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PubMed1992

Larval population dynamics in a community of nearctic Aedes inhabiting a temporary vernal pool.

The spatial distribution and preadult mortality patterns of 4 cohabiting species of Aedes mosquitoes were studied in a temporary vernal pool at Mt. Carmel, CT, from March to May 1990. The dominant species was Ae. stimulans (79.9%), followed by Ae. canadensis (10.7%), Ae. excrucians (7.5%) and Ae. cinereus (1.9%). First instar larvae of all species aggregated at the edge of the pool and then dispersed to deeper regions as they matured. Larval mortality was high, and the majority occurred during the first stadium (80.9% for Ae. canadensis, 88.9% for Ae. excrucians, 89.1% for Ae. stimulans and 90.0% for Ae. cinereus). A predatory chaobrid, Mochlonyx cinctipes, was implicated as the major mortality factor affecting larval populations.

Aedes↗

PubMed1986

Population dynamics of mosquito-borne disease: effects of flies which bite some people more frequently than others.

The consequences of non-homogeneous mixing (non-random contact) between vectors and hosts for the persistence, prevalence, and hence control, of any mosquito-borne disease are explored. When mosquitoes concentrate on certain hosts, the basic reproductive rate, R, of the disease (a measure of persistence) and the vectorial capacity are both greater than or equal to their values under homogeneous mixing. Field data suggest that R could be more than two and a half times as large as it would be under homogeneous mixing. Our calculations underestimate the importance of heterogeneity by ignoring mosquito patchiness and stochastic effects. Host selection limits the dependability of predictions, made from population models which assume homogeneous mixing, about the success of disease control (vaccines, chemotherapy, vector control). In particular, eradication or the maintenance of low prevalence will be more difficult than expected, unless localized control makes the distribution of infective bites on a community more nearly uniform. Age may explain most of the variability in biting in small communities (e.g., rural villages), in which case models incorporating age-specific biting will be appropriate tools in control programmes.

Anopheles↗

PubMed1995

Population dynamics, intervention and survival in African wild dogs (Lycaon pictus).

The demography of Serengeti wild dog study packs and their extinction in 1991 was documented by Burrows et al. (1994). One explanation for pack loss compatible with demographic evidence was viral disease induced by stress caused by intervention (vaccination, immobilization and radio-collaring). Several studies claim to reject this hypothesis. However, cortisol levels measured in immobilized Lycaon, whose pathogen exposure is unknown, do not demonstrate that interventions in the Serengeti were benign. The analysis of survivorship in Lycaon in other ecosystems minimized the chance of demonstrating any effect of intervention and failed to consider vaccinations as intervention. There is now evidence that intervention significantly decreased survivorship of Masai Mara Lycaon. Further simulations of the likelihood of population extinction in Serengeti Lycaon, evidence of limited population variability and a small scaling factor in Serengeti Lycaon strengthen Burrows et al.'s conclusion that the extinction was unlikely to be due to chance alone. Although some studies claim that Lycaon conservation is doomed without intervention, to date vaccinations, blood sampling and radio-telemetry have contributed little to Lycaon conservation. All studies fail to disprove the Burrows hypothesis or provide convincing alternatives.

Animals↗

PubMedDate not supplied

Population dynamics and feeding behavior of Triatoma brasiliensis and Triatoma pseudomaculata, main vectors of chagas disease in Northeastern Brazil.

Biological parameters of Triatoma brasiliensis and T. pseudomaculata that could influence the epidemiological importance of these insects as vectors of Trypanosoma cruzi were compared. The parameters studied were incubation period, interval between hatching or moulting and first feeding, number of blood meals, development time, mortality, net reproductive rate, instantaneous daily reproductive rate, time-lapse before starting feeding, duration of feeding, blood ingestion capacity, occurrence of defecation and blood ingestion velocity. Most aspects of feeding were similar for the two species, although T. pseudomaculata had a longer life cycle than T. brasiliensis producing one and two generations per year, respectively. The two species had similar instantaneous daily rates of population growth.

Animals↗

PubMed1992

Myxomatosis: population dynamics of rabbits (Oryctolagus cuniculus Linnaeus, 1758) and ecological effects in the United Kingdom.

