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PubMed2000

The Population Dynamics and Community Ecology of Root Hemiparasitic Plants.

Root hemiparasitic plants and their host plants interact directly, through parasitism, as well as indirectly, through scramble competition for resources. To understand the population dynamics and community ecology of root hemiparasitic plants and their hosts, models of resource-based competition have been extended to include resource parasitism. Parasitism provides a mechanism for parasitic plants to overcome deficits in their ability to compete for soil resources. The interaction ranges from competitive to exploiter-victim, depending on whether the benefits of parasitism overshadow the costs of competition. These models predict that as productivity in the system increases, parasitic plants should become more abundant. In diverse host communities, differences in the impact that parasites have on their hosts and the benefits that they receive from parasitizing different hosts may lead to nontransitive competitive relationships and a sort of apparent competition. The possible dynamics include paper-rock-scissors oscillations and indirect mutualisms between parasitic plants and their hosts that allow them to form coalitions that can exclude competitive dominants.

degree of parasitism↗

PubMed2004

[Effect of temperature and food concentration on the population dynamics of three Brachionus calyciflorus strains].

Effects of temperature (20 degrees C, 25 degrees C, 30 degrees C) and food concentration (1.5, 3.0, 6.0, 9.0 x 10(6) cells x ml(-1)) on the population dynamics of Brachionus calyciflorus of Qingdao, Wuhu and Guangzhou strains were studied by means of individual culture. The result showed that the temperature was an important factor affecting generation time and intrinsic rate of population increase. With rising of temperature, the intrinsic rate of population increase increased, but generation time decreased. There were significant effects of food concentration on life expectancy and average lifespan. The effect of strain on net reproductive rate, generation time, life expectancy and average lifespan was also significant. Net reproductive rate, generation time, life expectancy, and average lifespan of Guangzhou strain was all the maximum, and that of Wuhu strain minimum among the three strains. The rotifers fed on the algae at the concentration of 3.0 x 10(6) cells x ml(-1) had the longest life expectancy and average lifespan, but those at 9.0 x 10(6) cells x ml(-1) had the shortest. Net reproductive rate, generation time, gross reproductive rate, life expectancy, and average lifespan of the three strains decreased linearly with the rise of temperature, except for the net reproductive rate of Guangzhou strain, while the intrinsic rate of population increase of all the three strains and gross reproductive rate of Guangzhou strain increased linearly with the rise of temperature. The relationships between all the life history parameters of Qingdao and Guangzhou strains and food concentration were all curvilinear, however, those between generation time, average lifespan, and life expectancy of Wuhu strain and food concentration could all be described by linear regression.

Animals↗

PubMed2006

[Seed population dynamics and germination characteristics of Eupatorium adenophorum].

With bare land, farmland, and masson pine forestland in the Eupatorium adenophorum- invaded area of Dechang County, Sichuan Province as test habitats, this paper studied the seed population dynamics of E. adenophorum at the levels of seed rain and seed bank, and its seed germination characteristics under effects of light and soil medium. The results showed that in the three habitats, the seed population of E. adenophorum only existed from March to June, and reached its peak by the end of April. The annual seed rainfall in bare land habitat amounted to 2.4 x 10(5) individuals per square meter, and all the seeds were distributed in the soil layer above 2 cm. The thousand seed weight and seed activity of E. adenophorum in bare land habitat were significantly higher than those in another two habitats. No active seed was found in the three habitats by the first ten days of July. Under artificial light condition, full light had some inhibitory effects on seed germination, while 28% of full light gave the highest germination rate. Sandy loam soil was more favorable for the seed germination, while in un-reclaimed red soil, both the germination velocity and germination rate were the lowest.

Ageratina↗

PubMed2005

Evaluation of sampling methodology for determining the population dynamics of onion thrips (Thysanoptera: Thripidae) in Ontario onion fields.

