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PubMed1996

Seasonal population dynamics of Halipegus occidualis and Halipegus eccentricus (Digenea:Hemiuridae) in their amphibian host, Rana clamitans.

The seasonal population dynamics of Halipegus occidualis and Halipegus eccentricus (Hemiuridae) in their amphibian host, the green frog (Rana clamitans), were examined for 3 yr (weekly, April through October). Frogs were caught, marked, and examined for H. occidualis and H. eccentricus, both of which occur as immatures and adults in the buccal cavity. Frogs were then released and allowed to continue natural recruitment and loss of the parasites. It was thus possible to monitor individual infrapopulations over successive time periods. One-hundred and forty-nine frogs were caught and released, with a total of 328 observations. Overall, the levels of both parasites among male and female frogs were similar, as were levels of infection among adult and juvenile hosts. There was, however, no correlation between the total number of H. occidualis and the body size (snout-vent length) of R. clamitans. In contrast, there was a significant correlation between the total number of H. eccentricus and frog size. Recruitment of both species began in May, peaked in June/July, and ended in July (H. eccentricus) or August (H. occidualis). In general, both the prevalence and relative density of H. occidualis was greater than that of H. eccentricus and may be related to space constraints in the buccal cavity of R. clamitans. Adults of both species were observed from April through October. Following increases in parasite recruitment, infrapopulation sizes declined in September 1992 and in August of 1993 and 1994. Examination of variance to mean ratios indicated that both species were overdispersed in the frogs. Large declines in the variance to mean ratios for H. occidualis after periods of greatest recruitment are most likely associated with the loss of larger infrapopulations, suggesting that there may be density-dependent regulation of infrapopulation size. By monitoring individual hosts using the mark-release-recapture protocol, dynamic changes in parasite infrapopulations were observed, e.g., there were losses of immature worms and rapid changes in infrapopulation sizes, observations that would not be made with typical host-parasite systems.

Animals↗
PubMed2006

SCAR-based real time PCR to identify a biocontrol strain (T1) of Trichoderma atroviride and study its population dynamics in soils.

Strains of Trichoderma spp. are known for their antagonistic properties against plant pathogens, some are already on the market, others are under development. In order to launch a strain on the market its perfect identification at the species and strain levels is needed. The aim of this study is to (i) design a SCAR marker for specific identification of strain T1 of Trichoderma atroviride and (ii) monitor population dynamics of this strain in soil by real time PCR. A primer pair targeting a 141-bp fragment enabled specific detection of this strain without cross detection of autochthonous populations of Trichoderma in several field soils. In two soils, population dynamics assessed by real time PCR and the soil plate technique gave similar results. The molecular tools developed in this study satisfy the requirement for specific identification of the biocontrol strain and for detection and quantification of T. atroviride T1 population in complex environments.

DNA Fingerprinting↗
PubMed2004

Influence of plant species on population dynamics, genotypic diversity and antibiotic production in the rhizosphere by indigenous Pseudomonas spp.

The population dynamics, genotypic diversity and activity of naturally-occurring 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. was investigated for four plant species (wheat, sugar beet, potato, lily) grown in two different soils. All four plant species tested, except lily and in some cases wheat, supported relatively high rhizosphere populations (5 x 10(4) to 1 x 10(6) CFU/g root) of indigenous DAPG-producing Pseudomonas spp. during successive cultivation in both a take-all suppressive and a take-all conducive soil. Although lily supported on average the highest population densities of fluorescent Pseudomonas spp., it was the least supportive of DAPG-producing Pseudomonas spp. of all four plant species. The genotypic diversity of 492 DAPG-producing Pseudomonas isolates, assessed by Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the phlD gene, revealed a total of 7 genotypes. Some of the genotypes were found only in the rhizosphere of a specific plant, whereas the predominant genotypes were found at significantly higher frequencies in the rhizosphere of three plant species (wheat, sugar beet and potato). Statistical analysis of the phlD(+) genotype frequencies showed that the diversity of the phlD(+) isolates from lily was significantly lower than the diversity of phlD(+) isolates found on wheat, sugar beet or potato. Additionally, soil type had a significant effect on both the phlD(+) population density and the phlD(+) genotype frequencies, with the take-all suppressive soil being the most supportive. HPLC analysis further showed that the plant species had a significant effect on DAPG-production by the indigenous phlD(+) population: the wheat and potato rhizospheres supported significantly higher amounts of DAPG produced per cell basis than the rhizospheres of sugar beet and lily. Collectively, the results of this study showed that the host plant species has a significant influence on the dynamics, composition and activity of specific indigenous antagonistic Pseudomonas spp.