In 1953-1955, myxomatosis spread among rabbits (Oryctolagus cuniculus) in the United Kingdom, causing 99% mortality. Subsequently, there was a gradual increase in rabbit numbers. By 1955, the Ministry of Agriculture, Fisheries and Food (MAFF) had already found attenuated strains of myxoma virus. By 1970, genetic resistance had appeared. In the 1970s, mortality declined to 47-69% with only approximately 25% of rabbits infected, giving a field mortality of 12-19%. However, myxomatosis is persistent, generally showing a major prevalence peak in autumn and often a minor peak in spring. An eight-year MAFF experiment in which prevalence of the disease was artificially reduced indicates that myxomatosis remains a significant factor in population regulation. After rabbit numbers fell in the 1950s, important ecological changes took place: vegetation altered due to reduced grazing pressure, predators were affected by the reduction of a major prey species and these changes also affected many other animals. Currently, rabbit numbers have returned to approximately one-third of pre-myxomatosis levels and this is causing damage to farm and conservation habitats.

Animals↗

PubMed2005

Wheat archive links long-term fungal pathogen population dynamics to air pollution.

We used the PCR to study the presence of two plant pathogens in archived wheat samples from a long-term experiment started in 1843. The data were used to construct a unique 160-yr time-series of the abundance of Phaeosphaeria nodorum and Mycosphaerella graminicola, two important pathogens of wheat. During the period since 1970, the relative abundance of DNA of these two pathogens in the samples has reflected the relative importance of the two wheat diseases they cause in U.K. disease surveys. Unexpectedly, changes in the ratio of the pathogens over the 160-yr period were very strongly correlated with changes in atmospheric pollution, as measured by SO(2) emissions. This finding suggests that long-term, economically important, changes in pathogen populations can be influenced by anthropogenically induced environmental changes.

Air Pollution↗

PubMed2004

Microbial population dynamics in the sediments of a eutrophic lake (Aydat, France) and characterization of some heterotrophic bacterial isolates.

The bacterial populations of anoxic sediments in a eutrophic lake (Aydat, Puy-de-Dôme-France) were studied by phospholipid fatty acid analysis (PLFA) and also by culturing heterotrophic bacteria under strictly anaerobic conditions. The mean PLFA concentrations of prokaryotes and microeukaryotes were 5.7 +/- 2.9 mgC g(-1) DS and 9.6 +/- 6.7 mgC g(-1) DS, respectively. The analysis of bacterial PLFA markers was used to determine the dynamics of the Gram-positive and Gram-negative species of anaerobic bacteria, Clostridiae, and sulfate-reducing bacteria. Throughout the sampling period the concentrations of i15:0 (from 20 nmol g(-1) DS to 130 nmol g(-1) DS), markers of Gram-positive bacteria, were higher than those for Gram-negative bacteria. The dynamics of Clostridiae (Cy15:0) paralleled those of sulfate-reducing bacteria that were marked by i17:1omega7. Partial 16S rDNA sequencing and the physiological study of the various fermenting strains, whose abundance in the superficial sediment layer was 1.1 +/- 0.4 x 10(6) cells mL(-1), showed that all the isolates belonged to the Clostridiae and related taxa ( Lactosphaera pasteurii, Clostridium vincentii, C. butyricum, C. algidixylanolyticum, C. puniceum, C. lituseburense, and C. gasigenes). All the isolates were capable of metabolizing a wide range of organic substrates.

Anaerobiosis↗

PubMed2000

Emergence of individual behaviour at the population level. Effects of density-dependent migration on population dynamics.

The aim of this work is to study the effects of different individual behaviours on the overall growth of a spatially distributed population. The population can grow on two spatial patches, a source and a sink, that are connected by migrations. Two time scales are involved in the dynamics, a fast one corresponding to migrations and a slow one associated with the local growth on each patch. Different scenarios of density-dependent migration are proposed and their effects on the population growth are investigated. A general discussion on the use of aggregation methods for the study of integration of different ecological levels is proposed.

Animals↗

PubMed1987

Population dynamics of Culex quinquefasciatus and the fungal pathogen Lagenidium giganteum (Oomycetes: Lagenidiales) in stagnant water pools.

The fungal pathogen Lagenidium giganteum (California isolate), cultured on sunflower seed extract (SFE) and agar, was introduced once (May 15) into outdoor caged replicated stagnant water pools containing all instars of larval Culex quinquefasciatus. Subsequently, first-instar larvae were added daily (May 15-September 30) to simulate natural oviposition. The fungus persisted for the entire 138-day study period, which corresponded with the season of Cx. quinquefasciatus breeding in this region of North Carolina, and recycled in the mosquito larvae producing an 82% reduction of adult mosquitoes produced in comparison to untreated pools. The cycles of fungal activity varied among the pools with 2-4 major epizootics occurring during the study period. Data are presented on the cycling of populations of fungal zoospores, mosquito larvae, pupae and adults during the entire mosquito breeding season.