Onion thrips, Thrips tabaci Lindeman, are an economic pest of alliums worldwide. In Ontario onion-growing regions, seasonal abundance and population trends of onion thrips are not well known. The objectives of this research were to investigate onion thrips population dynamics by using both white sticky traps and plant counts, to gain insight into flight height, and to determine the genus and sex of thrips fauna present in monitored fields. Adult thrips were captured on white sticky traps placed in two commercial onion fields in the Thedford-Grand Bend Marsh region as early as mid-May in 2001, 2002, and 2003. Thrips were not recorded on onion plants in these fields until late June and early July. A comparison of sticky trap captures to plant counts revealed a strong, positive correlation, indicating that sticky traps, which consistently detected thrips earlier than plant counts, could be used instead of plant counts early in the season to monitor onion thrips populations. Pole traps placed in onion and an adjacent soybean, Glycine max (L.) Merr., field revealed that regardless of crop type, most thrips were captured 0.7-0.95 m above the soil surface. During this study, 70% of 137,000 thrips captured on sticky traps and 89% of 1,482 thrips captured in pan traps were female onion thrips. No male onion thrips were identified in this study: most of the remaining thrips were Frankliniella spp.

Animals↗

PubMed2003

Population dynamics of Panonychus osmanthi (Acari: Tetranychidae) on two Osmanthus species.

Panonychus osmanthi is a non-diapausing species of spider mite that superficially resembles P. citri. It infests Osmanthus species, which are evergreen roadside and garden trees. The population dynamics of P. osmanthi were studied on Osmanthus aurantiacus and O. x fortunei during a three-year period. Seasonal changes in P. osmanthi populations were fundamentally the same in each year, although their density differed greatly from year to year. The P. osmanthi population was bimodal, with one peak in spring (May-June) and another in winter (November-January). Populations abruptly declined after the spring peak. Predators showed a delayed density-dependent response to changes in spider mites from spring to summer, whereas in autumn and winter, predators were few because they had entered diapause. To determine the effect of predators on the rapid decline of spider mites just after the spring peak, the predators were removed by treating the trees with a synthetic pyrethroid. As a result, spider mite density did not decline after the spring peak and remained at a high level during the June-August period when spider mite density is usually very low. This suggests that predators play an important role in the drastic decline of P. osmanthi density just after the spring peak.

Animals↗

PubMed2002

Seasonal population dynamics of the greenhouse whitefly Trialeurodes vaporariorum (Homoptera: Aleyrodidae) on strawberries in Southern California.

The greenhouse whitefly, Trialeurodes vaporariorum (Westwood), has recently become a major insect pest of strawberries in Southern California. The population dynamics of this pest were monitored over 2 yr in six commercial strawberry fields near the coastal communities of Oxnard and Ventura under two crop-production regimes, summer- and fall-planted strawberries. Adult whitefly numbers generally peaked during the February through May period for fall-planted strawberries and during the October through November period for summer-planted strawberries. Population densities varied greatly among fields within each regime and the differences were likely caused by surrounding alternate host crops.

Animals↗

PubMed2001

A stochastic modeling of early HIV-1 population dynamics.

In a recent paper, Tuckwell and Le Corfec [J. Theor. Biol. 195 (1998) 450-463] applied the multi-dimensional diffusion process to model early human immunodeficiency virus type-1 (HIV-1) population dynamics. The purpose of this paper is to assess certain features and consequences of their model in the context of Tan and Wu's stochastic approach [Math. Biosci. 147 (1998) 173-205].

Computer Simulation↗

PubMed1982

Population dynamics of human helminth infections: control by chemotherapy.

An analysis is presented of the population dynamics of the major helminth parasites of man with the aim of understanding observed patterns in the age-specific prevalence and intensity of infection. Mathematical models are used to investigate the possibility of controlling helminth diseases by mass chemotherapy, and to explore the advantages of selective treatment of the most heavily infected individuals in a community.

Adolescent↗

PubMed1985

Population dynamics of ingested Clostridium difficile in the gastrointestinal tract of the Syrian hamster.

The population dynamics of Clostridium difficile in the hamster gastrointestinal tract were studied after intragastric inoculation with organisms and a 51Cr tracer. Seventy-eight percent of spores germinated within the small intestine within 1 hr. Germinated spores and vegetative cells both showed two phases of elimination from the hamster cecum--an initial phase of rapid death that was not affected by antibiotic treatment followed by a phase of complete inhibition of multiplication. The latter phase of inhibition was not seen in antibiotic-treated animals and was thus attributable to the indigenous flora. The 51Cr tracer mixed well with cecal contents and was eliminated exponentially with a dilution rate constant ranging from -0.46/hr to -0.31/hr in normal hamsters. The hamster cecum was therefore dynamically analogous to a continuous flow system, a finding supporting the concept that anaerobic continuous flow cultures are useful in vitro models of the cecal ecosystem.