Analysis of Variance↗
PubMed2006

Population dynamics of the ectomycorrhizal fungal species Tricholoma populinum and Tricholoma scalpturatum associated with black poplar under differing environmental conditions.

Fungi combine sexual reproduction and clonal propagation. The balance between these two reproductive modes affects establishment dynamics, and ultimately the evolutionary potential of populations. The pattern of colonization was studied in two species of ectomycorrhizal fungi: Tricholoma populinum and Tricholoma scalpturatum. The former is considered to be a host specialist whereas T. scalpturatum is a generalist taxon. Fruit bodies of both basidiomycete species were mapped and collected over several years from a black poplar (Populus nigra) stand, at two different sites. Multilocus genotypes (= genets) were identified based on the analysis of random amplified polymorphic DNA (RAPD) patterns, inter-simple sequence repeat (ISSR) patterns and restriction fragment length polymorphisms (RFLPs) in the ribosomal DNA intergenic spacer (rDNA IGS). The genetic analyses revealed differences in local population dynamics between the two species. Tricholoma scalpturatum tended to capture new space through sexual spores whereas T. populinum did this by clonal growth, suggesting trade-offs in allocation of resources at the genet level. Genet numbers and sizes strongly differ between the two study sites, perhaps as a result of abiotic disturbance on mycelial establishment and genet behaviour.

Agaricales↗
PubMed1985

A simplified model of spatiotemporal population dynamics.

This paper is an extension of the model of population growth and migration originally developed by H. Hotelling in 1921. This model consists of two ingredients, a logistic growth function and a linear spatial diffusion term. The author notes that the saturation population can be affected by the development of new technology and that improvements in transportation have increased the possibilities for migration. "Basic nonlinearities are introduced by use of a production technology with increasing-decreasing returns to scale. It is demonstrated how industrial takeoffs, population transitions, and agglomerative spatial patterns can emerge by changing the model parameters."

Conservation of Natural Resources↗
PubMed1999

Host-driven population dynamics in an herbivorous insect.

Understanding the nature and relative importance of endogenous (density-dependent) and exogenous (density-independent) effects on population dynamics remains a central problem in ecology. Evaluation of these forces has been constrained by the lack of long time series of population densities and largely limited to populations chosen for their unique dynamics (e.g., outbreak insects). Especially in herbivore populations, the relative contributions of bottom-up and top-down effects (resources and natural enemies, respectively) have been difficult to compare because population data have rarely been combined with resource measurements. The feeding scars of a wood-mining herbivorous insect (Phytobia betulae Kangas; Diptera: Agromyzidae) of birch trees (Betula pendula and Betula pubescens) provided long time series data (47 and 65 years) of absolute abundance (larvae/tree) in replicated trees within replicated stands. Measurements of tree annual rings provided matching time series of host age and physiological status. Analyses showed a powerful exogenous effect of stand age on temporal variation in insect abundance (58 and 32% of the variance in two populations, respectively). With the additional effects of variation among trees, 77 and 64% of the total variance in abundance was attributable to exogenous bottom-up effects of host plants. Potential endogenous effects were evident as immediate linear density dependence, but only accounted for approximately 10% of the total variance. Abundance of Phytobia is primarily a function of disturbance history, which produces a mosaic of different aged birch stands that harbor Phytobia populations of different sizes. Density-dependence tends to regulate local populations around levels determined by host suitability.