Animals↗

PubMed2005

DNA markers for identifying biotypes B and Q of Bemisia tabaci (Hemiptera: Aleyrodidae) and studying population dynamics.

The two most widespread biotypes of Bemisia tabaci (Gennadius) in southern Europe and the Middle East are referred to as the B and Q-type, which are morphologically indistinguishable. In this study various DNA markers have been developed, applied and compared for studying genetic diversity and distribution of the two biotypes. For developing sequence characterized amplified regions (SCAR) and cleaved amplified polymorphic sequences (CAPS) techniques, single random amplified polymorphic DNA (RAPD) fragments of B and Q biotypes, respectively, were used. The CAPS were investigated on the basis of nuclear sodium channel and the mitochondrial cytochrome oxidase I genes (mtCOI) sequences. In general, complete agreement was found between the different markers used. Analysis of field samples collected in Israel for several years, using these markers, indicated that the percentage of the Q biotype tends to increase in field populations as time progresses. This may be attributed to the resistance of the Q biotype to neonicotinoids and pyriproxyfen and the susceptibility of the B biotype to these insecticides.

Animals↗

PubMed1995

A statistical approach to schistosome population dynamics and estimation of the life-span of Schistosoma mansoni in man.

Dynamic models which predict changes in the intensity of schistosome infection with host age are fitted to pre-intervention Schistosoma mansoni data from Kenya. Age-specific post-treatment-reinfection data are used to estimate the force of infection, thus enabling investigation of the rate of worm death. An empirical and statistical approach is taken to the model fitting: where possible, distributional properties and function relationships are obtained from the data rather than assumed from theory. Attempts are made to remove known sources of bias. Maximum likelihood techniques, employed to allow for error in both the pre-intervention and reinfection data, yield confidence intervals for the worm life-span (CI95% = 5.7-10.5 years) and demonstrate that the worm death rate is unlikely to vary with host age. The possibilities and limitations of fitting dynamic models to data are discussed. We conclude that a detailed, quantitative approach will be necessary if progress is to be made with the interpretation of epidemiological data and the models intended to describe them.

Adolescent↗

PubMed2005

State aggregation and population dynamics in linear systems.

We consider complex systems that are composed of many interacting elements, evolving under some dynamics. We are interested in characterizing the ways in which these elements may be grouped into higher-level, macroscopic states in a way that is compatible with those dynamics. Such groupings may then be thought of as naturally emergent properties of the system. We formalize this idea and, in the case that the dynamics are linear, prove necessary and sufficient conditions for this to happen. In cases where there is an underlying symmetry among the components of the system, group theory may be used to provide a strong sufficient condition. These observations are illustrated with some artificial life examples.

Animals↗

PubMed1994

Population dynamics and density-dependent seasonal mortality indices of the tick Rhipicephalus appendiculatus in eastern and southern Africa.

Eight sets of previously published data on the seasonal abundance of the tick Rhipicephalus appendiculatus in Burundi, Uganda, Tanzania and Zimbabwe are analysed to yield seasonal mortality indices. Correlations between these indices and abiotic (climatic) and biotic (tick density) variables suggest that it is the stage from females to larvae that is most sensitive to adverse abiotic conditions, specifically low moisture availability. Mortality at the other stages of the tick's life cycle is strongly density-dependent. The precise nature of this density-dependence suggests that it may be caused by acquired resistance to ticks by cattle. Robust correlations between satellite-derived vegetation indices, climatic factors and mortality indices suggest that detailed climatic data, often unavailable, may be replaced by satellite data, now widely available, for use in modelling tick populations.

Animals↗

PubMed2000

Seasonal population dynamics of ixodes ticks and tick-borne encephalitis virus.