Animals↗

PubMedDate not supplied

Models for diseases with vertical transmission and nonlinear population dynamics.

Vertical transmission, the direct transfer of a disease from an infective parent to a new born offspring, is an important aspect of many diseases. Most of what is known for vertical transmission models assumes birth rates proportional to population size. We consider models with nonlinear population dynamics and finite carrying capacity and analyze the stability of equilibria in the special case in which the overall birth rate does not depend on infective population size.

Female↗

PubMed2004

Population dynamics of pathogens with multiple host species.

Pathogens that can infect multiple host species will have different dynamics than pathogens that are restricted to a single species of host. This article examines the conditions for establishment and long-term population dynamic behavior of pathogens that infect multiple species of hosts. The article attempts to address three major questions in this area: First, under which conditions will increases in the diversity of host species buffer infectious disease outbreaks, and under which conditions will host diversity amplify disease outbreaks? Second, under what conditions is it possible to control an infectious agent by focusing control against only one host species? Third, what role does host species diversity play in maintaining pathogen persistence? The answers to these questions supply some important general insights into the role that biodiversity plays in buffering humans and other species against new and emerging pathogens.

Animals↗

PubMed1998

[Phlebotomines of Senegal (Diptera: Psychodidae): population and population dynamics of the Mont-Rolland region].

Phlebotomine sandflies were captured on a monthly basis from May 1995 to April 1996 in the Mont-Rolland district in Western Senegal. The objectives were to study the population dynamics of sandflies and to make an inventory of the viruses they transmit. Among 10,315 specimens captured, belonging to 14 species, Sergentomyia dubia (35.9%), S. schwetzi (27.7%) and S. buxtoni (24.5%) were the most abundant. Species from the genus Sergentomyia accounted for 99.6% versus 0.4% for the genus Phlebotomus. The sandflies population was observed to peak in February. The most populated resting sites of the captured insects were in decreasing order tree-holes, termite-hills and burrows. S. dubia was the most abundant species captured in tree-holes. It was S. buxtoni in termite-hills, while S. schwetzi was found to dwell most often in burrows. No virus was isolated from 2,114 specimens tested.

Animals↗

PubMed1992

Heterogeneity, spatial population dynamics, and the migration rate.

"In this paper, I examine some of the ways in which widely used migration indices are affected by the impacts of heterogeneity and selection, which act within a multistate perspective of spatial population dynamics that permits increments as well as decrements in the selectivity (and return) process. As a result, several commonly used indices of migration introduce a specification bias into the analysis--a bias that reflects the relative weighting accorded to component migration rates by the initial population compositions and spatial distributions." This paper was originally presented at the 1991 Annual Meeting of the Population Association of America.

Bias↗

PubMed2004

Population dynamics of Wolbachia bacterial endosymbionts in Brugia malayi.

The human filarial nematode Brugia malayi contains an endosymbiotic bacterium, Wolbachia. We used real-time quantitative polymerase chain reaction (QPCR) and microscopy to investigate the population dynamics of the bacterium-nematode association. Two Wolbachia (wsp and ftsZ) and one nematode (gst) genes were amplified from all life-cycle stages of B. malayi and results expressed as gene copies per worm and as Wolbachia/nematode ratios. Since the genes were single copy and there was one genome per Wolbachia, the gene copy numbers were equivalent to the numbers of bacteria. These were similar in microfilariae and the mosquito-borne larval stages (L2 and L3), with the lowest ratios of Wolbachia/nematode DNA. However, within 7 days of infection of the mammalian host, bacteria had increased 600-fold and the bacteria/worm ratio was the highest of all life-cycle stages. The rapid multiplication continued throughout L4 development, so that the major period of bacterial population growth occurred within 4 weeks of infection of the definitive host. Microscopy confirmed that there were few bacteria in mosquito-derived L3 but many, in large groups, in L4 collected 9 and 21 days after infection. In adult male worms up to 15 months of age, the bacterial populations were maintained, whilst in females, bacteria numbers increased as the worms matured and as the ovary and embryonic larval stages became infected. These results support the hypothesis that the bacteria are essential for larval development in the mammalian host and for the long-term survival of adult worms.