Animals↗
PubMed1999

Population dynamics and the evolution of virulence in epidemiological models with discrete host generations

Chaos is the likely outcome of the interaction between a parasite and a host with discrete generations, if the parasite's virulence is high and if transmission from one generation to the next is held constant. We studied two alternative routes of transmission-vertical transmission from infecteds to their offspring, and transmission via long-lasting spores produced in those individuals that were killed by the infection-to investigate the influence of the transmission route on the system's evolution and population dynamics. The major results are: (1) vertical transmission often leads to low virulence, thus confirming most epidemiological models. However, if hosts can become super-infected, the evolutionary dynamics of virulence can have several equilibrium points, including 100% disease-induced mortality; (2) when parasites are transmitted with long-lasting spores, the evolutionary dynamics of virulence can become unstable, leading to the repeated bifurcation of two sub-populations with high and low virulence or to punctuated equilibria with sudden changes in the average level of virulence; (3) in general, the evolution of virulence moves the system to an area where the population dynamics are stable. When evolution leads to chaos, the system most often becomes extinct. Only for a restricted parameter space in the system where transmission from one generation to the next is via long-lasting spores do the dynamics become chaotic without extinction of the system. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Population dynamics of the feral macaques in the Kowloon Hills of Hong Kong.

Hong Kong's feral monkey population is controversial. Many people complain about the aggressiveness of the monkeys, while some conservationists urge the government to deal with the problem in a way that will not harm the monkeys. The population dynamics of the macaques in the Kowloon Hills were studied in 1992 and 1993. Vital statistics are provided from this study as a first step in resolving the problems of human provisioning and wildlife management. It is unlikely that these macaques are indigenous to the area. They are the descendents of macaques that were released in the early twentieth century to control the spread of a local poisonous plant, the strychnos, which contains alkaloids poisonous to livestock and humans but which is a favorite food of the macaques. The macaque population expanded dramatically during the 1980s. The census method employed in this study is direct head count and photo-identification. At the end of 1993, the estimated abundance was 690 (+/-6) in eight social groups in the Kowloon Hills. Species found were rhesus (Macaca mulatta) 65.3%, longtailed (M. fascicularis) 2.2%, Tibetan (M. thibetana) 0.2%, and hybrids 32.3%. The overall home ranges occupied 2.15 km2, resulting in a very high macaque density of 326 per km2. The birth rates were 56.9% and 69.4% in 1992 and 1993, respectively. Mean adult sex ratio (M:F) was 1:2.2 for social groups and 1:1.6 including all peripheral males. The main mortality factor was road accidents and these contributed to the "missing rate" of 9.8% and 10.6% in 1992 and 1993, respectively. Population growth was 5.6% in 1992 and 7.8% in 1993. The estimated macaque population in the year 2000 will be around 1,100 if conditions remain favorable. Management strategies are recommended.

Animals↗
PubMed2003

The characteristics of the bacterial community structure and population dynamics for phosphorus removal in SBR activated sludge processes.

The characteristics of the bacterial community structure and population dynamics for phosphorus removal in activated sludge were investigated using laboratory-scale sequencing batch reactor (SBR) activated sludge processes fed with four different carbon sources. Phosphorus removal activity, quinone profile of the activated sludge and isolated bacterial strains were monitored. An enhanced phosphorus removal activity was accompanied by the increase in ubiquinone-9 (Q-9). The relationships between phosphorus removal activity and Q-9 contents of the isolated bacterial strains were dependent neither on the organic substrates nor on the species of isolated bacterial strains. The enhanced phosphorus removal capability of activated sludge seemed to be due to the increase in the populations of bacteria with activity of phosphorus removal, i.e. species succession of bacteria in activated sludge ecosystems, rather than the increase in the phosphorus removal capability of phosphorus removal bacteria. Not only Acinetobacter but also Pseudomonas identified from isolated strains were regarded as representative polyphosphates-accumulating organisms and predominant species to the whole of bacterial population in activated sludge for phosphorus removal.

Acinetobacter↗
PubMed2002

Modelling population dynamics of denitrifying phosphorus accumulating organisms in activated sludge.

In this paper a kinetic model for simulating population dynamics is developed. The aim was to simulate anoxic and aerobic phosphorus accumulating organisms dynamics in a lab-scale sequencing batch reactor (SBR) operating under different conditions. Denitrifying phosphorus accumulating organisms (DNPAOs) successfully competed in almost all the simulated operational conditions tested. Using this model, the anoxic energy disadvantage of DNPAOs was not as strong as using metabolic models. The model was able to predict reasonably well N, P and acetate profiles in the SBR with only a minor modification of the ASM2d default values of the parameters.