Seasonality of the epidemic and epizootic processes of tick-borne encephalitis (TBE) depend on the period of activity of ixodid ticks Ixodes persulcatus Schulze and I. ricinus Linnaeus, which are the main reservoirs and vectors of TBE virus, and also on the process of their activation. The period of activity is the period during which the ticks occur in the active state. Activation is the transition into this state of ticks that moulted from the preceding stage and completed post-moulting development. For I. persulcatus, the first adult ticks generally emerge between April 10 and May 9. Under a variety of natural conditions, activation of adult I. persulcatus after wintering lasts for 45-86 days and this period may be even longer in certain areas of the Far East. The period during which one-half of the entire tick population becomes activated (AT50) comprises no more than 10-20 days. In adult I. ricinus ticks the activation period may last even longer than in I. persulcatus. The data on duration of the period of activity and on activation of larval and nymphal stages of both tick species were considered. Ticks exhausting their nutrient reserves and failing to find a host die quickly. The period during which 50% of the entire tick population die under natural conditions is designated LT50. The main types of I. persulcatus and I. ricinus seasonal activity within their species ranges were reviewed. Data on the relationship between TBE virus reproduction in a natural focus and physiological age, pattern of activation, and seasonal changes in age structure of the tick population were analyzed. Seasonal changes in the prevalence of infection among active unfed adult ticks in a natural population are determined by virus content in individual ticks at the moment of their activation and also by the duration of subsequent virus persistence (the rate of virus loss) in ticks. Apparently, the opportunity and frequency of horizontal TBE virus transmission under natural conditions, change during the season of tick activity.

Animals↗

PubMed2002

Population dynamics of calyptrate Diptera (Muscidae and Sarcophagidae) at the Rio-Zoo Foundation, Rio de Janeiro, RJ, Brazil.

Twenty-seven species of calyptrate muscoids (Muscidae and Sarcophagidae) were collected from December 1993 to November 1994 with wind oriented traps (W.O.T.) baited with decomposing beef liver at the Rio de Janeiro Zoo. The most abundant species found were Musca domestica (57.84%), Peckia chrysostoma (28.16%), Ophyra aenescens (17.11%), Oxysarcodexia thornax (17.82%), Synthesiomyia nudiseta (13.05%), and Oxysarcodexia diana (14.52%).

Animals↗

PubMed1993

[Preliminary studies of the effect of diseases and environmental pollution on the population dynamics of wild rabbits (Oryctolagus cuniculus Linnaeus, 1758) in the federal state of North Rhine-Westphalia (Germany)].

A survey was conducted of wild rabbits (Oryctolagus cuniculus) shot in all districts of the Federal State of North Rhine-Westphalia (Germany). A total of 104 rabbits were examined during 1988 and 1989. Attempts to isolate myxoma virus and other viruses were unsuccessful. Two serum samples neutralised myxoma virus. In 1990, 210 rabbits were examined; 57 animals were subjected to tests for the presence of the virus of viral haemorrhagic disease of rabbits and 42 were tested for specific antibody. No virus was isolated. Antibody titres were judged to be significant in 5% of the rabbits tested. Bacteriological, histological and virological tests showed no evidence of ill health in these animals. With the exception of abnormal cadmium content of tissues, detailed examination of ovaries and testes and lead assays failed to reveal reduced fertility as a reason for the fall in population.

Animals↗

PubMedDate not supplied

[Traveling waves in cross-diffusion models of population dynamics].

"Traveling wave"--type solutions of some models with cross-diffusion were considered. It was shown that "cross-diffusion" terms, as opposed to "diffusion" terms, do not increase the dimensionality of the automodel system. The bifurcation approach was used to study the dependence of the wave solutions on the parameters of the models being considered, and the waves were classified. It was shown that, at the same parameter values, both "fast" and "slow" waves can exist and that these waves are described by different automodel systems.

Models, Theoretical↗

PubMed1996

Population dynamics and theta rhythm phase precession of hippocampal place cell firing: a spiking neuron model.

O'Keefe and Recce ([1993] Hippocampus 68:317-330) have observed that the spatially selective firing of pyramidal cells in the CA1 field of the rat hippocampus tends to advance to earlier phases of the electroencephalogram theta rhythm as a rat passes through the place field of a cell. We present here a neural network model based on integrate- and-fire neurons that accounts for this effect. In this model, place selectivity in the hippocampus is a consequence of synaptic interactions between pyramidal neurons together with weakly selective external input. The phase shift of neuronal spiking arises in the model as result of asymmetric spread of activation through the network, caused by asymmetry in the synaptic interactions. Several experimentally observed properties of the phase shift effect follow naturally from the model, including 1) the observation that the first spikes a cell fires appear near the theta phase corresponding to minimal population activity, 2) the overall advance is less than 360 degrees, and 3) the location of the rat within the place field of the cell is the primary correlate of the firing phase, not the time the rat has been in the field. The model makes several predictions concerning the emergence of place fields during the earliest stages of exploration in a novel environment. It also suggests new experiments that could provide further constraints on a possible explanation of the phase precession effect.

Animals↗