Animals↗

PubMed2002

Nitrifying and heterotrophic population dynamics in biofilm reactors: effects of hydraulic retention time and the presence of organic carbon.

Two biofilm reactors operated with hydraulic retention times of 0.8 and 5.0 h were used to study the links between population dynamics and reactor operation performance during a shift in process operation from pure nitrification to combined nitrification and organic carbon removal. The ammonium and the organic carbon loads were identical for both reactors. The composition and dynamics of the microbial consortia were quantified by fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes combined with confocal laser scanning microscopy, and digital image analysis. In contrast to past research, after addition of acetate as organic carbon nitrification performance decreased more drastically in the reactor with longer hydraulic retention time. FISH analysis showed that this effect was caused by the unexpected formation of a heterotrophic microorganism layer on top of the nitrifying biofilm that limited nitrifiers oxygen supply. Our results demonstrate that extension of the hydraulic retention time might be insufficient to improve combined nitrification and organic carbon removal in biofilm reactors.

Acetates↗

PubMed2003

Comparative population dynamics of mosquito-borne flaviviruses.

Among the members of the genus Flavivirus are several important human pathogens, including the dengue (DEN) and Japanese encephalitis (JE) viruses. From the analysis of gene sequence data of samples of these virus populations it is possible to infer phylogenetic relationships, which in turn can yield important epidemiological information, including their demographic history in humans. In this study, we use a recently developed method, based on coalescent theory, to infer the population dynamics of a variety of mosquito-borne flaviviruses. Our study involves the testing of alternative hypotheses, the estimation of confidence intervals around demographic model parameter values, and the placing of the maximum likelihood (ML) demographic model into a "real time" epidemiological history. We reveal that all the Flavivirus populations studied are growing at an exponential rate, with the rates of population growth of dengue virus serotypes 2 and 3 increasing rapidly in the recent past, and that of Japanese encephalitis virus changing from constant population size to exponential growth within the last century. We therefore demonstrate that the use of these coalescent methods may be extremely valuable in monitoring responses to interventions such as vaccination or vector control.

Arboviruses↗

PubMed2002

Applications of Perron-Frobenius theory to population dynamics.

By the use of Perron-Frobenius theory, simple proofs are given of the Fundamental Theorem of Demography and of a theorem of Cushing and Yicang on the net reproductive rate occurring in matrix models of population dynamics. The latter result, which is closely related to the Stein-Rosenberg theorem in numerical linear algebra, is further refined with some additional nonnegative matrix theory. When the fertility matrix is scaled by the net reproductive rate, the growth rate of the model is $1$. More generally, we show how to achieve a given growth rate for the model by scaling the fertility matrix. Demographic interpretations of the results are given.

Female↗

PubMed1994

Population dynamics of sexual and resource competition.

Interspecific competition is usually thought of in terms of resource competition. Closely related species, however, may often compete also for a "sexual niche," a sexual resource. Both sexual and resource competition are likely to affect the dynamics of closely related sympatric species. Here, a combined model of sexual and resource competition is developed and analyzed in terms of phase planes. Population dynamics involving sexual competition alone are characterized by competitive exclusion and dependence on relative initial population size of the competing species. This dependence on initial population size is due to the nonlinear equilibrium isoclines of sexual competition, which contrast with the linear isoclines of the Lotka-Volterra competition equations. Dependence on initial population size is stronger when sexual competition is severe and/or when growth rates of the two species are low. Additional dynamic possibilities arise under combined sexual and resource competition. If the sexual competition is strong, competitive exclusion is the only outcome. But if sexual competition is weak, and if stable coexistence would occur without sexual competition, then both stable coexistence and competitive exclusion may occur simultaneously. A species that is relatively rare initially may be excluded, but when both species are initially of comparable abundance both will persist. Adding sexual competition to resource competition thus introduces additional uncertainty concerning the outcome of competition between two sympatric species.

Animals↗