Bacteria, Aerobic↗
PubMed2006

Climate and spatio-temporal variation in the population dynamics of a long distance migrant, the white stork.

1. A central question in ecology is to separate the relative contribution of density dependence and stochastic influences to annual fluctuations in population size. Here we estimate the deterministic and stochastic components of the dynamics of different European populations of white stork Ciconia ciconia. We then examined whether annual changes in population size was related to the climate during the breeding period (the 'tap hypothesis' sensu Saether, Sutherland & Engen (2004, Advances in Ecological Research, 35, 185 209) or during the nonbreeding period, especially in the winter areas in Africa (the 'tube hypothesis'). 2. A general characteristic of the population dynamics of this long-distance migrant is small environmental stochasticity and strong density regulation around the carrying capacity with short return times to equilibrium. 3. Annual changes in the size of the eastern European populations were correlated by rainfall in the wintering areas in Africa as well as local weather in the breeding areas just before arrival and in the later part of the breeding season and regional climate variation (North Atlantic Oscillation). This indicates that weather influences the population fluctuations of white storks through losses of sexually mature individuals as well as through an effect on the number of individuals that manages to establish themselves in the breeding population. Thus, both the tap and tube hypothesis explains climate influences on white stork population dynamics. 4. The spatial scale of environmental noise after accounting for the local dynamics was 67 km, suggesting that the strong density dependence reduces the synchronizing effects of climate variation on the population dynamics of white stork. 5. Several climate variables reduced the synchrony of the residual variation in population size after accounting for density dependence and demographic stochasticity, indicating that these climate variables had a synchronizing effect on the population fluctuations. In contrast, other climatic variables acted as desynchronizing agents. 6. Our results illustrate that evaluating the effects of common environmental variables on the spatio-temporal variation in population dynamics require estimates and modelling of their influence on the local dynamics.

Animal Migration↗
PubMed2004

Population dynamics of the constitutive biota of French dry sausages in a pilot-scale ripening chamber.

The population dynamic of constitutive biota on 84 samples belonging to two different types of French fermented dry sausages during the ripening process in a pilot-scale ripening chamber was investigated. Samples were analyzed in three steps of their production: fresh product, first drying stage, and finished product. In addition, 180 strains of lactic acid bacteria were identified using a miniaturized biochemical procedure of characterization. In general, the number of lactic acid bacteria that evolved during the ripening process of French dry sausages increased during the first days of the process after which the number of these organisms remained constant at approximately 8 log CFU/g. Lactobacillus sakei and Pediococcus pentosaceus, bacteria added as starter, were the dominant species. Pediococcus urinaeequi, Pediococcus acidilactici, and particularly Lactobacillus curvatus were also present. Finally, we have to take into account that the controlled conditions of the pilot plant generally contribute to the homogenization of the behavior of the starter biota.

Animals↗
PubMed1994

Population dynamics of DNA fingerprint patterns within and between populations.

DNA fingerprint is a pattern of a variable number of bands (DNA fragments) with different sizes on a Southern gel for each individual, generated by one or many VNTR loci. Genetic divergence between individuals within and between populations can be studied in terms of number of shared bands between individuals. Using a population genetic model we show that the expectations of measures of genetic distance between populations based on band sharing data from DNA fingerprint patterns are functions of composite parameters M = 4Nv, and time of divergence (t) between populations, where N is the effective size of the populations, and v, the mutation rate. The expected genetic distance remains linear with time of divergence at least up to N generations as long as the average heterozygosity at the DNA fingerprint loci remains at or below 90%. Neither incomplete knowledge of the allele frequencies at each locus, nor the unknown number of loci underlying DNA fingerprint pattern, compromise these evolutionary dynamics of DNA fingerprint patterns. Applications of this theory to data on three human populations, and review of literature indicate that co-migration of alleles, and the presence of syntenic loci underlying the fingerprint pattern have little impact of the reliability of evolutionary conclusions from DNA fingerprint studies.

DNA Fingerprinting↗
PubMed2003

An exactly solvable model of population dynamics with density-dependent migrations and the Allee effect.

