs in the community and their population dynamics, we studied the molecular epidemiology of a random sample (n=490) from a collection of 2154 inpatient and outpatient MRSA isolates during a 7-year period in San Francisco. We noted a progressive replacement of type II staphylococcal chromosomal cassette (SCC)mec-bearing isolates with type IV SCCmec-bearing isolates, which coincided with >4-fold increase in methicillin resistance between 1998 and 2002. Type IV SCCmec-bearing isolates involved in the increase in methicillin resistance belonged to 4 molecular genotypes. These 4 genotypes were associated predominantly with community-onset disease, rather than hospital- or long-term-care facility-onset disease (76.9% vs. 19.4% vs. 3.7%; P=.0005), suggesting that they are not feral descendants of hospital isolates. The longitudinal results linked the dramatic increase in MRSA infections to an expanding community reservoir of MRSA genotypes with intrinsic community survival advantage.

Anti-Bacterial Agents↗
PubMed1989

Bovine peripheral blood leukocyte population dynamics following treatment with recombinant bovine interferon-alpha I1.

The in vitro functional activity of bovine peripheral blood lymphocytes and the population dynamics of the major peripheral blood leukocyte subpopulations were investigated following the administration of recombinant bovine interferon-alpha I1 (rBoIFN-alpha I1). The intramuscular injection of rBoIFN-alpha I1 induced a 24-h lymphopenia characterized by a decrease in both circulating T and non-T/non-B lymphocytes. An increased CD4/CD8 ratio indicated that there was a relatively greater depletion of the CD8 equivalent subpopulation of T lymphocytes. These changes in lymphocyte trafficking were observed in the absence of a cortisolemia. Coincidental with the lymphopenia, there was a marked decrease in the amplitude of mitogen-induced lymphocyte proliferation responses that probably was caused by a numerical deficit rather than functional deficit in the responder T cells.

Animals↗