We consider a single-species model of population dynamics allowing for migrations and the Allee effect. Two types of migration are taken into account: one caused by environmental factors (e.g., a passive transport with the wind or water current) and the other associated with biological mechanisms. While the first type is apparently density-independent, the speed of migration in the second one can depend on the population density. Mathematically, this model consists of a non-linear partial differential equation of advection-diffusion-reaction type. Using an appropriate change of variables, we obtain an exact solution of the equation describing propagation of travelling population fronts. We show that, depending on parameter values and thus on the relative intensity of density-dependent and density-independent factors, the direction of the propagation can be different thus describing either species invasion or species retreat.

Animals↗
PubMed1999

Nutrition, fertility and steady-state population dynamics in a pre-industrial community in Penrith, northern England.

The effect of nutrition on fertility and its contribution thereby to population dynamics are assessed in three social groups (elite, tradesmen and subsistence) in a marginal, pre-industrial population in northern England. This community was particularly susceptible to fluctuations in the price of grains, which formed their basic foodstuff. The subsistence class, who formed the largest part of the population, had low levels of fertility and small family sizes, but women from all social groups had a characteristic and marked subfecundity in the early part of their reproductive lives. The health and nutrition of the mother during pregnancy was the most important factor in determining fertility and neonatal mortality. Inadequate nutrition had many subtle effects on reproduction which interacted to produce a complex web of events. A population boom occurred during the second half of the 18th century; fertility did not change but there was a marked improvement in infant mortality and it is suggested that the steadily improving nutritional standards of the population, particularly during crucial periods in pregnancy (i.e. the last trimester), probably made the biggest contribution to the improvement in infant mortality and so was probably the major factor in triggering the boom.

Adolescent↗
PubMed1992

Fundamental issues in nonlinear urban population dynamic models: theory and a synthesis.

"The main purpose of this paper is to examine certain basic similarities between three nonlinear models of urban dynamics which appeared in [1980], and seem to be driven by somewhat different mechanisms.... By looking at their implicit assumptions we set the stage for addressing certain fundamental premises underlying the process of urban growth or decline. Searching for these fundamental assumptions permits the construction of a comprehensive-unifying theory of urban population dynamics placing urban evolution squarely within the domain of evolutionary theory."

Demography↗
PubMed2005

[Population dynamics of pests and their enemies in different cultivated rice fields].

Through a whole year field investigation, this paper analyzed the population dynamics of pests and their enemies in organic and normally cultivated rice fields. The results indicated that the population of main pests varied more lightly in organic than in normally cultivated rice field, while subordinated pest species had little difference between these two fields. The individuals of enemies were more in organic than in normally cultivated rice field. It is suggested that the pest-control effect of enemies could be restored and became stronger when no chemical pesticides were applied.

Animals↗
PubMed2001

Seasonal population dynamics of Neoechinorhynchus qinghaiensis in the carp, Gymnocypris przewalskii przewalskii, from Qinghai Lake, China.

Studies on the seasonal population dynamics of Neoechinorhynchus qinghaiensis (Acanthocephala: Neoechinorhynchidae) in its fish host Gymnocypris przewalskii przewalskii in the Qinghai Lake, China, were carried out with samples taken in May 1991, August 1992, November 1992 and February 1993. Prevalences were higher than 44% in all seasons. The mean intensity of infection was above 124 worms per fish. The maximum intensity of worms recovered from a single fish was 1402 in the autumn of 1992. Differences in the mean abundance, mean intensity and prevalence are not statistically significant relative to season and this is likely to be related to the stable temperatures recorded at the bottom of Qinghai Lake. Over-dispersed distributions of N. qinghaiensis in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of N. qinghaiensis showed males to be less than 3.5 mm and females between 0.5 and 4.25 mm, with the main recruitment phase in the worm populations occurring in the autumn, extending through winter and spring with the lowest recruitment occurring in the summer. The maturation and copulation of worms were mainly focused in the summer season. The sex ratio of female to male was both high in winter (1.51:1) and spring (1.48:1). The higher proportion of females and the change in the worm sex ratio in winter can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.

Acanthocephala↗